Hi,
It is true that there are certain scalability issues with Multicast. However
the solution of this is to have a very good InterDomain multicast routing as
well as Intra Domain multiast routing protocols. With that the problem of
host affecting the entire routing core is greatly reduced.
The protocols like CBT and PIM-SM were developed because it was found that
protocols like DVMRP and PIM-DM cannot scale. It is also neceesary to note
the fact that PIM-SM is only efficient for the sparesely disributed hosts
and it is a Receiver initiated protocol. This has significant advantage over
flood and prune protocols like DVMRP.
If you think of the scenario where there are very less hosts receving the
session and why dont we just send data directly, then this solution cannot
scale. The whole purpose of multicast is lost. The server will be burdened
and each unicast stream will contribute more to a single multicast stream.
Cheers,
Pathik Gupta
-----Original Message-----
From: Gunnar Lindberg [mailto:lindberg(_at_)CDG(_dot_)CHALMERS(_dot_)SE]
Sent: Thursday, March 08, 2001 4:13 PM
To: idmr(_at_)CS(_dot_)UCL(_dot_)AC(_dot_)UK; ietf(_at_)ietf(_dot_)org
Subject: Re: Multicast
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