Re: The state of IPv6 multihoming development

[Iljitsch van Beijnum <iljitsch@muada.com>]

On Tue, 22 Oct 2002, J. Noel Chiappa wrote:

> Multi-homing is an additional "service" (if you will) of the network, a
> service that provides additional benefits. You don't get additional benefits
> without a price. (The old "There Ain't No Such Thing As A Free Lunch"
> principle.)

I'm not convinced this is an "extra" service.

> The benefit of multi-homing has a price - the only question is, who's going
> to pay the price? Simple fairness demands that it *ought* to be the entity
> which directly benefits. Multiple connectivity-based addresses do this; the
> end-site has to pay the bulk of the cost (in complexity, etc).

So who benefits if Google is multihomed? The user or the server? Or
both?

> Connectivity-independent addresses (such as Provider-Independent addresses)
> don't have this characteristic. CI-addresses make everyone *else* pay for
> that site's privilege in being multi-homed.

For straight PI (or "CI") it is true that many organizations other than
the multihomed one have to bear costs. However, this is far from
"everyone else": only people who are default-free _need_ to pay for the
extra memory and CPU power for their routers. In a multiple address
solution this is much, much worse: in that case, all IPv6 hosts may have
to implement extra functionality to be able to talk to multihomed
destinations.

But we're not debating straight PI, but geographically aggregatable PI
(GAPI). GAPI aggregation is essentially free after the initial
implementation efforts, as long as the routing tables within a region
("zone" in the draft) with interconnection within the region remain
small enough to fit in a single router. Only when the routing tables
grow beyond that, networks in the affected region need to install more
memory in existing routers or more routers. This is of course not a good
thing for networks that are active in the region but don't have
multihomed customers themselves (also, these networks will experience
less optimal traffic flow).

> It's all very simple, really. Who's going to pay for the benefits of
> multi-homing? That's the real question.

No, the real question is whether multihoming in IPv6 will be good enough
to get people who multihome "for free" to move to v6.

Iljitsch