Assigned BGP extended
communitiesFrance Telecom - Orange38 rue du General LeclercIssy Moulineaux cedex 992794Francebruno.decraene@orange.comIMDEA NetworksAvda. del Mar Mediterraneo, 22Leganese28918ESpierre.francois@imdea.orgThis document defines two IANA registries in order to assign
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 control of inter-AS community advertisement as a
community could be chosen as transitive or non-transitive across
ASes.For that purpose, this document defines the use of the reserved AS
number 0 for the transitive and non-transitive generic four-octet AS
specific extended community types.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. 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. Implementations which do not recognize those new reserved
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, 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, 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 is no IANA registry
to allocate one well-known extended community. 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.To address this limitation, this document
defines two IANA registries 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 but provides a control on inter-AS community
advertisement as a community could be chosen as transitive or
non-transitive across ASes.
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 and
defines the use of the Local Administrator sub-field when the AS number
encoded in the Global Administrator sub-field has the reserved value
0.When the AS number encoded in the Global Administrator sub-field has
the reserved value 0, 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 "Assigned
non-transitive extended communities" for the "non-transitive generic
four-octet AS specific" extended community type.Note that this use of the reserved AS number 0 in the AS field of the
communities is similar to the one defined by for the BGP Well-Known communities.The IANA is requested to create and maintain a registry entitled
"Assigned transitive extended communities" with the following
registration procedure:The IANA is requested to create and maintain
a registry entitled "Assigned non-transitive extended communities" with
the following registration procedure: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 IANA
SHOULD try to accommodate such request to get both a transitive and
non-transitive assigned community with the same value for both.This document defines IANA actions. In itself, it has no impact on
the security of the BGP protocol.