Subject: RE: The state of IPv6 multihoming development

From: "J. Noel Chiappa" <[email-masked]>
Date: Tue, 22 Oct 2002 16:57:59 -0400

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

    > Do you think one more time is all it will take...?

Given that we've been working on getting people to understand this since well
into the previous millenium, I have no hopes that we'll be there anytime soon.

    >> An "address", as used in the IPv4/v6 architectures, is a name that
    >> (among other functions) specifies *where* that entity is in the network
    >> it is attached to the network's connectivity topology.

    > I wouldn't call an address a name

It's a "name" in the general computer-science sense of the term "name".

    >> "geographical address" ->
    >> "geographical topological-location-name" ->
    >> "connectivity-independent topological-location-name" ->
    >> "topological-location-independent topological-location-name".

    > I have to say I don't quite follow your permutations

Perhaps you should go over it again. It's an important point, and I believe
it's been laid out in a fairly clearly.

    > if this is such a paradox, how come it has worked for years for E.164
    > addresses?

Well, for one, the international telephone system doesn't use dynamic
routing. Because of the close connections between topology, addresses, and
routing, one basically has the choice of either forcing the addressing to
follow the connectivity topology, or forcing the connectivity topology to
follow the addressing. The international telephone connectivity is pretty
heavily regulated (indeed, in many countries around the world, it's still a
government monopoly).

Those parts of the system that do have some number portability do it through
a mechanism which is basically identical to IPv6 Mobility - your "phone
number" is now a virtual 'name', and it gets translated into a different
phone number which is your actual phone 'address'. This corresponds exactly
to the "home address", etc of IPv6 Mobility.

So there's another possible solution for people who really want to
multi-home: use IPv6 Mobility. That's already supported in all hosts, right?

	Noel

---

From: Peter Tattam <[email-masked]>
Date: Wed, 23 Oct 2002 08:24:48 +1100 (EST)

I have not weighed in on this discussion yet as I wanted to see what the
general consensus was.

All I can say is that I believe the transport based solution I developed a
couple of years back will work, and could easily be extended to cover non-TCP
protocols.  However, I did find that the level of support for my ideas were
rather wanting which sadly made it difficult for me to devote time & effort to
rounding them off.  One other difficulty is that IPv6 deployment of
hardware/software is now a fait accomplit and it's unlikely that my ideas would
be implementable.

I too agree that the requirements document places an insurmountable hurdle as
there are mutually exclusive requirements that must be met.

I have recently wondered whether the multihoming problem could be solved by
isolating the requirement for global uniqueness of IP addresses from the
more fluid nature of routing.  Such proposals have been raised before, but
rejected as being too radical in my opinion.

One thing still remains clear though - multihoming is the thorn in the side for
IPv6.  Until it is finalized, IPv6 will be going nowhere.

Peter

--
Peter R. Tattam                            [email-masked]
Managing Director,    Trumpet Software International Pty Ltd
Hobart, Australia,  Ph. +61-3-6245-0220,  Fax +61-3-62450210

---

From: Iljitsch van Beijnum <[email-masked]>
Date: Wed, 23 Oct 2002 00:03:11 +0200 (CEST)

> routing.

Hm, hardly a good point. If you can train monkeys with a fax machine to
execute your routing algorithm, it must be simple enough to implement on
a router, I'd think...

> Because of the close connections between topology, addresses, and
> follow the addressing.

I think the last place where addressing follows topology is in old
electro-mechanical telephone exchanges, where the digit you dial is
translated to an actual crossconnect location. In IP, there is only a
slight overlap between the addressing and topology hierarchies.
Unfortunately, hierarchy -> tree structure -> no loops -> no redundancy.

Trying as hard as I can to think "out of the box" it seems reasonable to
me to see how far we can get by tying addresses to location. I know this
is an "ugly" solution as in theory, the network topology has nothing to
do with geography. And as we know, in theory there is no difference
between theory and practice, but in practice there is. Despite the fact
that I run a website under the domain "bgpexpert.com" I have no delusion
I'm the world's greatest routing expert, but on the other hand I'm not a
complete novice and I feel confident that this geographical aggregation
will work in practice. And the really good part is it's all completely
optional: you don't _have_ to geographically aggregate. If people don't
like the fact that addresses are geographically significant, they can
simply treat them as straight PI addresses and buy big routers.

> to the "home address", etc of IPv6 Mobility.

It's a bit more complicated than that. Some networks use the
"intelligent network" for everything, but first you have to reach the
"home" network for a "prefix". There is a three level hierarchy here:
country, city (state in the US?), operator. In IPv4, it's just
"operator". So does this mean we're smarter or stupider than the
bell-heads?

> multi-home: use IPv6 Mobility. That's already supported in all hosts, right?

Mobility has useful mechanisms, but unfortunately it will not do
anything useful in the presence of outages.

---

From: Tim Chown <[email-masked]>
Date: Wed, 23 Oct 2002 00:04:28 +0100

> IPv6.  Until it is finalized, IPv6 will be going nowhere.

Is it really that big a thorn?

To play devil's advocate...

What proportion of Internet sites are multihomed?  Academia generally isn't,
not to the universities, although the NRENs will have multiple peerings.

What proportion of Internet enterprise sites are mission critical?  My home
or small business DSL/cable network certainly isn't multihomed, in the
access network at least.   Itojun is a rare example with four home /48's,
I think :)

How frequently are multihomed sites calling on their resilient links?  Of
course ISPs like to sell additional connectivity.

How much of the IPv4 DFZ clutter is due to multihomed sites?  

Are 3GPP systems using IPv6 in Release 5 multihomed?
 
I don't see lack of multihoming stopping deployment to academic networks
(many 10's of millions of users), or to broadband home networks.  There's
a potentially big IPv6 market in the latter.

Multihoming is important, but is it that important?

Tim

---

From: Peter Tattam <[email-masked]>
Date: Wed, 23 Oct 2002 10:29:31 +1100 (EST)

While I agree that it may not be entirely necessary for the real deployment of
IPv6, it is IPv6 opponents that continually use it to denigrate IPv6.  So
that's why I said "thorn in the side" instead of a "gaping wound" :)  These
people are the kinds of people who have strong influence in teh spheres of
power.  Until they are silenced once and for all, they whittle away trying to
reduce any progress that IPv6 would make.

Peter

---

From: "Michael H. Lambert" <[email-masked]>
Date: Tue, 22 Oct 2002 20:27:27 -0400

Tim,

> What proportion of Internet sites are multihomed?  Academia generally
> isn't, not to the universities, although the NRENs will have multiple
> peerings.

In the US, all Internet2 member universities are multihomed (or at least 
the GigaPoPs to which they connect are, which helps with scaling but not 
the underlying problem).  This is true now for IPv4 and will be soon for 
IPv6.  Eventually the NRENs will impose the same Conditions of Use on IPv6 
as are currently in place for IPv4.  The end result is PA + multihoming + 
CoU = multiple addresses, some of which have special semantics.

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]        |
+-----------------------------------------------------------------------+

---

From: Pekka Savola <[email-masked]>
Date: Wed, 23 Oct 2002 09:34:51 +0300 (EEST)

> CoU = multiple addresses, some of which have special semantics.

Careful with the terminology...

In multihoming, two or more network connections to the same connectivity 
provider is a trivial case we don't have to worry about.  I believe this 
is what most academia do (we too).

Now, if a university would want to advertise it's /48 using commodity 
Internet as a backup too.. that would be the problem we're solving.

-- 
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: Iljitsch van Beijnum <[email-masked]>
Date: Wed, 23 Oct 2002 14:55:13 +0200 (CEST)

> not to the universities, although the NRENs will have multiple peerings.

But they do often have PI space. How would universities like it if they
had to renumber every time their transit ISP changes?

This could be called "serial multihoming": an organization doesn't
actually multihome, but changes ISPs relatively frequently.

> What proportion of Internet enterprise sites are mission critical?

Business still send out bills through regular mail. At some point in the
future, they're going to realize this costs a lot of money and is very
inconvenient. When they start sending out bills over the net, suddenly
their connectivity becomes mission ciritical.

I'm not sure our billion multihomers is very realistic, but expecting we
can do IPv4-style multihoming and not run into trouble is a very big
risk.

Don't forget that in IPv4, lots of organizations can't effectively
multihome, because they can't get a large enough block of addresses and
small blocks are filtered. In IPv6, everyone gets a /48 so filtering on
prefix length doesn't work anymore and it's all or nothing.

> How frequently are multihomed sites calling on their resilient links?

When you have extra links, you usually load balance/traffic engineer
your traffic over them. See http://www.oreilly.com/catalog/bgp/chapter/ch06.html
on how to do this.  :-)

> How much of the IPv4 DFZ clutter is due to multihomed sites?

Actually not that much. There are less than 30k ASes, and around half of
them are visible in the global routing table. Of those, a fair number
must be ISPs.

Iljitsch

---

From: "Michael H. Lambert" <[email-masked]>
Date: Wed, 23 Oct 2002 10:06:23 -0400

> is what most academia do (we too).

Understood.  On one side we have four universities and a few other 
entities.  On the other, three commodity providers and two R&E networks. 
I'd call that multihoming.

We currently have a PA allocation from one of the R&E networks; if we were 
to ask, we could receive addresses from the other R&E network and, 
probably, one of the commodity providers.  We haven't asked, because 
multiple PA addresses on an interface would be problematic in our 
environment.

Michael

---

From: Rick Summerhill <[email-masked]>
Date: Wed, 23 Oct 2002 09:45:18 -0500 (CDT)

> multiple PA addresses on an interface would be problematic in our

Let me chime in with an example from academia that is going to hit
is very soon if v6 is to take off.

Like Michael, I run a gigapop connected to research backbones and
multiple commodity providers.  Call my network A, and include in
that network a potential for 5 (PA) prefixes.

Below me, sits several state networks.  They connect to me, would
get our prefixes and they might also have their own commodity
connections, almost always multiple in number.  Call that network
B, and add another 2 prefixes.

Below that state network, sits a university.  They may have only
one connection to the state network, but they may have to deal with
the above prefixes.  They may also feel the necessity to have their
own commodity connection, or they may indeed connect to a specialized
research network, taking in another set of prefixes.  Call that
network C.

Below C, sits an extension office D out in a remote county that
connects to the university for research purposes, but they also has
as part of their mission serving the rural community.  They may
want to have redundancy in their connectivity, to simply serve their
county needs.  This simple site has multiple computers and other
research gathering devices in their offices and field equipment, and
therefore will most likely utilize a /48.

Finally, this is not way off in the future.  As Michael indicates,
we run a native v6 connection to a research backbone at this time and
want to connect to our commodity providers via v6 also.  If v6 is to
propagate, this issue must be dealt with.

--Rick

--
Rick Summerhill                          Executive Director, GPN
5008 Canyon Road                         [email-masked]
Manhattan, KS 66503                      Cell: 785-341-7878
Voice: 785-587-4642                      Fax:  785-587-4642