Network Working Group J. Abley

Network Working Group J. Abley
Request for Comments: 5095 Afilias
Updates: 2460, 4294 P. Savola
Category: Standards Track CSC/FUNET
G. Neville-Neil
Neville-Neil Consulting
December 2007

Deprecation of Type 0 Routing Headers in IPv6

Status of This Memo

This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.

Abstract

The functionality provided by IPv6's Type 0 Routing Header can be
exploited in order to achieve traffic amplification over a remote
path for the purposes of generating denial-of-service traffic. This
document updates the IPv6 specification to deprecate the use of IPv6
Type 0 Routing Headers, in light of this security concern.

Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Deprecation of RH0 . . . . . . . . . . . . . . . . . . . . . . 3
4. Operations . . . . . . . . . . . . . . . . . . . . . . . . . . 3
4.1. Ingress Filtering . . . . . . . . . . . . . . . . . . . . . 3
4.2. Firewall Policy . . . . . . . . . . . . . . . . . . . . . . 3
5. Security Considerations . . . . . . . . . . . . . . . . . . . . 4
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 4
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 4
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 5
8.1. Normative References . . . . . . . . . . . . . . . . . . . 5
8.2. Informative References . . . . . . . . . . . . . . . . . . 5

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RFC 5095 Deprecation of RH0 December 2007

1. Introduction

[RFC2460] defines an IPv6 extension header called "Routing Header",
identified by a Next Header value of 43 in the immediately preceding
header. A particular Routing Header subtype denoted as "Type 0" is
also defined. Type 0 Routing Headers are referred to as "RH0" in
this document.

A single RH0 may contain multiple intermediate node addresses, and
the same address may be included more than once in the same RH0.
This allows a packet to be constructed such that it will oscillate
between two RH0-processing hosts or routers many times. This allows
a stream of packets from an attacker to be amplified along the path
between two remote routers, which could be used to cause congestion
along arbitrary remote paths and hence act as a denial-of-service
mechanism. An 88-fold amplification has been demonstrated using this
technique [CanSecWest07].

This attack is particularly serious in that it affects the entire
path between the two exploited nodes, not only the nodes themselves
or their local networks. Analogous functionality may be found in the
IPv4 source route option, but the opportunities for abuse are greater
with RH0 due to the ability to specify many more intermediate node
addresses in each packet.

The severity of this threat is considered to be sufficient to warrant
deprecation of RH0 entirely. A side effect is that this also
eliminates benign RH0 use-cases; however, such applications may be
facilitated by future Routing Header specifications.

Potential problems with RH0 were identified in 2001 [Security]. In
2002 a proposal was made to restrict Routing Header processing in
hosts [Hosts]. These efforts resulted in the modification of the
Mobile IPv6 specification to use the type 2 Routing Header instead of
RH0 [RFC3775]. Vishwas Manral identified various risks associated
with RH0 in 2006 including the amplification attack; several of these
vulnerabilities (together with other issues) were later documented in
[RFC4942].

A treatment of the operational security implications of RH0 was
presented by Philippe Biondi and Arnaud Ebalard at the CanSecWest
conference in Vancouver, 2007 [CanSecWest07]. This presentation
resulted in widespread publicity for the risks associated with RH0.

This document updates [RFC2460] and [RFC4294].

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RFC 5095 Deprecation of RH0 December 2007

2. Definitions

RH0 in this document denotes the IPv6 Extension Header type 43
("Routing Header") variant 0 ("Type 0 Routing Header"), as defined in
[RFC2460].

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].

3. Deprecation of RH0

An IPv6 node that receives a packet with a destination address
assigned to it and that contains an RH0 extension header MUST NOT
execute the algorithm specified in the latter part of Section 4.4 of
[RFC2460] for RH0. Instead, such packets MUST be processed according
to the behaviour specified in Section 4.4 of [RFC2460] for a datagram
that includes an unrecognised Routing Type value, namely:

If Segments Left is zero, the node must ignore the Routing header
and proceed to process the next header in the packet, whose type
is identified by the Next Header field in the Routing header.

If Segments Left is non-zero, the node must discard the packet and
send an ICMP Parameter Problem, Code 0, message to the packet's
Source Address, pointing to the unrecognized Routing Type.

IPv6 implementations are no longer required to implement RH0 in any
way.

4. Operations

4.1. Ingress Filtering

It is to be expected that it will take some time before all IPv6
nodes are updated to remove support for RH0. Some of the uses of RH0
described in [CanSecWest07] can be mitigated using ingress filtering,
as recommended in [RFC2827] and [RFC3704].

A site security policy intended to protect against attacks using RH0
SHOULD include the implementation of ingress filtering at the site
border.

4.2. Firewall Policy

Blocking all IPv6 packets that carry Routing Headers (rather than
specifically blocking Type 0 and permitting other types) has very
serious implications for the future development of IPv6. If even a

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RFC 5095 Deprecation of RH0 December 2007

small percentage of deployed firewalls block other types of Routing
Headers by default, it will become impossible in practice to extend
IPv6 Routing Headers. For example, Mobile IPv6 [RFC3775] relies upon
a Type 2 Routing Header; wide-scale, indiscriminate blocking of
Routing Headers will make Mobile IPv6 undeployable.

Firewall policy intended to protect against packets containing RH0
MUST NOT simply filter all traffic with a Routing Header; it must be
possible to disable forwarding of Type 0 traffic without blocking
other types of Routing Headers. In addition, the default
configuration MUST permit forwarding of traffic using a Routing
Header other than 0.

5. Security Considerations

The purpose of this document is to deprecate a feature of IPv6 that
has been shown to have undesirable security implications. Specific
examples of vulnerabilities that are facilitated by the availability
of RH0 can be found in [CanSecWest07]. In particular, RH0 provides a
mechanism for traffic amplification, which might be used as a denial-
of-service attack. A description of this functionality can be found
in Section 1.

6. IANA Considerations

The IANA registry "Internet Protocol Version 6 (IPv6) Parameters"
should be updated to reflect that variant 0 of IPv6 header-type 43
("Routing Header") is deprecated.

7. Acknowledgements

This document benefits from the contributions of many IPV6 and V6OPS
working group participants, including Jari Arkko, Arnaud Ebalard, Tim
Enos, Brian Haberman, Jun-ichiro itojun Hagino, Bob Hinden, Thomas
Narten, Jinmei Tatuya, David Malone, Jeroen Massar, Dave Thaler, and
Guillaume Valadon.

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RFC 5095 Deprecation of RH0 December 2007

8. References

8.1. Normative References

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.

[RFC2460] Deering, S. and R. Hinden, "Internet Protocol,
Version 6 (IPv6) Specification", RFC 2460,
December 1998.

[RFC4294] Loughney, J., "IPv6 Node Requirements", RFC 4294,
April 2006.

8.2. Informative References

[CanSecWest07] Biondi, P. and A. Ebalard, "IPv6 Routing Header
Security", CanSecWest Security Conference 2007,
April 2007.
http://www.secdev.org/conf/IPv6_RH_security-csw07.pdf

[Hosts] Savola, P., "Note about Routing Header Processing on
IPv6 Hosts", Work in Progress, February 2002.

[RFC2827] Ferguson, P. and D. Senie, "Network Ingress
Filtering: Defeating Denial of Service Attacks which
employ IP Source Address Spoofing", BCP 38, RFC 2827,
May 2000.

[RFC3704] Baker, F. and P. Savola, "Ingress Filtering for
Multihomed Networks", BCP 84, RFC 3704, March 2004.

[RFC3775] Johnson, D., Perkins, C., and J. Arkko, "Mobility
Support in IPv6", RFC 3775, June 2004.

[RFC4942] Davies, E., Krishnan, S., and P. Savola, "IPv6
Transition/Co-existence Security Considerations",
RFC 4942, September 2007.

[Security] Savola, P., "Security of IPv6 Routing Header and Home
Address Options", Work in Progress, March 2002.

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RFC 5095 Deprecation of RH0 December 2007

Authors' Addresses

Joe Abley
Afilias Canada Corp.
Suite 204, 4141 Yonge Street
Toronto, ON M2P 2A8
Canada

Phone: +1 416 673 4176
EMail: [email protected]

Pekka Savola
CSC/FUNET
Espoo,
Finland

EMail: [email protected]

George Neville-Neil
Neville-Neil Consulting
2261 Market St. #239
San Francisco, CA 94114
USA

EMail: [email protected]

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RFC 5095 Deprecation of RH0 December 2007

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