Re: [RRG] some musings on PI v. PA, and assumptions, requirements, and tradeoffs

[Scott Brim <swb@employees.org>]

Dave, I'm missing what's new here.  Having a PI allocation means news
of available paths to you can be carried further (all over) in BGP
space without being aggregated, so people are aware of you further
away and may take different paths to reach you.  Good but costly.


On 07/13/2007 11:57 AM, Noel Chiappa allegedly wrote:
>   "JTW Principle: - The best design minimizes the overall cost of providing
> 	those benefits.

Just to be sure ... "overall cost" can include lots of things,
including loss of flexibility for the future.

> I'd say that any multi-homing solution which is benefitting only a few people
> has to involve the hosts more (which is why, architecturally, Multi6 went
> down that path). For your particular issue, hosts would have to e.g. notice
> that there's a service interruption, and try a different locator for the
> service.

or pre-announce them to the other end(s) at some higher layer, e.g.
SCTP.  (Aside: think about that and CONS.)

>   "Site multihoming is, fundamentally, a path-selection (routing) issue. That
>   is, there are multiple paths through the physical connectivity fabric, and
>   we wish to make more than one of them available for use.
>   This does not sound hard. Why is it so difficult? The issue turns out to be
>   simply one of efficiency - i.e. how high a cost (or overhead) do we want
>   the path selection to have/incur. If any infinite cost were acceptable,
>   there would be no problem."
> 
> I don't have any magical solution to this problem. Indeed, looking at it
> the way I laid it out in those two notes, graph theory kind of has you
> trapped...

The magical solution is the one we're all talking about -- to
distribute the problem differently, to use push and pull, time and
space. :-)

Scott


--
to unsubscribe send a message to rrg-request@psg.com with the
word 'unsubscribe' in a single line as the message text body.
archive: <http://psg.com/lists/rrg/> & ftp://psg.com/pub/lists/rrg