Re: Why MSDP?

["John M. Zwiebel" <jzwiebel@cisco.com>]

MSDP is required for ISM - or "internet standard multicast".
ISM is not SSM in that it allows building of shared-trees within
an AS which SSM does not.  The receiver does not need to know
who the senders to a given group are.

SSM builds only shortest-path trees because the host can signal
to the last hop router the specific hosts (senders) it wants to 
listen to.  This rendezvous mechanism is outside of the PIM 
protocol and can be discovered any way the application writer
wants it to be.

MSDP is not required (and not used) to support SSM groups.

Host routes are not needed in MBGP to be able to join toward the
shortest-path across the internet.  

 ^ Greetings,
 ^ 
 ^ I have a very basic question:
 ^ 
 ^ First, the context:
 ^ For inter-domain Multicasting, one would typically deploy
 ^ PIM-SM/MBGP/MSDP protocols.....
 ^ MBGP for announcing  routes that include subnets containing multicast
 ^ sources, and MSDP
 ^ to announce sources.
 ^ 
 ^ Since MBGP already has the capability to announce multicast routes, why
 ^ not announce host routes of multicast sources as well, using MBGP? If
 ^ necessary, one can think of a simple extension to MBGP to mark the host
 ^ route as a "source route". IMHO, this will make it much easier to deploy
 ^ Multicast without having to worry about delpoying MSDP.
 ^ 
 ^ Any comments?
 ^ 
 ^ Best Regards,
 ^ Nagesh
 ^ 

------------------------------------------------------------------------------
	John Zwiebel                       Phone: 408-526-5303
	Cisco Systems Inc.                 
	IP Multicast Group