Shim6, was: Re: filtering /48 is going to be necessary

Łukasz Bromirski lukasz at
Mon Mar 12 17:20:13 CDT 2012

On 2012-03-12 22:14, Iljitsch van Beijnum wrote:
> On 12 Mar 2012, at 21:15 , William Herrin wrote:
>> Not at all. You just build a second tier to the routing system.
> It's so strange how people think a locator/identifier split will solve
 > the scalability problem. We already have two tiers: DNS names and IP
 > addresses. So that didn't solve anything. I don't see any reason a
 > second second tier would.

Wrong analogy IMHO.

Using it, you'd know how to get to specific host in IPv4/IPv6-centric
Internet by looking up it's name. Knowing a host is ''
doesn't give you information needed to route IPv4/v6 packets that we
still use, to this specific system. You still need to lookup the IP
assigned to this name.

For LISP (other solutions may vary obviously) knowing node 54.100 is
available (after lookup) currently at 200.101 makes possibility for
core routers to only remember the paths to 200.101/16 and not
thousands of this prefix aggregates. This is aggregation of information
at the same level of lookup execution.

The real problems for world-wide LISP adoption are currently:
  - nobody sees a FIB explosion for IPv6, because
  - only around 8k worth of prefixes is in the global IPv6 table

Hardly a reason for anyone to implement aggregation. If IPv6 would
reach todays IPv4 level of 400k it would be still not a very compelling
reason apart from those SPs willing to run all their edge without MPLS
and with L3 devices that have very tiny FIBs - like 2/4/8k of entries.
Typical core router has ability to forward 2-3M of IPv4 prefixes in
hardware, and around 500k-2M of IPv6 prefixes in hardware - today.

Ideal LISP use case would be for example 4M of IPv6 prefixes with
steady clearly visible growth. Aggregating this down to for example
(I've made this completely up) 200k prefixes and still having
ability to traffic engineer the paths between the source and destination
almost at the levels of having all 4M prefixes in FIB is very compelling
reason to deploy LISP.

"There's no sense in being precise when |               Łukasz Bromirski
  you don't know what you're talking     |      jid:lbromirski at
  about."               John von Neumann |

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