First of all, thanks for clarification on how your current network design works
said by yaplej:As mentioned I agree that the best thing to do at this point is assign all our sites a unique private ASN and run BGP on both WANs. With both WANs running BGP we can route our traffic as needed.
Good decision. If you haven't done much of BGP work, then this is gonna be a good starting project
said by yaplej:Rather than redistributing OSPF to BGP and BGP to OSPF perhaps just network statements to OSPF and BGP?
I would agree to use the network commands under the router bgp configuration to advertise local networks off to other sites. With the network command, you have more control of which network should be advertised, compared to OSPF-to-BGP redistribution. Further, the use of the network command states that the networks you advertise via BGP is considered local (coming from internal network) from BGP perspective by default, hence it would appear with
i in BGP table.
said by yaplej:I am not sure if BGP/OSPF would advertise a network statement if that network were not directly connected but just a route from another routing protocol.
From BGP perspective, it does not matter if the networks you advertise via BGP is connected directly, is stated as static route in local router, or is advertised from "local" dynamic routing protocol (in your case, the local OSPF). All of these from BGP perspective is considered internal. As long as the networks are in the local routing table, BGP would advertise them.
said by yaplej:What can be done about the "CORE" routing? We are limited to an OSPF only core right now so there has to be some redistribution between BGP/OSPF at the DC-ROUTERs.
As a note that you still have to have local routing in place (whether as directly connected, static routes, or in your case OSPF) to maintain connectivity between your core switches and the DC-ROUTERs even when you run BGP internally. Since your core switches are only speaking OSPF, then you can keep maintaining the same OSPF domain between the DC-EDGE, DC-ASA, CORE, and DC-ROUTER.
Since your DC-EDGE and DC-ASA are considered outside network compared to CORE and DC-ROUTER, I would suggest to place the DC-EDGE and DC-ASA as their own OSPF area while you can keep CORE and DC-ROUTER as Area 0. The DC-ASA would then be ABR.
With this area segregation, you can do some network summarization so that the outside network don't have to see every little network you have internally. Similarly, the DC-ROUTER does not have to see every little network you have on the outside network with network summarization.
said by yaplej:I think we might need to keep the BGP admin distance set to 115 to prevent routing loops between DC-ROUTER1 and DC-ROUTER2. Without that it would prefer the BGP route to/from each other over delivering the traffic to OSPF where the destination network ultimately resides.
When you have different BGP AS between DC1, DC2, MPLS cloud, and remote sites; by default BGP route would prefer path with least hop (as the attribute of BGP being Path-Vector routing protocol). Therefore you don't need to change the default BGP administrative distance unless you are running BGP with non-Cisco devices that have different administrative distance by default than the Cisco devices.