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16-28 Riverstone Networks RS Switch Router User Guide Release 8.0
BGP Configuration Examples BGP Configuration Guide
Any communities specified with the
optional-attributes-list
option are sent in addition to any received with
the route or associated with a BGP export destination.
The community attribute may be a single community or a set of communities. A maximum of 10 communities may be
specified.
The community attribute can take any of the following forms:
•
Specific community
The specific community consists of the combination of the AS-value and community ID.
•
Well-known-community no-export
Well-known-community no-export is a special community which indicates that the routes associated with this
attribute must not be advertised outside a BGP confederation boundary.
For example, router R10 in Figure 16-6 has the following configuration:
•
Well-known-community no-advertise
Well-known-community no-advertise is a special community indicating that the routes associated with this
attribute must not be advertised to other bgp peers. A packet can be modified to contain this attribute and passed
to its neighbor. However, if a packet is received with this attribute, it cannot be transmitted to another BGP peer.
•
Well-known-community no-export-subconfed
Well-known-community no-export-subconfed is a special community indicating the routes associated with this
attribute must not be advertised to external BGP peers. (This includes peers in other members’ autonomous
systems inside a BGP confederation.)
A packet can be modified to contain this attribute and passed to its neighbor. However, if a packet is received with
this attribute, the routes (prefix-attribute pair) cannot be advertised to an external BGP peer.
•
Well-known-community none
This is not actually a community, but rather a keyword that specifies that a received BGP update is only to be
matched if no communities are present. It has no effect when originating communities.
Notes on Using Communities
When originating BGP communities, the set of communities that is actually sent is the union of the communities
received with the route (if any), those specified in group policy (if any), and those specified in export policy (if any).
When receiving BGP communities, the update is only matched if all communities specified in the
optional-attributes-list
option of the
ip-router policy create
command are present in the BGP update.
(If additional communities are also present in the update, it will still be matched.)
ip-router policy create optional-attributes-list noexport
well-known-community no-export
ip-router policy create bgp-export-destination 900to901dest
autonomous-system 64901 optional-attributes-list noexport
ip-router policy export destination 900to901dest source 900to901src
network all
ip-router policy export destination 900to901dest source 900to901dir
network all