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Re: multicast very fundamental posted 03/25/2007
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Bit Gossip wrote:
Group I am stuck for days on this very fundamental multicast
I noticed this strange thing while playing with the multicast task of
IEWB4-LAB02 and couldn't get to the bottom of it; then I gave up.
Now I have reproduced it in a very simple scenario, and the pb is still

| r2 ----< |

*) Frame relay hub'n'spoke with r2=hub, only serial physical interfaces
*) Full reachability via OSPF
*) PIM-SM with r2=RP; multicast source= attached to r2 f1/0
for group; receivers attached to r1 and r3
*) it works fine, all receivers get the group

And now the funny part !!
*) there is no layer 2 connectivity between r1 and r3 as you can see
below; but still r1 HEARS the prune from r3 and OVERRIDES it !!!!!!!!
How is it possible ??????

When r3 leaves the group this is the pim debug on r1:

PIM(0): Received v2 Join/Prune on Serial0/0 from, not to us
PIM(0): Prune-list: (*, RP
PIM(0): Set join delay timer to 1000 msec for (, on Serial0/0
PIM(0): Building Periodic (*,G) Join / (S,G,RP-bit) Prune message for
PIM(0): Insert (*, join in nbr's queue
PIM(0): Building Join/Prune packet for nbr
Bit Gossip,

Given the following, it seems to me that this result SHOULD surprise you!

1. PIM prunes are sent to the all PIM routers address:

2. Each PVC is a separate broadcast domain (traffic to is not normally forwarded between PVCs)

3. You have a hub and spoke topology, where R1 and R3 are spokes.

It seems to me that one of the three statements above must be false. I would bet a diet Pepsi on number 3. Could you do "show frame PVC" and verify that R1 has only 1 Active-Local DLCI?


Bob Sinclair CCIE 10427 CCSI 30427