How to advertise routes from same BGP AS, through ISP

[David Rollins]

I have a customer, who uses the same BGP AS for all of their sites(AS 65002). These sites only peer with the ISP MPLS(AS 65001). How does the ISP AS 65001, advertise routes learned from all the peers, to each other? 

I'm trying to replicate it in my lab, but am unable.

Here is a sample configuration, as configured in the wild(With the exception of the ISP, that's the part I'm trying to figure out)

Remote 1
router bgp 65002
bgp log-neighbor-changes
redistribute connected
neighbor 172.16.1.6 remote-as 65001




Remote 2
router bgp 65002
bgp log-neighbor-changes
redistribute connected
neighbor 172.16.1.10 remote-as 65001




HUB 1
router bgp 65002
bgp log-neighbor-changes
redistribute connected
redistribute static
neighbor 172.16.1.2 remote-as 65001




ISP
router bgp 65001
bgp router-id interface Loopback0
bgp log-neighbor-changes
redistribute connected
neighbor 172.16.1.1 remote-as 65002
neighbor 172.16.1.5 remote-as 65002
neighbor 172.16.1.9 remote-as 65002
default-information originate

Disregard the link between R1 and R2.

[Harold Ritter · Accepted solution]

Hi @David Rollins ,

On the SP side, this is normally done using the

as-override

configuration, which will replace the customer ASN with the SP ASN.

ISP:

router bgp 65001

neighbor 172.16.1.1 remote-as 65002

neighbor 172.16.1.1 as-override

neighbor 172.16.1.5 remote-as 65002

neighbor 172.16.1.5 as-override

neighbor 172.16.1.9 remote-as 65002

neighbor 172.16.1.9 as-override

This is normally done in a VRF context as the SP offers a MPLS L3VPN service.

Regards,

[David Rollins]

For those of you viewing and wondering, it was the following command on the ISP router.

neighbor x.x.x.x as-override