From: Joseph Brunner (joe@affirmedsystems.com)
Date: Thu May 22 2008 - 18:22:36 ART
I had 3 2811's with ONLY sparse MODE on the interfaces in the path.
Pc's on linksys switches at either end of the stack of routers. One pc was
generating multicast traffic with solarwinds "wan killer" app.
The last pc was running wireshark. The 2811 facing the pc with wireshark was
set to "ip igmp static" the group out the interface.
>Does that mean the no dense mode fallback mechanism is not any useful?
Not at all... if you HAVE no RP (due to an error, or other issue) and you
want to prevent traffic for that group altogether rather than allow dense
mode operation of that group, then use "no ip pim dm-fallback" just like the
doc cd says. So that is the value of the command - giving administrator
absolute control of how the router running multicast responds to losing an
RP or lack of RP from the start ;) Again, this is not tied to interface mode
configuration.
Thomas, regarding the 6509's operation, I haven't tested multicast in my lab
on those for multicast since last year. I would have to be on the box and do
some debugs to see how the joins were being processed. Perhaps some security
features or the RPF check was preventing things from working?
But I will know after next weekend. ;)
-Joe
-----Original Message-----
From: Sadiq Yakasai [mailto:sadiqtanko@gmail.com]
Sent: Thursday, May 22, 2008 5:04 PM
To: Thomas Perrier
Cc: Joseph Brunner; lei tian; ccie; Cisco certification
Subject: Re: no ip pim dm-fallback vs no ip pim autorp listener
Joe,
"again the interface modes decide how the router learns rp information. Not
how the multicast traffic is forwarded. I tested this in my lab last year by
running multicast traffic over a network of "sparse mode interfaces" with no
RP configured. I obviously did not remove the "ip pim dm-fallback" default
operation."
Does that mean the no dense mode fallback mechanism is not any useful?
From your explanation, even when you have a sparse mode interface, and
traffic arrives on a router and there is no RP for that group (due to
any reason) the group falls back to dense mode and the traffic is
pushed out of an interface configured for sparse mode alone?
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