Subject: Re: The state of IPv6 multihoming development

From: "J. Noel Chiappa" <[email-masked]>
Date: Tue, 22 Oct 2002 12:57:41 -0400

> From: Iljitsch van Beijnum <[email-masked]>

    > The way I see it is that we really need some level of working
    > multihoming in IPv6 to get it deployed, and probably in a way that
    > doesn't require much renumbering, preferably none, for large
    > organizations. Guess what? PI does that, and nothing else is even on
    > the horizon. So either IPv6 remains a playpen for several more years,
    > or we get some form of PI.

Hunh. Why don't you write a spec that says that IPv6 negates the Second Law
of Thermodynamics? (Hey, that makes as much sense as a design which offers
"topological-location-independent topological-location-names".) That way,
IPv6 could solve the energy crisis *and* fix global warming, all in one fell
swoop. That ought to drive IPv6 deployment.

Let's try this one more time.

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.)

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).

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. (That is, unless we have a system
of charging for route advertisements, where the charge is directly related to
the scope over which the advertisement is seen, which seems rather unlikely
to happen.)

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

	Noel

---

From: Iljitsch van Beijnum <[email-masked]>
Date: Tue, 22 Oct 2002 19:19:08 +0200 (CEST)

> without a price. (The old "There Ain't No Such Thing As A Free Lunch"

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

> 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?

> 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).

> 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

---

From: "Christian de Larrinaga" <[email-masked]>
Date: Tue, 22 Oct 2002 18:52:17 +0100

> multi-homing? That's the real question.

up to a point. The benefits really depend on where you are and what you are
doing so I don't know that there are any hard and fast rules to multi-homing
in terms of a generalised cost benefit analysis that we can apply here that
will make our job any easier/complicated.

I think the observation is that multi homing makes for a more robust network
environment and user experience and I guess that means we should ultimately
think of a resolution which allows most points on the Internet becoming
multi-homed is safer than thinking of multihoming as the exception.

To that end we should make it so it can be cheap and simple to implement so
it can be ubiquitous.

Christian

Christian de Larrinaga

---

From: "Craig A. Huegen" <[email-masked]>
Date: Tue, 22 Oct 2002 13:52:42 -0500 (Central Daylight Time)

> without a price. (The old "There Ain't No Such Thing As A Free Lunch"

Without multi-homing, demand for the network will be severely reduced
because end-users will not see the IPv6 as a reliable network to do
business on.

> end-site has to pay the bulk of the cost (in complexity, etc).

Content consumers benefit from the content providers being multi-homed,
just as content providers benefit from the content consumers being
multi-homed.  You can't make the argument that benefit is solely or even
primarily with the end-user that multihomes.

The cost of multiple PA/CA/whateveryouwanttocallthem addresses is far too
much compared with the return.  The complexity of multiple PA prefixes
across an infrastructure that has tens of thousands of subnets is
phenomenal from an operations perspective.

/cah

---
Craig A. Huegen, Chief Network Architect      C i s c o  S y s t e m s
IT Transport, Network Technology & Design           ||        ||
Cisco Systems, Inc., 400 East Tasman Drive          ||        ||
San Jose, CA  95134, (408) 526-8104                ||||      ||||
email: [email-masked]       CCIE #2100      ..:||||||:..:||||||:..

---

From: Eliot Lear <[email-masked]>
Date: Wed, 23 Oct 2002 02:10:42 -0700

Nothing like 60 messages in one day after nothing in 6 months ;-)

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

As Tony Li knows well I've never been one for artificial shortages and 
markets (which is what I think we have in v4).  On the other hand, you 
yourself later wrote the precise contradiction to this statement:

> Unfortunately, hierarchy -> tree structure -> no loops -> no redundancy.

Now, you could argue that the additional mechanism required should be at 
the transport or in a tunnel, or whatever.  But that's additional 
infrastructure as well.

By the way, Michel, when we use the term tunnel, in any form, we really 
ought to revisit existing technology to see if it can be adopted.  Thus 
Noel's allusion to MIPv6.

I'm not convinced.  I think we have to consider Craig's complexity 
question, but at the same time ask him what he's willing to pay for 
redundancy for his service, and what sort of redundancy he needs.

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

Google, or they wouldn't pay to be multihomed.  If their users 
experience a better service, in the end that is to Google's advantage. 
But let's also separate web services from Craig's case.  It's easy to do 
a service that knows about topology and delivers a single "close" 
address to a client name server or redirect to a client.  Been there 
done that.  In fact the actual physical hosts may not even be multihomed 
into the Internet, nor might their upstreams be.

Craig's problem is a lot more difficult.  Choosing the right source 
address in a large enterprise network is difficult.  Getting both the 
physics and economics correct here is important.

> to implement extra functionality to be able to talk to multihomed

This is only because there isn't a viable alternative in v6 yet.  When 
there is you can impose a cost model in v4 and let the market do its 
thing.  And that cost model would include things like "maintenance of 
legacy v4 infrastructure, route sourcing charges, etc."  The IETF 
actually has heard from game theory researchers on this topic.

Not new.

The *real* cost I want to understand is how much someone is willing to 
pay to have fine grain control over their policy as they do today with 
BGP, padding, etc.

Eliot

---

From: "Tony Hain" <[email-masked]>
Date: Wed, 23 Oct 2002 13:08:35 -0700

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

That is a direct function of the architecture and business models. If we
take the current state, the service provider ends up eating the cost in
terms of routing table maintenance because it is the only defense
against receiving undesired traffic. If we look at a different model,
the end sites could end up paying for the capability by subscribing to
an aggregation exchange point. This model would introduce a new player
into the mix between the ISP and the customer, so it is naturally
undesirable to the business side of the house. The real question is, is
that the necessary evil that makes it possible to scale?

Tony