Re: How to pick a Site-Local Scope multi cast address

[John Kristoff <jtk () ultradns net>]

On Fri, 8 Dec 2006 09:54:03 -0600
"Dave Raskin" <dave.raskin () rimage com> wrote:

> Hello, I have been directed to this list by IANA when I asked the
> following question:

An even better set of lists might be:

  <https://www1.ietf.org/mailman/listinfo/mboned>
  <https://mail.internet2.edu/wws/info/wg-multicast>

There is some overlap between the two, but the former is probably
the best place to start.  Both are good lists that may be relevant
for you to hang out in as they often cover the protocol and
operational aspects you may want to follow.  Both are low volume.

>  My question is this:

First, let me say... THANK YOU!  Presuming you are a multicast app
developer, you actually asked, terrific!  Most don't and what ends
up happening is growth in the "multicast swamp", where site local
apps like the one you're presuming working with end up leaking all
over the place taking up valuable mcast router memory space and cpu
time.

Now, the bad news.

>       How do I pick a group address within this range and not have a
> chance of colliding with some other application on the network already
> using the group  address I just picked?
>       Do I just randomly pick an address in that range and hope for
> the best? I am running on Windows and cannot assume that there is a
> MADCAP server available.

You can probably never expect to find a MADCAP server.  I don't think
I've even ever heard of anyone deploying one, though I'm sure a handful
have tried, I don't think it ever got much deployment outside a select
few environments or the lab.

IP multicast addressing has been a bit of a problem to say the least.
A couple of documents to read might be:

  <http://www.watersprings.org/pub/id/draft-ietf-mboned-addrarch-05.txt>
  <http://www.watersprings.org/pub/id/draft-ietf-mboned-addrdisc-problems-02.txt>

Then perhaps follow up on mboned if you still have questions.  Some
of the people that hang out there hang out here and may have more to
say since I haven't been following closely what's going on for the
past year.  I don't think you're going to find the satisfying answer
you were looking for, but that's IP multicast for you.

John