shim6 @ NANOG (forwarded note from John Payne)

David Barak thegameiam at
Wed Mar 1 16:22:01 UTC 2006

--- Joe Abley <jabley at> wrote:

> How about some actual technical complaints about
> shim6? The jerking  
> knees become tedious to watch, after a while.

Okay, if I'm an enterprise with 6 ISPs but don't
qualify for PI space, I'll need to get PA space from
all of them, for Shim6 to work, right?  Then each
server on my network is going to need to maintain
state for 6 different contexts for each of the various
external customers who attempt to reach them. 
Assuming that I have busy servers, that's a whole lot
of state.  

It's cheaper and easier to upgrade or modify N routers
than the M servers behind them, given that M is
certainly greater than N, and in many cases in
multiple orders of magnitude greater.  

Also, the current drafts don't support middleboxes,
which a huge number of enterprises use - in fact the
drafts specifically preclude their existence, which
renders this a complete non-starter for most of my

My single biggest issue here however is the
complexity: given that today's architecture can
deliver relatively simple and robust multihoming to
enterprises, and rerouting DOES work today for
persistent sessions (albeit imperfectly), what is the
benefit to be gained from doing something this hard?

As far as I can tell, the whole reason for these
discussions is the insistence on the strict
PA-addressing model, with no ability to advertise PA
space to other providers.  I think that we could spend
our time better in coming up with a different approach
to addressing hierarchy instead.  Besides, /48s are
cheap now, but if every enterprise gets multiple /48s
from multiple providers, they might become dear more
quickly than is desired.


David Barak
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