multihoming

Wed Nov 24 07:15:55 UTC 2021

Dave Taht wrote:

>> The proper solution is to have end to end multihoming:
>>
>>          https://tools.ietf.org/id/draft-ohta-e2e-multihoming-02.txt
> 
> I'd never read that. We'd made openwrt in particular use "source
> specific routing" for ipv6 by default,
> many years ago, but I don't know to what extent that facility is used.

Considering that most, if not all, multihomed sites should have
rich (maybe full) routing table in some part (at least) of the
sites between exit routers to balance load between the routers,
I can't see why source specific routing was considered necessary
only to cause routing loops.

For multihoming with PA address ranges with plain TCP/UDP,
what is necessary for ISP failure is to have routing
protocols to carry proper source address ranges for each
routing table entry and to modify end systems to listen to
routing protocol and choose proper source address, which
is against the poor architecture of IPv6/ND to assume
intelligent routers and dumb hosts.

But, even with that, if some ISP fails, TCP/UDP through
the ISP will fail and must be restarted with new source
address, which is not very useful. Moreover, if destination
is also inside another multihomed site with PA address ranges,
all the destination addresses must be tried.

So, as modifying end systems is inevitable, there is
no reason not to support full end to end multihoming
including modifications to support multiple addresses
by TCP and some applications.

					Masataka Ohta