draft-ietf-v6ops-scanning-implications-03.txt   draft-ietf-v6ops-scanning-implications-04.txt 
IPv6 Operations T. Chown IPv6 Operations T. Chown
Internet-Draft University of Southampton Internet-Draft University of Southampton
Intended status: Informational March 27, 2007 Intended status: Informational November 19, 2007
Expires: September 28, 2007 Expires: May 22, 2008
IPv6 Implications for Network Scanning IPv6 Implications for Network Scanning
draft-ietf-v6ops-scanning-implications-03 draft-ietf-v6ops-scanning-implications-04
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
skipping to change at page 1, line 34 skipping to change at page 1, line 34
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 28, 2007. This Internet-Draft will expire on May 22, 2008.
Copyright Notice Copyright Notice
Copyright (C) The IETF Trust (2007). Copyright (C) The IETF Trust (2007).
Abstract Abstract
The 128 bits of IPv6 address space is considerably bigger than the 32 The much larger default 64-bit subnet address space of IPv6 should in
bits of address space of IPv4. In particular, the IPv6 subnets to principle make traditional network (port) scanning techniques used by
which hosts attach will by default have 64 bits of host address certain network worms or scanning tools less effective. While
space. As a result, traditional methods of remote TCP or UDP network traditional network scanning probes (whether by individuals or
scanning to discover open or running services on a host will automated via network worms) may become less common, administrators
potentially become less feasible, due to the larger search space in should be aware that attackers may use other techniques to discover
the subnet. In addition automated attacks, such as those performed IPv6 addresses on a target network, and thus they should also be
by network worms, that pick random host addresses to propagate to, aware of measures that are available to mitigate against them. This
may be hampered. This document discusses this property of IPv6 and informational document discusses approaches that administrators could
describes related issues for IPv6 site network administrators to take when planning their site address allocation and management
consider, which may be of importance when planning site address strategies as part of a defence-in-depth approach to network
allocation and management strategies. While traditional network security.
scanning probes (whether by individuals or automated via network
worms) may become less common, administrators should be aware of
other methods attackers may use to discover IPv6 addresses on a
target network, and also be aware of appropriate measures to mitigate
them.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Target Address Space for Network Scanning . . . . . . . . . . 4 2. Target Address Space for Network Scanning . . . . . . . . . . 4
2.1. IPv4 . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2.1. IPv4 . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.2. IPv6 . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2.2. IPv6 . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.3. Reducing the IPv6 Search Space . . . . . . . . . . . . . . 4 2.3. Reducing the IPv6 Search Space . . . . . . . . . . . . . . 4
2.4. Dual-stack Networks . . . . . . . . . . . . . . . . . . . 5 2.4. Dual-stack Networks . . . . . . . . . . . . . . . . . . . 5
2.5. Defensive Scanning . . . . . . . . . . . . . . . . . . . . 5 2.5. Defensive Scanning . . . . . . . . . . . . . . . . . . . . 5
3. Alternatives for Attackers: Off-link . . . . . . . . . . . . . 5 3. Alternatives for Attackers: Off-link . . . . . . . . . . . . . 5
3.1. Gleaning IPv6 prefix information . . . . . . . . . . . . . 6 3.1. Gleaning IPv6 prefix information . . . . . . . . . . . . . 5
3.2. DNS Advertised Hosts . . . . . . . . . . . . . . . . . . . 6 3.2. DNS Advertised Hosts . . . . . . . . . . . . . . . . . . . 6
3.3. DNS Zone Transfers . . . . . . . . . . . . . . . . . . . . 6 3.3. DNS Zone Transfers . . . . . . . . . . . . . . . . . . . . 6
3.4. Log File Analysis . . . . . . . . . . . . . . . . . . . . 6 3.4. Log File Analysis . . . . . . . . . . . . . . . . . . . . 6
3.5. Application Participation . . . . . . . . . . . . . . . . 6 3.5. Application Participation . . . . . . . . . . . . . . . . 6
3.6. Multicast Group Addresses . . . . . . . . . . . . . . . . 7 3.6. Multicast Group Addresses . . . . . . . . . . . . . . . . 6
3.7. Transition Methods . . . . . . . . . . . . . . . . . . . . 7 3.7. Transition Methods . . . . . . . . . . . . . . . . . . . . 7
4. Alternatives for Attackers: On-link . . . . . . . . . . . . . 7 4. Alternatives for Attackers: On-link . . . . . . . . . . . . . 7
4.1. General on-link methods . . . . . . . . . . . . . . . . . 7 4.1. General on-link methods . . . . . . . . . . . . . . . . . 7
4.2. Intra-site Multicast or Other Service Discovery . . . . . 8 4.2. Intra-site Multicast or Other Service Discovery . . . . . 8
5. Site Administrator Tools . . . . . . . . . . . . . . . . . . . 8 5. Tools to Mitigate Against Scanning Attacks . . . . . . . . . . 8
5.1. IPv6 Privacy Addresses . . . . . . . . . . . . . . . . . . 8 5.1. IPv6 Privacy Addresses . . . . . . . . . . . . . . . . . . 8
5.2. Cryptographically Generated Addresses (CGAs) . . . . . . . 9 5.2. Cryptographically Generated Addresses (CGAs) . . . . . . . 9
5.3. Non-use of MAC addresses in EUI-64 format . . . . . . . . 9 5.3. Non-use of MAC addresses in EUI-64 format . . . . . . . . 9
5.4. DHCP Service Configuration Options . . . . . . . . . . . . 9 5.4. DHCP Service Configuration Options . . . . . . . . . . . . 10
5.5. Rolling Server Addresses . . . . . . . . . . . . . . . . . 10
5.6. Application-Specific Addresses . . . . . . . . . . . . . . 10
6. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 10 6. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 10
7. Security Considerations . . . . . . . . . . . . . . . . . . . 11 7. Security Considerations . . . . . . . . . . . . . . . . . . . 10
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11
10. Informative References . . . . . . . . . . . . . . . . . . . . 11 10. Informative References . . . . . . . . . . . . . . . . . . . . 11
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 12 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 12
Intellectual Property and Copyright Statements . . . . . . . . . . 13 Intellectual Property and Copyright Statements . . . . . . . . . . 13
1. Introduction 1. Introduction
One of the key differences between IPv4 and IPv6 is the much larger One of the key differences between IPv4 and IPv6 is the much larger
address space for IPv6, which also goes hand-in-hand with much larger address space for IPv6, which also goes hand-in-hand with much larger
subnet sizes. This change has a significant impact on the subnet sizes. This change has a significant impact on the
feasibility of TCP and UDP network scanning, whereby an automated feasibility of TCP and UDP network scanning, whereby an automated
process is run to detect open ports (services) on systems that may process is run to detect open ports (services) on systems that may
then be subject of a subsequent attack. Today many IPv4 sites are then be subject of a subsequent attack. Today many IPv4 sites are
subjected to such probing on a recurring basis. subjected to such probing on a recurring basis. Such probing is
common in part due to the relatively dense population of active hosts
in any given chunk of IPv4 address space.
The 128 bits of IPv6 [1] address space is considerably bigger than The 128 bits of IPv6 [1] address space is considerably bigger than
the 32 bits of address space in IPv4. In particular, the IPv6 the 32 bits of address space in IPv4. In particular, the IPv6
subnets to which hosts attach will by default have 64 bits of host subnets to which hosts attach will by default have 64 bits of host
address space [2]. As a result, traditional methods of remote TCP or address space [2]. As a result, traditional methods of remote TCP or
UDP network scanning to discover open or running services on a host UDP network scanning to discover open or running services on a host
will potentially become less feasible, due to the larger search space will potentially become less feasible, due to the larger search space
in the subnet. This document discusses this property of IPv6, and in the subnet. Similarly, worms that rely on off-link network
describes related issues for IPv6 site network administrators to scanning to propagate may also be potentially be more limited in
consider, which may be of importance when planning site address impact. This document discusses this property of IPv6, and describes
allocation and management strategies. related issues for IPv6 site network administrators to consider,
which may be useful when planning site address allocation and
management strategies.
For example, many worms, like Slammer, rely on such address scanning
methods to propagate, whether they pick subnets numerically (and thus
probably topologically) close to the current victim, or subnets in
random remote networks. The nature of these worms may change, if
detection of target hosts between sites or subnets is harder to
achieve by traditional methods. However, there are other worms that
propagate via methods such as email, for which the methods discussed
in this text are not relevant.
It must be remembered that the defence of a network must not rely
solely on the unpredictable sparseness of the host addresses on that
network. Such a feature or property is only one measure in a set of
measures that may be applied. This document discusses various
measures that can be used by a site to mitigate against attacks as
part of an overall strategy. Some of these have a lower cost to
deploy than others. For example, if numbering hosts on a subnet, it
may be as cheap to number hosts without any predictable pattern as it
is to number them sequentially. In contrast, use of IPv6 Privacy
Extensions [3] may complicate network management (identifying which
hosts use which addresses).
This document complements the transition-centric discussion of the This document complements the transition-centric discussion of the
issues that can be found in Appendix A of the IPv6 Transition/ issues that can be found in Appendix A of the IPv6 Transition/
Co-existence Security Considerations text [12], which takes a broad Co-existence Security Considerations text [12], which takes a broad
view of security issues for transitioning networks. view of security issues for transitioning networks. The reader is
also referred to a recent paper by Bellovin on network worm
The reader is also referred to a recent paper by Bellovin on worm
propagation strategies in IPv6 networks [13]. This paper discusses propagation strategies in IPv6 networks [13]. This paper discusses
some of the issues included in this document, from a slightly some of the issues included in this document, from a slightly
different perspective. different perspective.
Network scanning is quite a prevalent tactic used by would-be
attackers. There are two general classes of such scanning. In one
case, the probes are from an attacker outside a site boundary who is
trying to find weaknesses on any system in that network which they
may then subsequently be able to compromise. The other case is
scanning by worms that spread through (site) networks, looking for
further hosts to compromise. Many worms, like Slammer, rely on such
address scanning methods to propagate, whether they pick subnets
numerically (and thus probably topologically) close to the current
victim, or subnets in random remote networks.
It must be remembered that the defence of a network must not rely
solely on the unpredictable sparseness of the host addresses on that
network. Such a feature or property is only one measure in a set of
measures that may be applied. However, with a growth in usage of
IPv6 devices in open networks likely, and security becoming more
likely an issue for the end devices, such obfuscation can be useful
where its use is of little or no cost to the administrator to
implement it. However, a law of diminishing returns does apply. An
administrator who undertakes an address hiding policy through
unpredictable sparseness should be aware that while IPv6 host
addresses may be assigned to hosts that are likely to take
significant time to discover by traditional scanning methods, there
are other means by which such addresses may be discovered.
Implementing all of the mitigating methods described in this text may
be deemed unwarranted effort. But it is up to the site administrator
to be aware of the context and the options available, and in
particular what new methods may attackers use to glean IPv6 address
information, and how these can potentially be mitigated against.
Finally, note that this document is currently intended to be
informational; there is not yet sufficient deployment experience for
it to be considered BCP.
2. Target Address Space for Network Scanning 2. Target Address Space for Network Scanning
There are significantly different considerations for the feasibility There are significantly different considerations for the feasibility
of plain, brute force IPv4 and IPv6 address scanning. of plain, brute force IPv4 and IPv6 address scanning.
2.1. IPv4 2.1. IPv4
A typical IPv4 subnet may have 8 bits reserved for host addressing. A typical IPv4 subnet may have 8 bits reserved for host addressing.
In such a case, a remote attacker need only probe at most 256 In such a case, a remote attacker need only probe at most 256
addresses to determine if a particular service is running publicly on addresses to determine if a particular service is running publicly on
skipping to change at page 6, line 20 skipping to change at page 6, line 11
view information (e.g. from public looking glass services) or view information (e.g. from public looking glass services) or
information on allocated address space from RIRs. In general this information on allocated address space from RIRs. In general this
would only yield information at most at the /48 prefix granularity, would only yield information at most at the /48 prefix granularity,
but specific /64 prefixes may be observed from route views on some but specific /64 prefixes may be observed from route views on some
parts of some networks. parts of some networks.
3.2. DNS Advertised Hosts 3.2. DNS Advertised Hosts
Any servers that are DNS listed, e.g. MX mail relays, or web Any servers that are DNS listed, e.g. MX mail relays, or web
servers, will remain open to probing from the very fact that their servers, will remain open to probing from the very fact that their
IPv6 addresses will be published in the DNS. Where a site uses IPv6 addresses will be published in the DNS.
sequential host numbering, publishing just one address may lead to a
threat upon the other hosts.
Sites may use a two-faced DNS where internal system DNS information While servers are relatively easy to find because they are DNS-
is only published in an internal DNS. It is also worth noting that published, any systems that are not DNS-published will be much harder
the reverse DNS tree may also expose address information. In such to locate via traditional scanning than is the case for IPv4
cases, populating the reverse DNS tree for the entire subnet, even if networks. It is worth noting that where a site uses sequential host
not all addresses are actually used, may reduce that exposure. numbering, publishing just one address may lead to a threat upon the
other hosts.
3.3. DNS Zone Transfers 3.3. DNS Zone Transfers
In the IPv6 world a DNS zone transfer is much more likely to narrow In the IPv6 world a DNS zone transfer is much more likely to narrow
the number of hosts an attacker needs to target. This implies the number of hosts an attacker needs to target. This implies
restricting zone transfers is (more) important for IPv6, even if it restricting zone transfers is (more) important for IPv6, even if it
is already good practice to restrict them in the IPv4 world. is already good practice to restrict them in the IPv4 world.
There are some projects that provide Internet mapping data from There are some projects that provide Internet mapping data from
access to such transfers. Administrators may of course agree to access to such transfers. Administrators may of course agree to
skipping to change at page 7, line 44 skipping to change at page 7, line 35
likely that there are more. likely that there are more.
In the case of Teredo, the 64 bit node identifier is generated from In the case of Teredo, the 64 bit node identifier is generated from
the IPv4 address observed at a Teredo server along with a UDP port the IPv4 address observed at a Teredo server along with a UDP port
number. The Teredo specification also allows for discovery of other number. The Teredo specification also allows for discovery of other
Teredo clients on the same IPv4 subnet via a well-known IPv4 Teredo clients on the same IPv4 subnet via a well-known IPv4
multicast address (see Section 2.17 of RFC4380 [11]). multicast address (see Section 2.17 of RFC4380 [11]).
4. Alternatives for Attackers: On-link 4. Alternatives for Attackers: On-link
The main thrust of this text is considerations for off-link attackers
or probing of a network. In general, once one host on a link is
compromised, others on the link can be very readily discovered.
4.1. General on-link methods 4.1. General on-link methods
If the attacker is on link, then traffic on the link, be it Neighbour If the attacker already has access to a system on the current subnet,
Discovery or application based traffic, can invariably be observed, then traffic on that subnet, be it Neighbour Discovery or application
and target addresses learnt. In this document we are assuming the based traffic, can invariably be observed, and active node addresses
attacker is off link, but traffic to or from other nodes (in within the local subnet learnt.
particular server systems) is likely to show up if an attacker can
gain a presence on any one subnet in a site's network.
IPv6-enabled hosts on local subnets may be discovered through probing In addition to making observations of traffic on the link, IPv6-
the "all hosts" link local multicast address. Likewise any routers enabled hosts on local subnets may be discovered through probing the
on link may be found via the "all routers" link local multicast "all hosts" link local multicast address. Likewise any routers on
the subnet may be found via the "all routers" link local multicast
address. An attacker may choose to probe in a slightly more address. An attacker may choose to probe in a slightly more
obfuscated way by probing the solicited node multicast address of a obfuscated way by probing the solicited node multicast address of a
potential target host. potential target host.
Where a host has already been compromised, its Neighbour Discovery Where a host has already been compromised, its Neighbour Discovery
cache is also likely to include information about active nodes on cache is also likely to include information about active nodes on the
link, just as an ARP cache would do for IPv4. current subnet, just as an ARP cache would do for IPv4.
Also, depending on the node, traffic to or from other nodes (in
particular server systems) is likely to show up if an attacker can
gain a presence on a node in any one subnet in a site's network.
4.2. Intra-site Multicast or Other Service Discovery 4.2. Intra-site Multicast or Other Service Discovery
A site may also have site or organisational scope multicast A site may also have site or organisational scope multicast
configured, in which case application traffic, or service discovery, configured, in which case application traffic, or service discovery,
may be exposed site wide. An attacker may also choose to use any may be exposed site wide. An attacker may also choose to use any
other service discovery methods supported by the site. other service discovery methods supported by the site.
5. Site Administrator Tools 5. Tools to Mitigate Against Scanning Attacks
There are some tools that site administrators can apply to make the There are some tools that site administrators can apply to make the
task for IPv6 network scanning attackers harder. These methods arise task for IPv6 network scanning attackers harder. These methods arise
from the considerations in the previous section. from the considerations in the previous section.
The author notes that at his current (university) site, there is no The author notes that at his current (university) site, there is no
evidence of general network scanning running across subnets. evidence of general network scanning running across subnets.
However, there is network scanning over IPv6 connections to systems However, there is network scanning over IPv6 connections to systems
whose IPv6 addresses are advertised (DNS servers, MX relays, web whose IPv6 addresses are advertised (DNS servers, MX relays, web
servers, etc), which are presumably looking for other open ports on servers, etc), which are presumably looking for other open ports on
these hosts to probe. these hosts to probe. At the time of writing, DHCPv6 DHCPv6 [6] is
not yet in use, and clients use stateless autoconfiguration.
Therefore the author's site does not yet have sequentially numbered
client hosts deployed as may typically seen in today's IPv4 DHCP-
served networks.
5.1. IPv6 Privacy Addresses 5.1. IPv6 Privacy Addresses
By using the IPv6 Privacy Extensions [3] hosts in a network may only Hosts in a network using IPv6 Privacy Extensions [3] will typically
be able to connect to external systems using their current only connect to external systems using their current (temporary)
(temporary) privacy address. While an attacker may be able to port privacy address. The precise behaviour of a host with a stable
scan that address if they do so quickly upon observing or otherwise global address and one or more dynamic privacy address(es) when
learning of the address, the threat or risk is reduced due to the selecting a source address to use may be operating-system specific,
time-constrained value of the address. One implementation of RFC3041 or configuarable, but typical behaviour when initiating a connection
already deployed has privacy addresses active for one day, with such is use of a privacy address when available.
While an attacker may be able to port scan a privacy address if they
do so quickly upon observing or otherwise learning of the address,
the threat or risk is reduced due to the time-constrained value of
the address. One implementation of RFC4941 already deployed has
privacy addresses active (used by the node) for one day, with such
addresses reachable for seven days. addresses reachable for seven days.
Note that an RFC3041 host will usually also have a separate static Note that an RFC4941 host will usually also have a separate static
global IPv6 address by which it can also be reached, and that may be global IPv6 address by which it can also be reached, and that may be
DNS-advertised if an externally reachable service is running on it. DNS-advertised if an externally reachable service is running on it.
DHCPv6 can be used to serve normal global addresses and IPv6 Privacy DHCPv6 can be used to serve normal global addresses and IPv6 Privacy
Addresses. Addresses.
The implication is that while Privacy Addresses can mitigate the The implication is that while Privacy Addresses can mitigate the
long-term value of harvested addresses, an attacker creating an IPv6 long-term value of harvested addresses, an attacker creating an IPv6
application server to which clients connect will still be able to application server to which clients connect will still be able to
probe the clients by their Privacy Address as and when they visit probe the clients by their Privacy Address as and when they visit
that server. The duration for which Privacy Addresses are valid will that server. The duration for which Privacy Addresses are valid will
impact on the usefulness of such observed addresses to an external impact on the usefulness of such observed addresses to an external
attacker. The frequency with which such address get recycled could attacker. For example, a worm that may spread using such observed
addresses may be less effective if it relies on harvested privacy
addresses. The frequency with which such address get recycled could
be increased, though this may increase the complexity of local be increased, though this may increase the complexity of local
network management for the administrator, since doing so will cause network management for the administrator, since doing so will cause
more addresses to be used over time in the site. more addresses to be used over time in the site.
It may be worth exploring whether firewalls can be adapted to allow A further option here may be to consider using different addresses
the option to block traffic initiated to a known IPv6 Privacy Address for specific applications, or even each new application instance,
from outside a network boundary. While some applications may which may reduce exposure to other services running on the same host
genuinely require such capability, it may be useful to be able to when such an address is observed externally.
differentiate in some circumstances.
5.2. Cryptographically Generated Addresses (CGAs) 5.2. Cryptographically Generated Addresses (CGAs)
The use of Cryptographically Generated Addresses (CGAs) [9] may also The use of Cryptographically Generated Addresses (CGAs) [9] may also
cause the search space to be increased from that presented by default cause the search space to be increased from that presented by default
use of Stateless Autoconfiguration. Such addresses would be seen use of Stateless Autoconfiguration. Such addresses would be seen
where Secure Neighbour Discovery (SEND) [8] is in use. where Secure Neighbour Discovery (SEND) [8] is in use.
5.3. Non-use of MAC addresses in EUI-64 format 5.3. Non-use of MAC addresses in EUI-64 format
The EUI-64 identifier format does not require the use of MAC The EUI-64 identifier format does not require the use of MAC
addresses for identifier construction. At least one well-known addresses for identifier construction. At least one well-known
operating system currently defaults to generation of the 64 bit operating system currently defaults to generation of the 64 bit
interface identifier by use of random bits, and thus does not embed interface identifier by use of random bits, and thus does not embed
the MAC address. Where such a method exists as an option, an the MAC address. Where such a method exists as an option, an
administrator may wish consider use of that option. administrator may wish consider use of that option.
5.4. DHCP Service Configuration Options 5.4. DHCP Service Configuration Options
The administrator should configure DHCPv6 so that the first addresses One option open to an administrator is to configure DHCPv6, if
allocated from the pool begins much higher in the address space than possible, so that the first addresses allocated from the pool begins
at [prefix]::1. Further, it is desirable that allocated addresses much higher in the address space than at [prefix]::1. Further, it is
are not sequential, nor have any predictable pattern to them. desirable that allocated addresses are not sequential, nor have any
Unpredictable sparseness in the allocated addresses is a desirable predictable pattern to them. Unpredictable sparseness in the
property. DHCPv6 implementors should support configuration options allocated addresses is a desirable property. DHCPv6 implementers
to allow such behaviour. could reduce the cost for administrators to deploy such 'random'
addressing by supporting configuration options to allow such
behaviour.
DHCPv6 also includes an option to use Privacy Extension [3] DHCPv6 also includes an option to use Privacy Extension [3]
addresses, i.e. temporary addresses, as described in Section 12 of addresses, i.e. temporary addresses, as described in Section 12 of
the DHCPv6 [6] specification. the DHCPv6 [6] specification.
5.5. Rolling Server Addresses
Given the huge address space in an IPv6 subnet/link, and the support
for IPv6 multiaddressing, whereby a node or interface may have
multiple IPv6 valid addresses of which one is preferred for sending,
it may be possible to periodically change the advertised addresses
that certain long standing services use (where 'short' exchanges to
those services are used).
For example, an MX server could be assigned a new primary address on
a weekly basis, and old addresses expired monthly. Where MX server
IP addresses are detected and cached by spammers, such a defence may
prove useful to reduce spam volumes, especially as such IP lists may
also be passed between potential attackers for subsequent probing.
5.6. Application-Specific Addresses
By a similar reasoning, it may be possible to consider using
application-specific addresses for systems, such that a given
application may have exclusive use of an address, meaning that
disclosure of the address should not expose other applications or
services running on the same system.
6. Conclusions 6. Conclusions
Due to the much larger size of IPv6 subnets in comparison to IPv4 it Due to the much larger size of IPv6 subnets in comparison to IPv4 it
will become less feasible for network scanning methods to detect open will become less feasible for traditional network scanning methods to
services for subsequent attacks. If administrators number their IPv6 detect open services for subsequent attacks, assuming the attackers
subnets in 'random', non-predictable ways, attackers, whether they be are off-site and services are not listed in the DNS. If
in the form of automated network scanners or dynamic worm administrators number their IPv6 subnets in 'random', non-predictable
propagation, will need to use new methods to determine IPv6 host ways, attackers, whether they be in the form of automated network
addresses to target. Of course, if those systems are dual-stack, and scanners or dynamic worm propagation, will need to make wider use of
have open IPv4 services running, they will remain exposed to new methods to determine IPv6 host addresses to target (e.g. looking
traditional probes over IPv4 transport. to obtain logs of activity from a site and scanning addresses around
the ones observed). Such numbering schemes may be very low cost to
This document has discussed the considerations a site administrator deploy in comparison to conventional sequential numbering, and thus a
should bear in mind when considering IPv6 address planning issues and useful part of an overall defence-in-depth strategy. Of course, if
configuring various service elements. It highlights relevant issues those systems are dual-stack, and have open IPv4 services running,
and offers some informational guidance for administrators. While they will remain exposed to traditional probes over IPv4 transport.
some suggestions are currently more practical than others, it is up
to individual administrators to determine how much effort they wish
to invest in 'address hiding' schemes, given that this is only one
aspect of network security, and certainly not one to rely solely
upon. But by implementing the basic principle of allocating
addresses on the basis of unpredictable sparseness, some level of
obfuscation can be cheaply deployed.
7. Security Considerations 7. Security Considerations
There are no specific security considerations in this document There are no specific security considerations in this document
outside of the topic of discussion itself. outside of the topic of discussion itself. However, it must be noted
that the 'security through obscurity' discussions and commentary
within this text must be noted in their proper context. Relying
purely on obscurity of a node address is not prudent, rather the
advice here should be considered as part of a 'defence-in-depth'
approach to security for a site or network. This also implies that
these measures require coordination between network administrators
and those who maintain DNS services, though that is common in most
scenarios.
8. IANA Considerations 8. IANA Considerations
There are no IANA considerations for this document. There are no IANA considerations for this document.
9. Acknowledgements 9. Acknowledgements
Thanks are due to people in the 6NET project (www.6net.org) for Thanks are due to people in the 6NET project (www.6net.org) for
discussion of this topic, including Pekka Savola, Christian Strauf discussion of this topic, including Pekka Savola, Christian Strauf
and Martin Dunmore, as well as other contributors from the IETF v6ops and Martin Dunmore, as well as other contributors from the IETF v6ops
and other mailing lists, including Tony Finch, David Malone, Bernie and other mailing lists, including Tony Finch, David Malone, Bernie
Volz, Fred Baker, Andrew Sullivan, Tony Hain, Dave Thaler and Alex Volz, Fred Baker, Andrew Sullivan, Tony Hain, Dave Thaler and Alex
Petrescu. Petrescu. Thanks are also due for editorial feedback from Brian
Carpenter, Lars Eggert and Jonne Soininen amongst others.
10. Informative References 10. Informative References
[1] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) [1] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6)
Specification", RFC 2460, December 1998. Specification", RFC 2460, December 1998.
[2] Thomson, S. and T. Narten, "IPv6 Stateless Address [2] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless Address
Autoconfiguration", RFC 2462, December 1998. Autoconfiguration", RFC 4862, September 2007.
[3] Narten, T. and R. Draves, "Privacy Extensions for Stateless [3] Narten, T., Draves, R., and S. Krishnan, "Privacy Extensions
Address Autoconfiguration in IPv6", RFC 3041, January 2001. for Stateless Address Autoconfiguration in IPv6", RFC 4941,
September 2007.
[4] Carpenter, B. and K. Moore, "Connection of IPv6 Domains via [4] Carpenter, B. and K. Moore, "Connection of IPv6 Domains via
IPv4 Clouds", RFC 3056, February 2001. IPv4 Clouds", RFC 3056, February 2001.
[5] Haberman, B. and D. Thaler, "Unicast-Prefix-based IPv6 [5] Haberman, B. and D. Thaler, "Unicast-Prefix-based IPv6
Multicast Addresses", RFC 3306, August 2002. Multicast Addresses", RFC 3306, August 2002.
[6] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., and M. [6] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., and M.
Carney, "Dynamic Host Configuration Protocol for IPv6 Carney, "Dynamic Host Configuration Protocol for IPv6
(DHCPv6)", RFC 3315, July 2003. (DHCPv6)", RFC 3315, July 2003.
skipping to change at page 12, line 19 skipping to change at page 12, line 13
RFC 3972, March 2005. RFC 3972, March 2005.
[10] Templin, F., Gleeson, T., Talwar, M., and D. Thaler, "Intra- [10] Templin, F., Gleeson, T., Talwar, M., and D. Thaler, "Intra-
Site Automatic Tunnel Addressing Protocol (ISATAP)", RFC 4214, Site Automatic Tunnel Addressing Protocol (ISATAP)", RFC 4214,
October 2005. October 2005.
[11] Huitema, C., "Teredo: Tunneling IPv6 over UDP through Network [11] Huitema, C., "Teredo: Tunneling IPv6 over UDP through Network
Address Translations (NATs)", RFC 4380, February 2006. Address Translations (NATs)", RFC 4380, February 2006.
[12] Davies, E., Krishnan, S., and P. Savola, "IPv6 Transition/ [12] Davies, E., Krishnan, S., and P. Savola, "IPv6 Transition/
Co-existence Security Considerations Co-existence Security Considerations", RFC 4942,
(draft-ietf-v6ops-security-overview-06)", October 2007. September 2007.
[13] Bellovin, S. et al, "Worm Propagation Strategies in an IPv6 [13] Bellovin, S. et al, "Worm Propagation Strategies in an IPv6
Internet (http://www.cs.columbia.edu/~smb/papers/v6worms.pdf)", Internet (http://www.cs.columbia.edu/~smb/papers/v6worms.pdf)",
;login:, February 2006. ;login:, February 2006.
Author's Address Author's Address
Tim Chown Tim Chown
University of Southampton University of Southampton
Southampton, Hampshire SO17 1BJ Southampton, Hampshire SO17 1BJ
 End of changes. 34 change blocks. 
163 lines changed or deleted 145 lines changed or added

This html diff was produced by rfcdiff 1.34. The latest version is available from http://tools.ietf.org/tools/rfcdiff/