Multiple BGP sessions between the same router pairs at IXPs

Thu Feb 11 04:25:08 UTC 1999

Yes, you are correct.  In a NAP configuration that is changing this probably
would be difficult to avoid.

-----Original Message-----
From: Alex Bligh
To: nanog at merit.edu
Cc: amb at gxn.net
Sent: 2/10/99 12:37 AM
Subject: Multiple BGP sessions between the same router pairs at IXPs

Anyone feel like sanity checking this for me:

As far as I know, if you have this config

             RTRA   BGP ID 4.4.4.4 ASN 4
    2.2.2.4 /    \ 3.3.3.4
 2.2.2.0/24 |    | 3.3.3.0/24
    2.2.2.5 \   /  3.3.3.5
             RTRB   BGP ID 5.5.5.5 ASN 5

and you configure on router A

router bgp 4
 neighbor 2.2.2.5 remote-as 5
 nieghbor 3.3.3.5 remote-as 5

and on router B

router bgp 5
 neighbor 2.2.2.4 remote-as 4
 nieghbor 3.3.3.4 remote-as 4

then only one peering session will come up, as routers only
support one BGP session with any given router ID.

We hit this problem when renumbering the LINX, I think, in that
you have to make sure you take down old sessions to get new
sessions to work.

This would also affect people who set up new peerings over
the ATM MAE's, who also have existing peerings on the FDDI
fabric between the same routers, right?

-- 
Alex Bligh
GX Networks (formerly Xara Networks)