MULTIPLE AS NUMBERS FOR BGP IN ROUTER RUNNING VRFs

[davejumby]

Hi all

I have two routers running BGP with the below configs. I am getting a new router which is to run VRFs and replace the 2 routers. I'm trying to configure per VFR BGP but it appears the router can only have one AS number. Can anyone help with how I can achieve this BGP configuration to work just the way it was working when I had 2 separate routers. The last set of configs is my trial at this but not working so far

ROUTER A

router bgp 65001
no synchronization
bgp router-id 10.2.32.2
bgp log-neighbor-changes
network 10.2.32.1 mask 255.255.255.255
network 10.2.32.2 mask 255.255.255.255
network 172.16.0.0 mask 255.255.255.0
network 172.16.1.0 mask 255.255.255.0
redistribute eigrp 10 metric 25
neighbor 10.2.0.2 remote-as 12455
neighbor 10.2.0.6 remote-as 12455
neighbor 172.16.5.21 remote-as 64840
no auto-summary

ROUTER B

router bgp 64840
bgp log-neighbor-changes
neighbor 172.30.120.181 remote-as 37061
!
address-family ipv4
network 172.16.5.0 mask 255.255.255.0
network 172.24.203.124 mask 255.255.255.252
network 192.168.91.73 mask 255.255.255.255
redistribute static
redistribute eigrp 10
neighbor 172.30.120.181 activate
neighbor 172.30.120.181 weight 500
neighbor 172.30.120.181 soft-reconfiguration inbound

NEW ROUTER CONFIG

router bgp 65001
no synchronization
bgp router-id 10.2.32.2
bgp log-neighbor-changes
!
address-family ipv4 VRF-A
network 10.2.32.1 mask 255.255.255.255
network 10.2.32.2 mask 255.255.255.255
network 172.16.0.0 mask 255.255.255.0
network 172.16.1.0 mask 255.255.255.0
redistribute eigrp 10 metric 25
neighbor 10.2.0.2 remote-as 12455
neighbor 10.2.0.6 remote-as 12455
neighbor 172.16.5.21 remote-as 64840// I'm facing a problem at such configs because of AS numbers
no auto-summary

address-family ipv4 VRF-B
neighbor 172.30.120.181 remote-as 37061
network 172.16.5.0 mask 255.255.255.0
network 172.24.203.124 mask 255.255.255.252
network 192.168.91.73 mask 255.255.255.255
redistribute static
redistribute eigrp 10
neighbor 172.30.120.181 activate
neighbor 172.30.120.181 weight 500
neighbor 172.30.120.181 soft-reconfiguration inbound
exit-address-family

[davejumby]

Just to make my concern/question a bit clear there is a command where I need to enter a remote AS number for a neighbor(its in bold in the initial post) but in this case the neighbor is in the same router as a VRF instance so essentially the remote AS number will be the same as the AS number of the BGP configured on the router. This is what I need to work around

[paul driver · Accepted solution]

Hello

Only one bgp ASN is allowed on the one router however you can configure bgp so it peers with a different ASN other than the one specified in the routing process.

Example:
router bgp 65001
address-family ipv4 VRF-A
neighbor 172.16.5.21 remote-as 64840

address-family ipv4 VRF-B
neighbor 172.30.120.181 remote-as 37061
neighbor 172.30.120.181 local-as 64840 no-prepend  <-- this will allow the neighboring bgp router to peer with ASN 64840

[davejumby]

Hi Paul
I'll try it out and give feedback

[dbeattie]

Yes, this is exactly the way to do it. I know of this as AS masquerading.  The AS that you set in the router command needs to be a completely dummy AS, that is never used for peering. Each VRF that is used for peering needs to have the local-AS command in line with Paul's post. It also needs the RID to be set in each VRF so that you don't have RID clashes either.

Hope this helps

Dave

[davejumby]

thanks so much , it worked