Subject: Re: DVMRP Question

From: [email-masked]
Date: Mon, 3 Feb 1997 16:35:28 -0800 (PST)

Please ignore and forgive the following if it seems 
unusually obtuse.

someone wrote:

|> > Even though I know Steve Deering is cringing right now as the words
|> > multicast and policy are used in the same sentence, its a fact of life.

Steve Deering <[email-masked]> replied:
 
|> Yeah, but our job is to change the facts of life, to make a better world.
|> (Each of us has our own definition of "better", of course.)

Some of us are looking at this without benefit of 10 years of studying
multicast routing, and could use some more words on wisdom on this.  

Granting that some form of >>protocol independent<< multicast routing 
will arrive, e.g. PIM-SM, CBT, or some combination, and be agreed 
upon to provide global multicast connectivity, I am still confused 
regarding whether or not *all* the policy can be carried in the
underlying unicast routing policy.  e.g. When network providers
agree to exchange routes on an IX/nap/etc. via BGP4, there are
considerations, such as "symmetric-path" or "early-out", games
played with AS #'s to handle geographical considerations 
(e.g. east-west transit in the U.S.).  Do not the requirements
for RP's/DR's or whatever add additional policy requirements in 
order to get multicast routes to behave in ways that ISPs consider
"well-behaved"?  I have this nagging feeling that PIM-SM - 
source-based-trees - shared-trees, and CBT, need to be abstracted/
recombined in such a way that the policy-related portion of them
could be tunable by an ISP.  ISP's will certainly have a vested
interest in multicast routing tables with 10,000 entries as
opposed to, say, 3,000,000.  They will have a vested interest
in RP's/DR's being where they are supposed to be. Just as in 
the unicast routing policy consideration that ISP's don't want, 
given current technology, a class-C network in every garage.  
Aren't there going to have to be some "policy" knobs to tweak 
to deal with this? Is "policy" the wrong word to use to describe this?

(signed)
Confused