BGP Well Known Large Community
draft-heitz-idr-wklc-02

Document Type Active Internet-Draft (candidate for idr WG)
Authors Jakob Heitz  , Kotikalapudi Sriram  , Brian Dickson  , John Heasley 
Last updated 2021-03-09 (latest revision 2021-03-07)
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IDR                                                             J. Heitz
Internet-Draft                                                     Cisco
Intended status: Standards Track                               K. Sriram
Expires: September 8, 2021                                          NIST
                                                              B. Dickson

                                                               J. Heasly
                                                           March 7, 2021

                     BGP Well Known Large Community
                        draft-heitz-idr-wklc-02

Abstract

   A range of BGP Autonomous System Numbers is reserved to create a set
   of BGP Well Known Large Communities.

Requirements Language

   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].

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
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   This Internet-Draft will expire on September 8, 2021.

Copyright Notice

   Copyright (c) 2021 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents

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   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Encoding  . . . . . . . . . . . . . . . . . . . . . . . . . .   2
   3.  Transitivity  . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Discussion  . . . . . . . . . . . . . . . . . . . . . . . . .   4
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   7.  Normative References  . . . . . . . . . . . . . . . . . . . .   5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   5

1.  Introduction

   The Global Administrator field of the BGP Large community [RFC8092]
   is an Autonomous System Number (ASN).  To create a set of Well Known
   Large Communities, a set of ASNs must be reserved for them, such that
   a real ASN in the Global Administrator field cannot be mistaken for a
   Well Known Large Community.

2.  Encoding

   Each BGP Well Known Large Community value is encoded as a 12-octet
   quantity, as follows:

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |1 1 1 1 0 1| T |    WKLC ID    |          Data 1               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                             Data 2                            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                             Data 3                            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The fields are as shown below:

        T          - Transitivity field (2 bits).  This is further
                     described below.

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        WKLC ID    - Well Known Large Community Identifier (1 octet).
                     See IANA Considerations.  If an experimental type
                     is used, then it MUST NOT be hard coded in the BGP
                     speaker software; it MUST be configurable.
                     Different experiments can then run in the same
                     network without having to coordinate identifier
                     assignment during the coding stage.

        Data 1,2,3 - A 10 octet value specific to the WKLC.  Data 1 is
                     16 bits long and Data 2 and Data 3 are 32 bits long
                     each.  The data portion is divided into the three
                     fields only to encourage a canonical representation
                     that follows [RFC8092].  If any WKLC cannot make
                     use of this data division, it is free to define
                     another division.

3.  Transitivity

   The Large Community path attribute is a transitive attribute.  Thus,
   BGP speakers that do not implement the transitivity described here
   will transit the WKLC regardless.  If such a speaker wishes not to
   receive a particular large community, it MUST filter it out using
   local policy.  The transitivity field determines how BGP speakers
   transfer the WKLC across real Autonomous System (AS) boundaries.  The
   values are:

        0 - Transitive: The WKLC is transitive across ASes.

        1 - Non-transitive: The WKLC is not transitive across ASes.

        2 - Administration Transitive: The WKLC is transitive across
            ASes under the same administration only.  By default, every
            AS boundary is also an administration boundary.  If an
            external BGP session is configured as a non-administrative
            boundary, then it will send and receive WKLCs with
            transitivity 2, else it will discard the WKLC from the
            UPDATE message.

        3 - One-time Transitive: The WKLC is transitive across ASes
            under the same administration and into an AS under the
            neighboring administration, but not into an AS under a
            further administration.  A BGP speaker that receives a WKLC
            with transitivity 3 on an external BGP session on an
            administrative boundary SHOULD change the transitivity to 2.

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4.  Discussion

   A criterion considered important is the number of data octets
   available for any WKLC type.  This is maximized to 10 at the expense
   of ASN space and type space.

   8 bits for the type is considered to be plenty. 255 types are more
   than enough for WKLC, considering how many extended community types
   have been used so far (22 at time of this publication).  If a large
   set of types, each of which requires less than 10 octets of data, is
   required, then they can all be specified under a single type code and
   further distinguished by using the Data 1 field as a sub-type.  An
   equivalent example is the EVPN Extended Community type, which defines
   further sub types.

   The range of AS numbers currently unallocated by IANA is 399,261 to
   4,199,999,999.  The WKLC reserves 67,108,864 AS numbers.  That still
   leaves 4,132,491,874 unallocated AS numbers.  For comparison, there
   are 94,968,317 AS numbers reserved for private use.  Thus, the number
   of ASNs reserved for WKLCs is considered insignificant.

5.  Security Considerations

   The BGP Large Community Path attribute is transitive.  Thus, a BGP
   speaker that does not recognize the transitivity field may transmit
   the WKLC contrary to the advisement of the transitivity field.  If a
   BGP speaker wishes not to receive any Large Community, it must
   continue to filter it in the same way it was doing before the
   transitivity field was introduced.

   In some cases, a received route that contains an AS number from the
   range assigned to WKLC in its AS_PATH may be considered unusual.  A
   receiving BGP speaker MAY drop such a received route in route-policy.

6.  IANA Considerations

   IANA is requested to assign the range 4093640704 (0xF4000000) to
   4160749567 (0xF7FFFFFF) from the BGP ASN registry for BGP Well Known
   Large Communities.

   IANA is requested to create a registry of Well Known Large
   Communities in the range 0 to 255.  Numbers from this registry are to
   be assigned in accordance with the policies defined in [RFC8126].
   The policies for the following number ranges are:

        0-63    - RFC Required

        64-223  - First Come First Served

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        224-255 - Experimental

7.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC8092]  Heitz, J., Ed., Snijders, J., Ed., Patel, K., Bagdonas,
              I., and N. Hilliard, "BGP Large Communities Attribute",
              RFC 8092, DOI 10.17487/RFC8092, February 2017,
              <https://www.rfc-editor.org/info/rfc8092>.

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/info/rfc8126>.

Authors' Addresses

   Jakob Heitz
   Cisco
   170 West Tasman Drive
   San Jose, CA  95134
   USA

   Email: jheitz@cisco.com

   Kotikalapudi Sriram
   USA National Institute of Standards and Technology
   100 Bureau Drive
   Gaithersburg, MD  20899
   USA

   Email: kotikalapudi.sriram@nist.gov

   Brian Dickson

   Email: brian.peter.dickson@gmail.com

   John Heasly

   Email: heas@shrubbery.net

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