💾 Archived View for gemini.bortzmeyer.org › rfc-mirror › rfc7123.txt captured on 2023-07-22 at 18:29:24.
⬅️ Previous capture (2021-11-30)
-=-=-=-=-=-=-
Internet Engineering Task Force (IETF) F. Gont
Request for Comments: 7123 SI6 Networks/UTN-FRH
Category: Informational W. Liu
ISSN: 2070-1721 Huawei Technologies
February 2014
Security Implications of IPv6 on IPv4 Networks
Abstract
This document discusses the security implications of native IPv6
support and IPv6 transition/coexistence technologies on "IPv4-only"
networks and describes possible mitigations for the aforementioned
issues.
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/rfc7123.
Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Gont & Liu Informational [Page 1]
RFC 7123 Sec. Impl. of IPv6 on IPv4 Networks February 2014
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Security Implications of Native IPv6 Support . . . . . . . . 4
2.1. Filtering Native IPv6 Traffic . . . . . . . . . . . . . . 4
3. Security Implications of Tunneling Mechanisms . . . . . . . . 5
3.1. Filtering 6in4 . . . . . . . . . . . . . . . . . . . . . 6
3.2. Filtering 6over4 . . . . . . . . . . . . . . . . . . . . 7
3.3. Filtering 6rd . . . . . . . . . . . . . . . . . . . . . . 7
3.4. Filtering 6to4 . . . . . . . . . . . . . . . . . . . . . 8
3.5. Filtering ISATAP . . . . . . . . . . . . . . . . . . . . 9
3.6. Filtering Teredo . . . . . . . . . . . . . . . . . . . . 9
3.7. Filtering Tunnel Broker with Tunnel Setup Protocol (TSP) 11
3.8. Filtering AYIYA . . . . . . . . . . . . . . . . . . . . . 11
4. Additional Considerations when Filtering IPv6 Traffic . . . . 12
5. Security Considerations . . . . . . . . . . . . . . . . . . . 13
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 13
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 13
7.1. Normative References . . . . . . . . . . . . . . . . . . 13
7.2. Informative References . . . . . . . . . . . . . . . . . 14
Appendix A. Summary of Filtering Rules . . . . . . . . . . . . . 18
1. Introduction
Most general-purpose operating systems implement and enable native
IPv6 [RFC2460] support and a number of transition/coexistence
technologies by default. Support of IPv6 by all nodes is intended to
become best current practice [RFC6540]. Some enterprise networks
might, however, choose to delay active use of IPv6.
This document describes operational practices to prevent security
exposure in enterprise networks resulting from unplanned use of IPv6
on such networks. This document is only applicable to enterprise
networks: networks where the network operator is not providing a
general-purpose internet, but rather a business-specific network.
The solutions proposed here are not practical for home networks, nor
are they appropriate for provider networks such as ISPs, mobile
providers, WiFi hotspot providers, or any other public internet
service.
In scenarios in which IPv6-enabled devices are deployed on enterprise
networks that are intended to be IPv4-only, native IPv6 support and/
or IPv6 transition/coexistence technologies could be leveraged by
local or remote attackers for a number of (illegitimate) purposes.
For example,
Gont & Liu Informational [Page 2]
RFC 7123 Sec. Impl. of IPv6 on IPv4 Networks February 2014
o A Network Intrusion Detection System (NIDS) might be prepared to
detect attack patterns for IPv4 traffic, but might be unable to
detect the same attack patterns when a transition/coexistence
technology is leveraged for that purpose.
o An IPv4 firewall might enforce a specific security policy in IPv4,
but might be unable to enforce the same policy in IPv6.
o A NIDS or firewall might support both IPv4 and IPv6, but might not
be configured to enforce on IPv6 traffic the same controls/
policies it enforces on IPv4 traffic.
o Some transition/coexistence mechanisms could cause an internal
host with otherwise limited IPv4 connectivity to become globally
reachable over IPv6, therefore resulting in increased (and
possibly unexpected) host exposure.
NOTE: Some transition/coexistence mechanisms (notably Teredo)
are designed to traverse Network Address Port Translation
(NAPT) [RFC2663] devices, allowing incoming IPv6 connections
from the Internet to hosts behind the organizational firewall
or NAPT (which in many deployments provides a minimum level of
protection by only allowing those instances of communication
that have been initiated from the internal network).
o IPv6 support could, either inadvertently or as a result of a
deliberate attack, result in Virtual Private Network (VPN) traffic
leaks if IPv6-unaware VPN software is employed by dual-stacked
hosts [VPN-LEAKS].
In general, most of the aforementioned security implications can be
mitigated by enforcing security controls on native IPv6 traffic and
on IPv4-tunneled IPv6 traffic. Among such controls, is the
enforcement of filtering policies to block undesirable traffic.
While IPv6 widespread/global IPv6 deployment has been slower than
expected, it is nevertheless happening; and thus, filtering IPv6
traffic (whether native or transition/coexistence) to mitigate IPv6
security implications on IPv4 networks should (generally) only be
considered as a temporary measure until IPv6 is deployed.
NOTE: The aforementioned security controls should contemplate not
only network-based solutions, but also host-based solutions (such
as, e.g., personal firewalls).
Gont & Liu Informational [Page 3]
RFC 7123 Sec. Impl. of IPv6 on IPv4 Networks February 2014
2. Security Implications of Native IPv6 Support
Most popular operating systems include IPv6 support that is enabled
by default. This means that even if a network is expected to be
IPv4-only, much of its infrastructure is nevertheless likely to be
IPv6-enabled. For example, hosts are likely to have at least link-
local IPv6 connectivity, which might be exploited by attackers with
access to the local network.
Additionally, unless appropriate measures are taken, an attacker with
access to an "IPv4-only" local network could impersonate a local
router and cause local hosts to enable their 'non-link-local' IPv6
connectivity (e.g., by sending Router Advertisement messages),
possibly circumventing security controls that were enforced only on
IPv4 communications.
NOTE: [THC-IPV6] and [IPv6-Toolkit] include tools that implement
this attack vector (along with many others). [Waters2011]
provides an example of how this could be achieved using publicly
available tools.
Native IPv6 support could also possibly lead to VPN-traffic leakages
when hosts employ VPN software that, not only does not support IPv6,
but does nothing about IPv6 traffic. [VPN-LEAKS] describes this
issue, along with possible mitigations.
In general, networks should enforce on native IPv6 traffic the same
security policies currently enforced on IPv4 traffic. However, in
those networks in which IPv6 has not yet been deployed and enforcing
the aforementioned policies is deemed as infeasible, a network
administrator might mitigate IPv6-based attack vectors by means of
appropriate packet filtering.
2.1. Filtering Native IPv6 Traffic
Some layer-2 devices might have the ability to selectively filter
packets based on the type of layer-2 payload. When such
functionality is available, IPv6 traffic could be blocked at those
layer-2 devices by blocking, for example, Ethernet frames with the
Protocol Type field set to 0x86dd [IANA-ETHER]. We note, however,
that blocking IPv6 at layer-2 might create problems that are
difficult to diagnose, inclusive of intentional or incidental use of
link-local addressing (as in Multicast DNS/DNS-based Service
Discovery [RFC6762] [RFC6763]); sites that enforce such a filtering
policy should keep that possibility in mind when debugging the
network.
Gont & Liu Informational [Page 4]
RFC 7123 Sec. Impl. of IPv6 on IPv4 Networks February 2014
Attacks based on Stateless Address Autoconfiguration (SLAAC)
[RFC3756] can be mitigated with technologies such as Router
Advertisement Guard (RA-Guard) [RFC6105] [RA-GRD-IMP]. In a similar
way, DHCPv6-based attacks can be mitigated with technologies such as
DHCPv6-Shield [SHIELD]. However, both RA-Guard and DHCPv6-Shield are
incapable of mitigating attack vectors that employ IPv6 link-local
addresses, since configuration of such addresses does not rely on
Router Advertisement messages or DHCPv6-server messages.
Administrators considering the filtering of native IPv6 traffic at
layer-3 devices are urged to pay attention to the general
considerations for IPv6 traffic filtering discussed in Section 4.
NOTE: If native IPv6 traffic is filtered at layer-2, local IPv6
nodes would only get to configure IPv6 link-local addresses.
In order to mitigate attacks based on native IPv6 traffic, IPv6
security controls should be enforced on both IPv4 and IPv6 networks.
The aforementioned controls might include: deploying IPv6-enabled
NIDS, implementing IPv6 firewalling, etc.
NOTE: In some very specific scenarios (e.g., military operations
networks) in which only IPv4 service might be desired, a network
administrator might want to disable IPv6 support in all the
communicating devices.
3. Security Implications of Tunneling Mechanisms
Unless properly managed, tunneling mechanisms might result in
negative security implications. For example, they might increase
host exposure, might be leveraged to evade security controls, might
contain protocol-based vulnerabilities, and/or the corresponding code
might contain bugs with security implications.
NOTE: [RFC6169] describes the security implications of tunneling
mechanisms in detail. Of the plethora of tunneling mechanisms
that have so far been standardized and widely implemented, the so-
called "automatic tunneling" mechanisms (such as Teredo, Intra-
Site Automatic Tunnel Addressing Protocol (ISATAP), and 6to4) are
of particular interest from a security standpoint, since they
might be employed without prior consent or action of the user or
network administrator.
Tunneling mechanisms should be a concern not only to network
administrators that have consciously deployed them, but also to those
who have not deployed them, as these mechanisms might be leveraged to
bypass their security policies.
Gont & Liu Informational [Page 5]
RFC 7123 Sec. Impl. of IPv6 on IPv4 Networks February 2014
NOTE: [CERT2009] contains some examples of how tunnels can be
leveraged to bypass firewall rules.
The aforementioned issues could be mitigated by applying the common
security practice of only allowing traffic deemed as "necessary"
(i.e., the so-called "default deny" policy). Thus, when such policy
is enforced, IPv6 transition/coexistence traffic would be blocked by
default and would only be allowed as a result of an explicit
decision.
NOTE: It should be noted that this type of policy is usually
enforced on a network that is the target of such traffic (such as
an enterprise network). IPv6 transition traffic should generally
never be filtered, e.g., by an ISP when it is transit traffic.
In those scenarios in which transition/coexistence traffic is meant
to be blocked, it is highly recommended that, in addition to the
enforcement of filtering policies at the organizational perimeter,
the corresponding transition/coexistence mechanisms be disabled on
each node connected to the organizational network. This would not
only prevent security breaches resulting from accidental use of these
mechanisms, but would also disable this functionality altogether,
possibly mitigating vulnerabilities that might be present in the host
implementation of these transition/coexistence mechanisms.
IPv6-in-IPv4 tunneling mechanisms (such as 6to4 or configured
tunnels) can generally be blocked by dropping IPv4 packets that
contain a Protocol field set to 41. Security devices such as NIDS
might also include signatures that detect such transition/coexistence
traffic.
Administrators considering the filtering of transition/coexistence
traffic are urged to pay attention to the general considerations for
IPv6 traffic filtering discussed in Section 4.
We note that this document only covers standardized IPv6 tunneling
mechanisms; it does not aim to cover non-standard tunneling
mechanisms or tunneling based on IPsec [RFC4301] or on SSL/TLS
[RFC5246] [RFC6101].
3.1. Filtering 6in4
Probably the most basic type of tunnel employed for connecting IPv6
"islands" is the so-called "6in4", in which IPv6 packets are
encapsulated within IPv4 packets. These tunnels typically result
from manual configuration at the two tunnel endpoints.
Gont & Liu Informational [Page 6]
RFC 7123 Sec. Impl. of IPv6 on IPv4 Networks February 2014
6in4 tunnels can be blocked by blocking IPv4 packets with a Protocol
field of 41.
3.2. Filtering 6over4
[RFC2529] specifies a mechanism known as 6over4 or 'IPv6 over IPv4'
(or colloquially as 'virtual Ethernet'), which comprises a set of
mechanisms and policies to allow isolated IPv6 hosts located on
physical links with no directly connected IPv6 router to become fully
functional IPv6 hosts by using an IPv4 domain that supports IPv4
multicast as their virtual local link.
NOTE: This transition technology has never been widely deployed
because of the low level of deployment of multicast in most
networks.
6over4 encapsulates IPv6 packets in IPv4 packets with their Protocol
field set to 41. As a result, simply filtering all IPv4 packets that
have a Protocol field equal to 41 will filter 6over4 (along with many
other transition technologies).
A more selective filtering could be enforced such that 6over4 traffic
is filtered while other transition traffic is still allowed. Such a
filtering policy would block all IPv4 packets that have their
Protocol field set to 41, and that have a Destination Address that
belongs to the prefix 239.0.0.0/8.
This filtering policy basically blocks 6over4 Neighbor Discovery
traffic directed to multicast addresses, thus preventing SLAAC,
address resolution, etc. Additionally, it would prevent the 6over4
multicast addresses from being leveraged for the purpose of network
reconnaissance.
3.3. Filtering 6rd
6rd builds upon the mechanisms of 6to4 to enable the rapid deployment
of IPv6 on IPv4 infrastructures, while avoiding some downsides of
6to4. Usage of 6rd was originally documented in [RFC5569], and the
mechanism was generalized to other access technologies and formally
standardized in [RFC5969].
6rd can be blocked by blocking IPv4 packets with the Protocol field
set to 41.
Gont & Liu Informational [Page 7]
RFC 7123 Sec. Impl. of IPv6 on IPv4 Networks February 2014
3.4. Filtering 6to4
6to4 [RFC3056] is an address assignment and router-to-router, host-
to-router, and router-to-host automatic tunneling mechanism that is
meant to provide IPv6 connectivity between IPv6 sites and hosts
across the IPv4 Internet.
NOTE: The security considerations for 6to4 are discussed in detail
in [RFC3964]. [RFC6343] provides advice to network operators
about 6to4 (some of which relates to security mitigations).
As discussed in Section 3, all IPv6-in-IPv4 traffic, including 6to4,
could be easily blocked by filtering IPv4 packets that contain their
Protocol field set to 41. This is the most effective way of
filtering such traffic.
If 6to4 traffic is meant to be filtered while other IPv6-in-IPv4
traffic is allowed, then more finer-grained filtering rules could be
applied. For example, 6to4 traffic could be filtered by applying
filtering rules such as:
o Filter outgoing IPv4 packets that have the Destination Address set
to an address that belongs to the prefix 192.88.99.0/24.
o Filter incoming IPv4 packets that have the Source Address set to
an address that belongs to the prefix 192.88.99.0/24.
NOTE: These rules assume that the corresponding nodes employ
the "Anycast Prefix for 6to4 Relay Routers" [RFC3068]. It has
been suggested that 6to4 relays send their packets with their
IPv4 Source Address set to 192.88.99.1.
o Filter outgoing IPv4 packets that have the Destination Address set
to the IPv4 address of well-known 6to4 relays.
o Filter incoming IPv4 packets that have the Source Address set to
the IPv4 address of well-known 6to4 relays.
These last two filtering policies will generally be unnecessary,
and possibly infeasible to enforce (given the number of potential
6to4 relays, and the fact that many relays might remain unknown to
the network administrator). If anything, they should be applied
with the additional requirement that such IPv4 packets have their
Protocol field set to 41 to avoid the case where other services
available at the same IPv4 address as a 6to4 relay are mistakenly
made inaccessible.
Gont & Liu Informational [Page 8]
RFC 7123 Sec. Impl. of IPv6 on IPv4 Networks February 2014
If the filtering device has capabilities to inspect the payload of
IPv4 packets, then the following filtering rules could be enforced:
o Filter outgoing IPv4 packets that have their Protocol field set to
41, and that have an IPv6 Source Address (embedded in the IPv4
payload) that belongs to the prefix 2002::/16.
o Filter incoming IPv4 packets that have their Protocol field set to
41, and that have an IPv6 Destination address (embedded in the
IPv4 payload) that belongs to the prefix 2002::/16.
3.5. Filtering ISATAP
ISATAP [RFC5214] is an Intra-site tunneling protocol, and thus it is
generally expected that such traffic will not traverse the
organizational firewall of an IPv4-only network. Nevertheless,
ISATAP can be easily blocked by blocking IPv4 packets with a Protocol
field of 41.
The most popular operating system that includes an implementation of
ISATAP in the default installation is Microsoft Windows. Microsoft
Windows obtains the ISATAP router address by resolving the domain
name isatap.<localdomain> to DNS A resource records. Additionally,
it tries to learn the ISATAP router address by employing Link-Local
Multicast Name Resolution (LLMNR) [RFC4795] to resolve the name
"isatap". As a result, blocking ISATAP by preventing hosts from
successfully performing name resolution for the aforementioned names
and/or by filtering packets with specific IPv4 destination addresses
is both difficult and undesirable.
3.6. Filtering Teredo
Teredo [RFC4380] is an address assignment and automatic tunneling
technology that provides IPv6 connectivity to dual-stack nodes that
are behind one or more Network Address Port Translation (NAPT)
[RFC2663] devices, by encapsulating IPv6 packets in IPv4-based UDP
datagrams. Teredo is meant to be a 'last-resort' IPv6 connectivity
technology, to be used only when other technologies such as 6to4
cannot be deployed (e.g., because the edge device has not been
assigned a public IPv4 address).
As noted in [RFC4380], in order for a Teredo client to configure its
Teredo IPv6 address, it must contact a Teredo server through the
Teredo service port (UDP port number 3544).
To prevent the Teredo initialization process from succeeding, and
hence prevent the use of Teredo, an organizational firewall could
filter outgoing UDP packets with a Destination Port of 3544.
Gont & Liu Informational [Page 9]
RFC 7123 Sec. Impl. of IPv6 on IPv4 Networks February 2014
NOTE: It is clear that such a filtering policy does not prevent an
attacker from running its own Teredo server in the public
Internet, using a non-standard UDP port for the Teredo service
port (i.e., a port number other than 3544).
If the filtering device has capabilities to inspect the payload of
IPv4 packets, the following (additional) filtering policy could be
enforced:
o Filter outgoing IPv4/UDP packets that embed an IPv6 packet with
the "Version" field set to 6, and an IPv6 Source Address that
belongs to the prefix 2001::/32.
o Filter incoming IPv4/UDP packets that embed an IPv6 packet with
the "Version" field set to 6, and an IPv6 Destination Address that
belongs to the prefix 2001::/32.
NOTE: These two filtering rules could, at least in theory, result
in false positives. Additionally, they would generally require
the filtering device to reassemble fragments prior to enforcing
filtering rules, since the information required to enforce them
might be missing in the received fragments (which should be
expected if Teredo is being employed for malicious purposes).
The most popular operating system that includes an implementation of
Teredo in the default installation is Microsoft Windows. Microsoft
Windows obtains the Teredo server addresses (primary and secondary)
by resolving the domain name teredo.ipv6.microsoft.com into DNS A
records. A network administrator might want to prevent Microsoft
Windows hosts from obtaining Teredo service by filtering, at the
organizational firewall, outgoing UDP datagrams (i.e., IPv4 packets
with the Protocol field set to 17) that contain in the IPv4
Destination Address any of the IPv4 addresses that the domain name
teredo.ipv6.microsoft.com maps to (or the IPv4 address of any well-
known Teredo server). Additionally, the firewall would filter
incoming UDP datagrams from any of the IPv4 addresses to which the
domain names of well-known Teredo servers (such as
teredo.ipv6.microsoft.com) resolve.
NOTE: As these IPv4 addresses might change over time, an
administrator should obtain these addresses when implementing the
filtering policy, and should also be prepared to keep this list up
to date. The corresponding addresses can be easily obtained from
a UNIX host by issuing the command 'dig teredo.ipv6.microsoft.com
a' (without quotes), where dig(1) is a free-software tool (part of
the "dnsutils" package) produced by the Internet Software
Consortium (ISC).
Gont & Liu Informational [Page 10]
RFC 7123 Sec. Impl. of IPv6 on IPv4 Networks February 2014
It should be noted that even with all these filtering policies in
place, a node in the internal network might still be able to
communicate with some Teredo clients. That is, it could configure an
IPv6 address itself (without even contacting a Teredo server), and it
might send Teredo traffic to those peers for which intervention of
the host's Teredo server is not required (e.g., Teredo clients behind
a cone NAT).
3.7. Filtering Tunnel Broker with Tunnel Setup Protocol (TSP)
The tunnel broker model enables dynamic configuration of tunnels
between a tunnel client and a tunnel server. The tunnel broker
provides a control channel for creating, deleting, or updating a
tunnel between the tunnel client and the tunnel server.
Additionally, the tunnel broker may register the user's IPv6 address
and name in the DNS. Once the tunnel is configured, data can flow
between the tunnel client and the tunnel server. [RFC3053] describes
the tunnel broker model, while [RFC5572] specifies the Tunnel Setup
Protocol (TSP), which can be used by clients to communicate with the
Tunnel Broker.
TSP can use either TCP or UDP as the transport protocol. In both
cases, TSP uses port number 3653, which has been assigned by the IANA
for this purpose. As a result, TSP (the Tunnel Broker control
channel) can be blocked by blocking TCP and UDP packets originating
from the local network and destined to UDP port 3653 or TCP port
3653. Additionally, the data channel can be blocked by blocking UDP
packets originated from the local network and destined to UDP port
3653, and IPv4 packets with a Protocol field set to 41.
3.8. Filtering AYIYA
AYIYA ("Anything In Anything") [AYIYA] allows the tunneling of
packets across Network Address Port Translation (NAPT) [RFC2663]
devices. While the specification of this tunneling mechanism was
never published as an RFC, it is nevertheless widely deployed
[SixXS-stats].
AYIYA can be blocked by blocking TCP and UDP packets originating from
the local network and destined to UDP port 5072 or TCP port 5072.
Gont & Liu Informational [Page 11]
RFC 7123 Sec. Impl. of IPv6 on IPv4 Networks February 2014
4. Additional Considerations when Filtering IPv6 Traffic
IPv6 deployments in the Internet are continually increasing, and some
hosts default to preferring IPv6 connectivity whenever it is
available. This is likely to cause IPv6-capable hosts to attempt to
reach an ever-increasing number of popular destinations via IPv6,
even if this IPv6 connectivity relies on a transition technology over
an "IPv4-only" network.
A large source of IPv6 brokenness today comes from nodes that believe
that they have functional IPv6 connectivity, but the path to their
destination fails somewhere upstream [Anderson2010] [Anderson2011]
[Huston2010b] [Huston2012]. Upstream filtering of transition
technologies or situations where a misconfigured node attempts to
"provide" native IPv6 service on a given network without proper
upstream IPv6 connectivity may result in hosts attempting to reach
remote nodes via IPv6, and depending on the absence or presence and
specific implementation details of "Happy Eyeballs" [RFC6555], there
might be a non-trivial timeout period before the host falls back to
IPv4 [Huston2010a] [Huston2012].
For this reason, networks attempting to prevent IPv6 traffic from
traversing their devices should consider configuring their local
recursive DNS servers to respond to queries for AAAA DNS records with
a DNS RCODE of 0 (NOERROR) [RFC1035] or to silently ignore such
queries, and should even consider filtering AAAA records at the
network ingress point to prevent the internal hosts from attempting
their own DNS resolution. This will ensure that hosts that are on an
"IPv4-only" network will only receive DNS A records, and they will be
unlikely to attempt to use (likely broken) IPv6 connectivity to reach
their desired destinations.
We note that in scenarios where DNSSEC [RFC4033] is deployed,
stripping AAAA records from DNS responses would lead to DNS responses
elicited by queries with the DO and CD bits set [RFC4035] to be
considered invalid, and hence discarded. This situation is similar
to that of DNS64 [RFC6147] in the presence of DNSSEC and should be
considered a drawback associated with this approach.
Additionally, it should be noted that when filtering IPv6 traffic, it
is good practice to signal the packet drop to the source node, such
that it is able to react to the packet drop in a more appropriate and
timely way. For example, a firewall could signal the packet drop by
means of an ICMPv6 error message (or TCP [RFC0793] RST segment if
appropriate), such that the source node can, e.g., quickly react as
described in [RFC5461]. For obvious reasons, if the traffic being
Gont & Liu Informational [Page 12]
RFC 7123 Sec. Impl. of IPv6 on IPv4 Networks February 2014
filtered is IPv6 transition/coexistence traffic, the signaling packet
should be sent by means of the corresponding IPv6 transition/
coexistence technology.
5. Security Considerations
This document discusses the security implications of IPv6 on IPv4
networks and describes a number of techniques to mitigate the
aforementioned issues. In general, the possible mitigations boil
down to enforcing on native IPv6 and IPv6 transition/coexistence
traffic the same security policies currently enforced for IPv4
traffic and/or blocking the aforementioned traffic when it is deemed
as undesirable.
6. Acknowledgements
The authors would like to thank Wes George, who contributed most of
the text that comprises Section 4 of this document.
The authors would like to thank (in alphabetical order) Ran Atkinson,
Brian Carpenter, Stephen Farrell, Guillermo Gont, Joel Jaeggli, Panos
Kampanakis, Warren Kumari, Ted Lemon, David Malone, Joseph Salowey,
Arturo Servin, Donald Smith, Tina Tsou, and Eric Vyncke for providing
valuable comments on earlier versions of this document.
This document is based on the results of the project "Security
Assessment of the Internet Protocol version 6 (IPv6)" [CPNI-IPv6],
carried out by Fernando Gont on behalf of the UK Centre for the
Protection of National Infrastructure (CPNI). Fernando Gont would
like to thank the UK CPNI for their continued support.
7. References
7.1. Normative References
[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, November 1987.
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, December 1998.
[RFC2529] Carpenter, B. and C. Jung, "Transmission of IPv6 over IPv4
Domains without Explicit Tunnels", RFC 2529, March 1999.
[RFC3053] Durand, A., Fasano, P., Guardini, I., and D. Lento, "IPv6
Tunnel Broker", RFC 3053, January 2001.
Gont & Liu Informational [Page 13]
RFC 7123 Sec. Impl. of IPv6 on IPv4 Networks February 2014
[RFC3056] Carpenter, B. and K. Moore, "Connection of IPv6 Domains
via IPv4 Clouds", RFC 3056, February 2001.
[RFC3068] Huitema, C., "An Anycast Prefix for 6to4 Relay Routers",
RFC 3068, June 2001.
[RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "DNS Security Introduction and Requirements", RFC
4033, March 2005.
[RFC4035] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "Protocol Modifications for the DNS Security
Extensions", RFC 4035, March 2005.
[RFC4380] Huitema, C., "Teredo: Tunneling IPv6 over UDP through
Network Address Translations (NATs)", RFC 4380, February
2006.
[RFC4795] Aboba, B., Thaler, D., and L. Esibov, "Link-local
Multicast Name Resolution (LLMNR)", RFC 4795, January
2007.
[RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site
Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214,
March 2008.
[RFC5569] Despres, R., "IPv6 Rapid Deployment on IPv4
Infrastructures (6rd)", RFC 5569, January 2010.
[RFC5969] Townsley, W. and O. Troan, "IPv6 Rapid Deployment on IPv4
Infrastructures (6rd) -- Protocol Specification", RFC
5969, August 2010.
[RFC5572] Blanchet, M. and F. Parent, "IPv6 Tunnel Broker with the
Tunnel Setup Protocol (TSP)", RFC 5572, February 2010.
[RFC6147] Bagnulo, M., Sullivan, A., Matthews, P., and I. van
Beijnum, "DNS64: DNS Extensions for Network Address
Translation from IPv6 Clients to IPv4 Servers", RFC 6147,
April 2011.
7.2. Informative References
[RFC0793] Postel, J., "Transmission Control Protocol", STD 7, RFC
793, September 1981.
Gont & Liu Informational [Page 14]
RFC 7123 Sec. Impl. of IPv6 on IPv4 Networks February 2014
[RFC2663] Srisuresh, P. and M. Holdrege, "IP Network Address
Translator (NAT) Terminology and Considerations", RFC
2663, August 1999.
[RFC3756] Nikander, P., Kempf, J., and E. Nordmark, "IPv6 Neighbor
Discovery (ND) Trust Models and Threats", RFC 3756, May
2004.
[RFC3964] Savola, P. and C. Patel, "Security Considerations for
6to4", RFC 3964, December 2004.
[RFC4301] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC 4301, December 2005.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008.
[RFC5461] Gont, F., "TCP's Reaction to Soft Errors", RFC 5461,
February 2009.
[RFC6101] Freier, A., Karlton, P., and P. Kocher, "The Secure
Sockets Layer (SSL) Protocol Version 3.0", RFC 6101,
August 2011.
[RFC6105] Levy-Abegnoli, E., Van de Velde, G., Popoviciu, C., and J.
Mohacsi, "IPv6 Router Advertisement Guard", RFC 6105,
February 2011.
[RFC6169] Krishnan, S., Thaler, D., and J. Hoagland, "Security
Concerns with IP Tunneling", RFC 6169, April 2011.
[RFC6343] Carpenter, B., "Advisory Guidelines for 6to4 Deployment",
RFC 6343, August 2011.
[RFC6540] George, W., Donley, C., Liljenstolpe, C., and L. Howard,
"IPv6 Support Required for All IP-Capable Nodes", BCP 177,
RFC 6540, April 2012.
[RFC6555] Wing, D. and A. Yourtchenko, "Happy Eyeballs: Success with
Dual-Stack Hosts", RFC 6555, April 2012.
[RFC6762] Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762,
February 2013.
[RFC6763] Cheshire, S. and M. Krochmal, "DNS-Based Service
Discovery", RFC 6763, February 2013.
Gont & Liu Informational [Page 15]
RFC 7123 Sec. Impl. of IPv6 on IPv4 Networks February 2014
[RA-GRD-IMP]
Gont, F., "Implementation Advice for IPv6 Router
Advertisement Guard (RA-Guard)", Work in Progress,
November 2012.
[VPN-LEAKS]
Gont, F., "Virtual Private Network (VPN) traffic leakages
in dual-stack hosts/ networks", Work in Progress, August
2013.
[SHIELD] Gont, F., Liu, W., and G. Van de Velde, "DHCPv6-Shield:
Protecting Against Rogue DHCPv6 Servers", Work in
Progress, October 2013.
[AYIYA] Massar, J., "AYIYA: Anything In Anything", Work in
Progress, July 2004.
[IANA-ETHER]
IANA, "Ethernet Numbers",
<http://www.iana.org/assignments/ethernet-numbers>.
[CERT2009] Giobbi, R., "Bypassing Firewalls with IPv6 Tunnels", CERT/
CC Blog, April 2009, <http://www.cert.org/blogs/vuls/2009/
04/bypassing_firewalls_with_ipv6.html>.
[Huston2010a]
Huston, G., "IPv6 Measurements", 2010,
<http://www.potaroo.net/stats/1x1/>.
[Huston2010b]
Huston, G., "Flailing IPv6", The ISP Column: A monthly
column on things Internet, December 2010,
<http://www.potaroo.net/ispcol/2010-12/6to4fail.pdf>.
[Huston2012]
Huston, G., "Bemused Eyeballs: Tailoring Dual Stack
Applications in a CGN Environment", The ISP Column: A
monthly column on things Internet, May 2012,
<http://www.potaroo.net/ispcol/2012-05/notquite.pdf>.
[Anderson2010]
Anderson, T., "Measuring and combating IPv6 brokenness",
RIPE 61, Roma, November 2010,
<http://ripe61.ripe.net/presentations/162-ripe61.pdf>.
[Anderson2011]
Anderson, T., "IPv6 dual-stack client loss in Norway",
2011, <http://www.fud.no/ipv6/>.
Gont & Liu Informational [Page 16]
RFC 7123 Sec. Impl. of IPv6 on IPv4 Networks February 2014
[CPNI-IPv6]
Gont, F., "Security Assessment of the Internet Protocol
version 6 (IPv6)", UK Centre for the Protection of
National Infrastructure, (available on request), .
[IPv6-Toolkit]
SI6 Networks, "SI6 Networks' IPv6 Toolkit",
<http://www.si6networks.com/tools/ipv6toolkit>.
[THC-IPV6] The Hacker's Choice, "THC-IPV6 - attacking the IPV6
protocol suite", December 2013,
<http://www.thc.org/thc-ipv6/>.
[Waters2011]
Waters, A., "The SLAAC Attack - using IPv6 as a weapon
against IPv4", April 2011,
<http://wirewatcher.wordpress.com/2011/04/04/
the-slaac-attack-using-ipv6-as-a-weapon-against-ipv4/>.
[SixXS-stats]
SixXS, , "SixXS - IPv6 Deployment & Tunnel Broker ::
Statistics", 2013, <http://www.sixxs.net/misc/usage/>.
Gont & Liu Informational [Page 17]
RFC 7123 Sec. Impl. of IPv6 on IPv4 Networks February 2014
Appendix A. Summary of Filtering Rules
+-------------+-----------------------------------------------------+
| Technology | Filtering rules |
+-------------+-----------------------------------------------------+
| Native IPv6 | EtherType 0x86DD |
+-------------+-----------------------------------------------------+
| 6in4 | IP proto 41 |
+-------------+-----------------------------------------------------+
| 6over4 | IP proto 41 |
+-------------+-----------------------------------------------------+
| 6rd | IP proto 41 |
+-------------+-----------------------------------------------------+
| 6to4 | IP proto 41 |
+-------------+-----------------------------------------------------+
| ISATAP | IP proto 41 |
+-------------+-----------------------------------------------------+
| Teredo | UDP Dest Port 3544 |
+-------------+-----------------------------------------------------+
| TB with TSP | (IP proto 41) || (UDP Dest Port 3653 || TCP Dest |
| | Port 3653) |
+-------------+-----------------------------------------------------+
| AYIYA | UDP Dest Port 5072 || TCP Dest Port 5072 |
+-------------+-----------------------------------------------------+
Table 1: Summary of filtering rules
NOTE: the table above describes general and simple filtering rules
for blocking the corresponding traffic. More finer-grained rules
might be available in each of the corresponding sections of this
document.
Gont & Liu Informational [Page 18]
RFC 7123 Sec. Impl. of IPv6 on IPv4 Networks February 2014
Authors' Addresses
Fernando Gont
SI6 Networks / UTN-FRH
Evaristo Carriego 2644
Haedo, Provincia de Buenos Aires 1706
Argentina
Phone: +54 11 4650 8472
EMail: fgont@si6networks.com
URI: http://www.si6networks.com
Will (Shucheng) Liu
Huawei Technologies
Bantian, Longgang District
Shenzhen 518129
P.R. China
EMail: liushucheng@huawei.com
Gont & Liu Informational [Page 19]