13.5.2 Community configuration

(1) List of configuration commands

The following table lists the commands used to configure communities.

Table 13-16: List of configuration commands

Command name	Description
neighbor send-community	Specifies that the COMMUNITIES attribute should not be removed from route advertisements to peers.
distribute-list in (BGP4) #	Specifies the route filter to be used as BGP4 learned route filter conditions.
distribute-list out (BGP4) #	Specifies the route filter to be used as BGP4 advertised route filter conditions.
neighbor in (BGP4) #	Specifies in the route-map parameter the route filter to be used as learned route filter conditions for a specific BGP4 peer only.
neighbor out (BGP4) #	Specifies in the route-map parameter the route filter to be used as advertised route filter conditions for a specific BGP4 peer only.
redistribute (BGP4) #	Specifies the protocol of learned routes advertised by BGP4.

(2) Configuring Communities

Points to note

The example below shows how to add the COMMUNITIES attribute to advertised BGP4 routes by setting the neighbor send-community configuration command for the concerned peers.

Command examples

1. (config)# router bgp 65531

   (config-router)# bgp router-id 192.168.1.100

   (config-router)# neighbor 192.168.2.2 remote-as 65531

   (config-router)# neighbor 172.16.2.2 remote-as 65532

   (config-router)# neighbor 10.2.2.2 remote-as 65533

   Configure the BGP4 peers.

2. (config-router)# neighbor 172.16.2.2 send-community

   (config-router)# neighbor 10.2.2.2 send-community

   (config-router)# exit

   Specifies that the COMMUNITIES attribute is to be added to BGP4 routes advertised to the peers.

3. (config)# ip community-list 10 permit 1000:1002

   (config)# ip community-list 20 permit 1000:1003

   (config)# route-map SET_LOCPREF permit 10

   (config-route-map)# match community 10

   (config-route-map)# set local-preference 120

   (config-route-map)# exit

   (config)# route-map SET_LOCPREF permit 20

   (config-route-map)# match community 20

   (config-route-map)# set local-preference 80

   (config-route-map)# exit

   (config)# route-map SET_LOCPREF permit 30

   (config-route-map)# exit

   Sets 120 as the LOCAL_PREF attribute value of routes that have the community value 1000:1002 in their COMMUNITIES attribute, and 80 as the LOCAL_PREF attribute value of routes that have the community value 1000:1003 in their COMMUNITIES attribute.

4. (config)# ip prefix-list MY_NET seq 10 permit 192.168.0.0/16 ge 16 le 30

   (config)# route-map SET_COM permit 10

   (config-route-map)# match ip address prefix-list MY_NET

   (config-route-map)# set community 1000:1001

   (config-route-map)# exit

   Configures a COMMUNITIES in which the route whose destination network is 192.168.0.0/16 (mask length 16 to 30) has the community-value of 1000:1001.

5. (config)# router bgp 65531

   (config-router)# distribute-list route-map SET_LOCPREF in

   (config-router)# distribute-list route-map SET_COM out

   (config-router)# exit

   Sets a learned route filter and advertised route filter for all peers.

(3) Reflecting filter settings in operation

Points to note

The example below shows how to apply route filters as learned route and advertised route filter conditions by using the clear ip bgp operation command.

Command examples

1. # clear ip bgp * both

   Applies the community-based route filters to the network operation.