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Versions: 00 01 02 03 04 05                                             
Network Working Group                                       C. Jacquenet
Internet Draft                                        France Telecom R&D
Document: draft-jacquenet-qos-nlri-02.txt                  February 2001
Category: Experimental
Expires: August 2001

   Providing Quality of Service Indication by the BGP-4 Protocol: the
                           QOS_NLRI attribute

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC 2026 [1].

   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

   The list of Internet-Draft Shadow Directories can be accessed at


   This draft specifies an additional BGP4 (Border Gateway Protocol,
   version 4, [2]) attribute, named the "QOS_NLRI" attribute, which aims
   at providing QoS (Quality of Service)-related information associated
   to the NLRI (Network Layer Reachability Information) information
   conveyed in a BGP UPDATE message.

1. Introduction

   Providing end-to-end quality of service is probably one of the most
   important challenges of the Internet, not only because of the massive
   development of value-added IP service offerings, but also because of
   the various QoS policies that are currently deployed and enforced
   within an autonomous system, and which may well differ from one AS
   (Autonomous System) to another.

   For almost the last decade, value-added IP service offerings have
   been deployed over the Internet, thus yielding a dramatic development

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   of the specification effort, as far as quality of service in IP
   networks is concerned. Nevertheless, providing end-to-end quality of
   service by crossing administrative domains still remains an issue,
   mainly because:

   - QoS policies may dramatically differ from one service provider to
   - The enforcement of a specific QoS policy may also differ from one
    domain to another, although the definition of a set of basic and
    common quality of service indicators may be shared between the
    service providers.

   Activate the BGP4 protocol for exchanging reachability information
   between autonomous systems has been a must for many years, and, from
   this standpoint, the BGP4 protocol is one of the key components for
   the enforcement of end-to-end QoS policies.

   Therefore, exchanging QoS-related information as well as reachability
   information in a given BGP UPDATE message appears to be helpful in
   enforcing an end-to-end QoS policy.

   This draft aims at specifying a new BGP4 attribute, the QOS_NLRI
   attribute, that will convey QoS-related information associated to
   the routes described in the corresponding NLRI field of the

   This document is organized into the following sections:

   - Section 3 identifies the changes that have been made in the
    document since the last version,
   - Section 4 describes the attribute and its mode of operation,
   - Section 5 elaborates on the use of the capabilities advertisement
    feature of the BGP4 protocol,
   - Finally, sections 6 and 7 introduce IANA and some security
    considerations, respectively.

2. Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC-2119 [3].

3. Changes since the last version of this draft

   The current version of this draft reflects the following changes:

   - Slight re-wording of the Introduction section (section 1),

   - Development of Section 4 (introduction of new QoS metrics, as well
    as elaboration on the rate encoding scheme),

   - Correction of remaining typos.

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4. The QOS_NLRI attribute (Type Code XY*)

   (*): "XY" is subject to the IANA considerations section of this

   The QOS_NLRI attribute is an optional transitive attribute that can
   be used for the following purposes:

   (a) To advertise a QoS route to a peer. A QoS route is a route that
      meets one or a set of QoS requirement(s) to reach a given (set
      of) destination prefixes (see [4], for example). Such QoS
      requirements can be expressed in terms of minimum one-way delay
      ([5]) to reach a destination, the experienced delay variation for
      IP datagrams that are destined to a given destination prefix
      ([6]), the loss rate experienced along the path to reach a
      destination, and/or the identification of the traffic that is
      expected to use this specific route (identification means for
      such traffic include DSCP (DiffServ Code Point, [7]) marking).
      These QoS requirements can be used as an input for the route
      calculation process embedded in the BGP peers, e.g. thanks to the
      activation of a signaling protocol, such as RSVP (Resource
      ReSerVation Protocol, [8]),

   (b) To provide QoS information along with the NLRI information in a
      single BGP UPDATE message. It is assumed that this QoS
      information will be related to the route (or set of routes)
      described in the NLRI field of the attribute.

   This draft makes no specific assumption about the means to actually
  value this attribute, since this is mostly a matter of
  implementation, but the reader is kindly suggested to have a look on
  document [9], as an example of a means to feed the BGP peer with the
  appropriate information.

   The QOS_NLRI attribute is encoded as follows:

            | QoS Information Code (1 octet)                          |
            | QoS Information Sub-code (1 octet)                      |
            | QoS Information Value (2 octets)                        |
            | QoS Information Origin (1 octet)                        |
            | Address Family Identifier (2 octets)                    |
            | Subsequent Address Family Identifier (1 octet)          |
            | Network Address of Next Hop (4 octets)                  |

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            | Network Layer Reachability Information (variable)       |

   The use and meaning of the fields of the QOS_NLRI attribute are
   defined as follows:

   - QoS Information Code:

    This field carries the type of the QOS information. The following
    types have been identified so far:

   (0) Reserved
   (1) Packet rate, i.e. the number of IP datagrams that can be
      transmitted (or have been lost) per unit of time, this number
      being characterized by the elaboration provided in the QoS
      Information Sub-code (see below),
   (2) One-way delay, as defined in [5]
   (3) Inter-packet delay variation, as defined in [6]
   (4) PHB Identifier, as defined in [10]

   - QoS Information Sub-code:

    This field carries the sub-type of the QoS information. The
    following sub-types have been identified so far:

   (0) None (i.e. no sub-type, or sub-type unavailable, or unknown sub-
   (1) Reserved rate
   (2) Available rate
   (3) Loss rate
   (4) Minimum one-way delay
   (5) Maximum one-way delay
   (6) Average one-way delay

   The instantiation of this sub-code field MUST be compatible with the
   value conveyed in the QoS Information code field, as stated in the
   following table (the rows represent the QoS Information Code possible
   values, the columns represent the QoS Information Sub-code values
   identified so far, while the "X" sign indicates incompatibility).
            |    |  0 |  1 |  2 |  3 |  4 |  5 |  6 |
            |  0 |    |    |    |    |    |    |    |
            |  1 |    |    |    |    |  X |  X |  X |
            |  2 |    |  X |  X |  X |    |    |    |
            |  3 |    |  X |  X |  X |  X |  X |  X |
            |  4 |    |  X |  X |  X |  X |  X |  X |

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   - QoS Information Value:

    This field indicates the value of the QoS information. The
    corresponding units obviously depend on the instantiation of the
    QoS Information Code. Namely, if:

   (a) QoS Information Code field is "0", no unit specified,
   (b) QoS Information Code field is "1", unit is kbits per second
      (kbps), and the rate encoding rule is composed of a 3-bit
      exponent (with an assumed base of 8) followed by a 13-bit
      mantissa, as depicted in the figure below:

                             0      8       16
                             |       |       |
                             |Exp| Mantissa  |

     This encoding scheme advertises a numeric value that is 2^16 -1 -
      (exponential encoding of the considered rate), as depicted in
   (c) QoS Information Code field is "2", unit is milliseconds,
   (d) QoS Information Code field is "3", unit is milliseconds,
   (e) QoS Information Code field is "4", no unit specified.

   - QoS Information Origin:

    This field provides indication on the origin of the path
    information, as defined in section 4.3. of [2].

   - Address Family Identifier (AFI):

    This field carries the identity of the Network Layer protocol
    associated with the Network Address that follows. Presently defined
    values for this field are specified in [12] (see the Address Family
    Numbers section of this reference document).

   - Subsequent Address Family Identifier (SAFI):

    This field provides additional information about the type of the
    Network Layer Reachability Information carried in the QOS_NLRI

   - Network Address of Next Hop:

    This field contains the IPv4 Network Address of the next router on
    the path to the destination prefix, (reasonably) assuming that such
    routers can at least be addressed according to the IPv4 formalism.

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   - Network Layer Reachability Information:

    This variable length field lists the NLRI information for the
    feasible routes that are being advertised by this attribute. The
    next hop information carried in the QOS_NLRI path attribute defines
    the Network Layer address of the border router that should be used
    as the next hop to the destinations listed in the QOS_NLRI
    attribute in the UPDATE message.

   When advertising a QOS_NLRI attribute to an external peer, a router
   may use one of its own interface addresses in the next hop component
   of the attribute, given the external peer to which the route is being
   advertised shares a common subnet with the next hop address.  This is
   known as a "first party" next hop.

   A BGP speaker can advertise to an external peer an interface of any
   internal peer router in the next hop component, provided the external
   peer to which the route is being advertised shares a common subnet
   with the next hop address.  This is known as a "third party" next hop

   A BGP speaker can advertise any external peer router in the next hop
   component, provided that the Network Layer address of this border
   router was learned from an external peer, and the external peer to
   which the route is being advertised shares a common subnet with the
   next hop address. This is a second form of "third party" next hop

   Normally the next hop information is chosen so that the shortest
   available path will be taken. A BGP speaker must be able to support
   disabling advertisement of third party next hop information to handle
   imperfectly bridged media or for reasons of policy.

   A BGP speaker must never advertise an address of a peer to that peer
   as a next hop, for a route that the speaker is originating.  A BGP
   speaker must never install a route with itself as the next hop.

   When a BGP speaker advertises the route to an internal peer, the
   advertising speaker should not modify the next hop information
   associated with the route. When a BGP speaker receives the route via
   an internal link, it may forward packets to the next hop address if
   the address contained in the attribute is on a common subnet with the
   local and remote BGP speakers.

   A BGP UPDATE message that carries the QOS_NLRI MUST also carry the
   ORIGIN and the AS_PATH attributes (both in EBGP and in IBGP
   exchanges). Moreover, in IBGP exchanges such a message MUST also
   carry the LOCAL_PREF attribute. If such a message is received from an
   external peer, the local system shall check whether the leftmost AS
   in the AS_PATH attribute is equal to the autonomous system number of
   the peer than sent the message. If that is not the case, the local

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   system shall send the NOTIFICATION message with Error Code UPDATE
   Message Error, and the Error Subcode set to Malformed AS_PATH.

   An UPDATE message that carries no NLRI, other than the one encoded in
   the QOS_NLRI attribute, should not carry the NEXT_HOP attribute. If
   such a message contains the NEXT_HOP attribute, the BGP speaker that
   receives the message should ignore this attribute.

5. Use of Capabilities Advertisement with BGP-4

   A BGP speaker that uses the QOS_NLRI attribute SHOULD use the
   Capabilities Advertisement procedures, as defined in [13], so that it
   might be able to determine if it can use such an attribute with a
   particular peer.

   The fields in the Capabilities Optional Parameter are defined as

   - The Capability Code field is set to N (127 < N < 256, when
    considering the "Private Use" range, as specified in [14]), while
    the Capability Length field is set to "1".

   - The Capability Value field is a one-octet field, that contains the
    Type Code of the QOS_NLRI attribute, as defined in the introduction
    of section 4 of the present draft.

6. IANA Considerations

   Section 4 of this draft documents an optional transitive BGP-4
   attribute named "QOS_NLRI" whose type value will be assigned by IANA.
   Section 5 of this draft also documents a Capability Code whose value
   should be assigned by IANA.

7. Security Considerations

   This additional BGP-4 attribute specification does not change the
   underlying security issues inherent in the existing BGP-4 protocol
   specification [15].

8. References

   [1]  Bradner, S.,"The Internet Standards Process -- Revision 3", BCP
       9, RFC 2026, October 1996.

   [2]  Rekhter Y., Li T., "A Border Gateway Protocol 4 (BGP-4)", RFC
       1771, March 1995.

  [3] Bradner, S., "Key words for use in RFCs to Indicate Requirement
       Levels", BCP 14, RFC 2119, March 1997.

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   [4]  Goderis D., T'Joens Y., Jacquenet C., Memenios G., Pavlou G.,
       Egan R., Griffin D., Georgatsos P., Georgiadis L.,
       "Specification of a Service Level Specification (SLS) Template",
       draft-tequila-sls-00.txt, Work in Progress, November 2000. Check
       http://www.ist-tequila.org for additional information.

   [5] Almes G., Kalidindi S., "A One-Way-Delay Metric for IPPM", RFC
       2679, September 1999.

   [6]  Demichelis C., Chimento P., "IP Packet Delay Variation Metric
       for IPPM", draft-ietf-ippm-ipdv-06.txt, Work in Progress,
       February 2001.

   [7]  Nichols K., Blake S., Baker F., Black D., "Definition of the
       Differentiated Services Field (DS Field) in the IPv4 and IPv6
       Headers", RFC 2474, December 1998.

   [8]  Braden R. et al., "Resource ReSerVation Protocol (RSVP)- Version
       1 Functional Specification", RFC 2205, September 1997.

   [9] Jacquenet C., "A COPS client-type for IP traffic engineering",
       draft-jacquenet-ip-te-cops-00.txt, Work in Progress, November

   [10] Black D., Brim S., Carpenter B., Le Faucheur F., "Per Hop
       Behavior Identification Codes", draft-ietf-diffserv-2839bis-
       01.txt, Work in Progress, February 2001.

   [11] Apostolopoulos G. et al, "QoS Routing Mechanisms and OSPF
       Extensions", RFC 2676, August 1999.

   [12] Reynolds J., Postel J., "ASSIGNED NUMBERS", RFC 1700, October

   [13] R. Chandra, J. Scudder, "Capabilities Advertisement with BGP-4",
       RFC 2842, May 2000.

   [14] Narten T., Alvestrand H., "Guidelines for Writing an IANA
       Considerations Section in RFCs", RFC 2434, October 1998.

   [15] Heffernan A., "Protection of BGP sessions via the TCP MD5
       Signature Option", RFC 2385, August 1998.

9. Acknowledgments

   Part of this work is funded by the European Commission, within the
   context of the TEQUILA (Traffic Engineering for Quality of Service in
   the Internet At Large Scale, [4]) project, which is itself part of
   the IST (Information Society Technologies) research program.

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   The author would also like to thank all the partners of the TEQUILA
   project for the fruitful discussions that have been conducted within
   the context of the traffic engineering specification effort of the
   project, as well as O. Bonaventure and B. Carpenter for their
   valuable input.

10. Author's Addresses

   Christian Jacquenet
   France Telecom R & D
   42, rue des Coutures
   BP 6243
   14066 CAEN Cedex 04
   Phone: +33 2 31 75 94 28
   Email: christian.jacquenet@francetelecom.fr

11. Full Copyright Statement

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   The limited permissions granted above are perpetual and will not be
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   This document and the information contained herein is provided on an

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