a radical proposal (Re: protocols that don't meet the need...)

Vince Fuller vaf at cisco.com
Thu Feb 16 22:37:47 UTC 2006


Uh-oh, two postings to NANOG in as many days... hopefully, this will be
my last.

> [[pushed the wrong button last time. This is the complete reply]]

Oh, the irony in that statement... this whole argument has certainly pushed
"the wrong button" for me.

> 
> >   - join a local IXP, which may be a physical switch or
> >     virtualized by a set of bilateral agreements.
> 
> Why should they join an IXP if they already have
> private peering arrangements?
> 
> >   - outside the region, they advertise the prefix of the
> >     regional authority
> 
> Mixing government with operations? If you favor doing
> that then why not just give IPv6 addresses to the various
> national governments and let the UN sort it out?
> 
> Personally I disagree with any scheme which calls for 
> national or municipal governments to assign IPv6 addresses
> to end users. Dressing it up as a "regional authority"
> does not make it any nicer.
> 
> Forcing people to join an unecessary IX is not the way
> to solve the problem of regional aggregation of routes.
> This is a purely technical problem which can be solved
> by the RIR practices in allocating IPv6 addresses. If they
> would allocate addresses in a geo-topological manner then
> end users and ISPs would be free to aggregate routes 
> outside of their region without any involvement of governments
> or any requirement to join consortia or IXes. It does 
> require the users of such geo-topological addresses to
> ensure that in THEIR region, there is sufficient 
> interconnectivity (physical and policy) between ISPs for
> the addressing to work. But that does not need to be determined
> or managed centrally.
> 
> Geo-topological addressing refers to RIRs reserving large
> blocks of designated addresses for areas served my large
> cities (over 100,000) population. When end users are located
> in fringe areas roughly equidistant between two or more such
> centers, the RIR simply asks the end user (or ISP) which is
> the center to which they want to connect (communicate).
> This addressing scheme operates in parallel with the existing
> provider-oriented IPv6 addressing scheme but uses a different
> block of IPv6 addresses out of the 7/8ths that are currently
> reserved. No hardware or software changes are required for this
> to work, merely some geographical/economical research to determine
> the relative sizes of the address pool to be reserved for each
> of the world's 5000 largest cities.

The routing system doesn't particularly care whether your "geo-topo"
addressing is imposed by governments, RIRs, or a beneveolent dictator;
in all cases, the result is Soviet-style central planning to force the
network topology to conform to your idea of what it "should" be rather
than following the economic realities of the those who would build the
network.

A "geo-topo" addressing scheme works great for address assignment *within*
a single AS and it even could have worked pretty well back in 1990, when
there was a "core" NSFNET and a bunch of regional networks. But the key
attribute of these scanerios is the existance of centralized control of
the topology. There is no such control of the topology today; those who wish
to impose such control are asking for a regulatory environment that would
radically change the nature of the Internet.
> 
> > Whenever I have talked about the model with an ISP, I have gotten 
> > blasted. Basically, I have been told that
> > 
> > (1) any idea on operations proposed in the IETF is a bad idea because 
> > the IETF doesn't listen to operators
> 
> This is true. Top-down does not work in Internet operations.
> We need bottom-up, i.e. customer demand. The IETF needs to
> view their role as enablers of customer demand. If the IETF
> can create something that will work for ISP customers, then
> ISPs will be happy to go along, once the customers demand
> the service.

Interesting to see an argument for bottom-up design in a post which
otherwise calls for top-down planning of the network architecture.

What the IETF, and more specifically the IAB, really needs to do is to
acknowledge that there is a very real problem with the ipv6 routing
architecture (which is identical to the IPv4 routing architecture), one
that cannot be fixed without making incompatible changes to protocol
implementation. Band-aids like shim6 just aren't going to cut it if the
goal is to build a highly-scalable network of autonomous routing domains
(in other worse, a really big network where end sites have very flexible
choices of providers). The first step to finding a solution is to admit
that there is a problem.

> > (2) the ISPs aren't going to be willing to make settlement payments 
> > among themselves in accordance with the plan
> 
> Wait until this starts appearing as a requirement in
> custome RFPs.

Then wait until governmental bodies step in to offer their help in the
form of regulation. The two go hand-in-hand. If you want to re-invent the
telco model of interconnection, this is a pretty big step in that direction.

...

> > Note 2: Provider-provisioned addresses continue to make sense for 
> > folks that don't plan to multihome.
> 
> Indeed they do. But the current IPv6 addressing model is completely
> slanted towards provider-provisioned addresses for single-homed
> entities. Calling a small block of these provider-provisioned
> addresses PI (provider independent) does not really make the addresses
> provider independent and does not help small enterprises to implement
> meaningful multihoming. The IETF has imposed this provider-provisioned
> model on IPv4 and is thus directly responsible for the ISP cartel
> which now exists.

Methinks we are re-interpreting history here. The IETF didn't create an "ISP
cartel" for IPv4. What CIDR did, and I think I can speak with some degree
of authority on this subject, was to allow routing state to scale
in a non-exponential manner by encouraging address assignment to follow
topology. Of course, the fact is that it is the providers which determine
network topology because it is they who create it (this is something of a
tautology). There are consequences of this, namely that provider changes
imply renumbering, but this really isn't some grand scheme to lock customers
in to providers; it is an unfortunate consequence of the combination of
addressing following topology and a poor, late-1960's design decision to
combine endpoint identification and routing locator into a single quantity
known as an IP address.

It is important to note that CIDR was explicitly specified as a short-term
measure to prevent the explosion of routing state from causing the Internet
to become unmanageable, which was the alternative to its adoption back in
the early-to-mid-1990s. It was also explicitly intended to be replaced by
a scalable, long-term solution which, unfortunately, has yet to be designed.
If you don't believe me, go read the documents for yourself - they say 
exactly the same thing.

In the interests of demonstrating why "geo-topo" addressing can't possibly
work without radical changes to the business and regulatory models of the
Internet, consider the simple example of a provider who has connections
to two popular "geo-topo" addressing domains, say the Bay Area and the
DC area. Let's say that 10.0.0.0/8 is the "geo-topo" address block in the
Bay Area and 172.16.0.0/12 is the "geo-topo" block in the DC area. This
provider has four customers in the Bay Area:

  10.1.1.0/24
  10.10.4.0/22
  10.100.8.0/21
  10.200.0.0/16

How is the provider supposed to make use of the 10.0.0.0/8 aggregate? Does
he advertise it to other providers in the DC area or anywhere else where
he offers service (Asia, Europe, etc.)? By doing so, he is stating that he
can provide connectivity to all hosts which are numbered in that address
range. But he only provides transit service to the address ranges associated
with his customers. For him to provide connectivity to all the address range,
he must

  a) have full routing connectivity to all other providers that have
     addresses in the same range; this implies that he connects to all IXs
     within the region and maintaines a full-mesh of routing information
     (today, BGP sessions) to all of these providers

and

  b) must be willing to provide connectivity to all sites within the region
     to any place that he advertises the prefix 10.0.0.0/8 through routing
     exchanges; if he advertises this prefix to non-customers, it implies
     that he is will provide free transit to his competitors' customers
     which are numbered out of this block

Both of these requirements defy business sense, so absent the imposition of
strong regulation and negotiated settlements, they are unlikely to appeal to
any provider which wishes to offer service to and between multiple cities;
without such providers, you don't have a global Internet.

I'm not sure how I can make this much more clear. It seems appropriate to
re-state Dave's quote Yakov:

  "Addressing can follow topology or topology can follow addressing.
   Choose one."

and I'd offer a corollary:

  Transit relationships (i.e money) must follow topological relationships
  (and thus addressing); the alternative is some combination of inefficient
  or non-scalable routing, black holes, settlements, regulation, or other
  undesireable things.

If you really want to combine transport identifier and routing locator into
a single "address", you give up a lot of flexibility. For routing to scale,
addressing must follow topology, so in such a network architecture the term
"topology independent address" (aka "provider independent address") is truly
an oxymoron.

	--Vince



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