IPv6 Working Group J. Rajahalme INTERNET-DRAFT Nokia <draft-ietf-ipv6-flow-label-01.txt> A. Conta Transwitch B. Carpenter IBM S. Deering Cisco Expires: September 2002 March 2002 IPv6 Flow Label Specification draft-ietf-ipv6-flow-label-01.txt Status of this memo This document is an Internet-Draft and is subject to 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/1id-abstracts.html The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html Abstract This document specifies the usage of the IPv6 Flow Label field, the requirements for IPv6 source nodes labeling flows, and the requirements for flow state establishment methods. Rajahalme, et al. Expires: September 2002 [Page 1]
INTERNET-DRAFT draft-ietf-ipv6-flow-label-01.txt March 2002 1. Terminology and Definitions Classifier An IP layer entity that selects packets based on the content of packet headers according to defined rules. Flow A sequence of related packets sent from a source to a unicast, anycast, or multicast destination. A flow could consist of all packets in a specific transport connection, or a media stream. However, a flow is not necessarily 1:1 mapped to a transport connection. Flow state The information stored in an IP node driving the flow classification and the flow-specific treatment. The required information is specified by the method defining the flow- specific treatment. Flow state A control mechanism used to set up the flow establishment method state. A flow state establishment method can be either - Dynamic, under source node control (e.g. RSVP), - Quasi-dynamic, under network management control, or - Static, through manual configuration. - Algorithmic (e.g. load-spreading) 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. Introduction A flow is a sequence of related packets sent from a source to a unicast, anycast, or multicast destination. To enable specific processing for the flow, flow state needs to be established on the nodes providing the flow-specific treatment. The flow state defines what kind of treatment should be provided, and how to classify the packets to the flow. Traditionally, flow classifiers have been based on the 5-tuple of the Source and Destination Addresses, ports and the transport protocol type. However, these fields may be unavailable due to either fragmentation or encryption, or locating them past a chain of IPv6 option headers may be inefficient. Additionally, dependence on higher Rajahalme, et al. Expires: September 2002 [Page 2]
INTERNET-DRAFT draft-ietf-ipv6-flow-label-01.txt March 2002 layer headers by the IP layer represents a layer violation, possibly hindering the introduction of new transport protocols. The 3-tuple of the Flow Label and the Source and Destination Address fields enables efficient IPv6 flow classification, where only IPv6 main header fields in fixed positions are used. The specification of the IPv6 Flow Label field is given in section 3 below. The minimum level of IPv6 flow support consists of labeling the flows. IPv6 source nodes can label known flows (e.g. TCP connections, RTP streams), even if the node itself would not require any flow- specific treatment. Doing this enables e.g. receiver oriented resource reservations [RSVP]. Requirements for flow labeling are given in section 4. Specific flow state establishment methods and the related service models are out of scope for this specification, but the generic requirements enabling co-existence of different methods in IPv6 nodes are set forth in section 5. 3. IPv6 Flow Label Specification The 20-bit Flow Label field in the IPv6 header SHOULD be used by a source to label sequences of related packets sent to a specific unicast, anycast, or multicast destination. A non-zero Flow Label indicates that the IPv6 packet is labeled. IPv6 nodes receiving a labeled IPv6 packet can use the Flow Label, and Source and Destination Address fields to classify the packet to a certain flow. The packet MAY be given some flow-specific treatment based on the flow state established on a set of IPv6 nodes. The nature of the specific treatment and the methods for the flow state establishment are out of scope for this specification. The IPv6 node assigning a Flow Label value MUST keep track of all the Flow Label, Source Address, and Destination Address triplets in use to avoid creating conflicting classifiers. The Flow Label value set by the source MUST be delivered unchanged to the destination(s). IPv6 nodes MUST NOT assume any specific property on the Flow Label values assigned by source nodes. Router performance SHOULD NOT be dependent on the distribution of the Flow Label values. Especially, the Flow Label bits alone make poor material for a hash key. If an IPv6 node is not providing flow-specific treatment, it MUST ignore the field when receiving or forwarding a packet. Rajahalme, et al. Expires: September 2002 [Page 3]
INTERNET-DRAFT draft-ietf-ipv6-flow-label-01.txt March 2002 4. Flow Labeling Requirements To support e.g. receiver oriented flow state establishment, IPv6 source nodes SHOULD label known flows. Known flows may include e.g. transport connections, or media streams. The IPv6 source node MUST provide a facility for verifying and assigning new Flow Label values, and for storing the Flow Label, Source Address, Destination Address triplets currently in use. The facility MUST be used whenever a label needs to be assigned for a new flow. The facility MUST provide a programming interface with at least three functions: 1) to assign any Flow Label value for a new flow 2) to assign a specific Flow Label for a new flow, and 3) to free the Flow Label value of a specific flow. The interface definition is beyond the scope of this document. Flow Label values for flows MUST be included along with the Source and Destination addresses as part of any flow related signaling dealing with the flow, e.g. transport layer connection set up, RSVP for resource reservation, or SDP for media session parameters. With [RSVP] or [SDP] either the source or the destination of the flow could have a preference for the Flow Label value to be used. For example, a multicast destination could require all the sources to use the same Flow Label value in order to collapse the classifier state to a single flow state entry, instead of having separate flow state for each source (ref. the Wildcard-Filter reservation style in [RSVP]). Therefore the source SHOULD honor the destination's request to mark the packets with the Flow Label value specified. 5. Flow State Establishment Requirements To enable flow-specific treatment, flow state needs to be established on all or a subset of the IPv6 nodes on the path from the source to the destination(s). The methods for the state establishment, as well as the models for flow-specific treatment are defined in separate specifications. To enable co-existence of different methods in IPv6 nodes, the methods MUST meet the following basic requirements: (1) A packet is classified unambiguously to a flow on the basis of the Flow Label, and the Source and Destination Address fields. Depending on the method semantics, multiple such triplets MAY identify the same flow state (see the RSVP Wildcard-Filter example in section 4 above). Usage of any additional header Rajahalme, et al. Expires: September 2002 [Page 4]
INTERNET-DRAFT draft-ietf-ipv6-flow-label-01.txt March 2002 fields for flow classification is beyond the scope of this specification. (2) The IPv6 node facility keeping track of the Flow Label, Source Address, Destination Address triplets MUST be utilized when assigning Flow Label values to new flows (see section 4 above). (3) The Flow Label value 0 is reserved for non-labeled packets. (4) The method MUST provide the means for flow state clean-up from the IPv6 nodes providing the flow-specific treatment. Both soft- and hard-state methods are possible. (5) The method MUST provide the means for an IPv6 node to return an indication, if the requested flow state cannot be supported. (6) Flow state establishment methods SHOULD include the Mobile IP Home Addresses of the source and the destination in the state establishment process in addition to the Care-of Addresses, if available. This enables avoiding state duplication on fixed portions of the path when either end changes its Care-of Address. Security Considerations Anything that facilitates flow classification also increases the vulnerability to traffic analysis. The use of the Flow Label field in general enables flow classification also in the presence of ESP encryption of IPv6 payloads. This allows the transport header values to remain confidential, which may lessen the possibilities for some forms of traffic analysis. IANA Considerations This specification does not define any well-known values. Acknowledgements The discussion on the topic in the IPv6 WG mailing list has been instrumental for the definition of this specification. The authors want to thank Steve Blake, Jim Bound, Francis Dupont, Robert Elz, Tony Hain, Bob Hinden, Christian Huitema, Frank Kastenholz, Charles Perkins, Hesham Soliman, Michael Thomas, and Margaret Wasserman for their contributions. Rajahalme, et al. Expires: September 2002 [Page 5]
INTERNET-DRAFT draft-ietf-ipv6-flow-label-01.txt March 2002 Normative References [IPv6] S. Deering, R. Hinden, "Internet Protocol Version 6 Specification", RFC 2460, December 1998. Informative References [Rajahalme] J. Rajahalme, A. Conta, "An IPv6 Flow Label Specification Proposal", Internet Draft <draft-rajahalme-ipv6-flow- label-00.txt>, November 2001, expires May 2002, Work in progress. [RFC1809] C. Partridge, "Using the Flow Label Field in IPv6", RFC 1809, June 1995. [RSVP] R. Braden, L. Zhang, S. Berson, S. Herzog, S. Jamin, "Resource Reservation Protocol (RSVP) Version 1 Functional Specification", RFC 2205, September 1997. [SDP] M. Handley, V. Jacobson, "SDP: Session Description Protocol", RFC 2327, April 1998. Authors' Addresses Jarno Rajahalme Nokia Research Center P.O. Box 407 FIN-00045 NOKIA GROUP, Finland E-mail: jarno.rajahalme@nokia.com Alex Conta Transwitch Corporation 3 Enterprise Drive Shelton, CT 06484 USA Email: aconta@txc.com Brian E. Carpenter IBM Zurich Research Laboratory Saeumerstrasse 4 / Postfach 8803 Rueschlikon Switzerland Email: brian@hursley.ibm.com Steve Deering Cisco Systems, Inc. 170 West Tasman Drive San Jose, CA 95134-1706 USA Email: deering@cisco.com Rajahalme, et al. Expires: September 2002 [Page 6]
INTERNET-DRAFT draft-ietf-ipv6-flow-label-01.txt March 2002 Expiration Date This memo is filed as <draft-ietf-ipv6-flow-label-01.txt> and expires in September 2002. Rajahalme, et al. Expires: September 2002 [Page 7]
