Re: multi-homing vs multi-connecting

["J. Noel Chiappa" <jnc@ginger.lcs.mit.edu>]

    > From: Pekka Savola <pekkas@netcore.fi>

    > I group these differently .. basically:

    > 1) Host multi-homing ..
    > a) multiple interfaces and addresses: e.g. a mobile device with both
    > GPRS+WLAN interface active

I understand the class, but caution you not to use mobile examples because it
will confuse many people... :-)

    > 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.

My reaction to this classification is that you need to be careful not to mix
classifications based on the *kind of problem* one is trying to solve (which
is where my host/site distinction comes from) with classifications based on
the *mechanism* one is using.

Your classification is also an interesting one, but on the surface, because of
your mention of multiple addresses, it's a mechanism classification - not that
that's bad, just different.

Of course, your classification is also in some ways a problem classification,
because the former is the "classical" host/node multi-homing, whereas the
latter is really a subset of site multi-homing; more specifically, that subset
that we've been thinking is best handled with multiple addresses.


After reading Michael Lambert's message, I've been trying to work out if
there's a useful division at an architectural level, which would be yet
another level of classification, but I'm going to have to ponder that for
a while.

I mean, at some point there is an architectural division where multi-homing
turns into routing - e.g. if you have two tiers of upstream providers, local
ones L1-L3, and global ones G1-G3, all cross-connected, and you want to
specify which pair traffic to a particular destination takes, that's really a
routing problem, not a multi-homing problem. Whereas the single host with
multiple interfaces is clearly multi-homing.

But I need to think about it more...


    > so it would seem you'd rather place 1.b) under 2) as a network providing
    > multiple prefixes is a already a site.

Yes, you only get 1.b if you have an entire network with multiple addresses,
and you only get that (presumably) if that network is multi-homed, ergo it's
site multi-homing.

So maybe site multi-homing needs to be split up into sub-classes - whether
based on the *mechanism* used to support it (multiple addresses, routing,
whatever), or on some significant *situational* difference (e.g. a stub site
which is multi-homed to different local ISP's, versus some more complex
situation).


    > From IPv4 perspective ... but in IPv6

See previous message! Empty your mind of all this old junk! :-)

	Noel