Re: well-know multicast groups

[Yuri Pryadkin <yuri@who.isi.edu>]

Shuqian Yan <syan@jupiter.nal.utoronto.ca> writes:

> Hello, all
> 
> This is a question about the use of well-know groups(WKG) with local
> multicast/broadcast. 
> 
> If I want to broadcast a message to all the routersin the topology, 
> all I need to do is to specify the $agent dst_ ALL_ROUTERS??
> Can I assume that ALL_ROUTERS is already registered/defined in the
> McastProto.tcl under class mrtObject? or do I need to do something  before
> using it?

It is already registered in McastProto.tcl and you can just use it.

> 
> So once I set the <$agent set dst_ [ALL_ROUTERS]>, the message will be
> automatically broadcast to all routers in the topology. and if I set the
> message pkt ttl value to a relatively small value (the current default
> ttl_ 32), then the message will basically get routed around a circle
> limited by the ttl scope.

This is incorrect.  Your agents that are supposed join a WKG before
they can receive.  Multicasting to WKGs works pretty much like to any
other group, except that there are no upcalls (cache-miss or
wrong-iif) for them; I cannot tell you why it is implemented that way.

See an example of a wkg in tcl/mcast/detailedDM.tcl.  This protocol is
no longer supported, but you can learn something from the code...

Cheers,

  -Yuri

> 
> Any help is appreciated,
> 
> shuqian