The well known BGP community no export tells BGP neighbors to advertise a prefix only to iBGP neighbors. If you are not sure what BGP communities are and how they work then I advise you to read my introduction to BGP communities first before you continue. Having said that, let’s take a look at a configuration example. Here’s the topology we will use:

Above we see R1 with network 1.1.1.1/32 on a loopback interface. It will advertise this prefix with the no export community set. As a result, R2 will install it in its BGP table and advertises it to R4 (iBGP). It will not be advertised to R3 since this is a eBGP session.

Configuration

Basic BGP Configuration

Here’s the BGP configuration in case you want to try this example yourself:

R1#show running-config | section bgp
router bgp 1
 no synchronization
 bgp log-neighbor-changes
 network 1.1.1.1 mask 255.255.255.255
 neighbor 192.168.12.2 remote-as 24
 no auto-summary

R2#show running-config | section bgp
router bgp 24
 no synchronization
 bgp log-neighbor-changes
 neighbor 192.168.12.1 remote-as 1
 neighbor 192.168.23.3 remote-as 3
 neighbor 192.168.24.4 remote-as 24
 neighbor 192.168.24.4 next-hop-self
 no auto-summary

R3#show running-config | section bgp
router bgp 3
 no synchronization
 bgp log-neighbor-changes
 neighbor 192.168.23.2 remote-as 24
 no auto-summary

R4#show running-config | section bgp
router bgp 24
 no synchronization
 bgp log-neighbor-changes
 neighbor 192.168.24.2 remote-as 24
 no auto-summary

By default BGP does not send any communities. All routers will learn about 1.1.1.1/32:

R2#show ip bgp | include 1.1.1.1
*> 1.1.1.1/32       192.168.12.1             0             0 1 i

R3#show ip bgp | include 1.1.1.1
*> 1.1.1.1/32       192.168.23.2                           0 24 1 i

R4#show ip bgp | include 1.1.1.1
* i1.1.1.1/32       192.168.12.1             0    100      0 1 i

BGP Community No-Export Configuration

Let’s configure our BGP community. First we have to tell R1 to send communities:

R1(config)#router bgp 1
R1(config-router)#neighbor 192.168.12.2 send-community

Now we can create a route-map that sets the BGP community to no-export and we attach it to our neighbor R2: