Cisco 3845 Software Guide - Page 620

Configuring BGP Chapter 29 Configuring IP Unicast Routing community. The community is identified by the COMMUNITIES attribute, an optional, transitive, global attribute in the numerical range from 1 to 4294967200. These are some predefined, well-known communities: • internet-Advertise this route to the Internet community. All routers belong to it. • no-export-Do not advertise this route to EBGP peers. • no-advertise-Do not advertise this route to any peer (internal or external). • local-as-Do not advertise this route to peers outside the local autonomous system. Based on the community, you can control which routing information to accept, prefer, or distribute to other neighbors. A BGP speaker can set, append, or modify the community of a route when learning, advertising, or redistributing routes. When routes are aggregated, the resulting aggregate has a COMMUNITIES attribute that contains all communities from all the initial routes. You can use community lists to create groups of communities to use in a match clause of a route map. As with an access list, a series of community lists can be created. Statements are checked until a match is found. As soon as one statement is satisfied, the test is concluded. To set the COMMUNITIES attribute and match clauses based on communities, see the match community-list and set community route-map configuration commands in the "Using Route Maps to Redistribute Routing Information" section on page 29-97. By default, no COMMUNITIES attribute is sent to a neighbor. You can specify that the COMMUNITIES attribute be sent to the neighbor at an IP address by using the neighbor send-community router configuration command. Beginning in privileged EXEC mode, follow these steps to create and to apply a community list: Step 1 Step 2 Step 3 Step 4 Step 5 Step 6 Step 7 Step 8 Command Purpose configure terminal Enter global configuration mode. ip community-list community-list-number Create a community list, and assign it a number. {permit | deny} community-number • The community-list-number is an integer from 1 to 99 that identifies one or more permit or deny groups of communities. • The community-number is the number configured by a set community route-map configuration command. router bgp autonomous-system Enter BGP router configuration mode. neighbor {ip-address | peer-group name} Specify that the COMMUNITIES attribute be sent to the neighbor at send-community this IP address. set comm-list list-num delete (Optional) Remove communities from the community attribute of an inbound or outbound update that match a standard or extended community list specified by a route map. exit Return to global configuration mode. ip bgp-community new-format (Optional) Display and parse BGP communities in the format AA:NN. A BGP community is displayed in a two-part format 2 bytes long. The Cisco default community format is in the format NNAA. In the most recent RFC for BGP, a community takes the form AA:NN, where the first part is the AS number and the second part is a 2-byte number. end Return to privileged EXEC mode. 29-54 Cisco ME 3800X and 3600X Switch Software Configuration Guide OL-23400-01