Network Working Group B. Decraene
Intended status: Standards Track P. Francois
Expires: June 5, 2014 IMDEA Networks
December 2, 2013
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.
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 RFC 2119 [RFC2119].
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[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-
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
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
would both waste the resources and disable the ability to define