Sterling, We have several upstream providers, located at different physical locations.
We use layer 2 protocols to control the ring/path topology across the network, and OSPF to manage internal routing. The BGP speaking routers talk iBGP internally, and BGP externally. When we are not positive we can keep the BGP routers 'seeing' each other on our network we have created GRE tunnels between the routers through our external providers. The GRE tunnels are certainly not ideal but they are better then having a network 'split' where two or more BGP routers are announcing your aggregate space but are not talking to each other - that makes a giant hash of things.
On iBGP the size of the blocks is irrelevant - you can make them as small as you want. Externally you are likely limited to a /24 though there is no guarantee that other providers are going to accept the /24. Some providers, in an attempt to limit the number of routes they are seeing are filtering on /23, /22, etc. Others are accepting /24 in areas that traditionally had /24 allocations (the 'swamp' space) while only accepting larger blocks in other address ranges.
My recommendation is use a interior gateway protocol (ISIS, OSPF) that you are comfortable with internally. Use some type of tunneling if need be to make sure your external gateways can always talk to each other, and run BGP externally.
Mark On 11/19/14, 5:04 PM, Sterling Jacobson via Af wrote:
I know a lot of us here span networks across large areas and have multiple providers. I want my IP address space to be redundant and I guess I can either make sure I have a ring with OSPF/ static routes, or I can BGP. Since I sell to other providers that would like BGP and I would like to preserve my routing by /24 classes via BGP. Maybe I should just use BGP at each site/area? That would restrict me to keeping the sites at /24 class size or larger though, since external BGP doesn't like anything smaller. I think that's ok, but it does lend itself to waste if I come short of using the 254 IP's or I just break the barrier into another /24 for the site. But I can't think of any way around it without relying on infrastructure to ring me back to a central BGP point or two, using OSPF inside. What do you guys do?
-- Mark Radabaugh Amplex m...@amplex.net 419.837.5015 x 1021
