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Network Working Group                                            S. BrimRequest for Comments: 2836                                  B. CarpenterCategory: Standards Track                                 F. Le Faucheur                                                                May 2000Per Hop Behavior Identification CodesStatus of this Memo   This document specifies an Internet standards track protocol for the   Internet community, and requests discussion and suggestions for   improvements.  Please refer to the current edition of the "Internet   Official Protocol Standards" (STD 1) for the standardization state   and status of this protocol.  Distribution of this memo is unlimited.Copyright Notice   Copyright (C) The Internet Society (2000).  All Rights Reserved.Table of Contents:1. Introduction.................................................11.1. Usage Scenarios............................................22. Encoding.....................................................33. IANA Considerations..........................................44. Security considerations......................................4   References......................................................4   Authors' Addresses..............................................5   Intellectual Property...........................................6   Full Copyright Statement........................................71. 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.Brim, et al.                Standards Track                     [Page 1]

RFC 2836         Per Hop Behavior Identification Codes          May 2000   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   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].Brim, et al.                Standards Track                     [Page 2]

RFC 2836         Per Hop Behavior Identification Codes          May 2000   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, et al.                Standards Track                     [Page 3]

RFC 2836         Per Hop Behavior Identification Codes          May 20003. 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.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.References   [RFC 2119] Bradner, S., "Key words for use in RFCs to Indicate              Requirement Levels",BCP 14,RFC 2119, March 1997.   [RFC 2474] Nichols, K., Blake, S., Baker, F. and D. Black,              "Definition of the Differentiated Services Field (DS              Field) in the IPv4 and IPv6 Headers",RFC 2474, December              1998.   [RFC 2475] Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z.              and W. Weiss, "An Architecture for Differentiated              Services",RFC 2475, December 1998.   [RFC 2597] Heinanen, J., Baker, F., Weiss, W. and J. Wroclawski,              "Assured Forwarding PHB Group",RFC 2597, June 1999.Brim, et al.                Standards Track                     [Page 4]

RFC 2836         Per Hop Behavior Identification Codes          May 2000   [MPLS-DS]  MPLS Support of Differentiated Services, Francois Le              Faucheur, Liwen Wu, Bruce Davie, Shahram Davari, Pasi              Vaananen, Ram Krishnan, Pierrick Cheval, Juha Heinanen,              Work in Progress.Authors' Addresses   Scott W. Brim   146 Honness Lane   Ithaca, NY 14850   USA   EMail: sbrim@cisco.com   Brian E. Carpenter   IBM   c/o iCAIR   Suite 150   1890 Maple Avenue   Evanston, IL 60201   USA   EMail: brian@icair.org   Francois Le Faucheur   Cisco Systems   Petra B - Les Lucioles   291, rue Albert Caquot   06560 Valbonne   France   EMail: flefauch@cisco.comBrim, et al.                Standards Track                     [Page 5]

RFC 2836         Per Hop Behavior Identification Codes          May 2000Intellectual 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 inBCP-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.Brim, et al.                Standards Track                     [Page 6]

RFC 2836         Per Hop Behavior Identification Codes          May 2000Full Copyright Statement   Copyright (C) The Internet Society (2000).  All Rights Reserved.   This document and translations of it may be copied and furnished to   others, and derivative works that comment on or otherwise explain it   or assist in its implementation may be prepared, copied, published   and distributed, in whole or in part, without restriction of any   kind, provided that the above copyright notice and this paragraph are   included on all such copies and derivative works.  However, this   document itself may not be modified in any way, such as by removing   the copyright notice or references to the Internet Society or other   Internet organizations, except as needed for the purpose of   developing Internet standards in which case the procedures for   copyrights defined in the Internet Standards process must be   followed, or as required to translate it into languages other than   English.   The limited permissions granted above are perpetual and will not be   revoked by the Internet Society or its successors or assigns.   This document and the information contained herein is provided on an   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.Acknowledgement   Funding for the RFC Editor function is currently provided by the   Internet Society.Brim, et al.                Standards Track                     [Page 7]