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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
mechanics...
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
there.

r1
|
| r2 ----< |
|
r3


*) Frame relay hub'n'spoke with r2=hub, only serial physical interfaces
*) Full reachability via OSPF
*) PIM-SM with r2=RP; multicast source=132.1.26.8 attached to r2 f1/0
for group 228.28.28.28; 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 132.1.0.3, not to us
PIM(0): Prune-list: (*, 228.28.28.28) RP 150.1.2.2
PIM(0): Set join delay timer to 1000 msec for (150.1.2.2/32,
228.28.28.28) on Serial0/0
PIM(0): Building Periodic (*,G) Join / (S,G,RP-bit) Prune message for
228.28.28.28
PIM(0): Insert (*,228.28.28.28) join in nbr 132.1.0.2's queue
PIM(0): Building Join/Prune packet for nbr 132.1.0.2
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: 224.0.0.13.

2. Each PVC is a separate broadcast domain (traffic to 224.0.0.13 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 www.netmasterclass.net