Network Working Group                                        B. Decraene
Internet-Draft                                   France Telecom - Orange
Intended status: Standards Track                             P. Francois
Expires: June 7, November 22, 2012                                IMDEA Networks
                                                            Dec 05, 2011
                                                            May 21, 2012

                   Assigned BGP extended communities


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

   For that purpose, this document defines the use of the reserved AS
   Autonomous System number 0 for 0.65535 in the transitive and non-transitive generic four-octet four-
   octet AS specific extended community types. 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

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   This Internet-Draft will expire on June 7, November 22, 2012.

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   document authors.  All rights reserved.

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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. specified in the
   IANA registry.  Implementations which do not recognize those new reserved 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 non-transitive well-
   known community: 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 their 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
   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 two an IANA registries registry in
   order to allow the registration of transitive and 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 as a community could be chosen advertisement.  Indeed, as
   transitive or per [RFC4360] non-transitive across ASes.
   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 encoded in the Global Administrator sub-field has the reserved value 0. 0.65535 (0x0000FFFF).

   When the AS number number, encoded in the Global Administrator sub-field sub-field,
   has the reserved value 0, 0.65535, the communities have global
   significance.  The lists of those communities are maintained by the
   IANA in the
   registries "Assigned transitive extended communities" for the
   "transitive generic four-octet AS specific" extended community type
   and registry "Assigned non-transitive extended communities" for the "non-
   transitive generic four-octet AS specific" extended community type. communities".

   Note that this use of the reserved AS number 0 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.  IANA Considerations

   The IANA is requested  Assigned transitive extended communities

   As per [RFC4893], 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 create and maintain zero.  This applies to the reserved
   2-octet Autonous System number 65535 which could use either a registry entitled
   "Assigned transitive
   standard community or the 4-octet AS specific generic extended communities" with
   community.  As noted in
   [I-D.ietf-idr-as4octet-extcomm-generic-subtype], this is undesirable
   as they would be treated as different communities, even if they had
   the following
   registration procedure:

    Registry Name: Assigned transitive same values.

   Therefore, this document does not define a non-transitive extended
   community registry and transitive communities

       Range              Registration Procedures
       -----------        -------------------------
       0x0000-8000        First Come First Served
       0x8001-FFFF        Standards Action/Early are still to be
   assigned as per [RFC1997].

4.  IANA Allocation 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.  (Note that both extended communities will still be
   different as they will differ from their T bit).  The  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 non- a transitive assigned
   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 and Jeffrey Haas for their
   contribution to this document.

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-05 (work
              in progress), July 2011. March 2012.

   [RFC1997]  Chandrasekeran, R., Traina, P., and T. Li, "BGP
              Communities Attribute", RFC 1997, August 1996.

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

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

   [RFC4893]  Vohra, Q. and E. Chen, "BGP Support for Four-octet AS
              Number Space", RFC 4893, May 2007.

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

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.

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

Authors' Addresses

   Bruno Decraene
   France Telecom - Orange
   38 rue du General Leclerc
   Issy Moulineaux cedex 9  92794


   Pierre Francois
   IMDEA Networks
   Avda. del Mar Mediterraneo, 22
   Leganese  28918