Loopback in BGP confederation

[gzdillon73]

Normally, the Loopback is used for iBGP peers, not for eBGP peers, that connect directly. But with BGP confederation, how we use the update-source interface?

[Harold Ritter]

It depends. Some SPs are using a different IGPs in each sub-AS part of the confederation. This would prevent peering using the loopback address. On the other hand if you are using confederation under one IGP I would think that peering on the loopback address makes good sense.

Hope this helps,

[gzdillon73]

Thanks for your reply. I learned more.

But a new problem occurs, what about a AS with only one router runs between two AS that has its own IGP?

:)

[Harold Ritter]

I've never seen that in real life ;o)

[thisisshanky]

Or like your router having two parallel links to another AS and you peer using EBGP to to that AS using loopback.

neighbro 1.1.1.1 remote-as 100

neighbor 1.1.1.1 update-source lo 0

neighbor 1.1.1.1 ebgp-multihop...

[gzdillon73]

It likes this:

router A

rip

router B

ospf

router C

==================================

So, the router B knows the route to the loopback of A and C. There are external links between A and B, B and C also.

Should I use the loopback as update-source?

[Harold Ritter]

IGP between eBGP peers is kind of unsual but if there is only one link, therefore only one possible path between the peers, I would definitely use direct connection. On the other hand if there is multiple path, therefore multiple path, I would go for loopback connection.

Hope this helps,

[gzdillon73]

Under the confederation, the links are external and there more than one IGP, but I control all the routers and can provide all the loopback network to all routers. Maybe the loopback sounds good?

[Harold Ritter]

I'm sorry. I had forgotten about the confederation context. I agree with you then that it makes sense to use the loopback interface to peer.

Hoipe this helps,

[thisisshanky]

Yes, definitely loopbak sounds more logical...if you have redundant paths to reach that loopback address..