Per Hop Behavior Identification Codes
The information below is for an old version of the document that is already published as an RFC.
This is an older version of an Internet-Draft that was ultimately published as RFC 2836.
|Authors||Scott W. Brim , Brian E. Carpenter , François Le Faucheur|
|Last updated||2013-03-02 (Latest revision 1999-10-04)|
|RFC stream||Internet Engineering Task Force (IETF)|
|IESG||IESG state||RFC 2836 (Proposed Standard)|
|Send notices to||(None)|
IETF S. Brim Internet Draft B. Carpenter October 1999 F. Le Faucheur Per Hop Behavior Identification Codes Copyright Notice Placeholder for ISOC copyright. Abstract draft-ietf-diffserv-phbid-00.txt (updates draft-brim-diffserv-phbid-00.txt) This document defines a 16 bit encoding mechanism for the identification of differentiated services Per Hop Behaviors in protocol messages. 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. Brim, Carpenter, Le Faucheur Expires April 2000 [Page 1] Internet Draft Per Hop Behavior Identification Codes Oct 1999 Table of Contents: Status of this Memo.............................................1 1. Introduction.................................................3 1.1. Usage Scenarios............................................3 2. Encoding.....................................................4 3. IANA Considerations..........................................5 4. Security considerations......................................6 Acknowledgements................................................6 References......................................................6 Authors' Addresses..............................................6 Intellectual Property...........................................7 Full Copyright Statement........................................7 Brim, Carpenter, Le Faucheur Expires April 2000 [Page 2] Internet Draft Per Hop Behavior Identification Codes Oct 1999 1. Introduction Differentiated Services [RFC 2474, RFC 2475] introduces the notion of Per Hop Behaviors (PHBs) that define how traffic belonging to a particular behavior aggregate is treated at an individual network node. In IP packet headers, PHBs are not indicated as such; instead Differentiated Services Codepoint (DSCP) values are used. There are only 64 possible DSCP values, but there is no such limit on the number of PHBs. In a given network domain, there is a locally defined mapping between DSCP values and PHBs. Standardized PHBs recommend a DSCP mapping, but network operators may choose alternative mappings. In some cases it is necessary or desirable to identify a particular PHB in a protocol message, such as a message negotiating bandwidth management or path selection, especially when such messages pass between management domains. Examples where work is in progress include communication between bandwidth brokers, and MPLS support of diffserv. In certain cases, what needs to be identified is not an individual PHB, but a set of PHBs. One example is a set of PHBs that must follow the same physical path to prevent re-ordering. An instance of this is the set of three PHBs belonging to a single Assured Forwarding class, such as the PHBs AF11, AF12 and AF13 [RFC 2597]. This document defines a binary encoding to uniquely identify PHBs and/or sets of PHBs in protocol messages. This encoding MUST be used when such identification is required. 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]. 1.1. Usage Scenarios Diffserv services are expected to be supported over various underlying technologies which we broadly refer to as "link layers" for the purpose of this discussion. For the transport of IP packets, some of these link layers make use of connections or logical connections where the forwarding behavior supported by each link layer device is a property of the connection. In particular, within the link layer domain, each link layer node will schedule traffic depending on which connection the traffic is transported in. Examples of such "link layers" include ATM and MPLS. For efficient support of diffserv over these link layers, one model is for different Behavior Aggregates (BAs) (or sets of Behavior Aggregates) to be transported over different connections so that they are granted different (and appropriate) forwarding behaviors inside the link layer cloud. When those connections are dynamically established for the transport of diffserv traffic, it is very useful to communicate at connection establishment time what forwarding behavior(s) is(are) to be granted to each connection by the link Brim, Carpenter, Le Faucheur?Expires April 2000 [Page 3] Internet Draft Per Hop Behavior Identification Codes Oct 1999 layer device so that the BAs transported experience consistent forwarding behavior inside the link layer cloud. This can be achieved by including in the connection establishment signaling messages the encoding of the corresponding PHB, or set of PHBs, as defined in this document. Details on proposed usage of PHB encodings by some MPLS label distribution protocols (RSVP and LDP) for support of Diff-Serv over MPLS, can be found in [MPLS-DS]. In another approach, the ATM Forum has a requirement to indicate desired IP QOS treatments in ATM signaling, so that ATM switches can be just as supportive of the desired service as are IP forwarders. To do so the Forum is defining a new VC call setup information element is which will carry PHB identification codes (although will be generalized to do more if needed). 2. Encoding PHBs and sets of PHBs are encoded in an unsigned 16 bit binary field. The 16 bit field is arranged as follows: Case 1: PHBs defined by standards action, as per [RFC 2474]. The encoding for a single PHB is the recommended DSCP value for that PHB, left-justified in the 16 bit field, with bits 6 through 15 set to zero. Note that the recommended DSCP value MUST be used, even if the network in question has chosen a different mapping. The encoding for a set of PHBs is the numerically smallest of the set of encodings for the various PHBs in the set, with bit 14 set to 1. (Thus for the AF1x PHBs, the encoding is that of the AF11 PHB, with bit 14 set to 1.) 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ | DSCP | 0 0 0 0 0 0 0 0 X 0 | +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ Case 2: PHBs not defined by standards action, i.e. experimental or local use PHBs as allowed by [RFC 2474]. In this case an arbitrary 12 bit PHB identification code, assigned by the IANA, is placed left- justified in the 16 bit field. Bit 15 is set to 1, and bit 14 is zero for a single PHB or 1 for a set of PHBs. Bits 12 and 13 are zero. 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ | PHB id code | 0 0 X 1 | +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ Bits 12 and 13 are reserved either for expansion of the PHB identification code, or for other use, at some point in the future. Brim, Carpenter, Le Faucheur?Expires April 2000 [Page 4] Internet Draft Per Hop Behavior Identification Codes Oct 1999 3. IANA Considerations IANA is requested to create a new assignment registry for "Per-Hop Behavior Identification Codes", initially allowing values in the range 0 to 4095 decimal. Assignment of values in this field require: -the identity of the assignee -a brief description of the new PHB, with enough detail to distinguish it from existing standardized and non-standardized PHBs. In the case of a set of PHBs, this description should cover all PHBs in the set. -a reference to a stable document describing the PHB in detail. During the first year of existence of this registry, IANA is requested to refer all requests to the IETF diffserv WG for review. Subsequently, requests should be reviewed by the IETF Transport Area Directors or by an expert that they designate. If the number of assignments begins to approach 4096, the Transport Area Directors should be alerted. Brim, Carpenter, Le Faucheur?Expires April 2000 [Page 5] Internet Draft Per Hop Behavior Identification Codes Oct 1999 4. Security considerations This encoding in itself raises no security issues. However, users of this encoding should consider that modifying a PHB identification code may constitute theft or denial of service, so protocols using this encoding must be adequately protected. Acknowledgements Useful comments were made by Francois Le Faucheur and others. References [RFC 2119] Key words for use in RFCs to Indicate Requirement Levels, S. Bradner, RFC 2119, March 1997. [RFC 2474] Definition of the Differentiated Services Field (DS Field) in the IPv4 and IPv6 Headers. K. Nichols, S. Blake, F. Baker, D. Black, RFC 2474, December 1998. [RFC 2475] An Architecture for Differentiated Services. S. Blake, D. Black, M. Carlson, E. Davies, Z. Wang, W. Weiss, RFC 2475, December 1998. [RFC 2597] Assured Forwarding PHB Group, J. Heinanen, F. Baker, W. Weiss, J. Wroclawski, RFC 2597, June 1999. [MPLS-DS] <draft-ietf-mpls-diff-ext-02.txt>, work in progress Authors' Addresses Scott W. Brim 146 Honness Lane Ithaca, NY 14850 USA E-mail: email@example.com Brian E. Carpenter IBM c/o iCAIR Suite 150 1890 Maple Avenue Evanston, IL 60201 USA E-mail: firstname.lastname@example.org Brim, Carpenter, Le Faucheur?Expires April 2000 [Page 6] Internet Draft Per Hop Behavior Identification Codes Oct 1999 Francois Le Faucheur Cisco Systems Petra B - Les Lucioles 291, rue Albert Caquot 06560 Valbonne France E-mail: email@example.com Intellectual Property PLACEHOLDER for full IETF IPR Statement if needed. Full Copyright Statement PLACEHOLDER for full ISOC copyright Statement if needed. Brim, Carpenter, Le Faucheur?Expires April 2000 [Page 7]