INTERNET-DRAFT Dave Katz <draft-ietf-ipngwg-ipv6-router-alert-00.txt> Randall Atkinson cisco Systems 15 November 1996 IPv6 Router Alert Option Status of this Memo This document is an Internet Draft. 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. Internet Drafts may be updated, replaced, or obsoleted by other documents at any time. It is not appropriate to use Internet Drafts as reference material or to cite them other than as a "working draft" or "work in progress." Please check the I-D abstract listing contained in each Internet Draft directory to learn the current status of this or any Internet Draft. Abstract This memo describes a new IPv6 Hop-by-Hop Option type that alerts transit routers to more closely examine the contents of an IP packet. This is useful for protocols addressed to a destination but also require special processing in routers along the path. 1.0 Introduction IPv6 uses daisy-chained optional headers to increase flexibility and remove the IPv4 constraint on how large options can be. Because several optional headers can be present between the base IPv6 header and the final payload, more parsing effort is needed to determine what kind of upper layer information is present in a given IPv6 packet. Some control packets that are interesting to routers (e.g. RSVP messages) are addressed to the same destination as data packets belonging to that session. It is desirable to forward the data-only packets as rapidly as possible, while ensuring that the router processes control packets appropriately. At present, the router cannot easily fast switch packets containing optional headers because it needs to determine whether or not the upper layer information is control information needed by the router. As noted before, the parsing to determine this causes the packet to traverse the slow path Katz & Atkinson Expires in 6 months [Page 1]
INTERNET-DRAFT IPv6 Router Alert 3 June 1996 through the router. This situation is undesirable. This draft proposes the addition of a new mandatory option within the IPv6 Hop-by-Hop Header. The presence of this new option in an IPv6 packet informs the router to slow-path process this router and handle any control data accordingly. The absence of this option in an IPv6 packet informs the router that the packet does not contain information needed by the router and hence can safely be fast switched without further packet parsing. Hosts originating IPv6 packets are required to include this option in certain circumstances. 3.0 Proposal The goal is to provide a mechanism whereby routers can intercept packets not addressed to them directly without incurring any significant performance penalty. The proposed solution is to define a new IPv6 Hop-by-Hop Header option having the semantic "routers should examine this packet more closely" and require protocols such as RSVP to use this option. This would incur little performance penalty on the forwarding of normal data packets. Routers that support option processing in the fast path already demultiplex processing based on the Hop-by-Hop header options. If all hop-by-hop option types are supported in the fast path, then the addition of another option type to process is unlikely to impact performance. If some hop-by-hop option types are not supported in the fast path, this new option type will be unrecognized and cause packets carrying it to be kicked out into the slow path, so no change to the fast path is necessary, and no performance penalty will be incurred for regular data packets. Routers that do not support option processing in the fast path will cause packets carrying this new option to be forwarded through the slow path, so no change to the fast path is necessary and no performance penalty will be incurred for regular data packets. 3.1 Syntax The proposed option has the following format: +--------+--------+--------+--------+ |IANA=TBD| Len= 2 | Value (2 bytes) | +--------+--------+--------+--------+ "IANA-TBD" is the Hop-by-Hop Option Type number allocated by IANA for this option. Katz & Atkinson Expires in 6 months [Page 2]
INTERNET-DRAFT IPv6 Router Alert 3 June 1996 Nodes not recognising this option should skip over this option and continue processing the header. This option MUST NOT change en route. Value: A 2 octet code with the following values: 0 - Packet contains ICMPv6 Group Membership message. 1 - Packet contains RSVP message. 2-255 - Reserved to IANA for future use. 3.2 Semantics Hosts shall ignore this option upon receipt. Routers that do not recognize this option shall ignore it. Routers that recognize this option shall examine packets carrying it more closely (parse the entire packet checking for interesting values of NextHeader fields, for example) to determine whether or not further processing is necessary. The value field may be used by an implementation to speed processing of the packet within the transit router. Unrecognized value fields shall be silently ignored. All other values of the VALUE field are reserved to IANA for future use. 4.0 Impact on Other Protocols For this option to be effective, its use must be mandated in protocols that expect routers to perform significant processing on packets not directly addressed to them. All IPv6 packets containing an ICMPv6 Group Membership message MUST contain this option within the IPv6 Hop-by-Hop Options Header of such packets. All IPv6 packets containing an RSVP message MUST contain this option within the IPv6 Hop-by-Hop Options Header of such packets. 5.0 References [DH95] Deering, S. & R. Hinden, "IPv6 Specification", RFC-1883, Internet Engineering Task Force, December 1995. [BZEHJ95] Braden, B. (ed.), L. Zhang, D. Estrin, S. Herzog, S. Jamin, "Resource ReSerVation Protocol (RSVP)," Internet Draft, 1996. Katz & Atkinson Expires in 6 months [Page 3]
INTERNET-DRAFT IPv6 Router Alert 3 June 1996 Authors' Addresses Dave Katz cisco Systems 170 W. Tasman Dr. San Jose, CA 95134-1706 USA Phone: +1 (408) 526-8284 Email: dkatz@cisco.com Randall Atkinson cisco Systems 170 W. Tasman Drive San Jose, CA 95134-1706 USA Phone: +1 (408) 526-6566 Email: rja@cisco.com Katz & Atkinson Expires in 6 months [Page 4]
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