why we would use as-override in bgp

A reason to use as-override in bgp. Loop prevention in BGP is done by verifying the AS number in the AS Path. If the receiving router sees its own AS number in the AS Path of the received BGP packet, the packet is dropped. The receiving Router assumes that the packet was originated from its own AS and has reached the same place from where it originated initially.


In the above scenario lets say R4 in AS100 is sending routes and into AS6573 through R1, R3 will see the routes but in order for the routes to be accepted at R5 you will need to enable as-override in bgp configuration on router R3 towards router R5, below is how one would configure this:

Router R3 Cisco Example

Router R3 Juniper Example