Alternative to Allowas-in xx

[IrmanGhaffar]

In a lab I was comparing Cisco's BGP implementation to some other vendors.

If We have a customer with 2 locations (New York and Arizona), connected via a L3 IPVPN (MPLS service provider) we would be running BGP from the customer AS (at each location) to the Service provider's AS.

You see the problem, both locations use the same BGP AS number so routes will be rejected by each customer router because they have come from the same AS, BGP thinks its a loop. Ofcourse we can fix this by doing a "neighbour x.x.x.x allowas-in 2" as an example.

Can this actually be done on the service providers equipment instead so the customer wont have to put the command in? I know some vendors have an alternative solution which allows for the customer not needing the allowas-in command but have not managed to find anything for cisco.

I have attached a basic topology, ofcourse the CE AS is common and runs BGP to the PE.

Thanks

[Georg Pauwen]

Hello,

is this a theoretical, lab scenario ? In real life, an ISP would not give out the same AS to two different customers...

The ISP could configure local-as, which is a feature that 'tricks' the neighbor in believing it is peering with a different AS

neighbor x.x.x.x local-as local-AS-number

Unless an ISP has a need for that, which usually is only the case when two ISPs merge, I doubt they will do that.

[Harold Ritter · Accepted solution]

You can use the "neighbor <neighbor address> as-override" command on the PE in order to achieve what you want.

https://community.cisco.com/t5/network-architecture-documents/understanding-bgp-as-override-feature/ta-p/3111967

Regards,

[IrmanGhaffar]

Perfect,

  Thanks that worked!!

Rated!