BGP local-as, no-prepend, replace-as, dual-as

• local-as - this feature allows the router to appear in different AS in addition to the Global AS. The peer has to configure remote-as -> the local-as number. Working for eBGP only. With iBGP the neighborship is flapping:

With iBGP : 

• no-prepend - When configured this feature on the transit router (R1) , will not prepend the local-as number in the updates from R2 and sent to R3

Before:

After:

• replace-as - When configured to a neighbor (R2) , R1 will prepend only the local-as in the updates

Before:

After:

• dual-as - is a feature that allows a peering router to establish neighborship with either global-as, either local-as

R2(config-router)#

*Mar  1 01:08:59.171: %BGP-5-ADJCHANGE: neighbor 192.168.12.1 Up

R2(config-router)#neighbor 192.168.12.1 remote-as 3

R2(config-router)#

*Mar  1 01:09:12.383: %BGP-5-ADJCHANGE: neighbor 192.168.12.1 Down Remote AS changed

R2(config-router)#

*Mar  1 01:09:14.519: %BGP-5-ADJCHANGE: neighbor 192.168.12.1 Up