Hello David,
The PIM NBMA mode is not supported with PIM-DM. The NBMA mode has two important characteristics:
- PIM Joins and Prunes are tracked together with the IP address of their sender in the OIL list for a multicast routing table entry. A PIM Join or Prune is therefore always tied to a particular neighbor on an interface, not just to that interface as a whole.
- Multicast traffic sent to neighbors that have expressed their interest by a Join message will be encapsulated as unicast at the link layer.
These two characteristics make the PIM NBMA mode especially suited for PIM-SM as it allows to easily track interested neighbors thanks to their Join messages and to find out their link layer address in the appropriate L3/L2 database (IP/DLCI for example).
While technically, the NBMA mode could also be supported for PIM-DM, Cisco does not appear to support it.
http://www.cisco.com/en/US/docs/ios/solutions_docs/ip_multicast/White_papers/frm_rlay.html
http://www.cisco.com/en/US/docs/ios-xml/ios/ipmulti/command/imc_i3.html#GUID-F632E2F1-4326-44CE-883B-27C7CADFAC79
These two documents also state that the NBMA mode should not be used with PIM-DM.
Best regards,
Peter
