Brief Overview on Multicast NAT (12.0T)
                   (Sep 16, 1998).

When unicast address translation (NAT) is configured on 
Cisco IOS router, multicast sources/receivers or PIM entities, 
like RP/RP mapping agent, can work on either side of 
a NAT box without any additional configuration commands.

All the routers (inside/outside and NAT box itself) must be fully
multicast enabled as usual.

Supported Address Translation:

o Data packet source address translation.
o PIM control packet (PIM payload) address translation.
  Including Auto-rp, PIMv2 BSR.
o Mstat/mrinfo/mtrace requests/responses.
o SDR advertisement (SDR application payload).

With the above translations, PIM should just work "fine" in an
enterprise domain even if a part of the domain is behind NAT. 
All sources/receivers behind that NAT box should be
able to send/receive to the rest of the PIM cloud and take
advantage of the RP/RP mapping agent on either side of the cloud.

Caveats:

o Tunnels must be terminated on the NAT box and "ip nat inside/outside"
  should be configured on the Tunnel. Tunnel cannot run through the
  NAT box with end points on either side.

o Addresses in RTP/RTCP or other application payloads are not translated.

o This feature does not translate destination Group addresses.