Re: LIN6 and multihoming (+sec)

[Pekka Savola <pekkas@netcore.fi>]

On Sat, 18 Aug 2001, Howard C. Berkowitz wrote:
> >I don't think people generally want to multihome every node, rather
> >multihome a router and provide multihomed connection that way.
>
> This is where I partially disagree. Yes, I can understand that it is
> generally not required to multihome cellular mobile hosts.  I hope I
> may be forgiven for loose terminology if I call them "clients."

This isn't a point, but there might be some justification for it so...

Multihoming cellular clients might be feasible if the underlaying
structure is made so that the address would change if they changed their
radio base station.  Then, when you move to some direction, it might be
prudent to start to "prepare way for the handoff" by multihoming with
current and the next cell you're moving towards when you're close enough
to the edge.

> "Server" hosts, in contrast, very reasonably will be multihomed to
> routers. Indeed, there may be complex relationships of multiple
> servers and multiple routers.
>
> The mechanism of server to router multihoming will vary with the
> application. When the multiple routers are on the same subnet as the
> server, a mechanism as simple as VRRP may suffice, perhaps with
> multiple VRRP groups for a degree of load-sharing.  As the servers
> and routers become more distributed, some NAT or transport based
> mechanism may be needed, or the servers may need some awareness of
> routing.

(I'm assuming here that multihoming is done to ensure redundancy.  There
are other reasons too, of course, but I'll skip them here.)

I agree.  This depends heavily on how important and costly multihoming is
(ie. do you want to also multihome systems that strictly speaking might
not need it so much, e.g. workstations vs. critical web-servers).

If we can't find a good way to multihome entire sites, it just _might_
(for an intermediate approach, if not else) be sufficient to be able to
multihome certain critical systems.

The amount of critical systems and how they're located in the site's
network topology defines whether "server-based" or "network-based"
multihoming is a better alternative (if you actually could do it either
way).

-- 
Pekka Savola                 "Tell me of difficulties surmounted,
Netcore Oy                   not those you stumble over and fall"
Systems. Networks. Security.  -- Robert Jordan: A Crown of Swords