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PIM NBMA and Dense mode ???

Hi all,

I was wondering if it is possible to run PIM NBMA and Dense Mode on the hub router in a hub / spoke NBMA topology?  I know people generally run PIM NBMA and sparse mode on the hub router in this kind of topology but was curious if PIM NBMA w/ Dense mode is possible.


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Cisco Employee

PIM NBMA and Dense mode ???

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.

These two documents also state that the NBMA mode should not be used with PIM-DM.

Best regards,


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