Subject: Re: [arch-d] It's the routing, people!

From: "Fergie" <[email-masked]>
Date: Sun, 12 Nov 2006 20:46:12 GMT

-- David Meyer <[email-masked]>

>On Sun, Nov 12, 2006 at 04:34:49AM -0500, Bound, Jim wrote:
>> I question this unless the IAB processes wants to agree to this.  It was
>> stated at the plenary it is an address and routing problem.  Thus it is
>> on the table as we proceed with the discussion.  The IAB meeting is the
>> driver for this work and I will assume it will become more formalized
>> than a random set of opinions on our general architecture list as was
>> stated Thursday night at the plenary.
>> 
>> Would IAB rep like to comment and clarify?
>
>	Speaking as an individual, what I can say is that someone
>	got up during Leslie's "what's next" part and said
>	addressing should come before routing. I didn't
>	necessarily agree, but that's all I heard.
>
>	--dmm
>

I'm not so sure they can necessarily be decoupled in this context.

- ferg

--
"Fergie", a.k.a. Paul Ferguson
 Engineering Architecture for the Internet
 fergdawg(at)netzero.net
 ferg's tech blog: http://fergdawg.blogspot.com/

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---

From: David Meyer <[email-masked]>
Date: Sun, 12 Nov 2006 12:57:37 -0800

> I'm not so sure they can necessarily be decoupled in this context.

	I don't think that they can (I was trying play the
	"journalist role" and report on what I heard). So I'm not
	sure where this originated, but at the first IETF I ever
	attended (Columbus), Yakov told me that "Addressing can
	follow topology or topology can follow addressing. Choose
	one." I've been calling this Rehkter's Law ever since (he
	has mentioned to me that the advent of VPN technology weakens
	the "law"). 

	In any 	event, you can argue about the details, but if
	scaling the routing system depends on topological
	aggregation (such as the "aggressive topological
	aggregation" that Mike was designing for in 8+8/GSE) [0],
	this "law" would seem to hold. So either way, if you
	believe you need to topological aggregation, then you
	need some form of congruence at some point.

	--dmm

[0]	One might argue otherwise, cf Dima and Claffy's work
	(among others) on minimum stretch compact routing, or
	ROFL (routing on flat labels).

---

From: David Meyer <[email-masked]>
Date: Sun, 12 Nov 2006 13:04:19 -0800

> 	ROFL (routing on flat labels).

	BTW, I was just going to find some references for this
	work (but you can us goog or whatever for that). But I
	did want to say that I didn't want to diss anyone who is
	working on this stuff. The comment I made was close, but
	from memory, so not complete. Use goog (or whatever) to
	get a more complete bibliography.

	--dmm

---

From: John Day <[email-masked]>
Date: Sun, 12 Nov 2006 17:11:57 -0500

>  context.

As usual, Yakov only sort of gets it.  The topology of the address 
space must be compatible with the graph of the network.  Otherwise, 
why use that topology?  It will just get in your way.  It is a bit 
kludgy to try to apply the idea of topology to the Internet.   All 
you really have is a graph. Lets just say that if the graph is static 
then addressing can follow the graph.  However, if an address space 
is defined such that the network graph can grow, then it behooves the 
network to grow in ways compatible with the topology of the address 
space.  Otherwise, you are working at cross purposes.

>	need some form of congruence at some point.

This is indeed the case.

Take care,
john

---

From: "Bound, Jim" <[email-masked]>
Date: Sun, 12 Nov 2006 17:24:16 -0500

My hope is there will be a lot of views and brilliance shared lets not
assume any thing yet once we have what we are suppose to "get" then we
decide how we move forward with only discussing models and architectures
and within them the assumption by the many bright people who will
contribute in the IETF.  Right now as requested I am using a blank sheet
of paper.  What I believe is important is the business and
time-to-market reality check we need to make.  Some will say use IPv6
and go forward, some will say jack up v4 and move to v6 via the jackups,
some might even say no invent IPv15 or we could go where Dr. Preston
Marhall at DARPA is looking at using a new generation of wirless
communications pretty much replacing IP all together for the most part.
Fred said we need proposals and those proposals will have to address a
core set of base questions, what those questions are is an important
discussion too.  I think this is going to take a minimum of two years
and this is not the list to do the hands on work for as it is a general
IETF list that should support many topics besides this one.

Best,
/jim

> -----Original Message-----
> From: John Day [mailto:[email-masked]] 
> Sent: Sunday, November 12, 2006 5:12 PM
> To: David Meyer; Fergie
> Cc: [email-masked]; [email-masked]; Bound, Jim
> Subject: Re: [arch-d] It's the routing, people!
> 
> >  context.
> >
> As usual, Yakov only sort of gets it.  The topology of the 
> address space must be compatible with the graph of the 
> network.  Otherwise, why use that topology?  It will just get 
> in your way.  It is a bit 
> you really have is a graph. Lets just say that if the graph 
> is static then addressing can follow the graph.  However, if 
> an address space is defined such that the network graph can 
> grow, then it behooves the network to grow in ways compatible 
> with the topology of the address space.  Otherwise, you are 
> working at cross purposes.
>

---

From: Iljitsch van Beijnum <[email-masked]>
Date: Mon, 13 Nov 2006 15:42:30 +0100

On 12-nov-2006, at 21:57, David Meyer wrote:

>         at the first IETF I ever
> 	one."

[...]

>         if
> 	this "law" would seem to hold.

There is another caveat: the address space must look the same to  
everyone. But the topology of the network doesn't, due to the  
policies that are applied in BGP. This means that, even if we  
disregard the fact that topology is subject to constant change, it's  
impossible to have a direct mapping between addressing and topology.  
And then there's the issue of crossconnects (multihomed ASes) that  
can't be expressed in the hierarchy we need to view the address space  
as in order to do our longest-match-first lookups.

I remember someone saying something like "we can create any  
addressing architecture we want, routing will (have to) follow". Or  
maybe that's what the inventor of the Ethernet switch said? I'll file  
this next to "given sufficient thrust, pigs will fly just fine."

A correlation between addressing and topology that's strong enough to  
be useful to make routing scale can only realistically happen by  
making compromises. I.e., neither addressing nor topology can be  
completely free, both will have to be limited. An example of this is  
geographic aggregation, where addressing is aligned with geography,  
which means that a network topology that ignores geography either  
can't work at all or must break aggregation. [1]

If such a compromise is deemed undesireable or unacceptable, then,  
given the facts that the internet must support policy and multihoming  
and users require stable addressing (for your favorite value of  
"stable"), the only conclusion can be that the addressing seen by the  
users and the addressing seen by the core routers can't be the same.  
However, this doesn't really solve the problem, it only moves it away  
from the place where things are expensive (the fast routers that  
require the big tables), hopefully to a place where the information  
explosion caused by unaggregatable/unaggregated addressing is cheaper  
to manage.

[1] Note that geographic aggregation can be seen as a special case of  
increased stretch routing where the alignment between the placement  
of routers containing table entries for part of the network and the  
location of the address users reduces the problem of scenic routing.