INTERNET-DRAFT Dave Katz, Juniper Networks Craig Partridge, BBN Alden Jackson, BBN IPv6 Router Alert Option Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. 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 draft expires XXXX and reflects comments received during an earlier WG last call. It is intended to become an Internet Standard. 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 datagram. This option is useful for situations where a datagram addressed to a particular destination contains information that may require special processing by routers along the path. 1.0 Introduction New protocols, such as RSVP, use control datagrams which, while addressed to a particular destination, contain information that needs [Page 1] Internet Draft IPv6 Router Alert June 1999 to be examined, and in some case updated, by routers along the path between the source and destination. It is desirable to forward regular datagrams as rapidly as possible, while ensuring that the router processes these special control datagrams appropriately. Currently, however, the only way for a router to determine if it needs to examine a datagram is to at least partially parse upper layer data in all datagrams. This parsing is expensive and slow. This situation is undesirable. This document defines a new option within the IPv6 Hop-by-Hop Header. The presence of this option in an IPv6 datagram informs the router that the contents of this datagram is of interest to the router and to handle any control data accordingly. The absence of this option in an IPv6 datagram informs the router that the datagram does not contain information needed by the router and hence can be safely routed without further datagram parsing. Hosts originating IPv6 datagrams are required to include this option in certain circumstances. 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]. 2.0 Approach The goal is to provide an efficient mechanism whereby routers can know when to intercept datagrams not addressed to them without having to extensively examine every datagram. The described solution is to define a new IPv6 Hop-by-Hop Header option having the semantic "routers should examine this datagram more closely" and require protocols such as RSVP to use this option. This approach incurs little or no performance penalty on the forwarding of normal datagrams. Not including this option tells the router that there is no need to closely examine the contents of the datagram. 2.1 Syntax The router alert option has the following format: +--------+--------+--------+--------+ |000| 5 | 0000010 | Value (2 octets)| +--------+--------+--------+--------+ len=2 The first three bits of the first byte are zero and the value 5 in the remaining five bits is the Hop-by-Hop Option Type number. [Page 2] Internet Draft IPv6 Router Alert June 1999 [RFC-2460] specifies the meaning of the first three bits. By zeroing all three, this specification requires that nodes not recognizing this option type should skip over this option and continue processing the header and that the option must not change en route. There MUST only be one option of this type, regardless of value, per Hop-by-Hop header. Value: A 2 octet code in network byte order with the following values: 0 Datagram contains a Multicast Listener Discovery message [RFC-XXXX]. 1 Datagram contains RSVP message. 2 Datagram contains an Active Networks message. 3-65535 Reserved to IANA for future use. Values are registered and maintained by the IANA. New values will be assigned via documents approved by the IETF as defined in RFC 2434. 2.2 Semantics The option indicates that the contents of the datagram may be interesting to the router. The router's interest and the actions taken by employing Router Alert MUST be specified in the RFC of the protocol that mandates or allows the use of Router Alert. The final destination of the IPv6 datagram MUST ignore this option upon receipt to prevent multiple evaluations of the datagram. Unrecognized value fields MUST be silently ignored and the processing of the header continued. Routers that recognize the option will examine datagrams carrying it more closely to determine whether or not further processing is necessary. The router only needs to parse the packet in sufficient detail to decide whether the packet contains something of interest. The value field can be used by an implementation to speed processing of the datagram within the transit router. Observe that further processing can involve protocol layers above IPv6. E.g., for RSVP messages, the datagram will have to undergo UDP and RSVP protocol processing. Once the datagram leaves the IPv6 layer, there is considerable ambiguity about whether the router is acting as an IPv6 host or an IPv6 router. Precisely how the router handles the contents is value-field specific. However, if the processing required for the datagram involves examining the payload of the IPv6 datagram, then the interim router is performing a host function and SHOULD interpret the data as a host. [Page 3] Internet Draft IPv6 Router Alert June 1999 3.0 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 datagrams not directly addressed to them. Routers are not required to examine the datagrams not addressed to them unless the datagrams include the router alert option. All IPv6 datagrams containing an RSVP message MUST contain this option within the IPv6 Hop-by-Hop Options Header of such datagrams. 4.0 Security Considerations Gratuitous use of this option can cause performance problems in routers. A more severe attack is possible in which the router is flooded by bogus datagrams containing router alert options. The use of the option, if supported in a router, MAY therefore be limited by rate or other means by the transit router. 5.0 Notice on Intellectual Property The IETF takes no position regarding the validity or scope of any intellectual property 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; neither does it represent that it has made any effort to identify any such rights. Information on the IETF's procedures with respect to rights in standards-track and standards-related documentation can be found in BCP-11. Copies of claims of rights made available for publication 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 implementors or users of this specification can be obtained from the IETF Secretariat. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights which may cover technology that may be required to practice this standard. Please address the information to the IETF Executive Director. 5.0 References [RFC-2119] Bradner, S., "Key words for use in RFC's to Indicate Requirement Levels", Internet Request For Comments No. 2119, March 1977. [Page 4] Internet Draft IPv6 Router Alert June 1999 [RFC-2205] Braden, B. (ed.), L. Zhang, S. Berson, S. Herzog, S. Jamin, "Resource ReSerVation Protocol (RSVP)," Internet Request for Comments No. 2205, September 1997. [RFC-2434] T. Narten and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", Internet Request For Comments No. 2434, October 1998. [RFC-2460] S. Deering and R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification," Internet Request for Comments No. 2460, December 1998. [RFC-XXXX] S. Deering, W. Fenner and B. Haberman, "Multicast Listener Discovery (MLD) for IPv6," Internet Draft (draft- ietf-ipngwg-mld-02.txt), June 1999. 6.0 Authors' Addresses Dave Katz Phone: +1 (408) 327-0173 Juniper Networks Email: dkatz@jnx.com 3260 Jay Street Santa Clara, CA 95054 USA Craig Partridge Phone: +1 (617) 873-3000 BBN Technologies Email: craig@bbn.com 10 Moulton Street Cambridge, MA 02138 USA Alden Jackson Phone: +1 (617) 873-3000 BBN Technologies Email: awjacks@bbn.com 10 Moulton Street Cambridge, MA 02138 USA [Page 5]