Network Working Group                                        B. Decraene
Internet-Draft                                                    Orange
Intended status: Standards Track                             P. Francois
Expires: January 8, 2017                             Cisco Systems, Inc.
                                                            July 7, 2016

                   Assigned BGP extended communities


   This document defines an IANA registry in order to assign non-
   transitive extended communities from.  These are similar to the
   existing well-known BGP communities defined in RFC 1997 but provide a
   control over inter-AS community advertisement as, per RFC RFC 4360,
   they are not transitive across Autonomous System boundaries.

   For that purpose, this document defines the use of the reserved
   Autonomous System number 0.65535 in the non-transitive generic four-
   octet AS specific extended community type.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [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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   Internet-Drafts are draft documents valid for a maximum of six months
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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on January 8, 2017.

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Copyright Notice

   Copyright (c) 2016 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
   ( 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.

1.  Introduction

   [RFC1997] defines the BGP community attribute and some BGP well-known
   communities whose meaning SHALL be understood by all compliant
   implementations.  New communities can be registered in the IANA "BGP
   Well-known Communities" registry but it can't be assumed anymore that
   they will be known by all BGP implementations.  Implementations or
   BGP policies which recognize them will behave as specified in the
   IANA registry.  Implementations which do not recognize those new IANA
   assigned communities will propagate them from BGP neighbor to BGP
   neighbor and from AS to AS with an unlimited scope.

   There is currently no agreed way to register a non-transitive well-
   known community.

   On one hand, [RFC1997] defines BGP Well-known communities with no
   structure to set their transitiveness across ASes.  Without
   structure, communities can only be filtered by explicitly enumerating
   all community values that will be denied or allowed to BGP speakers
   in neighboring ASes.  This is not satisfactory as this would require
   upgrading all border routers to understand this community before its
   first usage.

   On the other hand, [RFC4360] defines the BGP extended community
   attribute with a structure including a type and a transitive bit "T".
   This transitive bit, when set, allows to restrict the scope of the
   community within an AS.  But there is no IANA registry to allocate
   one well-known extended community.  [RFC4360] defines IANA registries
   to allocate BGP Extended Communities types.  Each type is able to
   encode 2^48 or 2^56 values depending on the type being extended or
   regular.  Therefore, one needing to reserve a single non-transitive
   extended community would need to reserve an extended subtype which
   represents 2^48 communities, while a single value is used.  This

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   would both waste the resources and disable the ability to define
   global policies on reserved communities, such as to accept them or to
   filter them out.  In addition, using a new community type typically
   requires a software upgrade on both the router setting the community
   and the router using it in a BGP policy.  So this would not allow the
   networking community to quickly define and use a new community.

   To address this limitation, this document defines an IANA registry in
   order to allow the registration of non-transitive extended
   communities.  These are similar to the existing Well-known BGP
   communities defined in [RFC1997] but provides a control on inter-AS
   community advertisement.  Indeed, as per [RFC4360] non-transitive
   communities are removed from routes propagated to another AS.

2.  Assigned non-transitive extended communities

   [I-D.ietf-idr-as4octet-extcomm-generic-subtype] defines a generic
   sub-type for the four-octet AS specific extended community.  The
   value of the four-octets Global Administrator sub-field contains a
   four-octet Autonomous System number.  The value of their two-octet
   Local Administrator sub-field has semantics defined by the Autonomous
   System set in the Global Administrator sub-field.

   This document updates [I-D.ietf-idr-as4octet-extcomm-generic-subtype]
   and defines the use of the Local Administrator sub-field of the "non-
   transitive generic four-octet AS specific" extended community type
   when the AS number has the reserved value 0.65535 (0x0000FFFF).

   When the AS number, encoded in the Global Administrator sub-field,
   has the reserved value 0.65535, the communities have global
   significance.  The lists of those communities are maintained by the
   IANA in the registry "Assigned non-transitive extended communities".

   Note that this use of the reserved AS number 0.65535 in the AS field
   of the communities is similar to the one defined by [RFC1997] for the
   BGP Well-Known communities.  In particular, [RFC1997] also uses the
   reserved AS number 65535.

3.  Assigned transitive extended communities

   As per [RFC6793], a 2-octet Autonomous System number can be converted
   into a 4-octet Autonomous System number by setting the two high-order
   octets of the 4-octet field to zero.  This applies to the reserved
   2-octet Autonous System number 65535 which could use either a
   standard community or the 4-octet AS specific generic extended
   community.  As noted in
   [I-D.ietf-idr-as4octet-extcomm-generic-subtype], this is undesirable

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   as they would be treated as different communities, even if they had
   the same values.

   Therefore, this document does not define a transitive extended
   community registry.  Transitive communities are to be assigned as per

4.  IANA Considerations

   The IANA is requested to create and maintain a registry entitled
   "Assigned non-transitive extended communities" with the following
   registration procedure:

    Registry Name: Assigned non-transitive extended communities
                   with Global Significance

       Range              Registration Procedures
       -----------        -------------------------
       0x0000-8000        First Come First Served
       0x8001-FFFF        Standards Action/Early IANA Allocation

   An application may need both a transitive and a non-transitive
   community and it may be beneficial to have the same value for both
   communities.  Therefore, the IANA SHOULD try to accommodate such
   request to get both a non-transitive community from the above
   "Assigned non transitive extended communities" and a transitive
   community from [RFC1997] BGP Well-known Communities with the same
   (lower two-octets) value for both.

5.  Security Considerations

   This document defines IANA actions.  In itself, it has no impact on
   the security of the BGP protocol.

   It allows the allocation of non-transitive global communities which
   are not propagated across Autonomous System boundaries.  Compared to
   a transitive well-known community, a non-transitive community can
   provide some security benefit both for the sender and the receiver of
   the community.

6.  Acknowledgements

   We would like to acknowledge John Scudder, Jeffrey Haas and Yakov
   Rekhter for their contribution to this document.

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7.  Normative References

              Rao, D., Mohapatra, P., and J. Haas, "Generic Subtype for
              BGP Four-octet AS specific extended community", draft-
              ietf-idr-as4octet-extcomm-generic-subtype-08 (work in
              progress), June 2015.

   [RFC1997]  Chandra, R., Traina, P., and T. Li, "BGP Communities
              Attribute", RFC 1997, DOI 10.17487/RFC1997, August 1996,

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

   [RFC4360]  Sangli, S., Tappan, D., and Y. Rekhter, "BGP Extended
              Communities Attribute", RFC 4360, DOI 10.17487/RFC4360,
              February 2006, <>.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              DOI 10.17487/RFC5226, May 2008,

   [RFC6793]  Vohra, Q. and E. Chen, "BGP Support for Four-Octet
              Autonomous System (AS) Number Space", RFC 6793,
              DOI 10.17487/RFC6793, December 2012,

Appendix A.  Appendix A.  Changes / Author Notes

   [RFC Editor: Please remove this section before publication ]

   Changes -01:

   o  Name changed from 'Reserved BGP extended communities' to 'Assigned
      BGP extended communities'

   o  Addition of section 'Assigned extended communities'

   Changes -02: no change, refresh only.

   Changes -03:

   o  Use of AS number 0.65535 (0x0000FFFF) instead of AS 0.  This is
      better aligned with RFC 1997 which also uses AS 65535.

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   o  Remove the transitive flavor of assigned extended communities.
      RFC 1997 well-known standard communities to be used instead.

   Changes -04: no change, refresh only.

   Changes -05: minor editorial change (RFC 4893 obsoleted by 6793).

   Changes -06: typo fixed, minor editorial change.

   Changes -07, 08, 09: no change, refresh only.

Authors' Addresses

   Bruno Decraene


   Pierre Francois
   Cisco Systems, Inc.


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