I have a question regarding BGP Design.
Here's my setup:
BGP Enabled MPLS WAN
Site A is my primary location with all my servers and whatnot and it has internet connection via ISP-A. Site A advertises a default route to all other locations via default-originate.
Site B is the secondary site, serves as DR location, and has internet connection via ISP-A as well, but from a different location.
Routing at Site A is static and done by a pair of 4507R. one of the 4507R is also the BGP speaker for Site A.
BGP Speaker at Site B is a 3750.
Remote branches (17 in all) all access internet via the primary location. The routers at each branch just use a default-route advertised by site-a for connectivity.
Internet connection is NOT part of the MPLS cloud, it is separate and all traffic needs to be funneled through Site A or Site B.
All of the above is adjustable if needed.
My ultimate goal is to find an easy way to re-route internet traffic from site A to site B in the even that ISP-A at site A is down. It has happened twice in the past few months where ISP-A is down at Site A, but MPLS network is still up and ISP-A is still up at site B.
I figure I could remove the default-originate from the 4507 at site-a and add default-originate into the BGP config at site-b, but is there any way to do this automatically?
Can I have Site A and Site B do default-originate and then adjust the metric for the default route from Site B?
I have read the link regarding conditional advertisment in BGP based on a prefix being in the routing table or NOT in the routing table, but with static routes being used, that doesn't really help me.
I've thought about using an IGP at Site A, but the thing is, Site A is our "datacenter" site, but all the Layer 3 is done on the pair of 4507R, there is maybe one other Layer 3 device, otherwise there are a few other bigger Layer 2 switches. Also, I only have one connection to the MPLS network at Site A, Everything has to go through one of the 4507s anyway.
If I dont use the default-originate option, and I just advertise network 0.0.0.0, would that accomplish the same thing? If I do it this way, can I adjust the metric such that Site A is more desirable than Site Bs 0.0.0.0 network? I imagine I would then be able to just remove the default-route from the 4507 at Site A, and allow the default from Site B to take over...But, on another thought, i would probably have to use an IGP like OSPF or EIGRP to communicate to the other 4507 that its default route has changed.
What if I use route-tracking on the 4507 connected to the MPLS... I could ping out to the internet somewhere, maybe our ISP next-hop, then if it fails x times, remove the default route and allow the default route from Site B to take over.
I apologize if my thoughts seem jumbled, its still early :P. I'm trying to think and type.