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

  • From: Per Heldal
  • Date: Mon Oct 17 06:34:35 2005

man, 17,.10.2005 kl. 07.17 +0200, skrev Mikael Abrahamsson:
> Both MPLS and any tunneled VPN over IP means the core won't have to know 
> about all those prefixes (think aggregation of addresses regionally in the 
> IP case and outer label in the MPLS case).

Hope you don't imply NAT and private addresses like it is usually
associated with VPN in the IPv4 world ;)

> So if you're building a 100G capable platform that'll do IPv6 and MPLS, 
> how much difference would it be if you only had to support 16000 labels 
> and 16000 IPv6 prefixes, rather than 2 million?
> Then of course I guess the argument can be made to put everything on MPLS 
> to avoid the core knowing about anything but outer labels.

<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>

What this discussion boils down to is that a long term solution has to
remove the size of the routing-table as a limiting factor in internet
routing.  Something must eliminate the need for every node in the
default-free transit-network to know how to reach every allocated
address-block at all times. Allocation policies, operational agreements
on filtering, BCPs etc can only slow the growth of the routing-table.
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
be built and maintained automatically (may involve packet tagging /
tunnelling etc), similar to current route-cache mechanisms, but will
require a whole new set of routing protocols. Despite lots of research
there's no such solution today or anytime soon. Just think of the added
complexity. How do you build trust with remote nodes given the problems
you see in trusting your direct peers in the BGP world today? How can
routing loops be prevented in such a network? All we know is that if
there is no such solution, at some point in time the network will
fragment due to its size and complexity.

In the meantime we have to manage with what we've got, and treat v6 just
like we've done with v4 - multihoming and all. We know we'll run out of
v4 addresses at some point, and that v6 is the only realistic
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.
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
made it pretty clear that it is unacceptable to them to be tied to any
single provider. Besides, shim6 doesn't eliminate the need for a
mechanism to locate any globally unique address. What if there's
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