[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
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
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
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].
RH0 in this document denotes the IPv6 Extension Header type 43
("Routing Header") variant 0 ("Type 0 Routing Header"), as defined in
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
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
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
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.
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
Afilias Canada Corp.
Suite 204, 4141 Yonge Street
Toronto, ON M2P 2A8
Phone: +1 416 673 4176
2261 Market St. #239
San Francisco, CA 94114
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.
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
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
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at