Deprecation of Type 0 Routing Headers in IPv6

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 . 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 . In 2002 a proposal was made to restrict Routing Header processing in hosts . These efforts resulted in the modification of the Mobile IPv6 specification to use the type 2 Routing Header instead of RH0 . 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 . This presentation resulted in widespread publicity for the risks associated with RH0. This document updates and .

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 .

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 for RH0. Instead, such packets MUST be processed according to the behaviour specified in Section 4.4 of 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.

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 can be mitigated using ingress filtering, as recommended in and . A site security policy intended to protect against attacks using RH0 SHOULD include the implementation of ingress filtering at the site border.

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 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.

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 . 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 .

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 Guillaume Valadon.