BGP -Advertising a different AS to new connections

[ranga2002]

Hi Guys, If anyone can explain this, in brief, would be really appreciated.

Question :

Company A is running BGP to connect to external peers they were recently acquired and new peers(Company B) will be connecting using the acquiring company(Company A) AS number. What BGP feature would allow for Company A to maintain their current BGP configuration, while advertising a different AS number to new connections?

[Giuseppe Larosa · Accepted solution]

Hello @ranga2002 ,

the BGP command

neighbor x.x.x.x local-as yyy

is the command that can be used in this kind of migration scenarios.

The command has several options and parameters that change slightly its behaviour.

neighbor {ip-address | ipv6-address | peer-group-name} local-as [autonomous-system-number [no-prepend [replace-as [dual-as]]]]

see

https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_bgp/command/irg-cr-book/bgp-m1.html#wp2002403135

the no-prepend should hide the true AS number of the router.

Hope to help

Giuseppe

[ranga2002]

Thank you so much Giuseppe !