[c-nsp] Multicast routing on a 3725, IOS 12.3(7)T2 - (S, G) getting stuck in 'Registering' state

Rasmus Hansen rasmus.hansen at dante.org.uk
Thu Oct 14 08:15:27 EDT 2004

Evening NSP,

I'm trying to debug a strange multicast problem I'm having at the 
moment. Basically, when a source here starts to sending multicast 
traffic, the router gets the (S,G) stuck in the 'Registering' state. The 
DR and the RP are the same in this scenario.

Additionally, the source is never announced via MSDP and thus the world 
cannot see it. The source is attached to Fa0/0 on the router.

When the source starts broadcasting, the state gets stuck as follows:

getafix#sh ip mro my.group my.source
(my.source, my.group), 00:00:38/00:02:51, flags: T
   Incoming interface: FastEthernet0/0, RPF nbr, Registering
   Outgoing interface list:
     Serial0/3, Forward/Sparse, 00:00:38/00:02:51

With the following debug options:
IP multicast:
   IP multicast routing debugging is on for my.group
   IP multicast rpf debugging is on for my.group
   IGMP debugging is on for my.group
   PIM debugging is on for my.group

The only hint of anything going wrong is:

Oct 14 12:11:42.665: PIM(0): Received v2 Join/Prune on Serial0/3 from 
my.uplink, to us
Oct 14 12:11:42.665: PIM(0): Join-list: (my.source/32, my.group), S-bit set
Oct 14 12:11:42.665: PIM(0): Update Serial0/3/my.uplink to (my.source, 
my.group), Forward state, by PIM SG Join
Oct 14 12:11:42.665: MRT(0): Update Serial0/3/ in the olist of 
(my.source, my.group), Forward state - MAC not built

I'm not sure why the J/P from my uplink seems to trigger this join list, 
nor what 'Forward state - MAC not built' means. No amount of googling or 
CCOing has provided an answer as yet.

I should probably mention that this appears to work fine if I use 
another local machine to do the test.

Has anyone seen this before, or have any idea exactly what 'Forward 
state - MAC not built' means? The 'Registering' flag appears to simply 
mean it has not gotten a Register-Stop message back from the RP, which 
is bizarre because it _is_ the RP, and it even knows it:

#sh ip pim rp
Group: my.group, RP: my.router, next RP-reachable in 00:01:00

Any help would be much appreciated :)


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