Assuming you are talking about PIM-SM , then where you have two routers (PIM-SM)
connected to a shared network with a receiver, a single DR should be chosen for the
purpose of sending "joins" to the RP in order to build the share tree for that group.
If both routers sent joins to the RP for the group you would have duplicate paths and
the host/reciever would receive duplicate multicast traffic.
PIM-SM is centered on a single, unidirectional shared tree. The root of the tree is
the
RP. In a shared tree, sources must send the multicast traffic to the root (RP) for the
traffic to reach all receivers.
Here is two sites for your reading pleasure. Also the Cisco Press book by Beu
Willamson
is pretty good.
http://www.cisco.com/warp/public/732/Tech/multicast/index.html
ftp://ftp-eng.cisco.com/ipmulticast.html
"Bradley J. Wilson" wrote:
> Er...duh, the DR in a multicast environment. Sorry, brain lock there.
>
> The DR is again an element on a broadcast network. The DR acts as the
> "manager" for that broadcast network if and when it is the upstream network
> from another router. The downstream router sends its join/leave requests to
> the DR, regardless of the multicast group it is joining or leaving. This
> streamlines things from the downstream router's perspective, since it only
> needs to interact with one other router across this broadcast network. But
> the DR may not be the direct path to the source of the multicast stream, so
> the DR might have to forward the request to the correct upstream router
> across the same network.
>
> I'm getting my info from Maufer's "Deploying IP Multicast in the
> Enterprise" - which isn't Cisco-specific. Maybe someone else could post
> quotes from the Cisco Press books or CCO about the difference.
>
> BJ
>
> ----- Original Message -----
> From: Bradley J. Wilson
> To: cisco
> Sent: Saturday, March 03, 2001 5:07 PM
> Subject: Re: Difference between Rendezvous Point ,Designated Router
>
> The rendezvous point is an element in a multicasting environment - can't
> recall which protocol off the top of my head, it's probably either PIM-DM
> or -SM.
>
> The designated router is an element of OSPF on a broadcast network
> (ethernet, token ring, etc.). The other routers on the network form their
> adjacencies with the DR, and the DR makes sure that every router on the
> broadcast network have the same LSDB.
>
> BJ
>
> ----- Original Message -----
> From: rtc
> To: Cisco ; CISCO GROUPSTUDY
> Cc: Cisco ; CISCO GROUPSTUDY
> Sent: Saturday, March 03, 2001 4:48 PM
> Subject: Difference between Rendezvous Point ,Designated Router
>
> what is the Difference between Rendezvous Point and Designated Router?
>
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