| Rfc | 6104 |
|---|
| Title | Rogue IPv6 Router Advertisement Problem Statement |
|---|
| Author | T. Chown, S.
Venaas |
|---|
| Date | February 2011 |
|---|
| Format: | TXT, HTML |
|---|
| Status: | INFORMATIONAL |
|---|
|
Internet Engineering Task Force (IETF) T. Chown
Request for Comments: 6104 University of Southampton
Category: Informational S. Venaas
ISSN: 2070-1721 Cisco Systems
February 2011
Rogue IPv6 Router Advertisement Problem Statement
Abstract
When deploying IPv6, whether IPv6-only or dual-stack, routers are
configured to send IPv6 Router Advertisements (RAs) to convey
information to nodes that enable them to autoconfigure on the
network. This information includes the implied default router
address taken from the observed source address of the RA message, as
well as on-link prefix information. However, unintended
misconfigurations by users or administrators, or possibly malicious
attacks on the network, may lead to bogus RAs being present, which in
turn can cause operational problems for hosts on the network. In
this document, we summarise the scenarios in which rogue RAs may be
observed and present a list of possible solutions to the problem. We
focus on the unintended causes of rogue RAs in the text. The goal of
this text is to be Informational, and as such to present a framework
around which solutions can be proposed and discussed.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Not all documents
approved by the IESG are a candidate for any level of Internet
Standard; see Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc6104.
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Table of Contents
1. Introduction ....................................................4
2. Bogus RA Scenarios ..............................................4
2.1. Administrator Misconfiguration .............................5
2.2. User Misconfiguration ......................................5
2.3. Malicious Misconfiguration .................................5
3. Methods to Mitigate against Rogue RAs ...........................6
3.1. Manual Configuration .......................................6
3.2. Introducing RA Snooping ....................................6
3.3. Using ACLs on Managed Switches .............................7
3.4. SEcure Neighbor Discovery (SEND) ...........................7
3.5. Router Preference Option ...................................8
3.6. Relying on Layer 2 Admission Control .......................8
3.7. Using Host-Based Packet Filters ............................8
3.8. Using an "Intelligent" Deprecation Tool ....................8
3.9. Using Layer 2 Partitioning .................................9
3.10. Adding Default Gateway/Prefix Options to DHCPv6 ...........9
4. Scenarios and Mitigations ......................................10
5. Other Related Considerations ...................................11
5.1. Unicast RAs ...............................................11
5.2. The DHCP versus RA Threat Model ...........................11
5.3. IPv4-Only Networks ........................................12
5.4. Network Monitoring Tools ..................................12
5.5. Recovering from Bad Configuration State ...................12
5.6. Isolating the Offending Rogue RA Source ...................13
6. Conclusions ....................................................13
7. Security Considerations ........................................14
8. Acknowledgments ................................................14
9. Informative References .........................................15
1. Introduction
The Neighbor Discovery protocol [RFC4861] describes the operation of
IPv6 Router Advertisements (RAs) that are used to determine node
configuration information during the IPv6 autoconfiguration process,
whether that node's configuration is stateful, via the Dynamic Host
Configuration Protocol for IPv6 (DHCPv6) [RFC3315] or stateless, as
per [RFC4862], possibly in combination with DHCPv6 Light [RFC3736].
In observing the operation of deployed IPv6 networks, it is apparent
that there is a problem with undesired or "bogus" IPv6 RAs appearing
on network links or subnets. By "bogus" we mean RAs that were not
the intended configured RAs, but rather RAs that have appeared for
some other reason. While the problem appears more common in shared
wireless environments, it is also seen on wired enterprise networks.
The problem with rogue RAs is that they can cause partial or complete
failure of operation of hosts on an IPv6 link. For example, the
default router address is drawn directly from the source address of
the RA message. In addition, rogue RAs can cause hosts to assume
wrong prefixes to be used for stateless address autoconfiguration.
In a case where there may be mixing of "good" and "bad" RAs, a host
might keep on using the "good" default gateway, but pick a wrong
source address, leading to egress filtering problems. As such, rogue
RAs are an operational issue for which solution(s) are required, and
for which best practice needs to be conveyed. This not only includes
preventing or detecting rogue RAs, but also where necessary ensuring
the network (and hosts on the network) have the ability to quickly
recover from a state where host configuration is incorrect as a
result of processing such an RA.
In the next section, we discuss the scenarios that may give rise to
rogue RAs being present. In the following section, we present some
candidate solutions for the problem, some of which may be more
practical to deploy than others. This document focuses on
"accidental" rogue RAs; while malicious RAs are of course also
possible, the common problem today lies with unintended RAs. In
addition, a network experiencing malicious attack of this kind is
likely to also experience malicious Neighbor Advertisement (NA) and
related messages.
2. Bogus RA Scenarios
There are three broad classes of scenario in which bogus RAs may be
introduced to an IPv6 network.
2.1. Administrator Misconfiguration
Here an administrator incorrectly configures RAs on a router
interface, causing incorrect RAs to appear on links and causing hosts
to generate incorrect or unintended IPv6 address, gateway, or other
information. In such a case, the default gateway may be correct, but
a host might for example become multiaddressed, possibly with a
correct and incorrect address based on a correct and incorrect
prefix. There is also the possibility of other configuration
information being misconfigured, such as the lifetime option.
In the case of a Layer 2 IEEE 802.1Q Virtual LAN (VLAN)
misconfiguration, RAs may "flood" to unintended links, causing hosts
or more than one link to potentially become incorrectly
multiaddressed, with possibly two different default routers
available.
2.2. User Misconfiguration
In this case, a user's device "accidentally" transmits RAs onto the
local link, potentially adding an additional default gateway and
associated prefix information.
This seems to typically be seen on wireless (though sometimes wired)
networks where a laptop has enabled the Windows Internet Connection
Sharing (ICS) service, which can turn a host into a 6to4 [RFC3056]
gateway; this can be a useful feature, unless of course it is run
when not intended. This service can also cause IPv4 problems, as it
will typically start a "rogue" DHCPv4 server on the host.
We have also had reports that hosts may not see genuine IPv6 RAs on a
link due to host firewalls, causing them to turn on a connection-
sharing service and 6to4 as a result. In some cases, more technical
users may also use a laptop as a home gateway (e.g., again a 6to4
gateway) and then connect to another network, forgetting their
previous gateway configuration is still active.
There are also reported incidents in enterprise networks of users
physically plugging Ethernet cables into the wrong sockets and
bridging two subnets together, causing a problem similar to VLAN
flooding.
2.3. Malicious Misconfiguration
Here an attacker is deliberately generating RAs on the local network
in an attempt to perform some form of denial-of-service or man-in-
the-middle attack.
As stated above, while this is a genuine concern for network
administrators, there have been few if any reports of such activity,
while in contrast reports of accidental rogue RAs are very
commonplace. In writing this text, and with the feedback of the
v6ops working group, we came to the conclusion that the issue of
malicious attack, due to the other complementary attacks that are
likely to be launched using rogue NA and similar messages, are best
considered by further work and document(s). As a result, this text
intends to provide informational guidance for operators looking for
practical measures to take to avoid "accidental" rogue RAs on their
own networks.
3. Methods to Mitigate against Rogue RAs
In this section, we present a summary of methods suggested to date
for reducing or removing the possibility of rogue RAs being seen on a
network.
3.1. Manual Configuration
The default gateway and host address can usually be manually
configured on a node. This of course can be a resource intensive
solution, and also prone to administrative mistakes in itself.
Manual configuration implies that RA processing is disabled. Most
operating systems allow RA messages to be ignored, such that if an
IPv6 address is manually configured on a system, an additional global
autoconfigured address will not be added should an unexpected RA
appear on the link.
3.2. Introducing RA Snooping
It should be possible to implement "RA snooping" in Layer 2 switches
in a similar way to DHCP snooping, such that RAs observed from
incorrect sources are blocked or dropped, and not propagated through
a subnet. One candidate solution in this space, called "RA-Guard"
[RFC6105], has been proposed. This type of solution has appeal
because it is a familiar model for enterprise network managers, but
it can also be used to complement SEcure Neighbor Discovery (SEND)
[RFC3971], by a switch acting as a SEND proxy for hosts.
This type of solution may not be applicable everywhere, e.g., in
environments where there are not centrally controlled or manageable
switches.
3.3. Using ACLs on Managed Switches
Certain switch platforms can already implement some level of rogue RA
filtering by the administrator configuring Access Control Lists
(ACLs) that block RA ICMP messages that might be inbound on "user"
ports. Again this type of "solution" depends on the presence of such
configurable switches.
A recent document describes the RA message format(s) for filtering
[IPv6-AUTOCFG-FILTER]. The document also notes requirements for
DHCPv6 snooping, which can then be implemented similarly to DHCPv4
snooping.
3.4. SEcure Neighbor Discovery (SEND)
The SEcure Neighbor Discovery (SEND) [RFC3971] protocol provides a
method for hosts and routers to perform secure Neighbor Discovery.
Thus, it can in principle protect a network against rogue RAs.
SEND is not yet widely used at the time of writing, in part because
there are very few implementations of the protocol. Some other
deployment issues have been raised, though these are likely to be
resolved in due course. For example, routers probably don't want to
use autogenerated addresses (which might need to be protected by
ACLs), so SEND needs to be shown to work with non-autogenerated
addresses. Also, it has been argued that there are "bootstrapping"
issues, in that hosts wanting to validate router credentials (e.g.,
to a certificate server or Network Time Protocol (NTP) server) are
likely to need to communicate via the router for that information.
Further, it's not wholly clear how widely adopted SEND could or would
be in site networks with "lightweight" security (e.g., many campus
networks), especially where hosts are managed by users and not
administratively. Public or conference wireless networks may face
similar challenges. There may also be networks, like perhaps sensor
networks, where use of SEND is less practical. These networks still
require rogue RA protection.
While SEND clearly can provide a good, longer-term solution,
especially in networks where malicious activity is a significant
concern, there is a requirement today for practical solutions, and/or
solutions more readily applicable in more "relaxed" environments. In
the latter case, solutions like "RA snooping" or applied ACLs are
more attractive now.
3.5. Router Preference Option
[RFC4191] introduced a Router Preference option, such that an RA
could carry one of three Router Preference values: High, Medium
(default), or Low. Thus, an administrator could use "High" settings
for managed RAs, and hope that "accidental" RAs would be medium
priority. This of course would only work in some scenarios -- if the
user who accidentally sends out a rogue RA on the network has
configured their device with "High" precedence for their own intended
usage, the priorities would clash. But for accidental rogue RAs
caused by software like Windows ICS and 6to4, which would use the
default precedence, it could be useful. Obviously this solution
would also rely on clients (and routers) having implementations of
the Router Preference option.
3.6. Relying on Layer 2 Admission Control
In principle, if a technology such as IEEE 802.1x is used, devices
would first need to authenticate to the network before being able to
send or receive IPv6 traffic. Ideally, authentication would be
mutual. Deployment of 802.1x, with mutual authentication, may
however be seen as somewhat "heavyweight", akin to SEND, for some
deployments.
Improving Layer 2 security may help to mitigate against an attacker's
capability to join the network to send RAs, but it doesn't prevent
misconfiguration issues. A user can happily authenticate and still
launch a Windows ICS service, for example.
3.7. Using Host-Based Packet Filters
In a managed environment, hosts could be configured via their
"personal firewall" to only accept RAs from trusted sources. Hosts
could also potentially be configured to discard 6to4-based RAs in a
managed enterprise environment.
However, the problem is then pushed to keeping this configuration
maintained and correct. If a router fails and is replaced, possibly
with a new Layer 2 interface address, the link local source address
in the filter may become incorrect, and thus no method would be
available to push the new information to the host over the network.
3.8. Using an "Intelligent" Deprecation Tool
It is possible to run a daemon on a link (perhaps on the router on
the link) to watch for incorrect RAs and to send a deprecating RA
with a router lifetime of zero when such an RA is observed. The KAME
rafixd is an example of such a tool, which has been used at IETF
meetings with some success. A slightly enhanced tool called RAMOND
has since been developed from this code, and is now available as a
Sourceforge project. As with host-based firewalling, the daemon
would need to somehow know what "good" and "bad" RAs are, from some
combination of known good sources and/or link prefixes. In an
environment with native IPv6, though, 6to4-based RAs would certainly
be known to be rogue.
Whether or not use of such a tool is the preferred method, monitoring
a link for observed RAs seems prudent from a network management
perspective. Some such tools exist already, e.g., NDPMon, which can
also detect other undesirable behaviour.
3.9. Using Layer 2 Partitioning
If each system or user on a network is partitioned into a different
Layer 2 medium, then the impact of rogue RAs can be limited. In
broadband networks, bridging [RFC2684] may be available, for example.
The benefit may be scenario-specific, e.g., whether a given user or
customer has their own network prefix or whether the provisioning is
in a shared subnet or link. It is certainly desirable that any given
user or customer's system(s) are unable to see RAs that may be
generated by other users or customers.
However, such partitioning would probably increase address space
consumption significantly if applied in enterprise networks, and in
many cases, hardware costs and software licensing costs to enable
routing to the edge can be quite significant.
3.10. Adding Default Gateway/Prefix Options to DHCPv6
Adding Default Gateway and Prefix options for DHCPv6 would allow
network administrators to configure hosts to only use DHCPv6 for
default gateway and prefix configuration in managed networks, where
RAs would be required today. A new document has proposed such a
default router option, along with prefix advertisement options for
DHCPv6 [DHCPv6-DEFAULT-RTR]. Even with such options added to DHCPv6,
an RA is in principle still required to inform hosts to use DHCPv6.
An advantage of DHCPv6 is that should an error be introduced, only
hosts that have refreshed their DHCP information since that time are
affected, while a multicast rogue RA will most likely affect all
hosts immediately. DHCPv6 also allows different answers to be given
to different hosts.
While making host configuration possible via DHCPv6 alone is a viable
option that would allow IPv6 configuration to be done in a way
similar to IPv4 today, the problem has only been shifted: rather than
rogue RAs being the problem, rogue DHCPv6 servers would be an
equivalent issue. As with IPv4, a network would then still require
use of Authenticated DHCP, or DHCP(v6) snooping, as suggested in
[IPv6-AUTOCFG-FILTER].
There is certainly some demand in the community for DHCPv6-only host
configuration. While this may mitigate the rogue RA issue, it simply
moves the trust problem elsewhere, albeit to a place administrators
are familiar with today.
4. Scenarios and Mitigations
In this section, we summarise the error/misconfiguration scenarios
and practical mitigation methods described above in a matrix format.
We consider, for the case of a rogue multicast RA, which of the
mitigation methods helps protect against administrator and user
errors. For the administrator error, we discount an error in
configuring the countermeasure itself; rather, we consider an
administrator error to be an error in configuration elsewhere in the
network.
+------------------------+---------------------------+
| | Scenario |
| Mitigation |---------------------------|
| Method | Admin Error | User Error |
+------------------------+-------------+-------------+
| Manual configuration | Y | Y |
+------------------------+-------------+-------------+
| SEND | Y | Y |
+------------------------+-------------+-------------+
| RA snooping | Y | Y |
+------------------------+-------------+-------------+
| Use switch ACLs | Y | Y |
+------------------------+-------------+-------------+
| Router preference | N | Y |
+------------------------+-------------+-------------+
| Layer 2 admission | N | N |
+------------------------+-------------+-------------+
| Host firewall | Y | Y |
+------------------------+-------------+-------------+
| Deprecation daemon | Y | Y |
+------------------------+-------------+-------------+
| Layer 2 partition | N | Y |
+------------------------+-------------+-------------+
| DHCPv6 gateway option | Partly | If Auth |
+------------------------+-------------+-------------+
What the above summary does not consider is the practicality of
deploying the measure. An easy-to-deploy method that buys improved
resilience to rogue RAs without significant administrative overhead
is attractive. On that basis, the RA snooping proposal, e.g.,
RA-Guard, has merit, while approaches like manual configuration are
less appealing. However, RA-Guard is not yet fully defined or
available, while only certain managed switch equipment may support
the required ACLs.
5. Other Related Considerations
There are a number of related issues that have come out of
discussions on the rogue RA topic, which the authors believe are
worth capturing in this document.
5.1. Unicast RAs
The above discussion was initially held on the assumption that rogue
multicast RAs were the cause of problems on a shared network subnet.
However, the specifications for Router Advertisements allow them to
be sent unicast to a host, as per Section 6.2.6 of RFC 4861. If a
host sending rogue RAs sends them unicast to the soliciting host,
that RA may not be seen by other hosts on the shared medium, e.g., by
a monitoring daemon. In most cases, though, an accidental rogue RA
is likely to be multicast.
5.2. The DHCP versus RA Threat Model
Comparing the threat model for rogue RAs and rogue DHCPv6 servers is
an interesting exercise. In the case of Windows ICS causing rogue
6to4-based RAs to appear on a network, it is very likely that the
same host is also acting as a rogue IPv4 DHCP server. The rogue
DHCPv4 server can allocate a default gateway and an address to hosts,
just as a rogue RA can lead hosts to learning of a new (additional)
default gateway, prefix(es), and address. In the case of multicast
rogue RAs, however, the impact is potentially immediate to all hosts,
while the rogue DHCP server's impact will depend on lease timers for
hosts.
In principle, Authenticated DHCP can be used to protect against rogue
DHCPv4 (and DHCPv6) servers, just as SEND could be used to protect
against rogue IPv6 RAs. However, actual use of Authenticated DHCP in
typical networks is currently minimal. Were new DHCPv6 default
gateway and prefix options to be standardised as described above,
then without Authenticated DHCP the (lack of) security is just pushed
to another place.
The RA-Guard approach is essentially using a similar model to DHCP
message snooping to protect against rogue RAs in network (switch)
equipment. As noted above, DHCPv6 message snooping would also be
very desirable in IPv6 networks.
5.3. IPv4-Only Networks
The rogue RA problem should also be considered by administrators and
operators of IPv4-only networks, where IPv6 monitoring, firewalling,
and other related mechanisms may not be in place.
For example, a comment has been made that in the case of 6to4 being
run by a host on a subnet that is not administratively configured
with IPv6, some OSes or applications may begin using IPv6 to the 6to4
host (router) rather than IPv4 to the intended default IPv4 router,
because they have IPv6 enabled by default and some applications
prefer IPv6 by default. Technically aware users may also
deliberately choose to use IPv6, possibly for subversive reasons.
Mitigating against this condition can also be seen to be important.
5.4. Network Monitoring Tools
It would generally be prudent for network monitoring or management
platforms to be able to observe and report on observed RAs, and
whether unintended RAs (possibly from unintended sources) are present
on a network. Further, it may be useful for individual hosts to be
able to report their address status (assuming their configuration
status allowed it, of course), e.g., this could be useful during an
IPv6 renumbering phased process as described in RFC 4192 [RFC4192].
The above assumes, of course, that what defines a "good" (or "bad")
RA can be configured in a trustworthy manner within the network's
management framework.
5.5. Recovering from Bad Configuration State
After a host receives and processes a rogue RA, it may have multiple
default gateways, global addresses, and potentially clashing RA
options (e.g., M/O bits [RFC4861]). The host's behaviour may then be
unpredictable, in terms of the default router that is used, and the
(source) address(es) used in communications. A host that is aware of
protocols such as Shim6 [RFC5533] may believe it is genuinely
multihomed.
An important issue is how readily a host can recover from receiving
and processing bad configuration information, e.g., considering the
"2 hour rule" mentioned in Section 5.5.3 of RFC 4862 (though this
applies to the valid address lifetime and not the router lifetime).
We should ensure that methods exist for a network administrator to
correct bad configuration information on a link or subnet, and that
OS platforms support these methods. At least if the problem can be
detected, and corrected promptly, the impact is minimised.
5.6. Isolating the Offending Rogue RA Source
In addition to issuing a deprecating RA, it would be desirable to
isolate the offending source of the rogue RA from the network. It
may be possible to use Network Access Control methods to quarantine
the offending host, or rather the network point of attachment or port
that it is using.
6. Conclusions
In this text we have described scenarios via which rogue Router
Advertisements (RAs) may appear on a network, and some measures that
could be used to mitigate against these. We have also noted some
related issues that have arisen in the rogue RA discussions. Our
discussion is generally focused on the assumption that rogue RAs are
appearing as a result of accidental misconfiguration on the network,
by a user or administrator.
While SEND perhaps offers the most robust solution, implementations
and deployment guidelines are not yet widely available. SEND is very
likely to be a good, longer-term solution, but many administrators
are seeking solutions today. Such administrators are also often in
networks with security models for which SEND is a "heavyweight"
solution, e.g., campus networks, or wireless conference or public
networks. For such scenarios, simpler measures are desirable.
Adding new DHCPv6 Default Gateway and Prefix options would allow IPv6
host configuration by DHCP only and would be a method that IPv4
administrators are comfortable with (for better or worse), but this
simply shifts the robustness issue elsewhere.
While a number of the mitigations described above have their appeal,
the simplest solutions probably lie in switch-based ACLs and
RA-Guard-style approaches. Where managed switches are not available,
use of the Router Preference option and (more so in managed desktop
environments) host firewalls may be appropriate.
In the longer term, wider experience of SEND will be beneficial,
while the use of RA snooping will remain useful either to complement
SEND (where a switch running RA-Guard can potentially be a SEND
proxy) or to assist in scenarios for which SEND is not deployed.
7. Security Considerations
This Informational document is focused on discussing solutions to
operational problems caused by rogue RAs resulting from unintended
misconfiguration by users or administrators. Earlier versions of
this text included some analysis of rogue RAs introduced maliciously;
e.g., the text included an extra column in the matrix in Section 4.
However, the consensus of the v6ops working group feedback was to
instead focus on the common operational problem of "accidental" rogue
RAs seen today.
Thus, the final version of this text does not address attacks on a
network where rogue RAs are intentionally introduced as part of a
broader attack, e.g., including malicious NA messages. On the wire,
malicious rogue RAs will generally look the same as "accidental"
ones, though they are more likely, for example, to spoof the Media
Access Control (MAC) or IPv6 source address of the genuine router, or
to use a "High" Router Preference option. It is also likely that
malicious rogue RAs will be accompanied by other attacks on the IPv6
infrastructure, making discussion of mitigations more complex.
Administrators may be able to detect such activity by the use of
tools such as NDPMon.
It is worth noting that the deprecation daemon could be used as part
of a denial-of-service attack, should the tool be used to deprecate
the genuine RA.
8. Acknowledgments
Thanks are due to members of the IETF IPv6 Operations and DHCP
working groups for their inputs on this topic, as well as some
comments from various operational mailing lists, and private
comments, including but not limited to: Iljitsch van Beijnum, Dale
Carder, Remi Denis-Courmont, Tony Hain, Bob Hinden, Christian
Huitema, Tatuya Jinmei, Eric Levy-Abegnoli, David Malone, Thomas
Narten, Chip Popoviciu, Dave Thaler, Gunter Van de Velde, Goeran
Weinholt, and Dan White.
9. Informative References
[RFC2684] Grossman, D. and J. Heinanen, "Multiprotocol Encapsulation
over ATM Adaptation Layer 5", RFC 2684, September 1999.
[RFC3056] Carpenter, B. and K. Moore, "Connection of IPv6 Domains
via IPv4 Clouds", RFC 3056, February 2001.
[RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
and M. Carney, "Dynamic Host Configuration Protocol for
IPv6 (DHCPv6)", RFC 3315, July 2003.
[RFC3736] Droms, R., "Stateless Dynamic Host Configuration Protocol
(DHCP) Service for IPv6", RFC 3736, April 2004.
[RFC3971] Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure
Neighbor Discovery (SEND)", RFC 3971, March 2005.
[RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and
More-Specific Routes", RFC 4191, November 2005.
[RFC4192] Baker, F., Lear, E., and R. Droms, "Procedures for
Renumbering an IPv6 Network without a Flag Day", RFC 4192,
September 2005.
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
September 2007.
[RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", RFC 4862, September 2007.
[RFC5533] Nordmark, E. and M. Bagnulo, "Shim6: Level 3 Multihoming
Shim Protocol for IPv6", RFC 5533, June 2009.
[RFC6105] Levy-Abegnoli, E., Van de Velde, G., Popoviciu, C., and J.
Mohacsi, "IPv6 Router Advertisement Guard", RFC 6105,
February 2011.
[IPv6-AUTOCFG-FILTER]
Ward, N., "IPv6 Autoconfig Filtering on Ethernet
Switches", Work in Progress, March 2009.
[DHCPv6-DEFAULT-RTR]
Droms, R. and T. Narten, "Default Router and Prefix
Advertisement Options for DHCPv6", Work in Progress,
March 2009.
Authors' Addresses
Tim Chown
University of Southampton
Highfield
Southampton, Hampshire SO17 1BJ
United Kingdom
EMail: tjc@ecs.soton.ac.uk
Stig Venaas
Cisco Systems
Tasman Drive
San Jose, CA 95134
USA
EMail: stig@cisco.com