draft-ietf-v6ops-scanning-implications-01.txt   draft-ietf-v6ops-scanning-implications-02.txt 
IPv6 Operations T. Chown IPv6 Operations T. Chown
Internet-Draft University of Southampton Internet-Draft University of Southampton
Expires: April 26, 2007 October 23, 2006 Intended status: Informational March 5, 2007
Expires: September 6, 2007
IPv6 Implications for Network Scanning IPv6 Implications for Network Scanning
draft-ietf-v6ops-scanning-implications-01 draft-ietf-v6ops-scanning-implications-02
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 33 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 April 26, 2007. This Internet-Draft will expire on September 6, 2007.
Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2006). Copyright (C) The IETF Trust (2007).
Abstract Abstract
The 128 bits of IPv6 address space is considerably bigger than the 32 The 128 bits of IPv6 address space is considerably bigger than the 32
bits of address space of IPv4. In particular, the IPv6 subnets to bits of address space of IPv4. In particular, the IPv6 subnets to
which hosts attach will by default have 64 bits of host address which hosts attach will by default have 64 bits of host address
space. As a result, traditional methods of remote TCP or UDP network space. As a result, traditional methods of remote TCP or UDP network
scanning to discover open or running services on a host will scanning to discover open or running services on a host will
potentially become far less feasible, due to the larger search space potentially become less feasible, due to the larger search space in
in the subnet. In addition automated attacks, such as those the subnet. In addition automated attacks, such as those performed
performed by network worms, may be hampered. This document discusses by network worms, may be hampered. This document discusses this
this property of IPv6, and describes related issues for site property of IPv6, and describes related issues for site
administrators of IPv6 networks to consider, which may be of administrators of IPv6 networks to consider, which may be of
importance when planning site address allocation and management importance when planning site address allocation and management
strategies. While traditional network scanning probes (whether by strategies. While traditional network scanning probes (whether by
individuals or automated via network worms) may become less common, individuals or automated via network worms) may become less common,
administrators should be aware of other methods attackers may use to administrators should be aware of other methods attackers may use to
discover IPv6 addresses on a target network, and be aware of discover IPv6 addresses on a target network, and be aware of
appropriate measures to mitigate these. 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 . . . . . . . . . . . . . . . . . . 5 3. Alternatives for Attackers: Off-link . . . . . . . . . . . . . 5
3.1. On-link Methods . . . . . . . . . . . . . . . . . . . . . 6 3.1. Gleaning IPv6 prefix information . . . . . . . . . . . . . 6
3.2. Multicast or Other Service Discovery . . . . . . . . . . . 6 3.2. DNS Advertised Hosts . . . . . . . . . . . . . . . . . . . 6
3.3. Log File Analysis . . . . . . . . . . . . . . . . . . . . 6 3.3. DNS Zone Transfers . . . . . . . . . . . . . . . . . . . . 6
3.4. DNS Advertised Hosts . . . . . . . . . . . . . . . . . . . 6 3.4. Log File Analysis . . . . . . . . . . . . . . . . . . . . 6
3.5. DNS Zone Transfers . . . . . . . . . . . . . . . . . . . . 7 3.5. Application Participation . . . . . . . . . . . . . . . . 6
3.6. Application Participation . . . . . . . . . . . . . . . . 7 3.6. Transition Methods . . . . . . . . . . . . . . . . . . . . 7
3.7. Transition Methods . . . . . . . . . . . . . . . . . . . . 7 4. Alternatives for Attackers: On-link . . . . . . . . . . . . . 7
4. Site Administrator Tools . . . . . . . . . . . . . . . . . . . 7 4.1. General on-link methods . . . . . . . . . . . . . . . . . 7
4.1. IPv6 Privacy Addresses . . . . . . . . . . . . . . . . . . 8 4.2. Multicast or Other Service Discovery . . . . . . . . . . . 8
4.2. DHCP Service Configuration Options . . . . . . . . . . . . 8 5. Site Administrator Tools . . . . . . . . . . . . . . . . . . . 8
4.3. Rolling Server Addresses . . . . . . . . . . . . . . . . . 8 5.1. IPv6 Privacy Addresses . . . . . . . . . . . . . . . . . . 8
4.4. Application-Specific Addresses . . . . . . . . . . . . . . 9 5.2. Cryptographically Generated Addresses (CGAs) . . . . . . . 9
5. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 9 5.3. Non-use of MAC addresses in EUI-64 format . . . . . . . . 9
6. Security Considerations . . . . . . . . . . . . . . . . . . . 9 5.4. DHCP Service Configuration Options . . . . . . . . . . . . 9
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 5.5. Rolling Server Addresses . . . . . . . . . . . . . . . . . 10
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10 5.6. Application-Specific Addresses . . . . . . . . . . . . . . 10
9. Informative References . . . . . . . . . . . . . . . . . . . . 10 6. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 10
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 11 7. Security Considerations . . . . . . . . . . . . . . . . . . . 11
Intellectual Property and Copyright Statements . . . . . . . . . . 12 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11
10. Informative References . . . . . . . . . . . . . . . . . . . . 11
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 12
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.
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 [3]. 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 far less feasible, due to the larger search will potentially become less feasible, due to the larger search space
space in the subnet. This document discusses this property of IPv6, in the subnet. This document discusses this property of IPv6, and
and describes related issues for site administrators of IPv6 networks describes related issues for site administrators of IPv6 networks to
to consider, which may be of importance when planning site address consider, which may be of importance when planning site address
allocation and management strategies. allocation and management strategies.
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 [7] text, 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 worm The reader is also referred to a recent paper by Bellovin on worm
propogation strategies in IPv6 networks [8]. 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 Network scanning is quite a prevalent tactic used by would-be
attackers. There are two general classes of such scanning. In one attackers. There are two general classes of such scanning. In one
case, the probes are from an attacker outside a site boundary who is 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 trying to find weaknesses on any system in that network which they
may then subsequently be able to compromise. The other case is may then subsequently be able to compromise. The other case is
scanning by worms that spread through (site) networks, looking for scanning by worms that spread through (site) networks, looking for
further hosts to compromise. Many worms, like Slammer, rely on such further hosts to compromise. Many worms, like Slammer, rely on such
skipping to change at page 4, line 5 skipping to change at page 4, line 5
numerically (and thus probably topologically) close to the current numerically (and thus probably topologically) close to the current
victim, or subnets in random remote networks. victim, or subnets in random remote networks.
It must be remembered that the defence of a network must not rely It must be remembered that the defence of a network must not rely
solely on the obscurity of the hosts on that network. Such a feature solely on the obscurity of the hosts on that network. Such a feature
or property is only one measure in a set of measures that may be 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 applied. However, with a growth in usage of IPv6 devices in open
networks likely, and security becoming more likely an issue for the networks likely, and security becoming more likely an issue for the
end devices, such obfuscation can be useful where its use is of end devices, such obfuscation can be useful where its use is of
little or no cost to the administrator to implement it. However, a little or no cost to the administrator to implement it. However, a
law of diminuishing returns does apply. An administrator who law of diminishing returns does apply. An administrator who
undertakes an address hiding policy should be aware that while IPv6 undertakes an address hiding policy should be aware that while IPv6
host addresses may be picked that are likely to take significant time host addresses may be picked that are likely to take significant time
to discover by traditional scanning methods, there are other means by to discover by traditional scanning methods, there are other means by
which such addresses may be discovered. Implementing all of them may which such addresses may be discovered. Implementing all of them may
be deemed unwarranted effort. But it is up to the site administrator be deemed unwarranted effort. But it is up to the site administrator
to be aware of the context and the options available, and in to be aware of the context and the options available, and in
particular what new methods may attackers use to glean IPv6 address particular what new methods may attackers use to glean IPv6 address
information, and how these can potentially be mitigated against. information, and how these can potentially be mitigated against.
This document is intended to be informational; there is not yet This document is intended to be informational; there is not yet
sufficient deployment experience for it to be considered BCP. sufficient deployment experience for it to be considered BCP.
skipping to change at page 5, line 9 skipping to change at page 5, line 9
First, the attacker may rely on the administrator conveniently First, the attacker may rely on the administrator conveniently
numbering their hosts from [prefix]::1 upward. This makes scanning numbering their hosts from [prefix]::1 upward. This makes scanning
trivial, and thus should be avoided unless the host's address is trivial, and thus should be avoided unless the host's address is
readily obtainable from other sources (for example it is the site's readily obtainable from other sources (for example it is the site's
primary DNS or email MX server). Alternatively if hosts are numbered primary DNS or email MX server). Alternatively if hosts are numbered
sequentially, or using any regular scheme, knowledge of one address sequentially, or using any regular scheme, knowledge of one address
may expose other available addresses to scan. may expose other available addresses to scan.
Second, in the case of statelessly autoconfiguring [1] hosts, the Second, in the case of statelessly autoconfiguring [1] hosts, the
host part of the address will take a well-known format that includes host part of the address will usually take a well-known format that
the Ethernet vendor prefix and the "fffe" stuffing. For such hosts, includes the Ethernet vendor prefix and the "fffe" stuffing. For
the search space can be reduced to 48 bits. Further, if the Ethernet such hosts, the search space can be reduced to 48 bits. Further, if
vendor is also known, the search space may be reduced to 24 bits, the Ethernet vendor is also known, the search space may be reduced to
with a one probe per second scan then taking a less daunting 194 24 bits, with a one probe per second scan then taking a less daunting
days. Even where the exact vendor is not known, using a set of 194 days. Even where the exact vendor is not known, using a set of
common vendor prefixes can reduce the search. In addition, many common vendor prefixes can reduce the search. In addition, many
nodes in a site network may be procured in batches, and thus have nodes in a site network may be procured in batches, and thus have
sequential or near sequential MAC addresses; if one node's sequential or near sequential MAC addresses; if one node's
autoconfigured address is known, scanning around that address may autoconfigured address is known, scanning around that address may
yield results for the attacker. Again, any form of sequential host yield results for the attacker. Again, any form of sequential host
addressing should be avoided if possible. addressing should be avoided if possible.
2.4. Dual-stack Networks 2.4. Dual-stack Networks
Full advantage of the increased IPv6 address space in terms of Full advantage of the increased IPv6 address space in terms of
skipping to change at page 5, line 40 skipping to change at page 5, line 40
only accessible over IPv6, and that thus can only be discovered by only accessible over IPv6, and that thus can only be discovered by
IPv6 address scanning. IPv6 address scanning.
2.5. Defensive Scanning 2.5. Defensive Scanning
The problem faced by the attacker for an IPv6 network is also faced The problem faced by the attacker for an IPv6 network is also faced
by a site administrator looking for vulnerabilities in their own by a site administrator looking for vulnerabilities in their own
network's systems. The administrator should have the advantage of network's systems. The administrator should have the advantage of
being on-link for scanning purposes though. being on-link for scanning purposes though.
3. Alternatives for Attackers 3. Alternatives for Attackers: Off-link
If IPv6 hosts in subnets are allocated addresses 'randomly', and as a If IPv6 hosts in subnets are allocated addresses 'randomly', and as a
result IPv6 network scanning becomes relatively infeasible, attackers result IPv6 network scanning becomes relatively infeasible, attackers
will need to find new methods to identify IPv6 addresses for will need to find new methods to identify IPv6 addresses for
subsequent scanning. In this section, we discuss some possible paths subsequent scanning. In this section, we discuss some possible paths
attackers may take. In these cases, the attacker will attempt to attackers may take. In these cases, the attacker will attempt to
identify specific IPv6 addresses for subsequent targeted probes. identify specific IPv6 addresses for subsequent targeted probes.
3.1. On-link Methods 3.1. Gleaning IPv6 prefix information
If the attacker is on link, then traffic on the link, be it Neighbor
Discovery or application based traffic, can invariably be observed,
and target addresses learnt. In this document we are assuming the
attacker is off link, but traffic to or from other nodes (in
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
the "all hosts" link local multicast address. Likewise any routers
on link may be found via the "all routers" link local multicast
address.
Where a host has already been compromised, its Neighbor Discovery
cache is also likely to include information about active nodes on
link, just as an ARP cache would do for IPv4.
3.2. Multicast or Other Service Discovery
A site may also have site or organisational scope multicast
configured, in which case application traffic, or service discovery,
may be exposed site wide. An attacker may choose to use any other
service discovery methods supported by the site.
There are also issues with disclosure from multicast itself. Where
an Embedded RP [6] multicast group address is known, the unicast
address of the rendezvous point is implied by the group address.
Where unicast prefix based multicast group addresses [4] are used,
specific /64 link prefixes may also be disclosed.
3.3. Log File Analysis
IPv6 addresses may be harvested from recorded logs such as web site Note that in IPv6 an attacker would not be able to search across the
logs. Anywhere else where IPv6 addresses are explicitly recorded may entire IPv6 address space as they might in IPv4. An attacker may
prove a useful channel for an attacker, e.g. by inspection of the learn general prefixes to focus their efforts on by observing route
(many) Received from: or other header lines in archived email or view information (e.g. from public looking glass services) or
Usenet news messages. information on allocated address space from RIRs. In general this
would only yield information at most at the /48 prefix granularity,
but specific /64 prefixes may be observed from route views on some
parts of some networks.
3.4. 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. Where a site uses
sequential host numbering, publishing just one address may lead to a sequential host numbering, publishing just one address may lead to a
threat upon the other hosts. threat upon the other hosts.
Sites may use a two-faced DNS where internal system DNS information Sites may use a two-faced DNS where internal system DNS information
is only published in an internal DNS. It is also worth noting that is only published in an internal DNS. It is also worth noting that
the reverse DNS tree may also expose address information. the reverse DNS tree may also expose address information. In such
cases, populating the reverse DNS tree for the entire subnet, even if
not all addresses are actually used, may reduce that exposure.
3.5. 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.
3.6. Application Participation There are some projects that provide Internet mapping data from
access to such transfers. Administrators may of course agree to
provide such transfers where they choose to do so.
3.4. Log File Analysis
IPv6 addresses may be harvested from recorded logs such as web site
logs. Anywhere else where IPv6 addresses are explicitly recorded may
prove a useful channel for an attacker, e.g. by inspection of the
(many) Received from: or other header lines in archived email or
Usenet news messages.
3.5. Application Participation
More recent peer-to-peer applications often include some centralised More recent peer-to-peer applications often include some centralised
server which coordinates the transfer of data between peers. The server which coordinates the transfer of data between peers. The
BitTorrent application builds swarms of nodes that exchange chunks of BitTorrent application builds swarms of nodes that exchange chunks of
files, with a tracker passing information about peers with available files, with a tracker passing information about peers with available
chunks of data between the peers. Such applications may offer an chunks of data between the peers. Such applications may offer an
attacker a source of peer IP addresses to probe. attacker a source of peer IP addresses to probe.
3.7. Transition Methods 3.6. Transition Methods
Specific knowledge of the target network may be gleaned if that Specific knowledge of the target network may be gleaned if that
attacker knows it is using 6to4, ISATAP, Teredo, or other techniques attacker knows it is using 6to4 [4], ISATAP [10], Teredo [11] or
that derive low-order bits from IPv4 addresses (though in this case, other techniques that derive low-order bits from IPv4 addresses
unless they are using IPv4 NAT, the IPv4 addresses may be probed (though in this case, unless they are using IPv4 NAT, the IPv4
anyway). For example, the current Microsoft 6to4 implementation uses addresses may be probed anyway).
the address 2002:V4ADDR::V4ADDR while older Linux and FreeBSD
For example, the current Microsoft 6to4 implementation uses the
address 2002:V4ADDR::V4ADDR while older Linux and FreeBSD
implementations default to 2002:V4ADDR::1. This leads to specific implementations default to 2002:V4ADDR::1. This leads to specific
knowledge of specific hosts in the network. Given one host in the knowledge of specific hosts in the network. Given one host in the
network is observed as using a given transition technique, it is network is observed as using a given transition technique, it is
likely that there are more. likely that there are more.
4. Site Administrator Tools 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
number. The Teredo specification also allows for discovery of other
Teredo clients on the same IPv4 subnet via a well-known IPv4
multicast address (see Section 2.17 of RFC4380 [11]).
4. Alternatives for Attackers: On-link
4.1. General on-link methods
If the attacker is on link, then traffic on the link, be it Neighbour
Discovery or application based traffic, can invariably be observed,
and target addresses learnt. In this document we are assuming the
attacker is off link, but traffic to or from other nodes (in
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
the "all hosts" link local multicast address. Likewise any routers
on link may be found via the "all routers" link local multicast
address. An attacker may choose to probe in a slightly more
obfuscated way by probing the solicited node multicast address of a
potential target host.
Where a host has already been compromised, its Neighbour Discovery
cache is also likely to include information about active nodes on
link, just as an ARP cache would do for IPv4.
4.2. Multicast or Other Service Discovery
A site may also have site or organisational scope multicast
configured, in which case application traffic, or service discovery,
may be exposed site wide. An attacker may choose to use any other
service discovery methods supported by the site.
There are also issues with disclosure from multicast itself. Where
an Embedded RP [7] multicast group address is known, the unicast
address of the rendezvous point is implied by the group address.
Where unicast prefix based multicast group addresses [5] are used,
specific /64 link prefixes may also be disclosed in traffic that goes
off-site. An administrator may thus choose to put aside /64 bit
prefixes for multicast group addresses that are not in use for normal
unicast routing and addressing.
5. Site Administrator Tools
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.
4.1. IPv6 Privacy Addresses 5.1. IPv6 Privacy Addresses
By using the IPv6 Privacy Extensions [2] hosts in a network may only By using the IPv6 Privacy Extensions [3] hosts in a network may only
be able to connect to external systems using their current be able to connect to external systems using their current
(temporary) privacy address. While an attacker may be able to port (temporary) privacy address. While an attacker may be able to port
scan that address if they do so quickly upon observing or otherwise scan that address if they do so quickly upon observing or otherwise
learning of the address, the threat or risk is reduced due to the learning of the address, the threat or risk is reduced due to the
time-constrained value of the address. One implementation of RFC3041 time-constrained value of the address. One implementation of RFC3041
already deployed has privacy addresses active for one day, with such already deployed has privacy addresses active 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 RFC3041 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.
Both of these can be served by DHCPv6.
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. In the general context of hiding the addresses exposed that server. In the general context of hiding the addresses exposed
from a site, an administrator may choose to use IPv6 Privacy from a site, an administrator may choose to use IPv6 Privacy
Addresses. The duration for which these are valid will impact on the Addresses. The duration for which these are valid will impact on the
usefulness of such observed addresses to an external attacker. The usefulness of such observed addresses to an external attacker. The
frequency with which such address get recycled could be increased, frequency with which such address get recycled could be increased,
though this will present the site administrator with more addresses though this will present the site administrator with more addresses
to track the usage of. to track the usage of.
It may be worth exploring whether firewalls can be adapted to allow It may be worth exploring whether firewalls can be adapted to allow
the option to block traffic initiated to a known IPv6 Privacy Address the option to block traffic initiated to a known IPv6 Privacy Address
from outside a network boundary. While some applications may from outside a network boundary. While some applications may
genuinely require such capability, it may be useful to be able to genuinely require such capability, it may be useful to be able to
differentiate in some circumstances. differentiate in some circumstances.
4.2. DHCP Service Configuration Options 5.2. Cryptographically Generated Addresses (CGAs)
The use of Cryptographically Generated Addresses (CGAs) [9] may also
cause the search space to be increased from that presented by default
use of Stateless Autoconfiguration. Such addresses would be seen
where Secure Neighbour Discovery (SEND) [8] is in use.
5.3. Non-use of MAC addresses in EUI-64 format
The EUI-64 identifier format does not require the use of MAC
addresses for identifier construction. At least one well-known
operating system currently defaults to generation of the 64 bit
interface identifier by use of random bits, and thus does not embed
the MAC address. Where such a method exists as an option, an
administrator may wish consider use of that option.
5.4. DHCP Service Configuration Options
The administrator should configure DHCPv6 so that the first addresses The administrator should configure DHCPv6 so that the first addresses
allocated from the pool begins much higher in the address space than allocated from the pool begins much higher in the address space than
at [prefix]::1. DHCPv6 also includes an option to use Privacy at [prefix]::1. Further, it is desirable that allocated addresses
Extension [2] addresses, i.e. temporary addresses, as described in are not sequential, nor have any predictable pattern to them. DHCPv6
Section 12 of the DHCPv6 [5] specification. It is desirable that implementors should support configuration options to allow such
allocated addresses are not sequential, nor have any predictable behaviour.
pattern to them.
4.3. Rolling Server Addresses DHCPv6 also includes an option to use Privacy Extension [3]
addresses, i.e. temporary addresses, as described in Section 12 of
the DHCPv6 [6] specification.
5.5. Rolling Server Addresses
Given the huge address space in an IPv6 subnet/link, and the support Given the huge address space in an IPv6 subnet/link, and the support
for IPv6 multiaddressing, whereby a node or interface may have for IPv6 multiaddressing, whereby a node or interface may have
multiple IPv6 valid addresses of which one is preferred for sending, multiple IPv6 valid addresses of which one is preferred for sending,
it may be possible to periodically change the advertised addresses it may be possible to periodically change the advertised addresses
that certain long standing services use (where 'short' exchanges to that certain long standing services use (where 'short' exchanges to
those services are used). those services are used).
For example, an MX server could be assigned a new primary address on For example, an MX server could be assigned a new primary address on
a weekly basis, and old addresses expired monthly. Where MX server a weekly basis, and old addresses expired monthly. Where MX server
IP addresses are detected and cached by spammers, such a defence may IP addresses are detected and cached by spammers, such a defence may
prove useful to reduce spam volumes, especially as such IP lists may prove useful to reduce spam volumes, especially as such IP lists may
also be passed between potential attackers for subsequent probing. also be passed between potential attackers for subsequent probing.
4.4. Application-Specific Addresses 5.6. Application-Specific Addresses
By a similar reasoning, it may be possible to consider using By a similar reasoning, it may be possible to consider using
application-specific addresses for systems, such that a given application-specific addresses for systems, such that a given
application may have exclusive use of an address, meaning that application may have exclusive use of an address, meaning that
disclosure of the address should not expose other applications or disclosure of the address should not expose other applications or
services running on the same system. services running on the same system.
5. 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 network scanning methods to detect open
services for subsequent attacks. If administrators number their IPv6 services for subsequent attacks. If administrators number their IPv6
subnets in 'random', non-predictable ways, attackers, whether they be subnets in 'random', non-predictable ways, attackers, whether they be
in the form of automated network scanners or dynamic worm in the form of automated network scanners or dynamic worm
propagation, will need to use new methods to determine IPv6 host propagation, will need to use new methods to determine IPv6 host
addresses to target. Of course, if those systems are dual-stack, and addresses to target. Of course, if those systems are dual-stack, and
have open IPv4 services running, they will remain exposed to have open IPv4 services running, they will remain exposed to
traditional probes over IPv4 transport. traditional probes over IPv4 transport.
skipping to change at page 9, line 46 skipping to change at page 11, line 5
configuring various service elements. It highlights relevant issues configuring various service elements. It highlights relevant issues
and offers some informational guidance for administrators. While and offers some informational guidance for administrators. While
some suggestions are currently more practical than others, it is up some suggestions are currently more practical than others, it is up
to individual administrators to determine how much effort they wish to individual administrators to determine how much effort they wish
to invest in 'address hiding' schemes, given that this is only one to invest in 'address hiding' schemes, given that this is only one
aspect of network security, and certainly not one to rely solely on. aspect of network security, and certainly not one to rely solely on.
But by implementing the basic principle of allocating 'random', non But by implementing the basic principle of allocating 'random', non
predictable addresses, some level of obfuscation can be cheaply predictable addresses, some level of obfuscation can be cheaply
deployed. deployed.
6. 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.
7. IANA Considerations 8. IANA Considerations
There are no IANA considerations for this document. There are no IANA considerations for this document.
8. Acknowledgements 9. Acknowledgements
Thanks are due to people in the 6NET project for discussion of this Thanks are due to people in the 6NET project (www.6net.org) for
topic, including Pekka Savola, Christian Strauf and Martin Dunmore, discussion of this topic, including Pekka Savola, Christian Strauf
as well as other contributors from the IETF v6ops mailing list, and Martin Dunmore, as well as other contributors from the IETF v6ops
including Tony Finch, David Malone and Fred Baker. and other mailing lists, including Tony Finch, David Malone, Bernie
Volz, Fred Baker, Andrew Sullivan and Alex Petrescu.
9. 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] Narten, T. and R. Draves, "Privacy Extensions for Stateless [2] Thomson, S. and T. Narten, "IPv6 Stateless Address
Autoconfiguration", RFC 2462, December 1998.
[3] Narten, T. and R. Draves, "Privacy Extensions for Stateless
Address Autoconfiguration in IPv6", RFC 3041, January 2001. Address Autoconfiguration in IPv6", RFC 3041, January 2001.
[3] Thomson, S. and T. Narten, "IPv6 Stateless Address [4] Carpenter, B. and K. Moore, "Connection of IPv6 Domains via
Autoconfiguration", RFC 2462, December 1998. IPv4 Clouds", RFC 3056, February 2001.
[4] Haberman, B. and D. Thaler, "Unicast-Prefix-based IPv6 Multicast [5] Haberman, B. and D. Thaler, "Unicast-Prefix-based IPv6
Addresses", RFC 3306, August 2002. Multicast Addresses", RFC 3306, August 2002.
[5] 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 (DHCPv6)", Carney, "Dynamic Host Configuration Protocol for IPv6
RFC 3315, July 2003. (DHCPv6)", RFC 3315, July 2003.
[6] Savola, P. and B. Haberman, "Embedding the Rendezvous Point (RP) [7] Savola, P. and B. Haberman, "Embedding the Rendezvous Point
Address in an IPv6 Multicast Address", RFC 3956, November 2004. (RP) Address in an IPv6 Multicast Address", RFC 3956,
November 2004.
[7] Davies, E., "IPv6 Transition/Co-existence Security [8] Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure
Considerations", draft-ietf-v6ops-security-overview-05 (work in Neighbor Discovery (SEND)", RFC 3971, March 2005.
progress), September 2006.
[8] Bellovin, S. et al, "Worm Propagation Strategies in an IPv6 [9] Aura, T., "Cryptographically Generated Addresses (CGA)",
RFC 3972, March 2005.
[10] Templin, F., Gleeson, T., Talwar, M., and D. Thaler, "Intra-
Site Automatic Tunnel Addressing Protocol (ISATAP)", RFC 4214,
October 2005.
[11] Huitema, C., "Teredo: Tunneling IPv6 over UDP through Network
Address Translations (NATs)", RFC 4380, February 2006.
[12] Davies, E., Krishnan, S., and P. Savola, "IPv6 Transition/
Co-existence Security Considerations
(draft-ietf-v6ops-security-overview-06)", October 2007.
[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
United Kingdom United Kingdom
Email: tjc@ecs.soton.ac.uk Email: tjc@ecs.soton.ac.uk
Intellectual Property Statement Full Copyright Statement
Copyright (C) The IETF Trust (2007).
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, THE IETF TRUST 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
this document or the extent to which any license under such rights this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information made any independent effort to identify any such rights. Information
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 12, line 29 skipping to change at page 13, line 45
such proprietary rights by implementers or users of this such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr. http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at this standard. Please address the information to the IETF at
ietf-ipr@ietf.org. ietf-ipr@ietf.org.
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).
 End of changes. 46 change blocks. 
142 lines changed or deleted 217 lines changed or added

This html diff was produced by rfcdiff 1.33. The latest version is available from http://tools.ietf.org/tools/rfcdiff/