Subject: Re: [RRG] anycast/default as a transition tool [On the Transitionability of LISP]

From: Pekka Savola <[email-masked]>
Date: Fri, 3 Aug 2007 08:29:35 +0300 (EEST)

On Thu, 2 Aug 2007, Christian Vogt wrote:
> (The reason one needs anycast IDs is to let multiple alternative
> providers perform the same remote mapping for an edge network.  Unicast
> IDs would bind the remote mapping to a single provider.  This would
> create a dependency of the edge network on that provider, which is
> exactly what we want to avoid with multi-homing.)

The anycast model would (AFAICS) be similar if not identical to 
advertising a default route to the non-upgraded networks.

In fact, that is already somewhat common in today's Internet's smaller 
providers which don't want/need to carry the full BGP table.

Both anycast and default route also have similar failure modes, i.e., 
if a default/anycast route is advertised by a router which doesn't 
have full topology information (or at least a lead where to forward 
the packets to get it), connectivity of Internet is going to be 
balkanized depending on which anycast/default you happen to be using.

Maybe we don't need a solution at the edges, just more default routing
:-)

-- 
Pekka Savola                 "You each name yourselves king, yet the
Netcore Oy                    kingdom bleeds."
Systems. Networks. Security. -- George R.R. Martin: A Clash of Kings

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From: Christian Vogt <[email-masked]>
Date: Fri, 03 Aug 2007 20:10:53 +0300

> Maybe we don't need a solution at the edges, just more default routing

This actually seems to be a very attractive idea.

Packets destined to IDs, for which no entry exists in the global routing
table, would by definition be forwarded along a default route until they
get to a provider that performs the ID-to-locator mapping for the
destination edge network.

One disadvantage, though, would be that loops may become difficult to
prevent unless ALL providers (as of a certain tier) that advertise a
default route perform the mapping for ALL edge networks using ID space.

One would also have to think about changes in the Internet business
model.  As explained in my previous email, a transition towards mapped
IDs would require an edge network to subscribe to the remote-mapping
service of as many as possible providers -- in addition to the standard
subscriptions with the directly connected providers.

- Christian

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From: David Meyer <[email-masked]>
Date: Fri, 3 Aug 2007 10:20:05 -0700

> destination edge network.

	This is one of the ideas that both Darrel Lewis and Vince
	Fuller have suggested in the past. 

> subscriptions with the directly connected providers.

	I agree that we need to think (quite a bit) more about
	the/which business models that underly all of this.

	Dave

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From: Eliot Lear <[email-masked]>
Date: Sun, 05 Aug 2007 19:36:38 +0200

> Maybe we don't need a solution at the edges, just more default routing

Ultimately in the case of LISP all that is being offered is a mapping.  
And so any ITR that advertises a default or supernet for 
non-participants merely needs to have the entire mapping and offer to 
map for those mappings.

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From: Robin Whittle <[email-masked]>
Date: Mon, 06 Aug 2007 05:59:02 +1000

Hi Eliot,

I haven't been keeping up with this discussion, but will return to
it in the next few days.

> non-participants merely needs to have the entire mapping and offer to

LISP-CONS would not work very well because it will typically take a
few seconds (I guess - one, two or three) to get mapping from across
the global ITR-CAR-CDR*n-CAR network.  LISP-NERD ITRs have copies of
the full database, so they should be able to forward all packets
instantly.

  - Robin