All things related to multicast

[Zenon Mousmoulas <>]

Hi,

We have a client site that wants to receive multicast, but they want  
to limit traffic to specific groups. As is usual for most clients,  
they don't have their own PIM domain, but instead they rely on our  
national PIM domain (by use of GRNET's anycast RP).

The only easy way I've found to do this is by using a configuration  
that statically maps the few groups they want to the correct RP  
address, and everything else to a "fake" RP address, actually some  
interface of their own border router.

ip access-list standard good-mcast-groups
permit host 233.21.32.200
permit host 233.21.32.201
permit host 233.21.32.202
permit host 233.21.32.203
permit host 233.21.32.204
deny any
exit

ip pim rp-address grnet.RP.address good-mcast-groups
ip pim rp-address 195.251.32.33
ip pim accept-rp 194.177.210.61 good-mcast-groups
ip pim accept-rp 195.251.32.33

This used to work just fine for some time. Then, probably after some  
temporary loss of the PIM neighbor towards the "valid" RP  
(194.177.210.61), the PIM routing state was broken for all groups,  
including those matched by the above acl.

#show ip pim rp
Group: 224.0.1.40, RP: 195.251.32.33, next RP-reachable in 00:00:30
Group: 233.21.32.200, RP: 195.251.32.33, next RP-reachable in 00:00:32
Group: 233.21.32.201, RP: 195.251.32.33, next RP-reachable in 00:00:32
Group: 233.21.32.202, RP: 195.251.32.33, next RP-reachable in 00:00:32
Group: 233.21.32.203, RP: 195.251.32.33, next RP-reachable in 00:00:32
Group: 233.21.32.204, RP: 195.251.32.33, next RP-reachable in 00:00:32
Group: 239.255.255.250, RP: 195.251.32.33, next RP-reachable in 00:00:52
Group: 224.2.127.254, RP: 195.251.32.33, next RP-reachable in 00:01:13
Group: 239.195.255.255, RP: 195.251.32.33, next RP-reachable in 00:01:03
Group: 239.255.255.255, RP: 195.251.32.33, next RP-reachable in 00:01:13

#show ip pim rp mapping
PIM Group-to-RP Mappings

Acl: good-mcast-groups, Static
   RP: 194.177.210.61 (?)
Group(s): 224.0.0.0/4, Static
   RP: 195.251.32.33 (?)

If we reset the rp-address and accept-rp configuration commands, PIM  
routing returns to working as expected. But I don't know when it's  
going to break again.

Do you have any idea what could be going wrong here? What does this  
"next RP-reachable in" mean?

Thanks,
Z.