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Re: What is multihoming was (design of a real routing v. endpoint idseperation)

  • From: Crist Clark
  • Date: Tue Oct 25 14:12:43 2005

Robert Bonomi wrote:
From [email protected]  Mon Oct 24 15:33:02 2005
Date: Mon, 24 Oct 2005 13:31:17 -0700
Subject: Re: What is multihoming was (design of a real routing v. endpoint id

Stephen Sprunk wrote:

Other people use this term in very different ways. To some people
it means using having multiple IP addresses bound to a single
network interface. To others it means multiple websites on one

That is virtual hosting in a NANOG context. Some undereducated MCSEs might call it multihoming, but let's not endorse that here.
Unfortunately, this is a common and "standards blessed" way to refer to
any host with multiple interfaces/addresses (real or virtual). For example,
from the "Terminology" section, 1.1.3, of RFC1122, "Requirements for
Internet Hosts -- Communication Layers," says,

              A host is said to be multihomed if it has multiple IP
              addresses.  For a discussion of multihoming, see Section
              3.3.4 below.

*sigh* Multi-homing simply means 'having external connections to more than one network' -- be it a network with multiple, disjoint, ingress/egress paths,
or a host with interfaces (real or virtual) on distinct LAN subnets (even if
those subnets are agregated into a single net somewhere upstream.

A host with multiple adresses utilizing the _same_ netblock/netmask _should_
_not_ be called multi-homed (because there is only one path to that host), it
is simply a single-homed host with multiple identities. might be called
"poly-ip-any" or some such. <grin>
Depends who you ask. Again, RFC1122 says (section 1.1.1),

         A host is generally said to be multihomed if it has more than
         one interface to the same or to different networks.

And also section,

            A multihomed host has multiple IP addresses, which we may
            think of as "logical interfaces".  These logical interfaces
            may be associated with one or more physical interfaces, and
            these physical interfaces may be connected to the same or
            different networks.

As far as a "multihomed host" is concerned, RFC1122 sure seems to call
anything with multiple IPs multihomed. Multihomed is a trait of the host
independent of any network topology around the host.

But whatever. It just means people need to be clear what they are talking
about when they say "multihomed." As is clear from this thread, there is
not clear agreement on what the precise meaning is.
Crist J. Clark                               [email protected]
Globalstar Communications                                (408) 933-4387