Cisco Cisco IOS Software Release 12.2(25)S

network with multiple equal cost exits points, and the specific exit path will be preferred by the BGP 
best path selection process. See the scenario described in the 

 section. 

Aggregate routes and multipaths are supported by the BGP Cost Community feature. The cost 
community attribute can be applied to either type of route. The cost community attribute is passed to the 
aggregate or multipath route from component routes that carry the cost community attribute. Only 
unique IDs are passed, and only the highest cost of any individual component route will be applied to 
the aggregate on a per-ID basis. If multiple component routes contain the same ID, the highest 
configured cost is applied to the route. For example, the following two component routes are configured 
with the cost community attribute via an inbound route map:

10.0.0.1 (POI=IGP, ID=1, Cost=100)

192.168.0.1 (POI=IGP, ID=1, Cost=200)

If these component routes are aggregated or configured as a multipath, the cost value 200 (POI=IGP, 
ID=1, Cost=200) will be advertised because it is the highest cost. 

If one or more component routes does not carry the cost community attribute or if the component routes 
are configured with different IDs, then the default value (2147483647) will be advertised for the 
aggregate or multipath route. For example, the following three component routes are configured with the 
cost community attribute via an inbound route map. However, the component routes are configured with 
two different IDs. 

10.0.0.1 (POI=IGP, ID=1, Cost=100)

172.16.0.1 (POI=IGP, ID=2, Cost=100)

192.168.0.1 (POI=IGP, ID=1, Cost=200)

The single advertised path will include the aggregated cost communities as follows:

{POI=IGP, ID=1, Cost=2147483647} {POI=IGP, ID=2, Cost=2147483647}