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Configuring BGP
BGP Configuration Examples
IPC-343
Cisco IOS IP Configuration Guide
The next example shows how the route map named set-community is applied to the outbound updates to
neighbor 171.69.232.50 and the local-as community attribute is used to filter the routes. The routes that
pass access list 1 have the special community attribute value local-as. The remaining routes are
advertised normally. This special community value automatically prevents the advertisement of those
routes by the BGP speakers outside autonomous system 200.
router bgp 65000
network 1.0.0.0 route-map set-community
bgp confederation identifier 200
bgp confederation peers 65001
neighbor 171.69.232.50 remote-as 100
neighbor 171.69.233.2 remote-as 65001
!
route-map set-community permit 10
match ip address 1
set community local-as
!
The following example shows how to use the local-as community attribute to filter the routes.
Confederation 100 contains three autonomous systems: 100, 200, and 300. For network 1.0.0.0, the route
map named set-local-as specifies that the advertised routes have the community attribute local-as. These
routes are not advertised to any eBGP peer outside the local autonomous system. For network 2.0.0.0,
the route map named set-no-export specifies that the routes advertised have the community attribute
no-export.
A route between router 6500 and router 65001 does not cross the boundary between autonomous systems
within the confederation. A route between subautonomous systems for which router 65000 is the
controlling router does not cross the boundary between the confederation and an external autonomous
system, and also does not cross the boundary between subautonomous systems within the local
autonomous system. A route to from router 65000 to router 65001 would not be acceptable for network
1.0.0.0 because it crosses the boundary between subautonomous systems within the confederation.
router bgp 65001
bgp confederation identifier 200
bgp confederation peer 65000
network 2.0.0.0 route-map set-community
neighbor 171.69.233.1 remote-as 65000
route-map set-community permit 10
set community no-export
BGP Conditional Advertisement Configuration Examples
This section provides a configuration example of the BGP Conditional Advertisement feature. In the
following example, the ip-address argument refers to the IP address of the neighbor, and the map1-name
and map2-name arguments, refer to the names of the route maps:
neighbor{ip-address} advertise-map {map1-name} non-exist-map {map2-name}
no neighbor{ip-address} advertise-map {map1-name} non-exist-map {map2-name}
The route map associated with the non-exist-map specifies the prefix that the BGP speaker tracks. The
route map associated with the advertise map specifies the prefix that is advertised when the prefix in the
non-exist-map no longer exists. The prefix tracked by the BGP speaker must be present in the BGP table
for the conditional advertisement not to take place. In the following example, the router advertises
172.16.0.0/16 to its neighbor only if 192.168.7.0/24 is not present in the IP routing table.