6man Working Group S. Krishnan Internet-Draft Ericsson Intended status: Standards Track j h. woodyatt Expires: January 15, 2010 Apple E. Kline Google J. Hoagland Symantec July 14, 2009 An uniform format for IPv6 extension headers draft-krishnan-ipv6-exthdr-07 Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. 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." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on January 15, 2010. Copyright Notice Copyright (c) 2009 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 in effect on the date of publication of this document (http://trustee.ietf.org/license-info). Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Krishnan, et al. Expires January 15, 2010 [Page 1] Internet-Draft IPv6 extension headers July 2009 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 defines a format for defining a new family of IPv6 extension headers. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Conventions used in this document . . . . . . . . . . . . . 3 2. Generic IPv6 Extension Header (GIEH) format . . . . . . . . . . 4 3. Backward Compatibility . . . . . . . . . . . . . . . . . . . . 6 4. Exceptions . . . . . . . . . . . . . . . . . . . . . . . . . . 6 5. Future work . . . . . . . . . . . . . . . . . . . . . . . . . . 6 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6 7. Security Considerations . . . . . . . . . . . . . . . . . . . . 7 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 7 9. Normative References . . . . . . . . . . . . . . . . . . . . . 7 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 7 Krishnan, et al. Expires January 15, 2010 [Page 2] Internet-Draft IPv6 extension headers July 2009 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, some intermediate nodes such as firewalls, may need to look at the transport layer header fields in order to make a decision to allow or deny the packet. If new extension headers are defined and the intermediate node is not aware of them, the intermediate node cannot proceed further in the header chain since it does not know where the unknown header ends and the next header begins. The main issue is that the extension header format is not standardized and hence it is not possible to skip past the unknown header. This document defines a standard format for a new family of IPv6 extension headers. 1.1. 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 [RFC2119]. Krishnan, et al. Expires January 15, 2010 [Page 3] Internet-Draft IPv6 extension headers July 2009 2. Generic IPv6 Extension Header (GIEH) format This document proposes a new family of IPv6 extension headers that will be encoded in a consistent format so that it is possible for intermediate nodes to skip over unknown extension headers and continue to further process the header chain if they so desire. The intention of the base IPv6 Specification [RFC2460] that destination hosts not be permitted to skip unknown extension headers continues to apply. One key advantage of using such a generic IPv6 extension header is that it allows nodes to distinguish between unknown extension headers and unknown upper layer protocols, which was not possible earlier. Another one is that this generic extension header conserves values in the IPv4 protocol numbers registry. This documents requires the allocation of a single IP protocol number for the Generic IPv6 extension header (GIEH), say TBA1. Specifications of new extension headers SHOULD use this generic extension header format whenever feasible. The generic extension header will be identified by the value TBA1 occuring in the Next Header field of the preceding extension header. The second octet contains the length of the extension header. The third octet of the GIEH contains a specific extension header type (that identifies the actual extension header). All other data in the GIEH is type- specific. Krishnan, et al. Expires January 15, 2010 [Page 4] Internet-Draft IPv6 extension headers July 2009 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 | Specific Type | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | | . . . Header Specific Data . . . | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Next Header 8-bit selector. Identifies the type of header immediately following this Extension header. Uses the same values as the IPv4 Protocol field. Hdr Ext Len 8-bit unsigned integer. Length of the Extension header in 8-octet units, not including the first 8 octets. Specific Type 8-bit unsigned integer. The actual IPv6 extension header type. This will be allocated from a new IANA registry. Header Specific Variable length. Fields specific to the Data extension header. This field MUST be padded as required in order to ensure that the complete GIEH is a multiple of 8 octets long. Figure 1: Generic IPv6 Extension Header (GIEH) layout Krishnan, et al. Expires January 15, 2010 [Page 5] Internet-Draft IPv6 extension headers July 2009 3. Backward Compatibility The scheme proposed in this document is not backward compatible with all the currently defined IPv6 extension headers. It only applies to newly defined extension headers. Specifically, the following extension headers predate this document and do not follow the format proposed in this document. o IPv6 Hop-by-Hop Options Header o IPv6 Routing Header o IPv6 Fragment Header o IPv6 Destination Options Header 4. Exceptions The the Generic IPv6 extension header is generic enough that it is suitable to use for most applications. However, it is possible that the GIEH does not satisfy the requirements in all cases where new extension headers are required. Hence, the existence of this generic header does not necessarily preclude the definition of new independent IPv6 extension headers. 5. 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 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. 6. IANA Considerations This document requests a single allocation from the IANA for this generic IPv6 extension header type (TBA1) from the Assigned Internet Protocol Numbers registry located at http://www.iana.org/assignments/protocol-numbers. This document also requests the creation of a new registry for GIEH sub-types. The allocation policy for these subtypes is Standards Action. Krishnan, et al. Expires January 15, 2010 [Page 6] Internet-Draft IPv6 extension headers July 2009 7. Security Considerations This document proposes a standard format for the IPv6 extension headers so that intermediate nodes that do not understand the contents of these headers can look past them. Intermediate nodes, such as firewalls, skipping 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. 8. 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 and Alfred Hoenes for their reviews and suggestions that made this document better. 9. 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. Authors' Addresses Suresh Krishnan Ericsson 8400 Decarie Blvd. Town of Mount Royal, QC Canada Phone: +1 514 345 7900 x42871 Email: suresh.krishnan@ericsson.com james woodyatt Apple Inc. 1 Infinite Loop Cupertino, CA 95014 US Email: jhw@apple.com Krishnan, et al. Expires January 15, 2010 [Page 7] Internet-Draft IPv6 extension headers July 2009 Erik Kline Google 604 Arizona Avenue Santa Monica, CA 90401 US Phone: +1 310 460 4080 Email: ek@google.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 January 15, 2010 [Page 8]