I have two networks, which I want to join using BGP
The first network consists of 4 routers, with ethernet /30 links in line
A-B-C-D
Call it AS 65501
They run OSPF, and all is well.
I also have a large network running OSPF, with 2 routers, and gigabit connectivity, AS65500
E-F
| |
(various other bits)
Finally I have 2 ethernet links to connect the two networks, one from B to E, one from C to F
I want A and B to route via the B-E link, unless going to C/D
I want C and D to route via the C-F link, unless going to A/B
If any link goes down, routes should fail over. If the link from B to C goes down for example, route A-D should go A-B-E-F-C-D rather than A-B-C-D. If B-E goes down, A-B-E should become A-B-C-F-E, etc.
Diagram attached.
I’m keen on having BGP separating the two areas, as they are administrated by different groups. B,C, E and F all run BGP and OSPF, and the B-E and C-F links are set up to be OSPF passive.
So I started to set up a test network, and it mostly works (although I’m not readvertising )
However, as OSPF’s default metric is 110, and eBGP is 20, the route from E to C goes E-20-B-110-C. The route C to E is fine, with C-20-F-110-E.
Before I start down the routing filter path, I wanted to ensure that I wasn’t being silly. You see, on the whole I’d expect an OSPF network to be an “internal” network protocol, and BGP to be “external” protocol. In that case, why does eBGP have such a low default distance on its routes?
It’s that nagging question which makes me doubt my rather limited knowledge of OSPF and BGP.
My other nagging concern, which I was going to answer experimentally: If the B-C line goes down, will things work, or will BGP start to cry. Should I split A-B-C-D into 2 AS groups, which is what I’m currently thinking, but it seems a bit excessive to split such a small group of routers up any more.
This is a private network, so no problem with AS or IP use.
Please feel free to tell me to go back to networking 101 and stop being stupid.
Thanks
