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we have the following scenario:

MPLS_WAN_provider1 connects to our edge router1 via eBGP
MPLS_WAN_provider2 connects to our edge router2 via eBGP

Both edge routers are to connect to our LAN. We need to decide on a routing protocol, between our LAN and both edge routers, that will support rerouting should one of the MPLS circuits go down.

We are considering either OSPF or iBGP, can both do the failover re-routing?

What are the advantages of one routing protocol over the other?

  • What level of routing tables do you get from the ISPs (full, partial, or default-only)? You probably want to run iBGP between the two WAN routers, but if you run it with all your routers, you must have a full mesh. It really shouldn't matter what you run internally, since the routing table will change if a link goes down. – Ron Maupin Oct 18 '16 at 23:17
  • @RonMaupin We get full routing tables. Sorry, maybe ISP is the wrong term, they are "MPLS" private WAN providers, it's not the internet. – Tullio_IRL Oct 18 '16 at 23:20
  • What we do is run eBGP to our MPLS WAN, iBGP between the WAN routers at a site, and OSPF at the site. Normally, we just get a default route at the remote sites, and a full table at the head-end sites. That way we just let the MPLS cloud determine the routing. Even if you distribute the BGP routing tables into an IGP like OSPF, a down link will update the tables, and you should automatically fail over to the other router, but that's where running iBGP between the WAN routers comes in. Trying to set up a full mesh, or route reflectors, at a site can be a real pain, and you need that with iBGP. – Ron Maupin Oct 18 '16 at 23:24
  • @RonMaupin Thanks Ron. So iBGP between the two WAN Routers and OSPF between LAN and WAN Routers? What purpose does the iBGP relationship between the two WAN routers serve exactly? – Tullio_IRL Oct 18 '16 at 23:31
  • Yes. Using an IGP keeps you from having to have a full mesh on the LAN routers (or use route reflectors or confederations). – Ron Maupin Oct 18 '16 at 23:33
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You probably want to run iBGP between your WAN routers, but make sure you have a direct link between the WAN routers. There are failure scenarios where not having the direct link can cause prefixes to be blackholed, especially if you run iBGP to other routers on the LAN..

You can use either iBGP or OSPF for you LAN routers, but iBGP requires a full mesh or a mitigation (route reflectors or confederations). That is because an iBGP speaker cannot advertise an iBGP learned prefix to another iBGP speaker. This is often not appropriate because it can limit your LAN topology.

You can run OSPF without the full mesh limitation of iBGP, and you could use a single or multiple areas, whichever is most appropriate for your site.

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