An uniform format for IPv6 extension headers
Author(s): Suresh Krishnan, James Woodyatt, James Hoagland, Erik Kline, Manav Bhatia
In IPv6, optional internet-layer information is encoded in separate headers that may be placed between the IPv6 header and the transport layer header. There are a small number of such extension headers currently defined. This document describes the...
6man Working Group S. Krishnan Internet-Draft Ericsson Updates: 2460 (if approved) j h. woodyatt Intended status: Standards Track Apple Expires: July 15, 2012 E. Kline Google J. Hoagland Symantec M. Bhatia Alcatel-Lucent January 12, 2012 An uniform format for IPv6 extension headers draft-ietf-6man-exthdr-06 Abstract In IPv6, optional internet-layer information is encoded in separate headers that may be placed between the IPv6 header and the transport layer header. There are a small number of such extension headers currently defined. This document describes the issues that can arise when defining new extension headers and discusses the alternate extension mechanisms in IPv6. It also provides a common format for defining any new IPv6 extension headers if they are needed. Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on July 15, 2012. Copyright Notice Copyright (c) 2012 IETF Trust and the persons identified as the document authors. All rights reserved. Krishnan, et al. Expires July 15, 2012 [Page 1] Internet-Draft Format for IPv6 extension headers January 2012 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. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Conventions used in this document . . . . . . . . . . . . . . . 3 3. Applicability . . . . . . . . . . . . . . . . . . . . . . . . . 3 4. Proposed IPv6 Extension Header format . . . . . . . . . . . . . 5 5. Backward Compatibility . . . . . . . . . . . . . . . . . . . . 5 6. Future work . . . . . . . . . . . . . . . . . . . . . . . . . . 5 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6 8. Security Considerations . . . . . . . . . . . . . . . . . . . . 6 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 6 10. Normative References . . . . . . . . . . . . . . . . . . . . . 6 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 6 Krishnan, et al. Expires July 15, 2012 [Page 2] Internet-Draft Format for IPv6 extension headers January 2012 1. Introduction The base IPv6 standard [RFC2460] defines extension headers as an expansion mechanism to carry optional internet layer information. Extension headers, with the exception of the hop-by-hop options header, are not usually processed on intermediate nodes. However, Several existing deployed IPv6 routers and several existing deployed IPv6 firewalls, in contradiction to [RFC2460], are capable of parsing past or ignoring all currently defined IPv6 Extension Headers (e.g. to examine transport-layer header fields) at wire-speed (e.g. by using custom ASICs for packet processing). Hence, one must also consider that any new IPv6 Extension Header will break IPv6 deployments that use these existing capabilities. Any IPv6 header or option that has hop-by-hop behaviour, and is intended for general use in the public IPv6 Internet, could be subverted to create an attack on IPv6 routers processing packets containing such a header or option. Reports from the field indicate that some IP routers deployed within the global Internet are configured either to ignore the presence of headers with hop-by-hop behaviour or to drop packets containing headers with hop-by-hop behaviour. 2. Conventions used in this document 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 [RFC 2119]. 3. Applicability The base IPv6 standard [RFC2460] allows the use of both extension headers and destination options in order to encode optional destination information in an IPv6 packet. The use of destination options to encode this information, provides more flexible handling characteristics and better backward compatibility than using extension headers. Because of this, implementations SHOULD use destination options as the preferred mechanism for encoding optional destination information, and use a new extension header only if destination options do not satisfy their needs. The request for creation of a new IPv6 extension header MUST be accompanied by an specific explanation of why destination options could not be used to convey this information. The base IPv6 standard [RFC2460] defines 3 extension headers (i.e. Routing Header, Destination Options Header, Hop-by-Hop Options Krishnan, et al. Expires July 15, 2012 [Page 3] Internet-Draft Format for IPv6 extension headers January 2012 Header) to be used for any new IPv6 options. The same standard only allows the creation of new Extension Headers in limited circumstances [RFC2460] Section 4.6. As noted above, the use of any option with Hop-by-Hop behaviour can be problematic in the global public Internet. New IPv6 Extension Header(s) having hop-by-hop behaviour MUST NOT be created or specified. New options for the existing Hop-by-Hop Header SHOULD NOT be created or specified unless no alternative solution is feasible. Any proposal to create a new option for the existing Hop-by-Hop Header MUST include a detailed explanation of why the hop-by-hop behaviour is absolutely essential in the Internet-Draft proposing the new option with hop-by-hop behaviour. The use of IPv6 Destination Options to encode information provides more flexible handling characteristics and better backward compatibility than using a new Extension Header. Because of this, new optional information to be sent SHOULD be encoded in a new option for the existing IPv6 Destination Options Header. Mindful of the need for compatibility with existing IPv6 deployments, new IPv6 extension headers MUST NOT be created or specified, unless no existing IPv6 Extension Header can be used by specifying a new option for that existing IPv6 Extension Header. Any proposal to create or specify a new IPv6 Extension Header MUST include a detailed technical explanation of why no existing IPv6 Extension Header can be used in the Internet-Draft proposing the new IPv6 Extension Header. Krishnan, et al. Expires July 15, 2012 [Page 4] Internet-Draft Format for IPv6 extension headers January 2012 4. Proposed IPv6 Extension Header format Any IPv6 Extension Headers are defined in future, keeping in mind the restrictions specified in Section 3 and also the restrictions specified in [RFC2460], MUST use the consistent format defined in Figure 1. This minimizes breakage in intermediate nodes that examine these extension headers. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Next Header | Hdr Ext Len | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | | . . . Header Specific Data . . . | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Next Header 8-bit selector. Identifies the type of header immediately following the Extension header. Uses the same values as the IPv4 Protocol field [IANA_IP_PARAM]. Hdr Ext Len 8-bit unsigned integer. Length of the Extension header in 8-octet units, not including the first 8 octets. Header Specific Variable length. Fields specific to the Data extension header Figure 1: Extension header layout 5. Backward Compatibility The scheme proposed in this document is not intended to be backward compatible with all the currently defined IPv6 extension headers. It applies only to newly defined extension headers. Specifically, the fragment header predates this document and does not follow the format proposed in this document. 6. Future work This document proposes one step in easing the inspection of extension headers by middleboxes. There is further work required in this area. Some issues that are left unresolved beyond this document include Krishnan, et al. Expires July 15, 2012 [Page 5] Internet-Draft Format for IPv6 extension headers January 2012 o There can be an arbitrary number of extension headers. o Extension headers must be processed in the order they appear. o Extension headers may alter the processing of the payload itself, and hence the packet may not be processed properly without knowledge of said header. 7. IANA Considerations This document does not require any IANA actions. 8. Security Considerations This document proposes a standard format for the IPv6 extension headers that minimizes breakage at intermediate nodes that inspect but do not understand the contents of these headers. Intermediate nodes, such as firewalls, that skip over unknown headers might end up allowing the setup of a covert channel from the outside of the firewall to the inside using the data field(s) of the unknown extension headers. 9. Acknowledgements The authors would like to thank Albert Manfredi, Bob Hinden, Brian Carpenter, Erik Nordmark, Hemant Singh, Lars Westberg, Markku Savela, Tatuya Jinmei, Thomas Narten, Vishwas Manral, Alfred Hoenes, Joel Halpern, Ran Atkinson, Steven Blake, Jari Arkko, Kathleen Moriarty, Stephen Farrell, Ralph Droms, Sean Turner and Adrian Farrell for their reviews and suggestions that made this document better. 10. Normative References [IANA_IP_PARAM] IANA, "IP Parameters", <http://www.iana.org/assignments/ip-parameters>. [RFC 2119] 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", RFC2460, December 1998. Krishnan, et al. Expires July 15, 2012 [Page 6] Internet-Draft Format for IPv6 extension headers January 2012 Authors' Addresses Suresh Krishnan Ericsson 8400 Decarie Blvd. Town of Mount Royal, QC Canada Phone: +1 514 345 7900 x42871 Email: email@example.com james woodyatt Apple Inc. 1 Infinite Loop Cupertino, CA 95014 US Email: firstname.lastname@example.org Erik Kline Google Mori Tower 26F Roppongi 6-10-1 Minato ku Tokyo 106-6126 Japan Phone: +81 3-6384-9635 Email: email@example.com James Hoagland Symantec Corporation 350 Ellis St. Mountain View, CA 94043 US Email: Jim_Hoagland@symantec.com URI: http://symantec.com/ Krishnan, et al. Expires July 15, 2012 [Page 7] Internet-Draft Format for IPv6 extension headers January 2012 Manav Bhatia Alcatel-Lucent Bangalore India Email: firstname.lastname@example.org Krishnan, et al. Expires July 15, 2012 [Page 8]