BGP ROUTING FOR TWO DIFFERENT PEERS

mohh_network · ‎01-08-2015

Scenario:

We have an existing BGP connection in our infrastructure connected to a peer (Peer A). We want to create a new peer (Peer B) on their side but we are thinking of using the same BGP and AS number for Peer B. We will only change the neighbor IP for Peer B. They are logically connected to our router using sub-interface. Both peers are set as /30 IP. Is this is possible? Will there be an issue if this will be the setup?

Configuration on our end:

router bgp 65101
bgp log-neighbor-changes
network 10.1.1.1 mask 255.255.255.255 <- we are advertising this IP of one of our site which connectivity with our peers
neighbor 172.35.35.3 remote-as 1234
neighbor 192.35.35.3 remote-as 1234

Configuration of our IP connecting to Peer A and Peer B:

Peer A connection: 172.35.35.2 <- this is our IP connected to Peer A
Peer B connection: 172.35.35.2 <- this is our IP connected to Peer B

Boyan Sotirov · ‎01-08-2015

If I understood correctly...your router will be peering with another BGP peer from the same AS as Peer A.

If this is the case, than generally the configuration is not special anyway. You've already listed it.

Fee things to bear in mind though:

1. BGP is an attribute-driven routing protocol, so once the second peering session is established your router might choose a different outbound route for some destinations, based on the BGP attributes. You can change that, if you play around with the metrics.

2. You advertise you prefix to AS 1234 to both peers in exactly the same way. So how they will select a route to your AS, again depend on the BGP attributes, and whether they're not changing some of them locally.

Hope this helps,

Boyan

paul driver · ‎01-08-2015

Hello

Are A and B separate routers and do they have have locally connected lans?
And do these lans need to be accessible by either bgp peering from AS65101 - if so may I suggest creating a IBGP session between A and B also.

Lastly am I correct in assuming that A and B are going to peer to AS65101 via a logical address ( lookback interface) As this would be ideal for resiliency purposes in case either physical interface goes down?

res

Paul

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Kind Regards
Paul