Cisco Cisco IOS Software Release 12.2(14)S

The following example configures the router to not prepend autonomous system number 300 to routes 
that are received from external peers: 

router bgp 100

network 10.1.1.0

neighbor 10.1.1.1 remote-as 100

neighbor 10.1.1.1 local-as 300 no-prepend

end 

You can verify that this feature is configured correctly with the show ip bgp neighbors command. Go 
to the 

 section for instructions 

and example output. 

To verify that the local autonomous system number is not prepended to received external routes, use the 
show ip bgp neighbors command. The output of this command will display the local autonomous 
system number and then “no-prepend” for received external routes when this feature is configured.

The following example shows that autonomous system number 300 will not be prepended to the 10.1.1.1 
peer:

Router# show ip bgp neighbors 

BGP neighbor is 10.1.1.1,  remote AS 100,  local AS 300 no-prepend, external link

  BGP version 4, remote router ID 10.1.1.1

  BGP state = Established, up for 00:00:49

  Last read 00:00:49, hold time is 180, keepalive interval is 60 seconds

  Neighbor capabilities:

    Route refresh: advertised and received(new)

    Address family IPv4 Unicast: advertised and received

    IPv4 MPLS Label capability:

  Received 10 messages, 1 notifications, 0 in queue

 ip-address remote-as as-number 

Router(config-router-af)# neighbor 10.1.1.1 

remote-as 100

Establishes peering with the specified neighbor and 
configures the neighbor as internal to the local autonomous 
system.

 ip-address local-as 

as-number[no-prepend]

Router(config-router-af)# neighbor 10.1.1.1 

local-as 300 no-prepend

Allows the customization of the autonomous system 
number for eBGP peer groupings. 

Using the no-prepend keyword configures the router to 
not prepend the local autonomous system number to 
routes that are received from external peers.

 

Router(config-router)# end

Exits address-family configuration mode, and enters 
Privileged EXEC mode.