North American Network Operators Group

Date Prev | Date Next | Date Index | Thread Index | Author Index | Historical

Re: And Now for Something Completely Different (was Re: IPv6 news)

  • From: Per Heldal
  • Date: Mon Oct 17 09:40:56 2005

man, 17,.10.2005 kl. 12.55 +0000, skrev Mikael Abrahamsson:
> > <flame>MPLS on its own won't solve anything. Although MPLS has its uses,
> > it smells too much like another desperate attempt from the telco-heads
> > in the ITU crowd to make a packet-switched network look and behave like
> > a circuit-switched network.</flame>
> Why? The initial argument for MPLS was that it would solve the core 
> problem and put intelligence at the edge. You would have a core that only 
> needed to know about hundreds of nodes instead of 100.000:nds of nodes.

My comment about MPLS wasn't directed specifically at this problem.
Re-encapsulation may or may not be part of a future solution. If so,
what mechanism is tbd.

A true scalable solution will equire that the problem is distributed.
Isolation of the problem in one place (core or edge) is no solution. 

> > Growth can't be eliminated. In the future network you'll have routers
> > that may know a lot about their "local region" of the network but have
> > to rely on nodes that are several hops (even AS-hops) away to pass the
> > packets to more remote destinations. These trust-relationships have to
> Yes, that is what's being proposed. Know your internal nodes, announce 
> single big prefix externally. With ISPs only having a single prefix and no 
> "single customer" prefixes, routing table can be kept low. Redundancy can 
> be solved with for instance shim6.

What I suggested above is not what is being proposed. Current proposals
are limited to quirks to make your network appear less complex to the
world. Ok in the short term, but doesn't scale.

Well, let's try to turn the problem on its head and see if thats
clearer; Imagine an internet where only your closest neighbors know you
exist. The rest of the internet knows nothing about you, except there
are mechanisms that let them "track you down" when necessary. That is
very different from today's full-routing-table.

> > alternative. Without improved routing protocols, all we can do is to
> > pray that the development of routing hardware in terms of memory and
> > processing capability outpaces the growth of the routing table.
> We have done this for 15 years or so, what good has it brought us? Yes, 
> TCAM size etc has been fairly good in keeping up with routing table size, 
> but at quite high cost.

True, but there's no law saying that current routing protocols and
path-selection algorithms have to stay unchanged forever.

> > Initiatives like shim6 that changes the behaviour of leaf-nodes are only
> > a supplement and won't replace the need for true multi-homing for
> > end-sites. Here we have to adapt to business needs, and businesses have
> Why? What problem does multihoming with single prefix solve that a fully 
> working shim6 doesn't?

It does not provide 100% provider-indepence to begin with. Depending on
who you ask that alone is a show-stopper. 

>  What is the argument that the "internet" needs to 
> know about a lot of end-users, instead of the end-user knowing that each 
> end user might have n number of IP addresses and that there are n^2 
> combinations to send packets?

The internet shouldn't need to know anything about individual users to
begin with, provided there are mechanisms avilable track them down. By
that I mean that algorithms to locate end-nodes may include mechanisms
to "interrogate" a large number of nodes to find the desired location as
opposed to looking it up in a locally stored database (routing-table).

Note that I'm all for shim6 as a principle, just not in this context.
It's perfect for future communications devices that may need to switch
between GSM-UMTS, GSM-EDGE, WLAN, WIMAX, ethernet w/charging-power for
mobile units and whatever else is available by then. 

> Convergence time in the real world today is in the minutes, with shim6 it 
> would for the end user be much quicker to "route around" the problem. 
> Shouldn't be any problem to have failover in the subsecond timeframe, even 
> thought that might need some kind of hello mechanism that is suboptimal 
> because it sends traffic not carrying any data.
> > single provider. Besides, shim6 doesn't eliminate the need for a
> > mechanism to locate any globally unique address. What if there's
> I thought DNS solved that?

I thought DNS only provided a name for an address ;) How does DNS tell
us that e.g. is part of a subnet belonging to AS2838 and how
to get there?

> > suddenly 10M LIR's, or otherwise a trend towards a market with very
> > small providers each handling only a small number of customers? Who gets
> > to decide who may peer with whom, or decide which providers will be
> > denied the ability to build redundant connectivity with multiple
> > upstreams?
> It costs money to maintain a LIR which limits the number of LIRs 
> economically viable in the world.

True, but it's just another artificial limit. It doesn't address the
real problem of limitations in current core networking protocols.