Extended Community Lists

The router supports the BGP extended community attribute defined in
Internet draft BGP Extended Communities Attribute— draft-ietf-idr-bgp-ext-communities-07.txt (February 2004 expiration). This attribute enables the definition of a type of IP extended community and extended community list unrelated to the community list that uses regular expressions.

Note: IETF drafts are valid for only six months from the date of issuance. They must be considered as works in progress. For the latest drafts, please see the IETF Web site at http://www.ietf.org.

BGP devices can use the extended community attribute to control routes much like they use the community attribute to determine routes that they accept, reject, or redistribute. A BGP device can append the extended community attribute to a route that does not have the attribute before it advertises the route. For routes that do have the attribute, BGP can modify the attribute.

ip extcommunity-list

• Use to create an extended community list for BGP and control access to it.
• A route can belong to any number of communities, so an extended community list can have many entries comprising many communities.
• You can specify one or more community values when you create an extended community list. A clause in a route map that includes a list that has more than one value matches only a route that has all of the values; that is, the multiple values are logical ANDed.
• Use the rt keyword to specify a route target community, which consists of one or more routers that can receive a set of routes advertised by BGP that carry the extended community attribute.
• Use the soo keyword to specify a site-of-origin community, which consists of one or more routers that inject into BGP a set of routes that carry the extended community attribute.
• Example

  host1(config)#ip extcommunity-list boston1 permit rt 100:2 rt 100:3 rt 100:4

  host1(config)#route-map marengo permit 10

  host1(config-route-map)#match extcommunity boston1

  A route matches this community list only if it belongs to at least all three communities in extended community list boston1: communities 100:2, 100:3, and 100:4.

• Use the no version to remove a single extended community list entry if you specify the permit or deny keyword and a path expression. Otherwise, the router removes the entire community list.
• See ip extcommunity-list.

match extcommunity

• Use to match an extended community list in a route map.
• You can specify one or more extended community list names in a match clause. If you specify more than one extended community list, the lists are logically ORed.
• Example

  host1(config-route-map)#match extcommunity topeka10

• Use the no version to remove the match clause from a route map or a specified value from the match clause.
• See match extcommunity.

set extcommunity

• Use to set the extended community attributes in a route map for BGP updates.
• Use the rt keyword to specify a route target community, which consists of one or more routers that can receive a set of routes advertised by BGP that carry the extended community attribute.
• Use the soo keyword to specify a site-of-origin community, which consists of one or more routers that inject into BGP a set of routes that carry the extended community attribute.
• You can specify both a route target community and a site-of-origin community at the same time in a set clause without them overwriting each other.
• Example

  host1(config)#route-map 1

  host1(config-route-map)#set extcommunity rt 10.10.10.2:325

• Use the no version to remove the set clause from the route map.
• See set extcommunity.

show ip extcommunity-list

• Use to display information about a specific extended community list or all extended community lists.
• Example

  host1#show ip extcommunity-list
  IP Extended Community List dresden1:
      permit soo 10.10.10.10:15
  IP Extended Community List bonn:
      deny rt 12:12 

• See show ip extcommunity-list.

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