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)
Alex Bligh wrote:
then only one peering session will come up, as routers only support one BGP session with any given router ID.
You can get both sessions up, but you'll only use one set of routes, which if you don't toy with any knobs, will be the one with the lower router ID. However, you can use BGP max paths and set it to 2, and both routes will be sent to the route table. Or you could use eBGP multihop. /Sean Butler
On Wed, 10 Feb 1999, sean_butler@ibm.net wrote:
Alex Bligh wrote:
then only one peering session will come up, as routers only support one BGP session with any given router ID.
You can get both sessions up, but you'll only use one set of routes, which if you don't toy with any knobs, will be the one with the lower router ID. However, you can use BGP max paths and set it to 2, and both routes will be sent to the route table. Or you could use eBGP multihop.
I had the same situation and ended up dropping a static to the loopback of the remote router at both interfaces and then peering loop to loop.. (the remote end would have to static your loopback out their's too, of course) Added benefit of very good load balancing on the links.., I'm using CEF so CPU load is nill even on per-packet load sharing.. Tim ---------------------------------------------------- Timothy M. Wolfe | Why surf when you can Sail? tim@clipper.net | Join Oregon's Premier Sr. Network Engineer | Wireless Internet Provider! ClipperNet Corporation | http://www.clipper.net/ ----------------------------------------------------
participants (3)
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Alex Bligh -
sean_butler＠ibm.net -
Tim Wolfe