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RE: And Now for Something Completely Different (was Re: IPv6 news)
Nanog, I've been thinking a bunch about this IPv6 multihoming issue. It seems that the method of hierarchical summarization will keep the global tables small for all single-homed end user blocks. But the multihomed ones will be the problem. The possible solution I've been thinking about is 'adjacency blocks', for lack of a better term. In theory, the first customer to home to two different ISPs causes a new large address block to be advertised upstream by these two ISPs. Further customers homing to these two ISPs get an allocation out of this same block. The two ISPs will only announce the large block. Of course there are issues involving failure and scalability... Failure would involve an ISP losing contact with end customer, but still announcing the aggregate upstream. This can be solved by requiring that two ISPs must have a direct peering agreement, before they can accept dual-homed customers. Or a possible method (maybe using communities?) where ISP B will announce the customer's actual block (the small one) to it's upstreams, if notified by ISP A that it's not reachable by them. When ISP A resumes contact with end customer, ISP B retracts the smaller prefix. Scalability is an obvious issue, as the possible number of these 'adjacency blocks' would be N * (N-1), where N is the number of ISPs in the world. Obviously pretty large. But I feel the number of ISPs that people would actually dual home to (due to reputation, regional existence, etc) is a few orders of magnitude smaller. ~100,000 prefixes (each can be an ASN, I suppose) should cover all needs, doing some simple math. The downside is that end customers are going to lose the ability to prefer traffic from one ISP versus another for inbound traffic. That alone might be a show-stopper, not sure how important it is. Since IPv6 is a whole new ballgame, maybe it's ok to change the rules... Looking for any thoughts about it. I'm sure there's things I haven't considered, but the people I've bounced it off of haven't seen any obvious problems. Flame-retardant clothes on, just in case though. Chuck >Every multi-homer will be needing their own ASN, so that's what clutters >up your routing tables. It's economy there. Btw, a lot of ASNs advertise >one network only. People surely think multihoming is important to them >(and I cannot blame them for that). >Hierarchical routing is one possible solution, with a lot of drawbacks >and problems. Forget about geographic hierarchies; there's always people >who do not peer. Visibility radius limitation is another (I cannot believe >the idea is new, I only don't know what it's called).