[c-nsp] PIM-SM and 'more specific' RPs

[Jee Kay]

I'm trying to use the 'ip pim rp-address' command to give me a default
RP, and a 'more specific' RP for a set of multicast groups. Basically
I'd like our internal RPs to handle all multicast traffic by default,
but I have a requirement to use externally set RPs for some other
groups.

At the moment I'm trying to use an ACL to accomplish this but having
little luck. So far I have:

ip pim rp-address 12.1.2.3 ext-b-rp
ip pim rp-address 217.1.2.3

ip access-list standard cme-b-rp
 permit 233.1.2.64 0.0.0.63

The output of 'show ip pim rp map' gives me at least some hope of this:

PIM Group-to-RP Mappings

Acl: ext-b-rp, Static
    RP: 12.1.2.3 (?)
Group(s): 224.0.0.0/4, Static
    RP: 217.1.2.3 (?)


Unfortunately this doesn't actually seem to work. A 'show ip pim rp'
when a group is active ends up showing:

Group: 233.1.2.66, RP: 217.1.2.3, uptime 00:03:06, expires never

'show ip mroute' and a packet sniff confirms this is indeed what it's doing.

Why is it not using the 'more specific' RP? It seems to ignore the ACL
option completely and always use the default RP.

Failing that, how does one do this properly? It would be very
difficult for me to narrow down specific internal groups, and I don't
really want to have to maintain such a list.

Thanks in advance,
Ras