User Manual

Enterasys X-Pedition User Reference Manual 221
BGP Configuration Examples
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.
Since the X-Pedition’s implementation does not support Confederations, this boundary is an AS
boundary.
For example, router X-Pedition10 in Figure 16 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