Måns Nilsson wrote:
--On Wednesday, March 05, 2003 17:53:00 +0100 Jeroen Massar <jeroen@unfix.org> wrote:
<SNIP>
I also am wondering how people define "multihoming". Do they define it as: - Multiple prefixes over multiple cables from multiple upstreams. - One prefix over multiple cables from multiple upstreams. - One prefix over one cable from multiple upstreams.
If you are talking about the last case, where one only has one physical upstream... one shouldn't call that multihoming. I guess the second one is where people are talking about. And the first one is what I would call real multihoming, though one needs SCTP to make that work.
Cases one and two. One or more prefixes advertised over multiple upstreams.
Case one means having more than one prefixes on the cable, or in diagram style: +-----+ +-----------+ 2001:db8:11:22::/64 +------+ | the +---+ Cable ISP +------------------------+ eth0 | | N | +-----------+ | | | E | | YOU | | T | +-----------+ 3ffe:ffff:33:42::/64 | | | +---+ ADSL ISP +------------------------+ eth1 | +-----+ +-----------+ +------+ Thus YOU gets 2 different prefixes from 2 different upstreams. Ofcourse YOU could also get two /48's routed to him from these upstreams or more ofcourse. The fact is that a 'server' eg a web server will have 2 IP's; eg: www.example.com AAAA 2001:0db8:11:22::80 AAAA 3ffe:ffff:33:42::80 Ofcourse replace Cable and ADSL with the bigger lines, this is just to illustrate that the definition of 'multihoming' is quite a different thing for most people. As I said this will only work when using SCTP to 'multihome' when one of the two uplinks fail. In case two both upstreams carry "your" prefix, eg 2001:db8:11:22::/64 to the rest of the world, diagram style: +-----+ +-----------+ 2001:db8:11:22::/64 +------+ +------+ | the +---+ Cable ISP +------------------------+ R | | | | N | +-----------+ | o | | | | E | | u +----+ eth0 | | T | +-----------+ 2001:db8:11:22::/64 | t | | | | +---+ ADSL ISP +------------------------+ er | | | +-----+ +-----------+ +------+ +------+ Note that the moment you only have one physical path to the rest of the world you should not be talking about 'multihoming' any more (case 3) I always wonder why people want L3 level 'multihoming' even though their L1 and L2 path aren't.
Although my idea is to give people so much space in their initial allocation that only the biggest networks will need more than one prefix, thus keeping the routing table as close to "nPrefixes == nAS-numbers" as possible.
Every ISP that can match up to the current requirements for address space can get a /32 from all three RIRs. If you can't, you simply are not big enough and you won't have any multiple links either. If one really wants 99.9% certainty that their inet works one either needs to do it themselves and thus get multiple L1+L2 paths and the hardware along with it and then most of the times you are a big enough customer to get a /32 too. If you aren't you should just get a better upstream. Yes, I know, it all sounds quite harsh. Greets, Jeroen