Subject: Re: Multicast

From: Gunnar Lindberg <[email-masked]>
Date: Thu, 8 Mar 2001 09:12:57 +0100

Please explain what's wrong with my take on multicast scalability:

Every time a new sender shows up, the entire multicast core (RPs,
right now those running MSDP in the default free zone) has to be
informed. To "show up", the host just starts sending data.

Every time a new receiver shows up, its nearest RP has to initiate
a data distribution path (tree) torwards the sender(s). This is
likely to involve at least some of the core routers.

Scalability problems:

    1)	An indivivual sender - host, my Linux PC - affects routing
	information in the entire router core. Just send data.
	There are a few hosts on the Internet.

    2)	As if his wasn't enough, consider the potential for DoS-
	attacks. The recent Ramen worm was the first(?) example;
	who can claim it was the last?

Assume technology evolves fast enough to solve 1). We still have 2).

My claim is that it doesn't scale to allow individual hosts to affect
the Interet core routing system. What do I miss?

	Gunnar Lindberg

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From: Marshall Eubanks <[email-masked]>
Date: Thu, 08 Mar 2001 07:34:24 -0500

Hello;

   I removed the IETF list cc. 

>         There are a few hosts on the Internet.

Under ISM, a individual sender only affects routing AT THE
RP (in the absence of any receivers). 

Under SSM, sending without receivers only affects the first hop router.

For either, the FIRST receiver does
change state along the path. The Nth is not likely to (if N is sufficiently large).

>         who can claim it was the last?
I will present on this at the IETF. Basically, ISM is sensitive to DOS
at the RP, and can amplify certain ones (if nothing is done). 
SSM is much less sensitive, and does not amplify DOS attacks.

In any case, something can be done - rate and state limit filters. I
have no doubt that SSM can be made robust against d-DOS attacks.
ISM is less clear, but if broadcasting moves over to SSM,
multiparty conferences are not likely to last long enough to be
the subject of a DOS attack.

> the Interet core routing system. What do I miss?
ISM RP's and MSDP don't scale very well for IDMR. SSM does scale much better,
as only the routers involved between sender and receiver are affected. 

I would submit that SSM scales better than BGP, and that, for a long time to come,
router upgrades will be be driven by the need to keep up with BGP advertisements, not
the need to store SSM state. It would take a lot more than 100,000 SSM broadcasters to 
make this a worry. 

-- 

                                   Regards
                                   Marshall Eubanks

   Multicast Technologies, Inc.
   10301 Democracy Lane, Suite 410
   Fairfax, Virginia 22030
   Phone : 703-293-9624          Fax     : 703-293-9609     
   e-mail : [email-masked]     http://www.on-the-i.com

---

From: Masataka Ohta <[email-masked]>
Date: Sat, 10 Mar 2001 00:54:29 +0859 ()

Gunnar;

> informed. To "show up", the host just starts sending data.

You are wrong to say "multicast scalability" instead of "MSDP
scalability".

> Assume technology evolves fast enough to solve 1).

No, it does not.

> the Interet core routing system. What do I miss?

Then entire multicast (actually MSDP) core has nothing to do with
the Internet core routing system.

							Masataka Ohta