draft-ietf-v6ops-security-overview-04.txt   draft-ietf-v6ops-security-overview-05.txt 
IPv6 Operations E. Davies IPv6 Operations E. Davies
Internet-Draft Consultant Internet-Draft Consultant
Expires: September 7, 2006 S. Krishnan Intended status: Informational S. Krishnan
Ericsson Expires: March 4, 2007 Ericsson
P. Savola P. Savola
CSC/Funet CSC/Funet
March 6, 2006 August 31, 2006
IPv6 Transition/Co-existence Security Considerations IPv6 Transition/Co-existence Security Considerations
draft-ietf-v6ops-security-overview-04.txt draft-ietf-v6ops-security-overview-05.txt
Status of this Memo Status of this Memo
By submitting this Internet-Draft, each author represents that any By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79. aware will be disclosed, in accordance with Section 6 of BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that Task Force (IETF), its areas, and its working groups. Note that
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and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt. http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html. http://www.ietf.org/shadow.html.
This Internet-Draft will expire on September 7, 2006. This Internet-Draft will expire on March 4, 2007.
Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2006). Copyright (C) The Internet Society (2006).
Abstract Abstract
The transition from a pure IPv4 network to a network where IPv4 and The transition from a pure IPv4 network to a network where IPv4 and
IPv6 co-exist brings a number of extra security considerations that IPv6 co-exist brings a number of extra security considerations that
need to be taken into account when deploying IPv6 and operating the need to be taken into account when deploying IPv6 and operating the
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document attempts to give an overview of the various issues grouped document attempts to give an overview of the various issues grouped
into three categories: into three categories:
o issues due to the IPv6 protocol itself, o issues due to the IPv6 protocol itself,
o issues due to transition mechanisms, and o issues due to transition mechanisms, and
o issues due to IPv6 deployment. o issues due to IPv6 deployment.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Issues Due to IPv6 Protocol . . . . . . . . . . . . . . . . . 4 2. Issues Due to IPv6 Protocol . . . . . . . . . . . . . . . . . 4
2.1. IPv6 Protocol-specific Issues . . . . . . . . . . . . . . 4 2.1. IPv6 Protocol-specific Issues . . . . . . . . . . . . . . 5
2.1.1. Routing Headers and Hosts . . . . . . . . . . . . . . 4 2.1.1. Routing Headers and Hosts . . . . . . . . . . . . . . 5
2.1.2. Routing Headers for Mobile IPv6 and Other Purposes . . 5 2.1.2. Routing Headers for Mobile IPv6 and Other Purposes . . 6
2.1.3. Site-scope Multicast Addresses . . . . . . . . . . . . 6 2.1.3. Site-scope Multicast Addresses . . . . . . . . . . . . 7
2.1.4. ICMPv6 and Multicast . . . . . . . . . . . . . . . . . 6 2.1.4. ICMPv6 and Multicast . . . . . . . . . . . . . . . . . 7
2.1.5. Bogus Errored Packets in ICMPv6 Error Messages . . . . 7 2.1.5. Bogus Errored Packets in ICMPv6 Error Messages . . . . 8
2.1.6. Anycast Traffic Identification and Security . . . . . 7 2.1.6. Anycast Traffic Identification and Security . . . . . 9
2.1.7. Address Privacy Extensions Interact with DDoS 2.1.7. Address Privacy Extensions Interact with DDoS
Defenses . . . . . . . . . . . . . . . . . . . . . . . 8 Defenses . . . . . . . . . . . . . . . . . . . . . . . 9
2.1.8. Dynamic DNS: Stateless Address Auto-Configuration, 2.1.8. Dynamic DNS: Stateless Address Auto-Configuration,
Privacy Extensions and SEND . . . . . . . . . . . . . 9 Privacy Extensions and SEND . . . . . . . . . . . . . 10
2.1.9. Extension Headers . . . . . . . . . . . . . . . . . . 9 2.1.9. Extension Headers . . . . . . . . . . . . . . . . . . 11
2.1.10. Fragmentation: Reassembly and Deep Packet 2.1.10. Fragmentation: Reassembly and Deep Packet
Inspection . . . . . . . . . . . . . . . . . . . . . . 12 Inspection . . . . . . . . . . . . . . . . . . . . . . 14
2.1.11. Fragmentation Related DoS Attacks . . . . . . . . . . 13 2.1.11. Fragmentation Related DoS Attacks . . . . . . . . . . 15
2.1.12. Link-Local Addresses and Securing Neighbor 2.1.12. Link-Local Addresses and Securing Neighbor
Discovery . . . . . . . . . . . . . . . . . . . . . . 13 Discovery . . . . . . . . . . . . . . . . . . . . . . 15
2.1.13. Securing Router Advertisements . . . . . . . . . . . . 14 2.1.13. Securing Router Advertisements . . . . . . . . . . . . 17
2.1.14. Host to Router Load Sharing . . . . . . . . . . . . . 15 2.1.14. Host to Router Load Sharing . . . . . . . . . . . . . 17
2.1.15. Mobile IPv6 . . . . . . . . . . . . . . . . . . . . . 15 2.1.15. Mobile IPv6 . . . . . . . . . . . . . . . . . . . . . 18
2.2. IPv4-mapped IPv6 Addresses . . . . . . . . . . . . . . . . 15 2.2. IPv4-mapped IPv6 Addresses . . . . . . . . . . . . . . . . 18
2.3. Increased End-to-End Transparency . . . . . . . . . . . . 16 2.3. Increased End-to-End Transparency . . . . . . . . . . . . 20
2.3.1. IPv6 Networks without NATs . . . . . . . . . . . . . . 16 2.3.1. IPv6 Networks without NATs . . . . . . . . . . . . . . 20
2.3.2. Enterprise Network Security Model for IPv6 . . . . . . 17 2.3.2. Enterprise Network Security Model for IPv6 . . . . . . 20
2.4. IPv6 in IPv6 Tunnels . . . . . . . . . . . . . . . . . . . 18 2.4. IPv6 in IPv6 Tunnels . . . . . . . . . . . . . . . . . . . 22
3. Issues Due to Transition Mechanisms . . . . . . . . . . . . . 18 3. Issues Due to Transition Mechanisms . . . . . . . . . . . . . 22
3.1. IPv6 Transition/Co-existence Mechanism-specific Issues . . 19 3.1. IPv6 Transition/Co-existence Mechanism-specific Issues . . 22
3.2. Automatic Tunneling and Relays . . . . . . . . . . . . . . 19 3.2. Automatic Tunneling and Relays . . . . . . . . . . . . . . 23
3.3. Tunneling IPv6 Through IPv4 Networks May Break IPv4 3.3. Tunneling IPv6 Through IPv4 Networks May Break IPv4
Network Security Assumptions . . . . . . . . . . . . . . . 20 Network Security Assumptions . . . . . . . . . . . . . . . 23
4. Issues Due to IPv6 Deployment . . . . . . . . . . . . . . . . 21 4. Issues Due to IPv6 Deployment . . . . . . . . . . . . . . . . 25
4.1. Avoiding the Trap of Insecure IPv6 Service Piloting . . . 21 4.1. Avoiding the Trap of Insecure IPv6 Service Piloting . . . 25
4.2. DNS Server Problems . . . . . . . . . . . . . . . . . . . 23 4.2. DNS Server Problems . . . . . . . . . . . . . . . . . . . 27
4.3. Addressing Schemes and Securing Routers . . . . . . . . . 23 4.3. Addressing Schemes and Securing Routers . . . . . . . . . 27
4.4. Consequences of Multiple Addresses in IPv6 . . . . . . . . 24 4.4. Consequences of Multiple Addresses in IPv6 . . . . . . . . 27
4.5. Deploying ICMPv6 . . . . . . . . . . . . . . . . . . . . . 25 4.5. Deploying ICMPv6 . . . . . . . . . . . . . . . . . . . . . 28
4.5.1. Problems Resulting from ICMPv6 Transparency . . . . . 25 4.5.1. Problems Resulting from ICMPv6 Transparency . . . . . 29
4.6. IPsec Transport Mode . . . . . . . . . . . . . . . . . . . 25 4.6. IPsec Transport Mode . . . . . . . . . . . . . . . . . . . 29
4.7. Reduced Functionality Devices . . . . . . . . . . . . . . 26 4.7. Reduced Functionality Devices . . . . . . . . . . . . . . 30
4.8. Operational Factors when Enabling IPv6 in the Network . . 26 4.8. Operational Factors when Enabling IPv6 in the Network . . 30
4.9. Ingress Filtering Issues Due to Privacy Addresses . . . . 27 4.9. Ingress Filtering Issues Due to Privacy Addresses . . . . 31
4.10. Security Issues Due to ND Proxies . . . . . . . . . . . . 28 4.10. Security Issues Due to Neighbor Discovery Proxies . . . . 31
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 28 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 31
6. Security Considerations . . . . . . . . . . . . . . . . . . . 28 6. Security Considerations . . . . . . . . . . . . . . . . . . . 32
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 28 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 32
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 28 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 32
8.1. Normative References . . . . . . . . . . . . . . . . . . . 28 8.1. Normative References . . . . . . . . . . . . . . . . . . . 32
8.2. Informative References . . . . . . . . . . . . . . . . . . 30 8.2. Informative References . . . . . . . . . . . . . . . . . . 33
Appendix A. IPv6 Probing/Mapping Considerations . . . . . . . . . 33 Appendix A. IPv6 Probing/Mapping Considerations . . . . . . . . . 36
Appendix B. IPv6 Privacy Considerations . . . . . . . . . . . . . 34 Appendix B. IPv6 Privacy Considerations . . . . . . . . . . . . . 37
B.1. Exposing MAC Addresses . . . . . . . . . . . . . . . . . . 34 B.1. Exposing MAC Addresses . . . . . . . . . . . . . . . . . . 37
B.2. Exposing Multiple Devices . . . . . . . . . . . . . . . . 35 B.2. Exposing Multiple Devices . . . . . . . . . . . . . . . . 38
B.3. Exposing the Site by a Stable Prefix . . . . . . . . . . . 35 B.3. Exposing the Site by a Stable Prefix . . . . . . . . . . . 38
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 37 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 39
Intellectual Property and Copyright Statements . . . . . . . . . . 38 Intellectual Property and Copyright Statements . . . . . . . . . . 40
1. Introduction 1. Introduction
The transition from a pure IPv4 network to a network where IPv4 and The transition from a pure IPv4 network to a network where IPv4 and
IPv6 co-exist brings a number of extra security considerations that IPv6 co-exist brings a number of extra security considerations that
need to be taken into account when deploying IPv6 and operating the need to be taken into account when deploying IPv6 and operating the
dual-protocol network with its associated transition mechanisms. dual-protocol network with its associated transition mechanisms.
This document attempts to give an overview of the various issues This document attempts to give an overview of the various issues
grouped into three categories: grouped into three categories:
o issues due to the IPv6 protocol itself, o issues due to the IPv6 protocol itself,
o issues due to transition mechanisms, and o issues due to transition mechanisms, and
o issues due to IPv6 deployment. o issues due to IPv6 deployment.
It is important to understand that we have to be concerned not about It is important to understand that deployments are unlikely to be
replacing IPv4 with IPv6 (in the short term), but with adding IPv6 to replacing IPv4 with IPv6 (in the short term), but rather will be
be operated in parallel with IPv4 [I-D.savola-v6ops-transarch]. adding IPv6 to be operated in parallel with IPv4 over a considerable
period, so that security issues with transition mechanisms and dual
stack networks will be of ongoing concern. This extended transition
and coexistence period stems primarily from the scale of the current
IPv4 network. It is unreasonable to expect that the many millions of
IPv4 nodes will be converted overnight. It is more likely that it
will take two or three capital equipment replacement cycles (between
nine and 15 years) for IPv6 capabilities to spread through the
network and many services will remain available over IPv4 only for a
significant period whilst others are offered either just on IPv6 or
on both protocols. To maintain current levels of service,
enterprises and service providers will need to support IPv4 and IPv6
in parallel for some time.
This document also describes two matters that have been wrongly This document also describes two matters that have been wrongly
identified as potential security concerns for IPv6 in the past and identified as potential security concerns for IPv6 in the past and
explains why they are unlikely to cause problems: considerations explains why they are unlikely to cause problems: considerations
about probing/mapping IPv6 addresses (Appendix A), and considerations about probing/mapping IPv6 addresses (Appendix A), and considerations
with respect to privacy in IPv6 (Appendix B). with respect to privacy in IPv6 (Appendix B).
2. Issues Due to IPv6 Protocol 2. Issues Due to IPv6 Protocol
Administrators should be aware that some of the rules suggested in
this section could potentially lead to a small amount of legitimate
traffic being dropped because the source has made unusual and
arguably unreasonable choices when generating the packet. The IPv6
specification [RFC2460] contains a number of areas where choices are
available to packet originators that will result in packets that
conform to the specification but are unlikely to be the result of a
rational packet generation policy for legitimate traffic (e.g.,
sending a fragmented packet in a much larger than necessary number of
small segments). This document highlights choices that could be made
by malicious sources with the intention of damaging the target host
or network, and suggests rules that try to differentiate
specification conforming packets that are legitimate traffic from
conforming packets that may be trying to subvert the specification to
cause damage. The differentiation tries to offer a reasonable
compromise between securing the network and passing every possible
conforming packet. To avoid loss of important traffic,
administrators are advised to log packets dropped according to these
rules and examine these logs periodically to ensure that they are
having the desired effect, and are not excluding traffic
inappropriately.
The built-in flexibility of the IPv6 protocol may also lead to
changes in the boundaries between legitimate and malicious traffic as
identified by these rules. New options may be introduced in future
and rules may need to be altered to allow the new capabilities to be
(legitimately) exploited by applications. The document therefore
recommends that filtering needs to be configurable to allow
administrators the flexibility to update rules as new pieces of IPv6
specification are standardized.
2.1. IPv6 Protocol-specific Issues 2.1. IPv6 Protocol-specific Issues
There are significant differences between the features of IPv6 and There are significant differences between the features of IPv6 and
IPv4: some of these specification changes may result in potential IPv4: some of these specification changes may result in potential
security issues. Several of these issues have been discussed in security issues. Several of these issues have been discussed in
separate drafts but are summarized here to avoid normative references separate drafts but are summarized here to avoid normative references
that may not become RFCs. The following specification-related that may not become RFCs. The following specification-related
problems have been identified, but this is not necessarily a complete problems have been identified, but this is not necessarily a complete
list: list:
2.1.1. Routing Headers and Hosts 2.1.1. Routing Headers and Hosts
All IPv6 nodes must be able to process Routing Headers [RFC2460]. All IPv6 nodes must be able to process Routing Headers [RFC2460].
This RFC can be interpreted, although it is not clearly stated, to This RFC can be interpreted, although it is not clearly stated, to
mean that all nodes (including hosts) must have this processing mean that all nodes (including hosts) must have this processing
enabled. This can result in hosts forwarding received traffic if enabled. The Requirements for Internet Hosts [RFC1122] permits
there are segments left in the Routing Header when it arrives at the implementations to perform "local source routing", that is forwarding
host. a packet with a routing header through the same interface on which it
was received: no restrictions are placed on this operation even on
hosts. In combination, these rules can result in hosts forwarding
received traffic to another node if there are segments left in the
Routing Header when it arrives at the host.
A number of potential security issues associated with this behavior A number of potential security issues associated with this behavior
were documented in [I-D.savola-ipv6-rh-hosts]. Some of these issues have been identified. Some of these issues have been resolved (a
have been resolved (a separate routing header type is now used for separate routing header (Type 2) is now used for Mobile IPv6
Mobile IPv6 [RFC3775] and ICMP Traceback has not been standardized), [RFC3775] and ICMP Traceback has not been standardized), but two
but two issues remain: issues remain:
o Routing headers can be used to evade access controls based on o Routing headers can be used to evade access controls based on
destination addresses. This could be achieved by sending a packet destination addresses. This could be achieved by sending a packet
ostensibly to a publicly accessible host address but with a ostensibly to a publicly accessible host address but with a
routing header containing a 'forbidden' address. If the publicly routing header containing a 'forbidden' address. If the publicly
accessible host is processing routing headers it will forward the accessible host is processing routing headers it will forward the
packet to the destination address in the routing header that would packet to the destination address in the routing header that would
have been forbidden by the packet filters if the address had been have been forbidden by the packet filters if the address had been
in the destination field when the packet was checked. in the destination field when the packet was checked.
o If the packet source address in the previous case can be spoofed, o If the packet source address in the previous case can be spoofed,
any host could be used to mediate an anonymous reflection denial- any host could be used to mediate an anonymous reflection denial-
of-service attack by having any publicly accessible host redirect of-service attack by having any publicly accessible host redirect
the attack packets. the attack packets.
To counteract these threats, if a device is enforcing access controls To counteract these threats, if a device is enforcing access controls
based on destination addresses, it needs to examine both the based on destination addresses, it needs to examine both the
destination address in the base IPv6 header and any way point destination address in the base IPv6 header and any way point
destinations in a routing header that have not yet been reached by destinations in a routing header that have not yet been reached by
the packet at the point wher it is being checked. the packet at the point where it is being checked.
Various forms of amplication attack on routers and firewalls using Various forms of amplification attack on routers and firewalls using
the routing header could be envisaged. A simple form involves the routing header could be envisaged. A simple form involves
repeating the address of a way point several times in the routing repeating the address of a way point several times in the routing
header. More complex forms could involve alternating way point header. More complex forms could involve alternating way point
addresses that would result in the packet re-transiting the router or addresses that would result in the packet re-transiting the router or
firewall. These attacks can be counteracted by ensuring that routing firewall. These attacks can be counteracted by ensuring that routing
headers do not contain the same way point address more than once, and headers do not contain the same way point address more than once, and
performing ingress/egress filtering to check that the source address performing ingress/egress filtering to check that the source address
is appropriate to the destination: packets made to reverse their path is appropriate to the destination: packets made to reverse their path
will fail this test. will fail this test.
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Some of these addresses have current legitimate uses within a site. Some of these addresses have current legitimate uses within a site.
The risk can be minimized by ensuring that all firewalls and site The risk can be minimized by ensuring that all firewalls and site
boundary routers are configured to drop packets with site scope boundary routers are configured to drop packets with site scope
destination addresses. Also nodes should not join multicast groups destination addresses. Also nodes should not join multicast groups
for which there is no legitimate use on the site and site routers for which there is no legitimate use on the site and site routers
should be configured to drop packets directed to these unused should be configured to drop packets directed to these unused
addresses. addresses.
2.1.4. ICMPv6 and Multicast 2.1.4. ICMPv6 and Multicast
It is possible to launch a denial-of-service (DoS) attack using IPv6 It is possible to launch a Denial-of-Service (DoS) attack using IPv6
that could be amplified by the multicast infrastructure. that could be amplified by the multicast infrastructure.
Unlike ICMP for IPv4, ICMPv6 [RFC2463] allows error notification Unlike ICMP for IPv4, ICMPv6 [RFC4443] allows error notification
responses to be sent when certain unprocessable packets are sent to responses to be sent when certain unprocessable packets are sent to
multicast addresses. multicast addresses.
The cases in which responses are sent are: The cases in which responses are sent are:
o The received packet is longer than the next link MTU: 'Packet Too o The received packet is longer than the next link Maximum
Big' responses are needed to support Path MTU Discovery for Transmission Unit (MTU): 'Packet Too Big' responses are needed to
multicast traffic. support Path MTU Discovery for multicast traffic.
o The received packet contains an unrecognized option in a hop-by- o The received packet contains an unrecognized option in a hop-by-
hop or destination options extension header with the first two hop or destination options extension header with the first two
bits of the option type set to binary '10': 'Parameter Problem' bits of the option type set to binary '10': 'Parameter Problem'
responses are intended to inform the source that some or all of responses are intended to inform the source that some or all of
the recipients cannot handle the option in question. the recipients cannot handle the option in question.
If an attacker can craft a suitable packet sent to a multicast If an attacker can craft a suitable packet sent to a multicast
destination, it may be possible to elicit multiple responses directed destination, it may be possible to elicit multiple responses directed
at the victim (the spoofed source of the multicast packet). On the at the victim (the spoofed source of the multicast packet). On the
other hand, the use of 'reverse path forwarding' checks to eliminate other hand, the use of 'reverse path forwarding' checks to eliminate
loops in multicast forwarding automatically limits the range of loops in multicast forwarding automatically limits the range of
addresses that can be spoofed. addresses that can be spoofed.
In practice an attack using oversize packets is unlikely to cause In practice an attack using oversize packets is unlikely to cause
much amplification unless the attacker is able to carefully tune the much amplification unless the attacker is able to carefully tune the
packet size to exploit a network with smaller MTU in the edge than packet size to exploit a network with smaller MTU in the edge than
the core. Similarly a packet with an unrecognized hop-by-hop option the core. Similarly a packet with an unrecognized hop-by-hop option
would be dropped by the first router. However a packet with an would be dropped by the first router without resulting in multiple
unrecognized destination option could generate multiple responses. responses. However a packet with an unrecognized destination option
could generate multiple responses.
In addition to amplification, this kind of attack would potentially In addition to amplification, this kind of attack would potentially
consume large amounts of forwarding state resources in routers on consume large amounts of forwarding state resources in routers on
multicast-enabled networks. These attacks are discussed in more multicast-enabled networks.
detail in [I-D.savola-v6ops-firewalling].
2.1.5. Bogus Errored Packets in ICMPv6 Error Messages 2.1.5. Bogus Errored Packets in ICMPv6 Error Messages
Apart from the spurious load on the network, routers and hosts, bogus Apart from the spurious load on the network, routers and hosts, bogus
ICMPv6 error messages (types 0 to 127) containing a spoofed errored ICMPv6 error messages (types 0 to 127) containing a spoofed errored
packet can impact higher layer protocols when the alleged errored packet can impact higher layer protocols when the alleged errored
packet is referred to the higher layer at the destination of the packet is referred to the higher layer at the destination of the
ICMPv6 packet [RFC2463]. The potentially damaging effects on TCP ICMPv6 packet [RFC4443]. The potentially damaging effects on TCP
connections and some ways to mitigate the threats are documented in connections and some ways to mitigate the threats are documented in
[I-D.gont-tcpm-icmp-attacks]. [I-D.ietf-tcpm-icmp-attacks].
Specific countermeasures for particular higher layer protocols are Specific countermeasures for particular higher layer protocols are
beyond the scope of this document but firewalls may be able to help beyond the scope of this document but firewalls may be able to help
counter the threat by inspecting the alleged errored packet embedded counter the threat by inspecting the alleged errored packet embedded
in the ICMPv6 error message. The firewall and the receiving host in the ICMPv6 error message. Measures to mitigate the threat
should test that the embedded packet contains addresses that would include:
have been legitimate (i.e., would have passed ingress/egress o The receiving host should test that the embedded packet is all or
filtering) for a packet sent from the receiving host. The part of a packet that was transmitted by the host.
specification of ICMPv6 and the requirement that networks should have o The firewall may be able to test that the embedded packet contains
a minimum MTU of 1280 octets (as compared with ICMP and IPv4), means addresses that would have been legitimate (i.e., would have passed
that the ICMPv6 should normally carry all the header fields of the ingress/egress filtering) for a packet sent from the receiving
errored packet. Firewalls and destination hosts should therefore be host but the possibility of asymmetric routing of the outgoing and
suspicious of ICMPv6 error messages with very truncated errored returning packets may prevent this sort of test depending on the
packets (e.g., those that only carry the address fields of the IPv6 topology of the network, the location of the firewall, and whether
base header.) state synchronization between firewalls is in use.
o If the firewall is stateful and the test is not prevented by
asymmetric routing, the firewall may also be able to check that
the embedded packet is all or part of a packet which recently
transited the firewall in the opposite direction.
o Firewalls and destination hosts should be suspicious of ICMPv6
error messages with unnecessarily truncated errored packets (e.g.,
those that only carry the address fields of the IPv6 base header.)
The specification of ICMPv6 requires that error messages carry as
much of the errored packet as possible (unlike ICMP for IPv4 which
requires only a minimum amount of the errored packet) and IPv6
networks must have a guaranteed minimum MTU of 1280 octets.
Accordingly, the ICMPv6 message should normally carry all the
header fields of the errored packet together with a significant
amount of the payload allowing robust comparison against the
outgoing packet.
2.1.6. Anycast Traffic Identification and Security 2.1.6. Anycast Traffic Identification and Security
IPv6 introduces the notion of anycast addresses and services. IPv6 introduces the notion of anycast addresses and services.
Originally the IPv6 standards disallowed using an anycast address as Originally the IPv6 standards disallowed using an anycast address as
the source address of a packet. Responses from an anycast server the source address of a packet. Responses from an anycast server
would therefore supply a unicast address for the responding server. would therefore supply a unicast address for the responding server.
To avoid exposing knowledge about the internal structure of the To avoid exposing knowledge about the internal structure of the
network, it is recommended that anycast servers now take advantage of network, it is recommended that anycast servers now take advantage of
the ability to return responses with the anycast address as the the ability to return responses with the anycast address as the
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services: these addresses are arbitrary and not distinguishable from services: these addresses are arbitrary and not distinguishable from
any other IPv6 unicast address by structure or pattern. any other IPv6 unicast address by structure or pattern.
One particular class of anycast addresses that should be given One particular class of anycast addresses that should be given
special attention is the set of Subnet-Router anycast addresses special attention is the set of Subnet-Router anycast addresses
defined in The IPv6 Addressing Architecture [RFC4291]. All routers defined in The IPv6 Addressing Architecture [RFC4291]. All routers
are required to support these addresses for all subnets for which are required to support these addresses for all subnets for which
they have interfaces. For most subnets using global unicast they have interfaces. For most subnets using global unicast
addresses, filtering anycast requests to these addresses can be addresses, filtering anycast requests to these addresses can be
achieved by dropping packets with the lower 64 bits (the Interface achieved by dropping packets with the lower 64 bits (the Interface
Identifier) set to all zeroes. Identifier) set to all zeros.
2.1.7. Address Privacy Extensions Interact with DDoS Defenses 2.1.7. Address Privacy Extensions Interact with DDoS Defenses
The purpose of the privacy extensions for stateless address auto- The purpose of the privacy extensions for stateless address auto-
configuration [RFC3041][I-D.ietf-ipv6-privacy-addrs-v2] is to change configuration [I-D.ietf-ipv6-privacy-addrs-v2] is to change the
the interface identifier (and hence the global scope addresses interface identifier (and hence the global scope addresses generated
generated from it) from time to time. By varying the addresses used, from it) from time to time. By varying the addresses used,
eavesdroppers and other information collectors find it more difficult eavesdroppers and other information collectors find it more difficult
to identify which transactions actually relate to a specific node. to identify which transactions actually relate to a specific node.
A security issue may result from this if the frequency of node A security issue may result from this if the frequency of node
address change is sufficiently great to achieve the intended aim of address change is sufficiently great to achieve the intended aim of
the privacy extensions: with a relatively high rate of change, the the privacy extensions: with a relatively high rate of change, the
observed behavior of the node could look very like that of a observed behavior of the node could look very like that of a
compromised node that was the source of a distributed denial of compromised node that was the source of a Distributed Denial-of-
service (DDoS). It would thus be difficult for any future defenses Service (DDoS) attack. It would thus be difficult for any future
against DDoS attacks to distinguish between a high rate of change of defenses against DDoS attacks to distinguish between a high rate of
addresses resulting from genuine use of the privacy extensions and a change of addresses resulting from genuine use of the privacy
compromised node being used as the source of a DDoS with 'in-prefix' extensions and a compromised node being used as the source of a DDoS
spoofed source addresses as described in [I-D.dupont-ipv6- with 'in-prefix' spoofed source addresses as described in
rfc3041harmful]. [I-D.ietf-ipv6-privacy-addrs-v2].
Even if a node is well behaved, the change in the address could make Even if a node is well behaved, the change in the address could make
it harder for a security administrator to define a policy rule (e.g. it harder for a security administrator to define a policy rule (e.g.,
access control list) that takes into account a specific node. access control list) that takes into account a specific node.
2.1.8. Dynamic DNS: Stateless Address Auto-Configuration, Privacy 2.1.8. Dynamic DNS: Stateless Address Auto-Configuration, Privacy
Extensions and SEND Extensions and SEND
The introduction of Stateless Address Auto-Configuration (SLAAC) The introduction of Stateless Address Auto-Configuration (SLAAC)
[RFC2462] with IPv6 provides an additional challenge to the security [RFC2462] with IPv6 provides an additional challenge to the security
of Dynamic DNS (DDNS). With manual addressing or the use of DHCP, of Dynamic Domain Name System (DDNS). With manual addressing or the
the number of security associations that need to be maintained to use of DHCP, the number of security associations that need to be
secure access to the DNS server is limited, assuming any necessary maintained to secure access to the Domain Name Service (DNS) server
updates are carried out by the DHCP server. This is true equally for is limited, assuming any necessary updates are carried out by the
IPv4 and IPv6. DHCP server. This is true equally for IPv4 and IPv6.
Since SLAAC does not make use of a single and potentially trusted Since SLAAC does not make use of a single and potentially trusted
DHCP server, but depends on the node obtaining the address, securing DHCP server, but depends on the node obtaining the address, securing
the insertion of updates into DDNS may need a security association the insertion of updates into DDNS may need a security association
between each node and the DDNS server. This is discussed further in between each node and the DDNS server. This is discussed further in
[I-D.ietf-dnsop-ipv6-dns-issues]. [RFC4472].
Using the Privacy Extensions to SLAAC [RFC3041][I-D.ietf-ipv6- Using the Privacy Extensions to SLAAC
privacy-addrs-v2] may significantly increase the rate of updates of [I-D.ietf-ipv6-privacy-addrs-v2] may significantly increase the rate
DDNS. Even if a node using the Privacy Extensions does not publish of updates of DDNS. Even if a node using the Privacy Extensions does
its address for 'forward' lookup (as that would effectively not publish its address for 'forward' lookup (as that would
compromise the privacy which it is seeking), it may still need to effectively compromise the privacy which it is seeking), it may still
update the reverse DNS records so that reverse routability checks can need to update the reverse DNS records. If the reverse DNS records
be carried out. If the rate of change needed to achieve real privacy are not updated servers that perform reverse DNS checks will not
has to be increased as is mentioned in Section 2.1.7 the update rate accept connections from the node and it will not be possible to gain
for DDNS may be excessive. access to IP Security (IPsec) keying material stored in DNS
[RFC4025]. If the rate of change needed to achieve real privacy has
to be increased (see Section 2.1.7) the update rate for DDNS may be
excessive.
Similarly, the cryptographically generated addresses used by SEND Similarly, the cryptographically generated addresses used by SEND
[RFC3971] are expected to be periodically regenerated in line with [RFC3971] are expected to be periodically regenerated in line with
recommendations for maximum key lifetimes. This regeneration could recommendations for maximum key lifetimes. This regeneration could
also impose a significant extra load on DDNS. also impose a significant extra load on DDNS.
2.1.9. Extension Headers 2.1.9. Extension Headers
A number of issues relating to the specification of IPv6 Extension A number of security issues relating to IPv6 Extension headers have
headers have been identified. Several of these are discussed in been identified. Several of these are as a result of ambiguous or
[I-D.savola-v6ops-firewalling]. incomplete specification in the base IPv6 specification [RFC2460].
2.1.9.1. Processing Extension Headers in Middleboxes 2.1.9.1. Processing Extension Headers in Middleboxes
In IPv4 deep packet inspection techniques are used to implement In IPv4 deep packet inspection techniques are used to implement
policing and filtering both as part of routers and in middleboxes policing and filtering both as part of routers and in middleboxes
such as firewalls. Fully extending these techniques to IPv6 would such as firewalls. Fully extending these techniques to IPv6 would
require inspection of all the extension headers in a packet. This is require inspection of all the extension headers in a packet. This is
essential to ensure that policy constraints on the use of certain essential to ensure that policy constraints on the use of certain
headers and options are enforced and to remove, at the earliest headers and options are enforced and to remove, at the earliest
opportunity, packets containing potentially damaging unknown options. opportunity, packets containing potentially damaging unknown options.
This requirement appears to conflict with Section 4 of the IPv6 This requirement appears to conflict with Section 4 of the IPv6
specification in [RFC2460] which requires that destination options specification in [RFC2460] which requires that only hop-by-hop
are not processed at all until the packet reaches the appropriate options are processed at any node through which the packet passes
destination (either the final destination or a routing header until the packet reaches the appropriate destination (either the
waypoint). final destination or a routing header waypoint).
Also [RFC2460] forbids processing the headers other than in the order Also [RFC2460] forbids processing the headers other than in the order
in which they appear in the packet. in which they appear in the packet.
A further ambiguity relates to whether an intermediate node should A further ambiguity relates to whether an intermediate node should
discard a packet that contains a header or destination option which discard a packet that contains a header or destination option which
it does not recognize. If the rules above are followed slavishly, it it does not recognize. If the rules above are followed slavishly, it
is not (or may not be) legitimate for the intermediate node to is not (or may not be) legitimate for the intermediate node to
discard the packet because it should not be processing those headers discard the packet because it should not be processing those headers
or options. or options.
[RFC2460] therefore does not appear to take account of the behavior [RFC2460] therefore does not appear to take account of the behavior
of middleboxes and other non-final destinations that may be of middleboxes and other non-final destinations that may be
inspecting the packet, and thereby potentially limits the security inspecting the packet, and thereby potentially limits the security
protection of these boxes. protection of these boxes. Firewall vendors and administrators may
choose to ignore these rules in order to provide enhanced security as
this does not appear to have any serious consequences with the
currently defined set of extensions, but administrators should be
aware that future extensions might require different treatment.
2.1.9.2. Processing Extension Header Chains 2.1.9.2. Processing Extension Header Chains
There is a further problem for middleboxes that want to examine the There is a further problem for middleboxes that want to examine the
transport headers, which are located at the end of the IPv6 header transport headers that are located at the end of the IPv6 header
chain. In order to locate the transport header or other protocol chain. In order to locate the transport header or other protocol
data unit, the node has to parse the header chain. data unit, the node has to parse the header chain.
The IPv6 specification [RFC2460] does not mandate the use of the The IPv6 specification [RFC2460] does not mandate the use of the
Type-Length-Value format with a fixed layout for the start of each Type-Length-Value (TLV) format with a fixed layout for the start of
header although it is used for the majority of headers currently each header although it is used for the majority of headers currently
defined. (Only the Type field is guaranteed in size and offset). defined. (Only the Type field is guaranteed in size and offset).
A middlebox cannot therefore guarantee to be able to process header A middlebox cannot therefore guarantee to be able to process header
chains that may contain headers defined after the box was chains that may contain headers defined after the box was
manufactured. As noted in Section 2.1.9.1, middleboxes ought not to manufactured. As discussed further in Section 2.1.9.3, middleboxes
have to know about all header types in use but still need to be able ought not to have to know the detailed layout of all header types in
to skip over such headers to find the transport PDU start. This use but still need to be able to skip over such headers to find the
either limits the security that can be applied in firewalls or makes transport payload start. If this is not possible, it either limits
it difficult to deploy new extension header types. the security policy that can be applied in firewalls or makes it
difficult to deploy new extension header types.
At the time of writing, only the Fragment Header does not fully At the time of writing, only the Fragment Header does not fully
conform to the TLV format used for other extension headers. In conform to the TLV format used for other extension headers. In
practice, many firewalls reconstruct fragmented packets before practice, many firewalls reconstruct fragmented packets before
performing deep packet inspection, so this divergence is less performing deep packet inspection, so this divergence is less
problematic than it might have been, and is at least partially problematic than it might have been, and is at least partially
justified because the full header chain is not present in all justified because the full header chain is not present in all
fragments. fragments.
Destination Options may also contain unknown options. However, the Hop-by-hop and Destination Options may also contain unknown options.
options are encoded in TLV format so that intermediate nodes can skip However, the options are required to be encoded in TLV format so that
over them during processing, unlike the enclosing extension headers. intermediate nodes can skip over them during processing, unlike the
enclosing extension headers.
2.1.9.3. Unknown Headers/Destination Options and Security Policy 2.1.9.3. Unknown Headers/Destination Options and Security Policy
A strict security policy might dictate that packets containing either A strict security policy might dictate that packets containing either
unknown headers or destination options are discarded by firewalls or unknown headers or destination options are discarded by firewalls or
other filters. This requires the firewall to process the whole other filters. This requires the firewall to process the whole
extension header chain, which may be currently in conflict with the extension header chain, which may be currently in conflict with the
IPv6 specification as discussed in Section 2.1.9.1. IPv6 specification as discussed in Section 2.1.9.1.
Even if the firewall does inspect the whole header chain, it may not Even if the firewall does inspect the whole header chain, it may not
be sensible to discard packets with items unrecognized by the be sensible to discard packets with items unrecognized by the
firewall: the intermediate node has no knowledge of which options and firewall: the intermediate node has no knowledge of which options and
headers are implemented in the destination node. Hence it is highly headers are implemented in the destination node and IPv6 has been
desirable to make the discard policy configurable. This will avoid deliberately designed to be extensible through adding new header
firewalls dropping packets with legitimate items that they do not options. This poses a dilemma for firewall administrators. On the
recognize because their hardware or software is not aware of a new one hand admitting packets with 'unknown' options is a security risk
definition. but dropping them may disable a useful new extension. The best
compromise appears to be to select firewalls that provide a
configurable discard policy based on the types of the extensions.
Then, if a new extension is standardized, administrators can
reconfigure firewalls to pass packets with legitimate items that they
would otherwise not recognize because their hardware or software is
not aware of a new definition. Provided that the new extensions
conform to the TLV layout followed by current extensions the firewall
would not need detailed knowledge of the function or layout of the
extension header.
2.1.9.4. Excessive Hop-by-Hop Options 2.1.9.4. Excessive Hop-by-Hop Options
IPv6 does not limit the number of hop by hop options that can be IPv6 does not limit the number of hop-by-hop options that can be
present in a hop-by-hop option header. The lack of a limit can be present in a hop-by-hop option header and any option can appear
used to mount denial of service attacks affecting all nodes on a path multiple times. The lack of a limit and the provision of
as described in [I-D.krishnan-ipv6-hopbyhop]. extensibility bits that force nodes to ignore classes of options
which they do not understand can be used to mount denial of service
attacks affecting all nodes on a path. A packet with large numbers
of unknown hop-by-hop options will be processed at every node through
which it is forwarded, consuming significant resources to determine
what action should be taken for each option. Current options with
the exception of Pad1 and PadN should not appear more than once so
that packets with inappropriately repeated options can be dropped but
keeping track of which options have been seen adds complexity to
firewalls and may not apply to future extensions. See
Section 2.1.9.3 for a discussion of the advisability of dropping
packets with unknown options in firewalls.
2.1.9.5. Misuse of Pad1 and PadN Options 2.1.9.5. Misuse of Pad1 and PadN Options
IPv6 allows multiple padding options of arbitrary sizes to be placed IPv6 allows multiple padding options of arbitrary sizes to be placed
in both Hop-by-Hop and Destination option headers. There is no in both Hop-by-Hop and Destination option headers.
legitimate reason for having a sequence of padding option fields -
the required padding can be done with one field and there is PadN options are required to contain zero octets as 'payload': there
currently no legitimate reason for padding beyond the next four or, is, however, no incentive for receivers to check this. It may
at worst, eight octet boundary. PadN options are required to contain therefore be possible to use the 'payload' of padding options as a
zero octets as 'payload': there is, however, no incentive for covert channel. Firewalls and receiving hosts should actively check
receivers to check this. It may therefore be possible to use padding that PadN only has zero octets in its 'payload'.
options as a covert channel. Firewalls and receiving hosts should
consider dropping packets that have sequences of Pad0 or PadN options There is no legitimate reason for padding beyond the next eight octet
or use PadN of more than length 3 or 7, and should actively check boundary since the whole option header is aligned on a eight octet
that PadN does not have other than zero octets in its 'payload'. boundary but cannot be guaranteed to be on a 16 (or higher power of
two) octet boundary. The IPv6 specification allows multiple Pad1 and
PadN options to be combined in any way that the source chooses to
make up the required padding. Reasonable design choices would appear
to be using however many Pad1 options (i.e., zero octets) are needed
or using a single PadN option of the required size (two up to seven
octets). Administrators should consider at least logging unusual
padding patterns, and may consider dropping packets that contain
unusual patterns if they are certain of expected source behavior.
2.1.9.6. Overuse of Router Alert Option 2.1.9.6. Overuse of Router Alert Option
The IPv6 router alert option specifies a hop-by-hop option that, if The IPv6 router alert option specifies a hop-by-hop option that, if
present, signals the router to take a closer look at the packet. present, signals the router to take a closer look at the packet.
This can be used for denial of service attacks. By sending a large This can be used for denial of service attacks. By sending a large
number of packets containing a router alert option an attacker can number of packets containing a router alert option an attacker can
deplete the processor cycles on the routers available to legitimate deplete the processor cycles on the routers available to legitimate
traffic. traffic.
skipping to change at page 12, line 26 skipping to change at page 14, line 30
The current specifications of IPv6 in [RFC2460] do not mandate any The current specifications of IPv6 in [RFC2460] do not mandate any
minimum packet size for the fragments of a packet before the last minimum packet size for the fragments of a packet before the last
one, except for the need to carry the unfragmentable part in all one, except for the need to carry the unfragmentable part in all
fragments. fragments.
The unfragmentable part does not include the transport port numbers The unfragmentable part does not include the transport port numbers
so that it is possible that the first fragment does not contain so that it is possible that the first fragment does not contain
sufficient information to carry out deep packet inspection involving sufficient information to carry out deep packet inspection involving
the port numbers. the port numbers.
Also the reassembly rules for fragmented packets in [RFC2460] do not Packets with overlapping fragments are considered to be a major
mandate behavior that would minimize the effects of overlapping security risk, but the reassembly rules for fragmented packets in
fragments. [RFC2460] do not mandate behavior that would minimize the effects of
overlapping fragments.
Depending on the implementation of packet reassembly and the In order to ensure that deep packet inspection can be carried out
treatment of packet fragments in firewalls and other nodes that use correctly on fragmented packets, many firewalls and other nodes that
deep packet inspection for traffic filtering, this potentially leaves use deep packet inspection will collect the fragments and reassemble
IPv6 open to the sort of attacks described in [RFC1858] and [RFC3128] the packet before examining the packet. Depending on the
for IPv4. implementation of packet reassembly and the treatment of packet
fragments in these nodes, the specification issues mentioned
potentially leave IPv6 open to the sort of attacks described in
[RFC1858] and [RFC3128] for IPv4.
There is no reason to allow overlapping packet fragments and overlaps The following steps can be taken to mitigate these threats:
could be prohibited in a future revision of the protocol o Although permitted in [RFC2460] there is no reason for a source to
specification. Some implementations already drop all packets with generate overlapping packet fragments and overlaps could be
overlapped fragments. prohibited in a future revision of the protocol specification.
Firewalls should drop all packets with overlapped fragments:
certain implementations both in firewalls and other nodes already
drop such packets.
Specifying a minimum size for packet fragments does not help in the o Specifying a minimum size for packet fragments does not help in
same way as it does for IPv4 because IPv6 extension headers can be the same way as it does for IPv4 because IPv6 extension headers
made to appear very long: an attacker could insert one or more can be made to appear very long: an attacker could insert one or
undefined destination options with long lengths and the 'ignore if more undefined destination options with long lengths and the
unknown' bit set. Given the guaranteed minimum MTU of IPv6 it seems 'ignore if unknown' bit set. Given the guaranteed minimum MTU of
reasonable that hosts should be able to ensure that the transport IPv6 it seems reasonable that hosts should be able to ensure that
port numbers are in the first fragment in almost all cases and that the transport port numbers are in the first fragment in almost all
deep packet inspection should be very suspicious of first fragments cases and that deep packet inspection should be very suspicious of
that do not contain them. first fragments that do not contain them (see also the discussion
of fragment sizes in Section 2.1.11).
2.1.11. Fragmentation Related DoS Attacks 2.1.11. Fragmentation Related DoS Attacks
Packet reassembly in IPv6 hosts also opens up the possibility of Packet reassembly in IPv6 hosts also opens up the possibility of
various fragment-related security attacks. Some of these are various fragment-related security attacks. Some of these are
analogous to attacks identified for IPv4. Of particular concern is a analogous to attacks identified for IPv4. Of particular concern is a
DoS attack based on sending large numbers of small fragments without DoS attack based on sending large numbers of small fragments without
a terminating last fragment that would potentially overload the a terminating last fragment that would potentially overload the
reconstruction buffers and consume large amounts of CPU resources. reconstruction buffers and consume large amounts of CPU resources.
Mandating the size of packet fragments could reduce the impact of Mandating the size of packet fragments could reduce the impact of
this kind of attack by limiting the rate at which fragments could this kind of attack by limiting the rate at which fragments could
arrive and limiting the number of fragments that need to be arrive and limiting the number of fragments that need to be processed
processed. but this is not currently specified by the IPv6 standard. In
practice reasonable design choices in protocol stacks are likely to
either maximise the size of all fragments except the final one using
the path MTU (most likely choice), or distribute the data evenly in
the required minimum number of fragments. In either case the
smallest non-final fragment would be at least half the guaranteed
minimum MTU (640 octets) - the worst case arises when a payload is
just too large for a single packet and is divided approximately
equally between two packets. Administrators should consider
configuring firewalls and hosts to drop non-final fragments smaller
than 640 octets.
2.1.12. Link-Local Addresses and Securing Neighbor Discovery 2.1.12. Link-Local Addresses and Securing Neighbor Discovery
All IPv6 nodes are required to configure a link-local address on each All IPv6 nodes are required to configure a link-local address on each
interface. This address is used to communicate with other nodes interface. This address is used to communicate with other nodes
directly connected to the link accessed via the interface, especially directly connected to the link accessed via the interface, especially
during the neighbor discovery and auto-configuration processes. during the neighbor discovery and auto-configuration processes.
Link-local addresses are fundamental to the operation of the Neighbor Link-local addresses are fundamental to the operation of the Neighbor
Discovery Protocol (NDP) [RFC2461] and SLAAC [RFC2462]. NDP also Discovery Protocol (NDP) [RFC2461] and Stateless Address
provides the functionality of associating link layer and IP addresses Autoconfiguration (SLAAC) [RFC2462]. NDP also provides the
provided by the Address Resolution Protocol (ARP) in IPv4 networks. functionality of associating link layer and IP addresses provided by
the Address Resolution Protocol (ARP) in IPv4 networks.
The standard version of NDP is subject to a number of security The standard version of NDP is subject to a number of security
threats related to ARP spoofing attacks on IPv4. These threats have threats related to ARP spoofing attacks on IPv4. These threats have
been documented in [RFC3756] and mechanisms to combat them specified been documented in [RFC3756] and mechanisms to combat them specified
in SEcure Neighbor Discovery (SEND) [RFC3971]. SEND is an optional in SEcure Neighbor Discovery (SEND) [RFC3971]. SEND is an optional
mechanism that is particularly applicable to wireless and other mechanism that is particularly applicable to wireless and other
environments where it is difficult to physically secure the link. environments where it is difficult to physically secure the link.
Because the link-local address can, by default, be acquired without Because the link-local address can, by default, be acquired without
external intervention or control, it allows an attacker to commence external intervention or control, it allows an attacker to commence
communication on the link without needing to acquire information communication on the link without needing to acquire information
about the address prefixes in use or communicate with any authorities about the address prefixes in use or communicate with any authorities
on the link. This feature gives a malicious node the opportunity to on the link. This feature gives a malicious node the opportunity to
mount an attack on any other node that is attached to this link; this mount an attack on any other node that is attached to this link; this
vulnerability exists in addition to possible direct attacks on NDP. vulnerability exists in addition to possible direct attacks on NDP.
Link-local addresses may also facilitate the unauthorized use of the Link-local addresses may also facilitate the unauthorized use of the
link bandwidth ('bandwidth theft') to communicate with another link bandwidth ('bandwidth theft') to communicate with another
unauthorized node on the same link. unauthorized node on the same link.
Link-local addresses allocated from the prefix 169.254.0.0/16 are The vulnerabilities of IPv6 link local addresses in NDP can be
available in IPv4 as well and procedures for using them are described mitigated in several ways. A general solution will require
in [RFC3927] but the security issues were not as pronounced as for
IPv6 for the following reasons:
o link-local addresses are not mandatory in IPv4 and are primarily
intended for isolated or ad hoc networks that cannot acquire a
routable IPv4 address by other means,
o IPv4 link-local addresses are not universally supported across
operating systems, and
o the IPv4 link-local address should be removed when a non-link-
local address is configured on the interface and will generally
not be allocated unless other means of acquiring an address are
not available.
These vulnerabilities can be mitigated in several ways. A general
solution will require
o authenticating the link layer connectivity, for example by using o authenticating the link layer connectivity, for example by using
IEEE 802.1x functionality, port-based MAC address security IEEE 802.1X functionality [IEEE.802-1X.2004] or physical security,
(locking), or physical security, and and
o using SEcure Neighbor Discovery (SEND) to create a o using SEcure Neighbor Discovery (SEND) to create a
cryptographically generated link-local address as described in cryptographically generated link-local address as described in
[RFC3971] that is tied to the authenticated link layer address. [RFC3971] that is tied to the authenticated link layer address.
This solution would be particularly appropriate in wireless LAN This solution would be particularly appropriate in wireless LAN
deployments where it is difficult to physically secure the deployments where it is difficult to physically secure the
infrastructure infrastructure, but may not be considered necessary in wired
environments where the physical infrastructure can be kept secure by
other means.
In wired environments, where the physical infrastructure is Limiting the potentiality for abuse of link local addresses in
reasonably secure, it may be sufficient to ignore communication general packet exchanges is more problematic because there may be
requests originating from a link-local address for other than local circumstances, such as isolated networks, where usage is appropriate
network management purposes. This requires that nodes should only and discrimination between use and abuse requires complex filtering
accept packets with link-local addresses for a limited set of rules which have to be implemented on hosts. The risk of misuse may
protocols including NDP, MLD and other functions of ICMPv6. be deemed too small compared with the effort needed to control it,
but special attention should be paid to tunnel end-points (see
Section 2.4, Section 3.2 and Section 3.3).
Any filtering has to be provided by a host-based or bridging
firewall. In general link local addresses are expected to be used by
applications that are written to deal with specific interfaces and
links. Typically these application are used for control and
management, A node which is attached to multiple links has to deal
with the potentially overlapping link local address spaces associated
with these links. IPv6 provides for this through zone identifiers
that are used to discriminate between the different address scopes
[RFC4007] and the scope identifier that can be associated with a
socket address structure [RFC3493]. Most users are unfamiliar with
these issues and general purpose applications are not intended to
handle this kind of discrimination. Link local addresses are not
normally used with the Domain Name System (DNS) and DNS cannot supply
zone identifiers. If it is considered necessary to prevent the use
of link local addresses by other than control and management
protocols, administrators may wish to consider limiting the protocols
that can be used with link local addresses. At a minimum ICMPv6 and
any intra-domain routing protocol (such as Open Shortest Path First
(OSPF) or Routing Information Protocol (RIP)) in use need to be
allowed but other protocols may also be needed. RIP illustrates the
complexity of the filtering problem: its messages are encapsulated as
User Datagram Protocol (UDP) payloads and filtering needs to
distinguish RIP messages addressed to UDP port 521 from other UDP
messages.
2.1.13. Securing Router Advertisements 2.1.13. Securing Router Advertisements
As part of the Neighbor Discovery process, routers on a link As part of the Neighbor Discovery process, routers on a link
advertise their capabilities in Router Advertisement messages. The advertise their capabilities in Router Advertisement messages. The
version of NDP defined in [RFC2461] does not protect the integrity of version of NDP defined in [RFC2461] does not protect the integrity of
these messages or validate the assertions made in the messages with these messages or validate the assertions made in the messages with
the result that any node that connects to the link can maliciously the result that any node that connects to the link can maliciously
claim to offer routing services that it will not fulfil, and claim to offer routing services that it will not fulfil, and
advertise inappropriate prefixes and parameters. These threats have advertise inappropriate prefixes and parameters. These threats have
skipping to change at page 15, line 38 skipping to change at page 18, line 26
The threats and solutions are described in [RFC3775] and a more The threats and solutions are described in [RFC3775] and a more
extensive discussion of the security aspects of the design can be extensive discussion of the security aspects of the design can be
found in [RFC4225]. found in [RFC4225].
2.1.15.1. Obsolete Home Address Option in Mobile IPv6 2.1.15.1. Obsolete Home Address Option in Mobile IPv6
The Home Address option specified in early drafts of Mobile IPv6 The Home Address option specified in early drafts of Mobile IPv6
would have allowed a trivial source spoofing attack: hosts were would have allowed a trivial source spoofing attack: hosts were
required to substitute the source address of incoming packets with required to substitute the source address of incoming packets with
the address in the option, thereby potentially evading checks on the the address in the option, thereby potentially evading checks on the
packet source address. This is discussed at greater length in packet source address. The version of Mobile IPv6 as standardized in
[I-D.savola-ipv6-rh-ha-security]. The version of Mobile IPv6 as [RFC3775] has removed this issue by ensuring that the Home Address
standardized in [RFC3775] has removed this issue by ensuring that the destination option is only processed if there is a corresponding
Home Address destination option is only processed if there is a binding cache entry and securing Binding Update messages.
corresponding binding cache entry and securing Binding Update
messages.
A number of pre-standard implementations of Mobile IPv6 were A number of pre-standard implementations of Mobile IPv6 were
available that implemented this obsolete and insecure option: care available that implemented this obsolete and insecure option: care
should be taken to avoid running such obsolete systems. should be taken to avoid running such obsolete systems.
2.2. IPv4-mapped IPv6 Addresses 2.2. IPv4-mapped IPv6 Addresses
Overloaded functionality is always a double-edged sword: it may yield Overloaded functionality is always a double-edged sword: it may yield
some deployment benefits, but often also incurs the price that comes some deployment benefits, but often also incurs the price that comes
with ambiguity. with ambiguity.
One example of such is IPv4-mapped IPv6 addresses: a representation One example of such is IPv4-mapped IPv6 addresses (::ffff/96): a
of an IPv4 address as an IPv6 address inside an operating system. representation of an IPv4 address as an IPv6 address inside an
Since the original specification, the use of IPv4-mapped addresses operating system as defined in [RFC3493]. Since the original
has been extended to a transition mechanism, Stateless IP/ICMP specification, the use of IPv4-mapped addresses has been extended to
Translation algorithm (SIIT) [RFC2765], where they are potentially a transition mechanism, Stateless IP/ICMP Translation algorithm
used in the addresses of packets on the wire. (SIIT) [RFC2765], where they are potentially used in the addresses of
packets on the wire.
Therefore, it becomes difficult to unambiguously discern whether an Therefore, it becomes difficult to unambiguously discern whether an
IPv4 mapped address is really an IPv4 address represented in the IPv6 IPv4 mapped address is really an IPv4 address represented in the IPv6
address format *or* an IPv6 address received from the wire (which may address format (basic API behavior ) *or* an IPv6 address received
be subject to address forgery, etc.). from the wire (which may be subject to address forgery, etc.) (SIIT
behavior). The security issues that arise from the ambiguous
behavior when IPv4-mapped addresses are used on the wire include:
o If an attacker transmits an IPv6 packet with ::ffff:127.0.0.1 in
the IPv6 source address field, he might be able to bypass a node's
access controls by deceiving applications into believing that the
packet is from the node itself (specifically, the IPv4 loopback
address, 127.0.0.1). The same attack might be performed using the
node's IPv4 interface address instead.
o If an attacker transmits an IPv6 packet with IPv4-mapped addresses
in the IPv6 destination address field corresponding to IPv4
addresses inside a site's security perimeter (e.g., ::ffff:
10.1.1.1), he might be able to bypass IPv4 packet filtering rules
and traverse a site's firewall.
o If an attacker transmits an IPv6 packet with IPv4-mapped addresses
in the IPv6 source and destination fields to a protocol that swaps
IPv6 source and destination addresses, he might be able to use a
node as a proxy for certain types of attacks. For example, this
might be used to construct broadcast multiplication and proxy TCP
port scan attacks.
In addition, special cases like these, while giving deployment In addition, special cases like these, while giving deployment
benefits in some areas, require a considerable amount of code benefits in some areas, require a considerable amount of code
complexity (e.g. in the implementations of bind() system calls and complexity (e.g., in the implementations of bind() system calls and
reverse DNS lookups) that is probably undesirable. Some of these reverse DNS lookups) that is probably undesirable but can be managed
issues are discussed in [I-D.cmetz-v6ops-v4mapped-api-harmful] and in this case.
[I-D.itojun-v6ops-v4mapped-harmful].
In practice, although the packet translation mechanisms of SIIT are In practice, although the packet translation mechanisms of SIIT are
specified for use in the Network Address Translator - Protocol specified for use in the Network Address Translator - Protocol
Translator (NAT-PT) [RFC2765], NAT-PT uses a mechanism different from Translator (NAT-PT) [RFC2766], NAT-PT uses a mechanism different from
IPv4-mapped IPv6 addresses for communicating embedded IPv4 addresses IPv4-mapped IPv6 addresses for communicating embedded IPv4 addresses
in IPv6 addresses. Also SIIT is not recommended for use as a in IPv6 addresses. Also SIIT is not recommended for use as a
standalone transition mechanism. Given the issues that have been standalone transition mechanism. Given the issues that have been
identified, it seems appropriate that mapped addresses should not be identified, it seems appropriate that mapped addresses should not be
used on the wire. However, changing application behavior by used on the wire. However, changing application behavior by
deprecating the use of mapped addresses in the operating system deprecating the use of mapped addresses in the operating system
interface would have significant impact on application porting interface would have significant impact on application porting
methods [RFC4038] and needs further study. methods as described in [RFC4038] and it is expected that IPv4-mapped
IPv6 addresses will continue to be used within the API to aid
application portability.
Using the basic API behavior has some security implications in that
it adds additional complexity to address-based access controls. The
main issue that arises is that an IPv6 (AF_INET6) socket will accept
IPv4 packets even if the node has no IPv4 (AF_INET) sockets open.
This has to be taken into account by application developers and may
allow a malicious IPv4 peer to access a service even if there are no
open IPv4 sockets. This violates the security principle of "least
surprise".
2.3. Increased End-to-End Transparency 2.3. Increased End-to-End Transparency
One of the major design aims of IPv6 has been to maintain the One of the major design aims of IPv6 has been to maintain the
original IP architectural concept of end-to-end transparency. original IP architectural concept of end-to-end transparency.
Transparency can help foster technological innovation in areas such Transparency can help foster technological innovation in areas such
as peer-to-peer communication but maintaining the security of the as peer-to-peer communication but maintaining the security of the
network at the same time requires some modifications in the network network at the same time requires some modifications in the network
architecture. Ultimately, it is also likely to need changes in the architecture. Ultimately, it is also likely to need changes in the
security model as compared with the norms for IPv4 networks. security model as compared with the norms for IPv4 networks.
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nodes and increasing usage of end-to-end security is a challenge nodes and increasing usage of end-to-end security is a challenge
to current autonomous firewalls that are unable to perform deep to current autonomous firewalls that are unable to perform deep
packet inspection on encrypted packets. It is also incompatible packet inspection on encrypted packets. It is also incompatible
with NATs because they modify the packets, even when packets are with NATs because they modify the packets, even when packets are
only authenticated rather than encrypted. only authenticated rather than encrypted.
o Acknowledgement that over-reliance on the perimeter model is o Acknowledgement that over-reliance on the perimeter model is
potentially dangerous. An attacker who can penetrate today's potentially dangerous. An attacker who can penetrate today's
perimeters will have free rein within the perimeter, in many perimeters will have free rein within the perimeter, in many
cases. Also a successful attack will generally allow the attacker cases. Also a successful attack will generally allow the attacker
to capture information or resources and make use of them. to capture information or resources and make use of them.
o Development of mechanisms such as 'Trusted Computing' that will o Development of mechanisms such as 'Trusted Computing' [TCGARCH]
increase the level of trust that network managers are able to that will increase the level of trust that network managers are
place on hosts. able to place on hosts.
o Development of centralized security policy repositories and secure o Development of centralized security policy repositories and secure
distribution mechanisms that, in conjunction with trusted hosts, distribution mechanisms that, in conjunction with trusted hosts,
will allow network managers to place more reliance on security will allow network managers to place more reliance on security
mechanisms at the end points. The mechanisms are likely to mechanisms at the end points. The mechanisms are likely to
include end-node firewalling and intrusion detection systems as include end-node firewalling and intrusion detection systems as
well as secure protocols that allow end points to influence the well as secure protocols that allow end points to influence the
behavior of perimeter security devices. behavior of perimeter security devices.
o Review of the role of perimeter devices with increased emphasis on o Review of the role of perimeter devices with increased emphasis on
intrusion detection, network resource protection and coordination intrusion detection, network resource protection and coordination
to thwart distributed denial of service attacks. to thwart distributed denial of service attacks.
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Several of the technologies required to support an enhanced security Several of the technologies required to support an enhanced security
model are still under development, including secure protocols to model are still under development, including secure protocols to
allow end points to control firewalls: the complete security model allow end points to control firewalls: the complete security model
utilizing these technologies is now emerging but still requires some utilizing these technologies is now emerging but still requires some
development. development.
In the meantime, initial deployments will need to make use of similar In the meantime, initial deployments will need to make use of similar
firewalling and intrusion detection techniques to IPv4 that may limit firewalling and intrusion detection techniques to IPv4 that may limit
end-to-end transparency temporarily, but should be prepared to use end-to-end transparency temporarily, but should be prepared to use
the new security model as it develops and avoid the use of NATs by the new security model as it develops and avoid the use of NATs by
the use of the architectural techniques described in [I-D.ietf-v6ops- the use of the architectural techniques described in
nap]. In particular, using NAT-PT [RFC2766] as a general purpose [I-D.ietf-v6ops-nap]. In particular, using NAT-PT [RFC2766] as a
transition mechanism should be avoided as it is likely to limit the general purpose transition mechanism should be avoided as it is
exploitation of end-to-end security and other IPv6 capabilities in likely to limit the exploitation of end-to-end security and other
future as explained in [I-D.ietf-v6ops-natpt-to-exprmntl]. IPv6 capabilities in future as explained in
[I-D.ietf-v6ops-natpt-to-exprmntl].
2.4. IPv6 in IPv6 Tunnels 2.4. IPv6 in IPv6 Tunnels
IPv6 in IPv6 tunnels can be used to circumvent security checks, so it IPv6 in IPv6 tunnels can be used to circumvent security checks, so it
is essential to filter packets both at tunnel ingress and egress is essential to filter packets both at tunnel ingress and egress
points (the encapsulator and decapsulator) to ensure that both the points (the encapsulator and decapsulator) to ensure that both the
inner and outer addresses are accpetable, and the tunnel is not being inner and outer addresses are acceptable, and the tunnel is not being
used to carry inappropriate traffic. The security discussions in used to carry inappropriate traffic. The security discussions in
[RFC3964], which is primarily about the 6to4 transition tunneling [RFC3964], which is primarily about the 6to4 transition tunneling
mecahnism (see Section 3.1) contains useful discussion of possible mechanism (see Section 3.1) contains useful discussion of possible
attacks and ways to counteract these threats. attacks and ways to counteract these threats.
3. Issues Due to Transition Mechanisms 3. Issues Due to Transition Mechanisms
3.1. IPv6 Transition/Co-existence Mechanism-specific Issues 3.1. IPv6 Transition/Co-existence Mechanism-specific Issues
The more complicated the IPv6 transition/co-existence becomes, the The more complicated the IPv6 transition/co-existence becomes, the
greater the danger that security issues will be introduced either greater the danger that security issues will be introduced either
o in the mechanisms themselves, o in the mechanisms themselves,
o in the interaction between mechanisms, or o in the interaction between mechanisms, or
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Threats related to 6to4 and measures to combat them are discussed in Threats related to 6to4 and measures to combat them are discussed in
[RFC3964]. [RFC4380] incorporates extensive discussion of the [RFC3964]. [RFC4380] incorporates extensive discussion of the
threats to Teredo and measures to combat them. threats to Teredo and measures to combat them.
3.3. Tunneling IPv6 Through IPv4 Networks May Break IPv4 Network 3.3. Tunneling IPv6 Through IPv4 Networks May Break IPv4 Network
Security Assumptions Security Assumptions
NATs and firewalls have been deployed extensively in the IPv4 NATs and firewalls have been deployed extensively in the IPv4
Internet, as discussed in Section 2.3. Operators who deploy them Internet, as discussed in Section 2.3. Operators who deploy them
typically have some security/operational requirements in mind (e.g. a typically have some security/operational requirements in mind (e.g.,
desire to block inbound connection attempts), which may or may not be a desire to block inbound connection attempts), which may or may not
misguided. be misguided.
The addition of tunneling can change the security model that such The addition of tunneling can change the security model that such
deployments are seeking to enforce. IPv6-over-IPv4 tunneling using deployments are seeking to enforce. IPv6-over-IPv4 tunneling using
protocol 41 is typically either explicitly allowed, or disallowed protocol 41 is typically either explicitly allowed, or disallowed
implicitly. Tunneling IPv6 over IPv4 encapsulated in UDP constitutes implicitly. Tunneling IPv6 over IPv4 encapsulated in UDP constitutes
a more difficult problem as UDP must usually be allowed to pass a more difficult problem as UDP must usually be allowed to pass
through NATs and firewalls. Consequently, using UDP implies the through NATs and firewalls. Consequently, using UDP implies the
ability to punch holes in NAT's and firewalls although, depending on ability to punch holes in NAT's and firewalls although, depending on
the implementation, this ability may be limited or only achieved in a the implementation, this ability may be limited or only achieved in a
stateful manner. In practice, the mechanisms have been explicitly stateful manner. In practice, the mechanisms have been explicitly
designed to traverse both NATs and firewalls in a similar fashion. designed to traverse both NATs and firewalls in a similar fashion.
One possible view is that use of tunneling is especially questionable One possible view is that use of tunneling is especially questionable
in home/SOHO environments where the level of expertise in network in home and SOHO (small office/home office) environments where the
administration is typically not very high; in these environments the level of expertise in network administration is typically not very
hosts may not be as tightly managed as in others (e.g., network high; in these environments the hosts may not be as tightly managed
services might be enabled unnecessarily), leading to possible as in others (e.g., network services might be enabled unnecessarily),
security break-ins or other vulnerabilities. leading to possible security break-ins or other vulnerabilities.
Holes can be punched both intentionally and unintentionally. In Holes allowing tunneled traffic through NATs and firewalls can be
cases where the administrator or user makes an explicit decision to punched both intentionally and unintentionally. In cases where the
create the hole, this is less of a problem, although (for example) administrator or user makes an explicit decision to create the hole,
some enterprises might want to block IPv6 tunneling explicitly if this is less of a problem, although (for example) some enterprises
employees were able to create such holes without reference to might want to block IPv6 tunneling explicitly if employees were able
administrators. On the other hand, if a hole is punched to create such holes without reference to administrators. On the
transparently, it is likely that a proportion of users will not other hand, if a hole is punched transparently, it is likely that a
understand the consequences: this will very probably result in a proportion of users will not understand the consequences: this will
serious threat sooner or later. very probably result in a serious threat sooner or later.
When deploying tunneling solutions, especially tunneling solutions When deploying tunneling solutions, especially tunneling solutions
that are automatic and/or can be enabled easily by users who do not that are automatic and/or can be enabled easily by users who do not
understand the consequences, care should be taken not to compromise understand the consequences, care should be taken not to compromise
the security assumptions held by the users. the security assumptions held by the users.
For example, NAT traversal should not be performed by default unless For example, NAT traversal should not be performed by default unless
there is a firewall producing a similar by-default security policy to there is a firewall producing a similar by-default security policy to
that provided by IPv4 NAT. IPv6-in-IPv4 (protocol 41) tunneling is that provided by IPv4 NAT. IPv6-in-IPv4 (protocol 41) tunneling is
less of a problem, as it is easier to block if necessary; however, if less of a problem, as it is easier to block if necessary; however, if
the host is protected in IPv4, the IPv6 side should be protected as the host is protected in IPv4, the IPv6 side should be protected as
well. well.
As has been shown in Appendix A, it is relatively easy to determine As is shown in Appendix A, it is relatively easy to determine the
the IPv6 address corresponding to an IPv4 address in tunneling IPv6 address corresponding to an IPv4 address in tunneling
deployments. It is therefore vital NOT to rely on "security by deployments. It is therefore vital NOT to rely on "security by
obscurity" i.e., assuming that nobody is able to guess or determine obscurity" i.e., assuming that nobody is able to guess or determine
the IPv6 address of the host especially when using automatic the IPv6 address of the host especially when using automatic
tunneling transition mechanisms. tunneling transition mechanisms.
The network architecture must provide separate IPv4 and IPv6 The network architecture must provide separate IPv4 and IPv6
firewalls with tunnelled IPv6 traffic arriving encapsulated in IPv4 firewalls with tunnelled IPv6 traffic arriving encapsulated in IPv4
packets routed through the IPv4 firewall before being decapsulated, packets routed through the IPv4 firewall before being decapsulated,
and then through the IPv6 firewall as shown in Figure 1. and then through the IPv6 firewall as shown in Figure 1.
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4. Issues Due to IPv6 Deployment 4. Issues Due to IPv6 Deployment
4.1. Avoiding the Trap of Insecure IPv6 Service Piloting 4.1. Avoiding the Trap of Insecure IPv6 Service Piloting
Because IPv6 is a new service for many networks, network managers Because IPv6 is a new service for many networks, network managers
will often opt to make a pilot deployment in a part of the network to will often opt to make a pilot deployment in a part of the network to
gain experience and understand the problems as well as the benefits gain experience and understand the problems as well as the benefits
that may result from a full production quality IPv6 service. that may result from a full production quality IPv6 service.
Unless IPv6 service piloting is done in a manner that is as secure as Unless IPv6 service piloting is done in a manner that is as secure as
possible there is a risk that security in the pilot that does not possible there is a risk that if security in the pilot does not match
match up to what is achievable with current IPv4 production service up to what is achievable with current IPv4 production service the
can adversely impact the overall assessment of the IPv6 pilot comparison can adversely impact the overall assessment of the IPv6
deployment. This may result in a decision to delay or even avoid pilot deployment. This may result in a decision to delay or even
deploying an IPv6 production service. For example, hosts and routers avoid deploying an IPv6 production service. For example, hosts and
might not be protected by IPv6 firewalls, even if the corresponding routers might not be protected by IPv6 firewalls, even if the
IPv4 service is fully protected by firewalls as described in corresponding IPv4 service is fully protected by firewalls. The use
[I-D.ietf-v6ops-v6onbydefault]. This is particularly critical where of tunneling transition mechanisms (see Section 3.3) and the
IPv6 capabilities are turned on by default in new equipment or new interaction with virtual private networks also need careful attention
releases of operating systems: network managers may not be fully to ensure that site security is maintained. This is particularly
aware of the security exposure that this creates. critical where IPv6 capabilities are turned on by default in new
equipment or new releases of operating systems: network managers may
not be fully aware of the security exposure that this creates.
In some cases a perceived lack of availability of IPv6 firewalls and In some cases a perceived lack of availability of IPv6 firewalls and
other security capabilities, such as intrusion detection systems may other security capabilities, such as intrusion detection systems may
have lead network managers to resist any kind of IPv6 service have lead network managers to resist any kind of IPv6 service
deployment. These problems may be partly due to the relatively slow deployment. These problems may be partly due to the relatively slow
development and deployment of IPv6-capable security equipment, but development and deployment of IPv6-capable security equipment, but
the major problems appear to have been a lack of information, and the major problems appear to have been a lack of information, and
more importantly a lack of documented operational experience on which more importantly a lack of documented operational experience on which
managers can draw. In actual fact, as of the time of writing (2006) managers can draw. In actual fact, as of the time of writing (2006)
there are a significant number of alternative IPv6 packet filters and there are a significant number of alternative IPv6 packet filters and
firewalls already in existence, which could be used for provide firewalls already in existence, which could be used for provide
sufficient access controls. sufficient access controls.
However, there are a small number of areas that where the available However, there are a small number of areas that where the available
equipment and capabilities may still be a barrier to secure equipment and capabilities may still be a barrier to secure
deployment: deployment as of the time of writing (2006):
o 'Personal firewalls' intended for use on hosts are not yet widely o 'Personal firewalls' with support for IPv6 and intended for use on
available. hosts are not yet widely available.
o Enterprise firewalls are at an early stage of development and may o Enterprise firewalls are at an early stage of development and may
not provide the full range of capabilities needed to implement the not provide the full range of capabilities needed to implement the
necessary IPv6 filtering rules. network managers often expect the necessary IPv6 filtering rules. Network managers often expect the
same devices that support and are used for IPv4 today to also same devices that support and are used for IPv4 today to also
become IPv6-capable -- even though this is not really required and become IPv6-capable -- even though this is not really required and
the equipment may not have the requisite hardware capabilities to the equipment may not have the requisite hardware capabilities to
support fast packet filtering for IPv6. Suggestions for the support fast packet filtering for IPv6. Suggestions for the
appropriate deployment of firewalls are given in Section 3.3 -- as appropriate deployment of firewalls are given in Section 3.3 -- as
will be seen from this section it is usually desirable that the will be seen from this section it is usually desirable that the
firewalls are in separate boxes and there is no necessity for them firewalls are in separate boxes and there is no necessity for them
to be same model of equipment. to be same model of equipment.
o A lesser factor may be that some design decisions in the IPv6 o A lesser factor may be that some design decisions in the IPv6
protocol make it more difficult for firewalls to be implemented protocol make it more difficult for firewalls to be implemented
and work in all cases, and to be fully future proof (e.g. when new and work in all cases, and to be fully future proof (e.g., when
extension headers are used) as discussed in Section 2.1.9: it is new extension headers are used) as discussed in Section 2.1.9: it
significantly more difficult for intermediate nodes to process the is significantly more difficult for intermediate nodes to process
IPv6 header chains than IPv4 packets. the IPv6 header chains than IPv4 packets.
o Adequate Intrusion Detection Systems (IDS) are more difficult to o Adequate Intrusion Detection Systems (IDS) are more difficult to
construct for IPv6. IDSs are now beginning to become available construct for IPv6. IDSs are now beginning to become available
but the pattern-based mechanisms used for IPv4 may not be the most but the pattern-based mechanisms used for IPv4 may not be the most
appropriate for long-term development of these systems as end-to- appropriate for long-term development of these systems as end-to-
end encryption becomes more prevalent. Future systems may be more end encryption becomes more prevalent. Future systems may be more
reliant on traffic flow pattern recognition. reliant on traffic flow pattern recognition.
o Implementations of high availability capabilities supporting IPv6 o Implementations of high availability capabilities supporting IPv6
are also in short supply. In particular, development of the IPv6 are also in short supply. In particular, development of the IPv6
version of the Virtual Router Redundancy Protocol (VRRP) version of the Virtual Router Redundancy Protocol (VRRP)
[I-D.ietf-vrrp-ipv6-spec] has lagged the development of the main [I-D.ietf-vrrp-ipv6-spec] has lagged the development of the main
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Because the unmemorability of complete IPv6 addresses there is a Because the unmemorability of complete IPv6 addresses there is a
temptation for administrators to use small integers as interface temptation for administrators to use small integers as interface
identifiers when manually configuring them, as might happen on point- identifiers when manually configuring them, as might happen on point-
to-point links or when provisioning complete addresses from a DHCPv6 to-point links or when provisioning complete addresses from a DHCPv6
server. Such allocations make it easy for an attacker to find active server. Such allocations make it easy for an attacker to find active
nodes that they can then port scan. nodes that they can then port scan.
To make use of the larger address space properly, administrators To make use of the larger address space properly, administrators
should be very careful when entering IPv6 addresses in their should be very careful when entering IPv6 addresses in their
configurations (e.g. Access Control List), since numerical IPv6 configurations (e.g., Access Control Lists), since numerical IPv6
addresses are more prone to human error than IPv4 due to their length addresses are more prone to human error than IPv4 due to their length
and unmemorability. and unmemorability.
It is also essential to ensure that the management interfaces of It is also essential to ensure that the management interfaces of
routers are well secured as the router will usually contain a routers are well secured (e.g., allowing remote access using Secure
significant cache of neighbor addresses in its neighbor cache. Shell (SSH) only and ensuring that local craft interfaces have non-
default passwords) as the router will usually contain a significant
cache of neighbor addresses in its neighbor cache.
4.4. Consequences of Multiple Addresses in IPv6 4.4. Consequences of Multiple Addresses in IPv6
One positive consequence of IPv6 is that nodes that do not require One positive consequence of IPv6 is that nodes that do not require
global access can communicate locally just by the use of a link-local global access can communicate locally just by the use of a link-local
address (if very local access is sufficient) or across the site by address (if very local access is sufficient) or across the site by
using a Unique Local Address (ULA). In either case it is easy to using a Unique Local Address (ULA). In either case it is easy to
ensure that access outside the assigned domain of activity can be ensure that access outside the assigned domain of activity can be
controlled by simple filters (which may be the default for link- controlled by simple filters (which should be the default for link-
locals). However, the security hazards of using link-local addresses locals). However, the security hazards of using link-local addresses
for non-management purposes as documented in Section 2.1.12 should be for general purposes, as documented in Section 2.1.12, should be
borne in mind. borne in mind.
On the other hand, the possibility that a node or interface can have On the other hand, the possibility that a node or interface can have
multiple global scope addresses makes access control filtering both multiple global scope addresses makes access control filtering both
on ingress and egress more complex and requires higher maintenance on ingress and egress more complex and requires higher maintenance
levels. Vendors and network administrators need to be aware that levels. Vendors and network administrators need to be aware that
multiple addresses are the norm rather than the exception in IPv6: multiple addresses are the norm rather than the exception in IPv6:
when building and selecting tools for security and management a when building and selecting tools for security and management a
highly desirable feature is the ability to be able to 'tokenize' highly desirable feature is the ability to be able to 'tokenize'
access control lists and configurations in general to cater for access control lists and configurations in general to cater for
multiple addresses and/or address prefixes. multiple addresses and/or address prefixes.
The addresses could be from the same network prefix (for example, The addresses could be from the same network prefix (for example,
privacy mechanisms [RFC3041][I-D.ietf-ipv6-privacy-addrs-v2] will privacy mechanisms [I-D.ietf-ipv6-privacy-addrs-v2] will periodically
periodically create new addresses taken from the same prefix and two create new addresses taken from the same prefix and two or more of
or more of these may be active at the same time), or from different these may be active at the same time), or from different prefixes
prefixes (for example, when a network is multihomed or is (for example, when a network is multihomed, when for management
implementing anycast services). In either case, it is possible that purposes a node belongs to several subnets on the same link or is
a single host could be using several different addresses with implementing anycast services). In all these cases, it is possible
different prefixes. It would be desirable that the security that a single host could be using several different addresses with
administrator should be able to identify that the same host is behind different prefixes and/or different interface identifiers. It would
all these addresses. be desirable that the security administrator should be able to
identify that the same host is behind all these addresses.
Some network administrators may find the mutability of addresses when Some network administrators may find the mutability of addresses when
privacy mechanisms are used in their network to be undesirable privacy mechanisms are used in their network to be undesirable
because of the current difficulties in maintaining access control because of the current difficulties in maintaining access control
lists and knowing the origin of traffic. In general, disabling the lists and knowing the origin of traffic. In general, disabling the
use of privacy addresses is only possible if the full stateful DHCPv6 use of privacy addresses is only possible if the full stateful DHCPv6
mechanism [RFC3315] is used to allocate IPv6 addresses and DHCPv6 mechanism [RFC3315] is used to allocate IPv6 addresses and DHCPv6
requests for privacy addresses are not honored. requests for privacy addresses are not honored.
4.5. Deploying ICMPv6 4.5. Deploying ICMPv6
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functions, the simple set of dropping rules that are usually applied functions, the simple set of dropping rules that are usually applied
in IPv4 need to be significantly developed for IPv6. The blanket in IPv4 need to be significantly developed for IPv6. The blanket
dropping of all ICMP messages that is used in some very strict dropping of all ICMP messages that is used in some very strict
environments is simply not possible for IPv6. environments is simply not possible for IPv6.
In an IPv6 firewall, policy needs to allow some messages through the In an IPv6 firewall, policy needs to allow some messages through the
firewall but also has to permit certain messages to and from the firewall but also has to permit certain messages to and from the
firewall, especially those with link-local sources on links to which firewall, especially those with link-local sources on links to which
the firewall is attached. These messages must be permitted to ensure the firewall is attached. These messages must be permitted to ensure
that Neighbor Discovery [RFC2462], Multicast Listener Discovery that Neighbor Discovery [RFC2462], Multicast Listener Discovery
[RFC2710], [RFC3810] and Stateless Address Configuration [RFC2463] [RFC2710], [RFC3810] and Stateless Address Configuration [RFC4443]
work as expected. work as expected.
Recommendations for filtering ICMPv6 messages can be found in Recommendations for filtering ICMPv6 messages can be found in
[I-D.davies-v6ops-icmpv6-filtering-bcp]. [I-D.ietf-v6ops-icmpv6-filtering-recs].
4.5.1. Problems Resulting from ICMPv6 Transparency 4.5.1. Problems Resulting from ICMPv6 Transparency
As described in Section 4.5, certain ICMPv6 error packets need to be As described in Section 4.5, certain ICMPv6 error packets need to be
passed through a firewall in both directions. This means that some passed through a firewall in both directions. This means that some
ICMPv6 error packets can be exchanged between inside and outside ICMPv6 error packets can be exchanged between inside and outside
without any filtering. without any filtering.
Using this feature, malicious users can communicate between the Using this feature, malicious users can communicate between the
inside and outside of a firewall bypassing the administrator's inside and outside of a firewall bypassing the administrator's
skipping to change at page 26, line 32 skipping to change at page 30, line 11
in Section 2.3.2. Another example is an IPsec-based DoS (e.g., in Section 2.3.2. Another example is an IPsec-based DoS (e.g.,
sending malformed ESP/AH packets) that can be especially detrimental sending malformed ESP/AH packets) that can be especially detrimental
to software-based IPsec implementations. to software-based IPsec implementations.
4.7. Reduced Functionality Devices 4.7. Reduced Functionality Devices
With the deployment of IPv6 we can expect the attachment of a very With the deployment of IPv6 we can expect the attachment of a very
large number of new IPv6-enabled devices with scarce resources and large number of new IPv6-enabled devices with scarce resources and
low computing capacity. The resource limitations are generally low computing capacity. The resource limitations are generally
because of a market requirement for cost reduction. Although the because of a market requirement for cost reduction. Although the
IPv6 Node Requirements [I-D.ietf-ipv6-node-requirements] specifies IPv6 Node Requirements [RFC4294] specifies some mandatory security
some mandatory security capabilities for every conformant node, these capabilities for every conformant node, these do not include
do not include functions required for a node to be able to protect functions required for a node to be able to protect itself.
itself. Accordingly, some such devices may not be able even to Accordingly, some such devices may not be able even to perform the
perform the minimum set of functions required to protect themselves minimum set of functions required to protect themselves (e.g.,
(e.g. 'personal' firewall, automatic firmware update, enough CPU 'personal' firewall, automatic firmware update, enough CPU power to
power to endure DoS attacks). This means a different security scheme endure DoS attacks). This means a different security scheme may be
may be necessary for such reduced functionality devices. necessary for such reduced functionality devices.
4.8. Operational Factors when Enabling IPv6 in the Network 4.8. Operational Factors when Enabling IPv6 in the Network
There are a number of reasons that make it essential to take There are a number of reasons that make it essential to take
particular care when enabling IPv6 in the network equipment: particular care when enabling IPv6 in the network equipment:
Initially, IPv6-enabled router software may be less mature than Initially, IPv6-enabled router software may be less mature than
current IPv4-only implementations and there is less experience with current IPv4-only implementations and there is less experience with
configuring IPv6 routing, which can result in disruptions to the IPv6 configuring IPv6 routing, which can result in disruptions to the IPv6
routing environment and (IPv6) network outages. routing environment and (IPv6) network outages.
IPv6 processing may not happen at (near) line speed (or at a IPv6 processing may not happen at (near) line speed (or at a
comparable performance level to IPv4 in the same equipment). A high comparable performance level to IPv4 in the same equipment). A high
level of IPv6 traffic (even legitimate, e.g. Network News Transport level of IPv6 traffic (even legitimate, e.g., Network News Transport
Protocol, NNTP) could easily overload IPv6 processing especially when Protocol, NNTP) could easily overload IPv6 processing especially when
it is software-based without the hardware support typical in high-end it is software-based without the hardware support typical in high-end
routers. This may potentially have deleterious knock-on effects on routers. This may potentially have deleterious knock-on effects on
IPv4 processing, affecting availability of both services. IPv4 processing, affecting availability of both services.
Accordingly, if people don't feel confident enough in the IPv6 Accordingly, if people don't feel confident enough in the IPv6
capabilities of their equipment, they will be reluctant to enable it capabilities of their equipment, they will be reluctant to enable it
in their "production" networks. in their "production" networks.
Sometimes essential features may be missing from early releases of Sometimes essential features may be missing from early releases of
vendors' software; an example is provision of software enabling IPv6 vendors' software; an example is provision of software enabling IPv6
skipping to change at page 27, line 39 skipping to change at page 31, line 17
both IPv4 and IPv6. It is possible to run the both in one routing both IPv4 and IPv6. It is possible to run the both in one routing
protocol, or have two separate routing protocols; either approach has protocol, or have two separate routing protocols; either approach has
its tradeoffs [RFC4029]. If multiple routing protocols are used, one its tradeoffs [RFC4029]. If multiple routing protocols are used, one
should note that this causes double the amount of processing when should note that this causes double the amount of processing when
links flap or recalculation is otherwise needed -- which might more links flap or recalculation is otherwise needed -- which might more
easily overload the router's CPU, causing slightly slower convergence easily overload the router's CPU, causing slightly slower convergence
time. time.
4.9. Ingress Filtering Issues Due to Privacy Addresses 4.9. Ingress Filtering Issues Due to Privacy Addresses
[RFC3041][I-D.ietf-ipv6-privacy-addrs-v2] describes a method for [I-D.ietf-ipv6-privacy-addrs-v2] describes a method for creating
creating temporary addresses on IPv6 nodes to address privacy issues temporary addresses on IPv6 nodes to address privacy issues created
created by the use of a constant identifier. In a large network by the use of a constant identifier. In a large network implementing
implementing such a mechanism new temporary addresses may be created such a mechanism new temporary addresses may be created at a fairly
at a fairly high rate. This might make it hard for ingress filtering high rate. As discussed in Section 2.1.7, this might make it hard
mechanisms to distinguish between legitimately changing temporary for ingress filtering mechanisms to distinguish between legitimately
addresses and spoofed source addresses, which are "in-prefix" (i.e., changing temporary addresses and spoofed source addresses, which are
they use a topologically correct prefix and non-existent interface "in-prefix" (i.e., they use a topologically correct prefix and non-
ID). This can be addressed by using finer grained access control existent interface ID). This can be addressed by using finer grained
mechanisms on the network egress point. access control mechanisms on a per address basis at the network
egress point as suggested in the Security Considerations section of
[I-D.ietf-ipv6-privacy-addrs-v2].
4.10. Security Issues Due to ND Proxies 4.10. Security Issues Due to Neighbor Discovery Proxies
In order to span a single subnet over multiple physical links, a new In order to span a single subnet over multiple physical links, a new
capability is being introduced in IPv6 to proxy Neighbor Discovery experimental capability is being trialled in IPv6 to proxy Neighbor
messages. This node will be called an NDProxy (see [I-D.ietf-ipv6- Discovery messages. A node with this capability will be called an
ndproxy]. NDProxies are susceptible to the same security issues as NDProxy (see [RFC4389]. NDProxies are susceptible to the same
the ones faced by hosts using unsecured Neighbor Discovery or ARP. security issues as the ones faced by hosts using unsecured Neighbor
These proxies may process unsecured messages, and update the neighbor Discovery or ARP. These proxies may process unsecured messages, and
cache as a result of such processing, thus allowing a malicious node update the neighbor cache as a result of such processing, thus
to divert or hijack traffic. This may undermine the advantages of allowing a malicious node to divert or hijack traffic. This may
using SEND [RFC3971]. undermine the advantages of using SEND [RFC3971].
To resolve the security issues introduced by NDProxies, SEND needs to If a form of NDProxy is standardized, SEND will need to be extended
be extended to be NDProxy aware. to support this capability.
5. IANA Considerations 5. IANA Considerations
This memo does not contain any actions for IANA. This memo does not contain any actions for IANA.
6. Security Considerations 6. Security Considerations
This memo attempts to give an overview of security considerations of This memo attempts to give an overview of security considerations of
the different aspects of IPv6, particularly as they relate to the the different aspects of IPv6, particularly as they relate to the
transition to a network in which IPv4- and IPv6-based communications transition to a network in which IPv4- and IPv6-based communications
need to coexist. need to coexist.
7. Acknowledgements 7. Acknowledgements
Alain Durand, Alain Baudot, Luc Beloeil, Tim Chown, Andras Kis-Szabo, This document draws together the work of many people who have
Vishwas Manral, Janos Mohacsi, Alvaro Vives and Mark Smith provided contributed security-related drafts to the ipv6 and v6ops working
feedback to improve this memo. Satoshi Kondo, Shinsuke Suzuki and groups. Alain Durand, Alain Baudot, Luc Beloeil, Sharon Chisholm,
Alvaro Vives provided additional inputs in cooperation with the Tim Chown, Lars Eggert, Andras Kis-Szabo, Vishwas Manral, Janos
Mohacsi, Mark Smith, Alvaro Vives and Margaret Wassermann provided
feedback to improve this document. Satoshi Kondo, Shinsuke Suzuki
and Alvaro Vives provided additional inputs in cooperation with the
Deployment Working Group of the Japanese IPv6 Promotion Council and Deployment Working Group of the Japanese IPv6 Promotion Council and
the Euro6IX IST co-funded project, together with inputs from Jordi the Euro6IX IST co-funded project, together with inputs from Jordi
Palet, Brian Carpenter, and Peter Bieringer. Michael Wittsend and Palet, Brian Carpenter, and Peter Bieringer. Michael Wittsend and
Michael Cole discussed issues relating to probing/mapping and Michael Cole discussed issues relating to probing/mapping and
privacy. privacy. Craig Metz and Jun-ichiro itojun Hagino did the original
work identifying the problems of using IPv4-mapped IPv6 addresses on
the wire. Vishwas Manral made further investigations of the impact
of tiny fragments on IPv6 security. Francis Dupont raised the issues
relating to IPv6 Privacy Addresses. Finally, Pekka Savola wrote a
number of drafts on aspects IPv6 security which have been subsumed
into this work. His draft on "Firewalling Considerations for IPv6"
(draft-savola-v6ops-firewalling-02.txt) originally identified many of
the issues with the base IPv6 specification which are documented
here.
8. References 8. References
8.1. Normative References 8.1. Normative References
[I-D.ietf-ipv6-privacy-addrs-v2] [I-D.ietf-ipv6-privacy-addrs-v2]
Narten, T., "Privacy Extensions for Stateless Address Narten, T., "Privacy Extensions for Stateless Address
Autoconfiguration in IPv6", Autoconfiguration in IPv6",
draft-ietf-ipv6-privacy-addrs-v2-04 (work in progress), draft-ietf-ipv6-privacy-addrs-v2-04 (work in progress),
December 2005. December 2005.
[I-D.ietf-v6ops-natpt-to-exprmntl] [RFC1122] Braden, R., "Requirements for Internet Hosts -
Aoun, C. and E. Davies, "Reasons to Move NAT-PT to Communication Layers", STD 3, RFC 1122, October 1989.
Experimental", draft-ietf-v6ops-natpt-to-exprmntl-03 (work
in progress), October 2005.
[I-D.ietf-vrrp-ipv6-spec]
Hinden, R., "Virtual Router Redundancy Protocol for IPv6",
draft-ietf-vrrp-ipv6-spec-07 (work in progress),
October 2004.
[RFC2375] Hinden, R. and S. Deering, "IPv6 Multicast Address [RFC2375] Hinden, R. and S. Deering, "IPv6 Multicast Address
Assignments", RFC 2375, July 1998. Assignments", RFC 2375, July 1998.
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, December 1998. (IPv6) Specification", RFC 2460, December 1998.
[RFC2461] Narten, T., Nordmark, E., and W. Simpson, "Neighbor [RFC2461] Narten, T., Nordmark, E., and W. Simpson, "Neighbor
Discovery for IP Version 6 (IPv6)", RFC 2461, Discovery for IP Version 6 (IPv6)", RFC 2461,
December 1998. December 1998.
[RFC2462] Thomson, S. and T. Narten, "IPv6 Stateless Address [RFC2462] Thomson, S. and T. Narten, "IPv6 Stateless Address
Autoconfiguration", RFC 2462, December 1998. Autoconfiguration", RFC 2462, December 1998.
[RFC2463] Conta, A. and S. Deering, "Internet Control Message
Protocol (ICMPv6) for the Internet Protocol Version 6
(IPv6) Specification", RFC 2463, December 1998.
[RFC2710] Deering, S., Fenner, W., and B. Haberman, "Multicast [RFC2710] Deering, S., Fenner, W., and B. Haberman, "Multicast
Listener Discovery (MLD) for IPv6", RFC 2710, Listener Discovery (MLD) for IPv6", RFC 2710,
October 1999. October 1999.
[RFC3041] Narten, T. and R. Draves, "Privacy Extensions for
Stateless Address Autoconfiguration in IPv6", RFC 3041,
January 2001.
[RFC3056] Carpenter, B. and K. Moore, "Connection of IPv6 Domains [RFC3056] Carpenter, B. and K. Moore, "Connection of IPv6 Domains
via IPv4 Clouds", RFC 3056, February 2001. via IPv4 Clouds", RFC 3056, February 2001.
[RFC3775] Johnson, D., Perkins, C., and J. Arkko, "Mobility Support [RFC3775] Johnson, D., Perkins, C., and J. Arkko, "Mobility Support
in IPv6", RFC 3775, June 2004. in IPv6", RFC 3775, June 2004.
[RFC3810] Vida, R. and L. Costa, "Multicast Listener Discovery [RFC3810] Vida, R. and L. Costa, "Multicast Listener Discovery
Version 2 (MLDv2) for IPv6", RFC 3810, June 2004. Version 2 (MLDv2) for IPv6", RFC 3810, June 2004.
[RFC3964] Savola, P. and C. Patel, "Security Considerations for [RFC3964] Savola, P. and C. Patel, "Security Considerations for
6to4", RFC 3964, December 2004. 6to4", RFC 3964, December 2004.
[RFC4007] Deering, S., Haberman, B., Jinmei, T., Nordmark, E., and
B. Zill, "IPv6 Scoped Address Architecture", RFC 4007,
March 2005.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, February 2006. Architecture", RFC 4291, February 2006.
[RFC4380] Huitema, C., "Teredo: Tunneling IPv6 over UDP through [RFC4380] Huitema, C., "Teredo: Tunneling IPv6 over UDP through
Network Address Translations (NATs)", RFC 4380, Network Address Translations (NATs)", RFC 4380,
February 2006. February 2006.
[RFC4443] Conta, A., Deering, S., and M. Gupta, "Internet Control
Message Protocol (ICMPv6) for the Internet Protocol
Version 6 (IPv6) Specification", RFC 4443, March 2006.
8.2. Informative References 8.2. Informative References
[FNAT] Bellovin, S., "Technique for Counting NATted Hosts", Proc. [FNAT] Bellovin, S., "Technique for Counting NATted Hosts", Proc.
Second Internet Measurement Workshop , November 2002, Second Internet Measurement Workshop , November 2002,
<http://www.research.att.com/~smb/papers/fnat.pdf>. <http://www.research.att.com/~smb/papers/fnat.pdf>.
[I-D.chown-v6ops-port-scanning-implications] [I-D.ietf-tcpm-icmp-attacks]
Chown, T., "IPv6 Implications for TCP/UDP Port Scanning",
draft-chown-v6ops-port-scanning-implications-02 (work in
progress), October 2005.
[I-D.cmetz-v6ops-v4mapped-api-harmful]
Metz, C. and J. Hagino, "IPv4-Mapped Address API
Considered Harmful",
draft-cmetz-v6ops-v4mapped-api-harmful-01 (work in
progress), October 2003.
[I-D.davies-v6ops-icmpv6-filtering-bcp]
Davies, E. and J. Mohacsi, "Best Current Practice for
Filtering ICMPv6 Messages in Firewalls",
draft-davies-v6ops-icmpv6-filtering-bcp-00 (work in
progress), July 2005.
[I-D.dupont-ipv6-rfc3041harmful]
Dupont, F. and P. Savola, "RFC 3041 Considered Harmful",
draft-dupont-ipv6-rfc3041harmful-05 (work in progress),
June 2004.
[I-D.gont-tcpm-icmp-attacks]
Gont, F., "ICMP attacks against TCP", Gont, F., "ICMP attacks against TCP",
draft-gont-tcpm-icmp-attacks-05 (work in progress), draft-ietf-tcpm-icmp-attacks-00 (work in progress),
October 2005. February 2006.
[I-D.ietf-dnsop-ipv6-dns-issues]
Durand, A., "Operational Considerations and Issues with
IPv6 DNS", draft-ietf-dnsop-ipv6-dns-issues-12 (work in
progress), October 2005.
[I-D.ietf-ipv6-ndproxy]
Thaler, D., "Neighbor Discovery Proxies (ND Proxy)",
draft-ietf-ipv6-ndproxy-04 (work in progress),
October 2005.
[I-D.ietf-ipv6-node-requirements] [I-D.ietf-v6ops-icmpv6-filtering-recs]
Loughney, J., "IPv6 Node Requirements", Davies, E. and J. Mohacsi, "Recommendations for Filtering
draft-ietf-ipv6-node-requirements-11 (work in progress), ICMPv6 Messages in Firewalls",
August 2004. draft-ietf-v6ops-icmpv6-filtering-recs-02 (work in
progress), July 2006.
[I-D.ietf-v6ops-nap] [I-D.ietf-v6ops-nap]
Velde, G., "IPv6 Network Architecture Protection", Velde, G., "IPv6 Network Architecture Protection",
draft-ietf-v6ops-nap-02 (work in progress), October 2005. draft-ietf-v6ops-nap-03 (work in progress), July 2006.
[I-D.ietf-v6ops-v6onbydefault]
Roy, S., Durand, A., and J. Paugh, "Issues with Dual Stack
IPv6 on by Default", draft-ietf-v6ops-v6onbydefault-03
(work in progress), July 2004.
[I-D.itojun-v6ops-v4mapped-harmful]
Metz, C. and J. Hagino, "IPv4-Mapped Addresses on the Wire
Considered Harmful",
draft-itojun-v6ops-v4mapped-harmful-02 (work in progress),
October 2003.
[I-D.krishnan-ipv6-hopbyhop]
Krishnan, S., "Arrangement of Hop-by-Hop options",
draft-krishnan-ipv6-hopbyhop-00 (work in progress),
June 2004.
[I-D.savola-ipv6-rh-ha-security]
Savola, P., "Security of IPv6 Routing Header and Home
Address Options", draft-savola-ipv6-rh-ha-security-02
(work in progress), March 2002.
[I-D.savola-ipv6-rh-hosts] [I-D.ietf-v6ops-natpt-to-exprmntl]
Savola, P., "Note about Routing Header Processing on IPv6 Aoun, C. and E. Davies, "Reasons to Move NAT-PT to
Hosts", draft-savola-ipv6-rh-hosts-00 (work in progress), Experimental", draft-ietf-v6ops-natpt-to-exprmntl-03 (work
February 2002. in progress), October 2005.
[I-D.savola-v6ops-firewalling] [I-D.ietf-v6ops-scanning-implications]
Savola, P., "Firewalling Considerations for IPv6", Chown, T., "IPv6 Implications for Network Scanning",
draft-savola-v6ops-firewalling-02 (work in progress), draft-ietf-v6ops-scanning-implications-00 (work in
October 2003. progress), June 2006.
[I-D.savola-v6ops-transarch] [I-D.ietf-vrrp-ipv6-spec]
Savola, P., "A View on IPv6 Transition Architecture", Hinden, R., "Virtual Router Redundancy Protocol for IPv6",
draft-savola-v6ops-transarch-03 (work in progress), draft-ietf-vrrp-ipv6-spec-07 (work in progress),
January 2004. October 2004.
[I-D.schild-v6ops-guide-v4mapping] [IEEE.802-1X.2004]
Schild, C., "Guide to Mapping IPv4 to IPv6 Subnets", Institute of Electrical and Electronics Engineers, "Port-
draft-schild-v6ops-guide-v4mapping-00 (work in progress), Based Network Access Control", IEEE Standard for Local and
January 2004. Metropolitan Area Networks 802.1X-2004, December 2004.
[JpIPv6DC] [JpIPv6DC]
Deployment WG, "IPv6 Deployment Guideline (2005 Edition)", Deployment WG, "IPv6 Deployment Guideline (2005 Edition)",
IPv6 Promotion Council (Japan) Deployment Working Group, IPv6 Promotion Council (Japan) Deployment Working Group,
2005, <http://www.v6pc.jp/>. 2005, <http://www.v6pc.jp/>.
[RFC1858] Ziemba, G., Reed, D., and P. Traina, "Security [RFC1858] Ziemba, G., Reed, D., and P. Traina, "Security
Considerations for IP Fragment Filtering", RFC 1858, Considerations for IP Fragment Filtering", RFC 1858,
October 1995. October 1995.
skipping to change at page 32, line 34 skipping to change at page 35, line 13
Translation - Protocol Translation (NAT-PT)", RFC 2766, Translation - Protocol Translation (NAT-PT)", RFC 2766,
February 2000. February 2000.
[RFC3128] Miller, I., "Protection Against a Variant of the Tiny [RFC3128] Miller, I., "Protection Against a Variant of the Tiny
Fragment Attack (RFC 1858)", RFC 3128, June 2001. Fragment Attack (RFC 1858)", RFC 3128, June 2001.
[RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., [RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
and M. Carney, "Dynamic Host Configuration Protocol for and M. Carney, "Dynamic Host Configuration Protocol for
IPv6 (DHCPv6)", RFC 3315, July 2003. IPv6 (DHCPv6)", RFC 3315, July 2003.
[RFC3493] Gilligan, R., Thomson, S., Bound, J., McCann, J., and W.
Stevens, "Basic Socket Interface Extensions for IPv6",
RFC 3493, February 2003.
[RFC3756] Nikander, P., Kempf, J., and E. Nordmark, "IPv6 Neighbor [RFC3756] Nikander, P., Kempf, J., and E. Nordmark, "IPv6 Neighbor
Discovery (ND) Trust Models and Threats", RFC 3756, Discovery (ND) Trust Models and Threats", RFC 3756,
May 2004. May 2004.
[RFC3927] Cheshire, S., Aboba, B., and E. Guttman, "Dynamic
Configuration of IPv4 Link-Local Addresses", RFC 3927,
May 2005.
[RFC3971] Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure [RFC3971] Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure
Neighbor Discovery (SEND)", RFC 3971, March 2005. Neighbor Discovery (SEND)", RFC 3971, March 2005.
[RFC4025] Richardson, M., "A Method for Storing IPsec Keying
Material in DNS", RFC 4025, March 2005.
[RFC4029] Lind, M., Ksinant, V., Park, S., Baudot, A., and P. [RFC4029] Lind, M., Ksinant, V., Park, S., Baudot, A., and P.
Savola, "Scenarios and Analysis for Introducing IPv6 into Savola, "Scenarios and Analysis for Introducing IPv6 into
ISP Networks", RFC 4029, March 2005. ISP Networks", RFC 4029, March 2005.
[RFC4038] Shin, M-K., Hong, Y-G., Hagino, J., Savola, P., and E. [RFC4038] Shin, M-K., Hong, Y-G., Hagino, J., Savola, P., and E.
Castro, "Application Aspects of IPv6 Transition", Castro, "Application Aspects of IPv6 Transition",
RFC 4038, March 2005. RFC 4038, March 2005.
[RFC4074] Morishita, Y. and T. Jinmei, "Common Misbehavior Against [RFC4074] Morishita, Y. and T. Jinmei, "Common Misbehavior Against
DNS Queries for IPv6 Addresses", RFC 4074, May 2005. DNS Queries for IPv6 Addresses", RFC 4074, May 2005.
[RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and [RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and
More-Specific Routes", RFC 4191, November 2005. More-Specific Routes", RFC 4191, November 2005.
[RFC4225] Nikander, P., Arkko, J., Aura, T., Montenegro, G., and E. [RFC4225] Nikander, P., Arkko, J., Aura, T., Montenegro, G., and E.
Nordmark, "Mobile IP Version 6 Route Optimization Security Nordmark, "Mobile IP Version 6 Route Optimization Security
Design Background", RFC 4225, December 2005. Design Background", RFC 4225, December 2005.
[RFC4294] Loughney, J., "IPv6 Node Requirements", RFC 4294,
April 2006.
[RFC4301] Kent, S. and K. Seo, "Security Architecture for the [RFC4301] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC 4301, December 2005. Internet Protocol", RFC 4301, December 2005.
[RFC4311] Hinden, R. and D. Thaler, "IPv6 Host-to-Router Load [RFC4311] Hinden, R. and D. Thaler, "IPv6 Host-to-Router Load
Sharing", RFC 4311, November 2005. Sharing", RFC 4311, November 2005.
[RFC4389] Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery
Proxies (ND Proxy)", RFC 4389, April 2006.
[RFC4472] Durand, A., Ihren, J., and P. Savola, "Operational
Considerations and Issues with IPv6 DNS", RFC 4472,
April 2006.
[SIXNET] 6Net, "Large Scale International IPv6 Pilot Network", EU [SIXNET] 6Net, "Large Scale International IPv6 Pilot Network", EU
Information Society Technologies Project , 2005, Information Society Technologies Project , 2005,
<http://www.6net.org/>. <http://www.6net.org/>.
[TCGARCH] The Trusted Computing Group, "TCG Specification
Architecture Overview", April 2004, <https://
www.trustedcomputinggroup.org/groups/
TCG_1_0_Architecture_Overview.pdf>.
Appendix A. IPv6 Probing/Mapping Considerations Appendix A. IPv6 Probing/Mapping Considerations
One school of thought wants the IPv6 numbering topology (either at One school of thought wanted the IPv6 numbering topology (either at
network or node level) [I-D.schild-v6ops-guide-v4mapping] to match network or node level) to match IPv4 as exactly as possible, whereas
IPv4 as exactly as possible, whereas others see IPv6 as giving more others see IPv6 as giving more flexibility to the address plans, not
flexibility to the address plans, not wanting to constrain the design wanting to constrain the design of IPv6 addressing. Mirroring the
of IPv6 addressing. Mirroring the address plans may also be seen as address plans is now generally seen as a security threat because an
a security threat because an IPv6 deployment may have different IPv6 deployment may have different security properties from IPv4.
security properties from IPv4.
Given the relatively immature state of IPv6 network security, if an Given the relatively immature state of IPv6 network security, if an
attacker knows the IPv4 address of the node and believes it to be attacker knows the IPv4 address of the node and believes it to be
dual-stacked with IPv4 and IPv6, he might want to try to probe the dual-stacked with IPv4 and IPv6, he might want to try to probe the
corresponding IPv6 address, based on the assumption that the security corresponding IPv6 address, based on the assumption that the security
defenses might be lower. This might be the case particularly for defenses might be lower. This might be the case particularly for
nodes which are behind a NAT in IPv4, but globally addressable in nodes which are behind a NAT in IPv4, but globally addressable in
IPv6. Naturally, this is not a concern if similar and adequate IPv6. Naturally, this is not a concern if similar and adequate
security policies are in place. security policies are in place.
On the other hand, brute-force scanning or probing of addresses is On the other hand, brute-force scanning or probing of addresses is
computationally infeasible due to the large search space of interface computationally infeasible due to the large search space of interface
identifiers on most IPv6 subnets (somewhat less than 64 bits wide, identifiers on most IPv6 subnets (somewhat less than 64 bits wide,
depending on how identifiers are chosen), always provided that depending on how identifiers are chosen), always provided that
identifiers are chosen at random out of the available space, as identifiers are chosen at random out of the available space, as
discussed in [I-D.chown-v6ops-port-scanning-implications]. discussed in [I-D.ietf-v6ops-scanning-implications].
For example, automatic tunneling mechanisms typically use For example, automatic tunneling mechanisms typically use
deterministic methods for generating IPv6 addresses, so probing/ deterministic methods for generating IPv6 addresses, so probing/
port-scanning an IPv6 node is simplified. The IPv4 address is port-scanning an IPv6 node is simplified. The IPv4 address is
embedded at least in 6to4, Teredo and ISATAP addresses. embedded at least in 6to4, Teredo and ISATAP addresses.
Additionally, it is possible (in the case of 6to4 in particular) to Additionally, it is possible (in the case of 6to4 in particular) to
learn the address behind the prefix; for example, Microsoft 6to4 learn the address behind the prefix; for example, Microsoft 6to4
implementation uses the address 2002:V4ADDR::V4ADDR while older Linux implementation uses the address 2002:V4ADDR::V4ADDR while older Linux
and FreeBSD implementations default to 2002:V4ADDR::1. This could and FreeBSD implementations default to 2002:V4ADDR::1. This could
also be used as one way to identify an implementation and hence also be used as one way to identify an implementation and hence
target any specific weaknesses. target any specific weaknesses.
One proposal has been to randomize the addresses or subnet identifier One proposal has been to randomize the addresses or subnet identifier
in the address of the 6to4 router. This does not really help, as the in the address of the 6to4 router. This does not really help, as the
6to4 router (whether a host or a router) will return an ICMPv6 Hop 6to4 router (whether a host or a router) will return an ICMPv6 Hop
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learn the address behind the prefix; for example, Microsoft 6to4 learn the address behind the prefix; for example, Microsoft 6to4
implementation uses the address 2002:V4ADDR::V4ADDR while older Linux implementation uses the address 2002:V4ADDR::V4ADDR while older Linux
and FreeBSD implementations default to 2002:V4ADDR::1. This could and FreeBSD implementations default to 2002:V4ADDR::1. This could
also be used as one way to identify an implementation and hence also be used as one way to identify an implementation and hence
target any specific weaknesses. target any specific weaknesses.
One proposal has been to randomize the addresses or subnet identifier One proposal has been to randomize the addresses or subnet identifier
in the address of the 6to4 router. This does not really help, as the in the address of the 6to4 router. This does not really help, as the
6to4 router (whether a host or a router) will return an ICMPv6 Hop 6to4 router (whether a host or a router) will return an ICMPv6 Hop
Limit Exceeded message, revealing the IP address. Hosts behind the Limit Exceeded message, revealing the IP address. Hosts behind the
6to4 router can use methods such as RFC 3041 addresses to conceal 6to4 router can use methods such as privacy addresses
themselves, provided that they are not meant to be reachable by [I-D.ietf-ipv6-privacy-addrs-v2]to conceal themselves, provided that
sessions started from elsewhere: they would still require a globally they are not meant to be reachable by sessions started from
accessible static address if they wish to receive communications elsewhere: they would still require a globally accessible static
initiated elsewhere. address if they wish to receive communications initiated elsewhere.
To conclude, it seems that when an automatic tunneling mechanism is To conclude, it seems that when an automatic tunneling mechanism is
being used, given an IPv4 address, the corresponding IPv6 address being used, given an IPv4 address, the corresponding IPv6 address
could possibly be guessed with relative ease. This has significant could possibly be guessed with relative ease. This has significant
implications if the IPv6 security policy is less adequate than that implications if the IPv6 security policy is less adequate than that
for IPv4. for IPv4.
Appendix B. IPv6 Privacy Considerations Appendix B. IPv6 Privacy Considerations
The generation of IPv6 addresses of IPv6 addresses from MAC addresses The generation of IPv6 addresses from MAC addresses potentially
potentially allows the behavior of users to be tracked in a way which allows the behavior of users to be tracked in a way which may
may infringe their privacy. [RFC3041] specifies mechanisms which can infringe their privacy. [I-D.ietf-ipv6-privacy-addrs-v2] specifies
be used to reduce the risk of infringement. It has also been claimed mechanisms which can be used to reduce the risk of infringement. It
that IPv6 harms the privacy of the user, either by exposing the MAC has also been claimed that IPv6 harms the privacy of the user, either
address, or by exposing the number of nodes connected to a site. by exposing the MAC address, or by exposing the number of nodes
connected to a site.
Additional discussion of privacy issues can be found in the IPv6 Additional discussion of privacy issues can be found in the IPv6
Network Architecture Protection document [I-D.ietf-v6ops-nap]. Network Architecture Protection document [I-D.ietf-v6ops-nap].
B.1. Exposing MAC Addresses B.1. Exposing MAC Addresses
Using stateless address autoconfiguration results in the MAC address Using stateless address autoconfiguration results in the MAC address
being incorporated in an EUI64 that exposes the model of network being incorporated in an EUI64 that exposes the model of network
card. The concern has been that a user might not want to expose the card. The concern has been that a user might not want to expose the
details of the system to outsiders, e.g., fearing a resulting details of the system to outsiders, e.g., fearing a resulting
burglary if a thief identifies expensive equipment from the vendor burglary if a thief identifies expensive equipment from the vendor
identifier embedded in MAC addresses. identifier embedded in MAC addresses, or allowing the type of
equipment in use to be identified so facilitating an attack on
specific security weaknesses.
In most cases, this seems completely unfounded. First, such an In most cases, this seems completely unfounded. First, such an
address must be learned somehow -- this is a non-trivial process; the address must be learned somehow -- this is a non-trivial process; the
addresses are visible e.g., in web site access logs, but the chances addresses are visible e.g., in web site access logs, but the chances
that a random web site owner is collecting this kind of information that a random web site owner is collecting this kind of information
(or whether it would be of any use) are quite slim. Being able to (or whether it would be of any use) are quite slim. Being able to
eavesdrop the traffic to learn such addresses (e.g., by the eavesdrop the traffic to learn such addresses (e.g., by the
compromise of DSL or Cable modem physical media) seems also quite compromise of DSL (Digital Subscriber Line) or Cable modem physical
far-fetched. Further, using RFC 3041 addresses for such purposes is media) seems also quite far-fetched. Further, using statically
straightforward if worried about the risk. Second, the burglar would configured interface identifiers or privacy addresses
have to be able to map the IP address to the physical location; [I-D.ietf-ipv6-privacy-addrs-v2] for such purposes is straightforward
typically this would only be possible with information from the if worried about the risk. Second, the burglar would have to be able
private customer database of the ISP and, for large sites, the to map the IP address to the physical location; typically this would
administrative records of the site. only be possible with information from the private customer database
of the Internet Service Provider (ISP) and, for large sites, the
administrative records of the site, although some physical address
information may be available from the WHOIS database of Internet
registries.
B.2. Exposing Multiple Devices B.2. Exposing Multiple Devices
Another concern that has been aired involves the user wanting to Another concern that has been aired involves the user wanting to
conceal the presence of a large number of computers or other devices conceal the presence of a large number of computers or other devices
connected to a network; NAT can "hide" all this equipment behind a connected to a network; NAT can "hide" all this equipment behind a
single address, but is not perfect either [FNAT]. single address, but is not perfect either [FNAT].
One practical reason why some administrators may find this desirable One practical reason why some administrators may find this desirable
is being able to thwart certain ISPs' business models. These models is being able to thwart certain ISPs' business models. These models
require payment based on the number of connected computers, rather require payment based on the number of connected computers, rather
than the connectivity as a whole. than the connectivity as a whole.
Similar feasibility issues as described above apply. To a degree, Similar feasibility issues as described above apply. To a degree,
the number of machines present could be obscured by the sufficiently the number of machines present could be obscured by the sufficiently
frequent re-use of RFC 3041 addresses -- that is, if during a short frequent re-use of privacy addresses [I-D.ietf-ipv6-privacy-addrs-v2]
period, dozens of generated addresses seem to be in use, it's -- that is, if during a short period, dozens of generated addresses
difficult to estimate whether they are generated by just one host or seem to be in use, it's difficult to estimate whether they are
multiple hosts. generated by just one host or multiple hosts.
B.3. Exposing the Site by a Stable Prefix B.3. Exposing the Site by a Stable Prefix
When an ISP provides IPv6 connectivity to its customers, it delegates When an ISP provides IPv6 connectivity to its customers, including
a fixed global routing prefix (usually a /48) to them. home or consumer users, it delegates a fixed global routing prefix
(usually a /48) to them. This is in contrast to the typical IPv4
situation where home users typically receive a dynamically allocated
address that may be stable only for period of hours.
Due to this fixed allocation, it is easier to correlate the global Due to this fixed allocation, it is easier to correlate the global
routing prefix to a network site. In case of consumer users, this routing prefix to a network site. In case of consumer users, this
correlation leads to a privacy issue, since a site is often correlation leads to a privacy issue, since a site is often
equivalent to an individual or a family in such a case. That is, equivalent to an individual or a family in such a case. Consequently
some users might be concerned about being able to be tracked based on some users might be concerned about being able to be tracked based on
their /48 allocation if it is static [I-D.dupont-ipv6- their /48 allocation if it is static
rfc3041harmful]. On the other hand many users may find having a [I-D.ietf-ipv6-privacy-addrs-v2]. On the other hand many users may
static allocation desirable as it allows them to offer services find having a static allocation desirable as it allows them to offer
hosted in their network more easily. services hosted in their network more easily.
This problem remains unsolved even when a user changes his/her This situation is not affected even if a user changes his/her
interface ID or subnet ID, because malicious users can still discover interface ID or subnet ID, because malicious users can still discover
this binding. This problem can be solved by untraceable IPv6 this binding. On larger sites the situation can be mitigated by
addresses as described in [I-D.ietf-v6ops-nap]. using "untraceable" IPv6 addresses as described in
[I-D.ietf-v6ops-nap] and it is possible that in future ISPs might be
prepared to offer untraceable addresses to their consumer customers
to minimize the privacy issues.
This privacy issue is common to both IPv4 and IPv6 and is inherent in
the use of IP addresses as both identifiers for node interfaces and
locators for the nodes.
Authors' Addresses Authors' Addresses
Elwyn B. Davies Elwyn B. Davies
Consultant Consultant
Soham, Cambs Soham, Cambs
UK UK
Phone: +44 7889 488 335 Phone: +44 7889 488 335
Email: elwynd@dial.pipex.com Email: elwynd@dial.pipex.com
skipping to change at page 38, line 5 skipping to change at page 40, line 5
Canada Canada
Phone: +1 514-345-7900 Phone: +1 514-345-7900
Email: suresh.krishnan@ericsson.com Email: suresh.krishnan@ericsson.com
Pekka Savola Pekka Savola
CSC/Funet CSC/Funet
Email: psavola@funet.fi Email: psavola@funet.fi
Intellectual Property Statement Full Copyright Statement
Copyright (C) The Internet Society (2006).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Intellectual Property
The IETF takes no position regarding the validity or scope of any The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in pertain to the implementation or use of the technology described in
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on the procedures with respect to rights in RFC documents can be on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79. found in BCP 78 and BCP 79.
skipping to change at page 38, line 29 skipping to change at page 40, line 45
such proprietary rights by implementers or users of this such proprietary rights by implementers or users of this
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The IETF invites any interested party to bring to its attention any The IETF invites any interested party to bring to its attention any
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Disclaimer of Validity
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Copyright Statement
Copyright (C) The Internet Society (2006). This document is subject
to the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights.
Acknowledgment Acknowledgment
Funding for the RFC Editor function is currently provided by the Funding for the RFC Editor function is provided by the IETF
Internet Society. Administrative Support Activity (IASA).
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