Question for all you BGP/OSPF Gurus

Admittedly, I am not a routing guru. However, I have to get some redundancy built in to our existing Internet infrastructure. The proposed setup is pretty simple; 2 sites w/ different ISPs and a total of 4 routers, switches, and firewalls. Please visit

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to see the logical diagram (for anonymity I have used someone else's external IP blocks). Anyway, if you look at the diagram you will see that we have routers A and C and routers B and D connected over some high speed metro Ethernet links.

We are peering with Time Warner in Austin, and SBC in Taylor. Within our network we want all four routers to peer with each other over iBGP. For our IGP, we will use OSPF. My understanding is the BGP will not advertise routes learned via another iBGP neighbor unless that route is known by an IGP (in this case OSPF).

What we want is simple, if Time Warner dies, SBC needs to be able to handle routes to and from the /24 block, and if SBC dies, Time Warner needs to be able to handle routers to and from the /24 block. Also, any router and switch failures should be relatively transparent to our Internal and External users.

My question is this; should all four routers be a member of Area 0, or should we have disparate areas between sites? The reason I ask is because when we brought this topology up last night, we established BGP peering just fine. The problem was that as the BGP routes were being propagated between iBGP peers, they would climb up to 156,000, and then suddenly drop to roughly 4000. They would then slowly creep back up, only to plummet again. This, of course, made for a very unstable network. We were forced to remove the secondary routers for the time being to stabilize the network.

Sorry to ramble, but if anyone has any suggestions on how to configure this in a highly available and stable manner PLEASE make a suggestion. Thanks in advance for the help.


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You can use the "no sync" option in BGP to turn off that check. You should *not* redistribute the routes learned via EBGP into OSPF.

OSPF should handle detecting failures within your infrastructure.

Do you really need to get full routes from both ISPs? I think you would do better to have each of them send you just their customer routes and a default route.

I don't think you need to worry about multiple OSPF areas with your simple configuration.

Reply to
Barry Margolin

seeing this i suspect you have not enough memory in your bgp routers, and they simply drop bgp session after receiving portion of prefixes, then restarts again. what routers are you using for bgp and how much memory do they have? if there is no reason to have the full bgp table, you should consider receiving only router for your provider's customers and default route, as suggested by Barry Margolin, otherwise you probably have to upgrade your routers or at leas optimize memory usage.

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