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Re: multi-homing

  • From: Leo Bicknell
  • Date: Tue Aug 28 21:08:31 2001

On Tue, Aug 28, 2001 at 05:11:51PM -0700, steve uurtamo wrote:
> iii) the number of prefixes that _would_ multihome if they:
>      a) had the appropriate equipment
>      b) had the appropriate tech-brains
>      c) had an ASN
>      d) had connections through multiple providers
>      is _not_ known.

It is known.  You forget one point, e) find it financially attractive,
but all together the upper bound is all sites.  There is a good
technical argument (in the abstract, not with today's system) to
be made that everyone should be multihomed, down to dual-DSL lines,
dual-dial up lines, dual whatever access is available.

Of course, for a number of reasons this will never happen, most of
them come back to it not being financially attractive for the users
or for the service providers.

If you design everything from the ground up such that each "site"
is multihomed by default, and can develop systems that scale to
that goal than no matter how many people choose to multihome the
system will work.

I believe it is technologically possible to make every site
requirement.  It would never happen with today's protocols, and
alias with the direction IPv6 is taking I don't see a light at the
end of that tunnel wrt multihoming.  The technology may be
prohibitively expensive at some cut off point, but at least at that
point it would come down to simple dollars and cents for the users
and an ISP, and not a maze of similar but slightly different rules.

I know someone will want to argue that it is not possible to allow
_everyone_ to multihome, so I will go ahead and suggest an example
of a network very close to that goal, in fact one you can run IP
over (if a tad slowly).  The cellular telephone network for the
most part has this property.  Every phone has a number.  It can
dynamically connect to multiple providers, and can change providers
as conditions change, or the device moves.  The only property it
doesn't have that IP multihoming doesn't have is the ability to
use two providers at the same time; however the technology for a
handset that could make a CDMA and a TMDA call at the same time on
two different networks definitely exists.

This is not to say I think 'cellular phone routing' would solve
the IP issues if directly translated, in fact I think quite the
opposite.  That said, I do belive large scale systems that allow
individual users to move, or multihome (I think those two items
are more closely related than people think) while keeping their
"address" exist.

I don't do the IETF thing, but has any development effort there
tried to make multihoming / mobility a requirement of a new protocol,
and if so why hasn't there been more progress on that front?

Leo Bicknell - [email protected]
Systems Engineer - Internetworking Engineer - CCIE 3440
Read TMBG List - [email protected],