IPv6 addresses for EP or why are exhanges so special ?
Hans Petter Holen
Fri May 11 20:33:47 CEST 2001
Havard Eidnes writes: > o Addresses for the exchange point medium itself (usually a > layer-two network of some sort) I agree, this was the discussion i added to. >For the exchange point medium itself, if the medium is a "multiple- >access broadcast network" it *is* actually a benefit to use the >"natural" way to number such networks, i.e. use a single IP subnet, >as in that case you can use BGP in the "standard configuration". I agree that this has been the simple way of doing things in routers as we know them today. >Starting to muddle with secondary IP addresses and run "multiple >subnet on the same layer-two medium" when you in reality don't have >to, just causes extra complications, and should therefore be >avoided. I would again agree with you if I were discussing how to do this in current implementations. But my thinking was more on the lines: how would the ideal solution look if I didn't have the constraints of the current implementations. And since we are rather early in implementation of v6 based technology it may still be time to engineer more convenient solutions. Such an implementation should also give me SNMP access to relevant counters on such an interface. But again, I realise, this it not how the current implementations are, and mabe such suggestions should better be discussed in some IETF wg, or directy with vendors. >If your exchange point is implemented using a "multiple- >access non-broadcast network" of some sort, the multiple point-to- >point links, each with their own subnet out of a connected peer's >address block makes sense. Yes indeed. >Some have said that the IP network used to number the exchange >itself does not have to be announced on the global level. However, >it would appear that practices vary quite widely on this point for >IPv4, and many are announced globally. You mention the possible use >of link-local addresses; I wonder if that won't make it difficult to >handle such things as ICMP; it'll probably be met with similar >issues as folks who use RFC 1918 addresses in today's network (e.g. >breaking Path MTU discovery because RFC 1918-originated datagrams >are often summarily dropped on the floor). I have just been reminded that at least some routers can be configured how to reply to ICMP requests, so this may solve that address. Link local addresses may actualy not be a good idea since I probably would have to carry my peers IP address in my internal routing tables and with multiple peerings I need to ensure uniqueness at least within my network. Maybe the soulution would be that all routers had a loopback like interface with a suitably sized subnet set aside, and that you could trough a DHCP like auto configure this end and discover the remote AS number. The only other thing needed to be added would be the routing policy... >I may have misunderstood something fundamental, but I also don't >quite know what's so bad with using IP(v4) addresses out of a >provider's block to number the exchange point medium. Technicaly I don't think there are any disadvantages in doing this. Politicaly or emotionaly I think there are several reasons: * if the provider who donated the IP addresses in the first case deceides to disconnect from the exchange, one may want to renumber the exchange * I have repeatedly heard (at RIPE and ARIN meetings) that it is bad practice to advertise more specific routes out of a provider block. (this tends to come up more in multihoming discussions than in IX discussions tough) It seems to me that there is a notion that if somebody else announces a more specific route as an alternative path to parts of your address space it hurts in some way ("I dont allow others to punch holes in my blocks"). My personal opinion is the quite the oposite, it is better (as in more socialy acceptable to the global internet) to do multi homing with address space from one of the providers, as this allows other to save router resources with prefix length filters without risking loosing connectivity to the multi-homed networks. >As for the "service network", it will of course need global >connectivity, and thus has to get transit service from one or more >ISPs. What I don't understand is why this service network needs to >be so special up and above other normal customers when it comes to >IP address assignment? Well, if it is "critical internet infrastructure" it requires maximum connectivity. Some tend to argue that that is best taken care of trough a separate entry in the routing table. >Creating these "special cases" as exceptions to the rules just opens >up the floor for other folks who will stand up and say "My Cause is >Extremely Worthy too, so I want some too under those conditions!!". I could not agree more. -hph
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