Description

This article provides information on how to export the BGP community attribute to routes that are being advertised to a BGP neighbor.

Symptoms

How to add the BGP community attribute to the routes that are being advertised to a BGP neighbor.

Solution


Two eBGP neighbors - 1.1.1.1 and 1.1.1.2 are present. The community attribute has to be added to the routes that are being exported from 1.1.1.1 to 1.1.1.2 .

Before making the changes, the routes that are being received on 1.1.1.2 from 1.1.1.1 are as follows: 

[edit]
root@3400-2# run show route receive-protocol bgp 1.1.1.1 detail 

inet.0: 6 destinations, 6 routes (6 active, 0 holddown, 0 hidden)
* 3.3.3.3/32 (1 entry, 1 announced)
     Accepted
     Nexthop: 1.1.1.1
     AS path: 2 I

* 4.4.4.4/32 (1 entry, 1 announced)
     Accepted
     Nexthop: 1.1.1.1
     AS path: 2 I
Now, to add the community attribute to the above route, the following policy has to be created: 
[edit]
root@240-2# show policy-options 
policy-statement p1 {
    term t1 {
        from {
            protocol static;
            route-filter 3.3.3.3/32 exact;
        }
        then {
            community add test-1;
            accept;
        }
    }
    term t2 {
        from {
            protocol static;
            route-filter 4.4.4.4/32 exact;
        }
        then {
            community add test-2;
            accept;
        }
    }
    term t3 {
        then reject;
    }                                   
}
community test-1 members 1:2;
community test-2 members 1:3;
Apply the above policy as an export policy in BGP: 
[edit]
root@240-2# show protocols bgp 
group g1 {
    export p1;
    peer-as 1;
    local-as 2;
    neighbor 1.1.1.2;
}
Verification :

After committing the above changes, you will see the community attribute on 1.1.1.2 as follows: 
root@3400-2# run show route receive-protocol bgp 1.1.1.1 detail 

inet.0: 5 destinations, 5 routes (5 active, 0 holddown, 0 hidden)
* 3.3.3.3/32 (1 entry, 1 announced)
     Accepted
     Nexthop: 1.1.1.1
     AS path: 2 I
     Communities: 1:2

* 4.4.4.4/32 (1 entry, 1 announced)
     Accepted
     Nexthop: 1.1.1.1
     AS path: 2 I
     Communities: 1:3