Extended Community Attribute

The Extended Community Attribute provides a mechanism for labeling information carried in BGP. It provides two important enhancements over the existing BGP Community Attribute:

• An extended range of use, ensuring that communities can be assigned to many different non-overlapping uses.
• The ability to specify a community type, providing structure for the community space. The S- and 7100-Series supports extended community types:
  • IP, AS, and AS 4-octet route target
  • IP, AS, and AS 4-octet site-of-origin
  • OSPF domain ID, router ID, and route type

Use the set clause for the appropriate extended community type to label a route with the specified extended community. The extended community is labeled with a set value appropriate to the extended community. For example: The IPv4 route-target extended community requires a set value consisting of a valid IPv4 address followed by a colon (:) followed by a number in the range 0 - 65535. The firmware converts this set value into a hex identifier. The hex identifier for each set extended community is displayed in the show ip bgp output. When configuring an extended community match clause, use the show ip bgp command to determine the appropriate extended community identifier.

This example shows how to remove all matching extended communities from the AS route target 1001:10000 when all match clauses match for route-map bgprm1:

System(su)->configure
System(su-config)->route-map bgp bgprm1 permit
System(su-config-route-map-bgp)->match prefix-list permit200
System(su-config-route-map-bgp)->set extended-community as-route-target 1001:10000 remove-specific
System(su-config-route-map-bgp)->

This example shows how to match a packet against the extended community AS route target attribute 000203E9000186A0:

System(su)->show ip bgp 1.0.0.0/8 detail
Route status codes: > - active
    Network                  Next Hop              Rib MED Local-Pref Origin AS Path
>   1.0.0.0/8                192.168.121.112       U   0      100    IGP     121 2013
Community attributes in route:
121:100
Extended Community attributes in route:
Route Target: 1001:10000 (0x000203E9000186A0)
System(su)->configure
System(su-config)->route-map bgp bgprm1 permit
System(su-config-route-map-bgp)->match extended-community 000203E9000186A0
System(su-config-route-map-bgp)->