Subject: Re: multi-homing vs multi-connecting

From: "J. Noel Chiappa" <[email-masked]>
Date: Thu, 2 Jan 2003 10:00:13 -0500

> From: Pekka Savola <[email-masked]>

    > the terms "multi-homed" (always different ISP's) and "multi-attached"
    > (same ISP) are separated.
    > I don't think this terminology has been well established? At least as
    > far as I've seen, multihoming has been used to refer to both (to some
    > extent).

Another place where one term, "multi-homing", has been used to cover two
fairly different things are with so-called "site multi-homing" and "host
multi-homing" - the latter being a single host with multiple physical
interfaces.

	Noel

---

From: Pekka Savola <[email-masked]>
Date: Thu, 2 Jan 2003 17:24:57 +0200 (EET)

On Thu, 2 Jan 2003, J. Noel Chiappa wrote:
> fairly different things are with so-called "site multi-homing"  and
> "host multi-homing" - the latter being a single host with multiple
> physical interfaces.

Hmm.. I group these differently (though I can see why the above could also
be a useful classification), basically:

1) Host multi-homing (strictly speaking, "node" multihoming..)
 a) multiple interfaces and addresses: e.g. a mobile device with both 
GPRS+WLAN interface active
 b) one interface and more addresses: network is providing multiple 
prefixes (of possibly different properties).  It is the _host's task_ to 
deal with the issues.

 * a special case of either a) and b) are mechanisms employing a mapping
function between addresses (HIP, MIPv6 to a lesser degree of success) or
parts of addresses (LIN6).

2) Site multi-homing

 Either something like 3) possibly restricted a bit or the framework for 1)

3) ISP multi-homing
 * BGP-only, trivial case

.. so it would seem you'd rather place 1.b) under 2) as a network 
providing multiple prefixes is a already a site.  From IPv4 perspective, 
it's definitely more in the 1), but in IPv6, perhaps a bit closer to 2).

Does this make sense?  Thoughts?

(Actually I'm writing a thesis on the subject.. :-)

-- 
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

---

From: "Michael H. Lambert" <[email-masked]>
Date: Thu, 02 Jan 2003 10:30:52 -0500

> multi-homing" - the latter being a single host with multiple physical

Is there a fundamental difference in these two "types" of multihoming?  In 
the IPv4 world, I would argue that there is not--it's just that the site 
router has better knowledge with which to make an interface selection than 
does the host (listen to RIP?).

Other than adding the non-trivial problem of source address selection to 
the mix, I don't see that IPv6 changes things.  The distinction seems to 
rest primarily in the WG charter.

Michael

+-----------------------------------------------------------------------+
| Michael H. Lambert, Network Engineer           Phone: +1 412 268-4960 |
| Pittsburgh Supercomputing Center               FAX:   +1 412 268-8200 |
| 4400 Fifth Avenue, Pittsburgh, PA  15213       [email-masked]        |
+-----------------------------------------------------------------------+