On Thursday, December 15, 2011 09:56:04 PM Brian Johnson wrote:
I think you will learn a lot of /128s from IGP, but not from eBGP. I consider the "wild" to be the DFZ or similar type of network and in that case, you should not see advertisements for anything longer than a /48. This is not hard and fast, but please correct me if I'm wrong.
Ideally, yes. Good filtering (against your peers, customers and upstreams) will ensure you keep anything longer than a /48 out of your AS. However, do note that if you provide customer-induced automated blackhole routing (where customers attach an "evil" community to an "evil" host route and send that to you in an eBGP update because you expect it), that's one other way to see /128's (or more appropriately, something longer than a /48) across eBGP sessions with customers. Also, if customers multi-home to you and they want to be able to load share traffic across the various links between their network and yours, you may be inclined to allow them to send longer subnets that have a NO_EXPORT community attached to them so that load sharing occurs within your network for their inbound traffic, but de-aggregated routes do not flood the rest of the Internet. This is another way you could get "longer" routes into your network, with the benefit of not polluting the global Internet. Among other scenarios... :-). Mark.