Riverstone Networks WICT1-12

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 Figure16-6 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.

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.)