RFC 4601, "Protocol Independent Multicast - Sparse Mode (PIM-SM): Protocol Specification (Revised)", August 2006

Note: This RFC has been obsoleted by RFC 7761

Errata ID: 1162
Status: Held for Document Update
Type: Technical
Publication Format(s) : TEXT
Reported By: Maren Peasley
Date Reported: 2007-12-21
Held for Document Update by: David Ward
Date Held: 2009-03-22

Section 4.5.7 says:

     RPF'(*,G) changes not due to an Assert
          An event occurred that caused the next hop towards the RP for
          G to change.  This may be caused by a change in the MRIB
          routing database or the group-to-RP mapping.  Note that this
          transition does not occur if an Assert is active and the
          upstream interface does not change.

          The upstream (*,G) state machine remains in Joined state.
          Send Join(*,G) to the new upstream neighbor, which is the new
          value of RPF'(*,G).  Send Prune(*,G) to the old upstream
          neighbor, which is the old value of RPF'(*,G).  Use the new
          value of RP(G) in the Prune(*,G) message or all zeros if RP(G)
          becomes unknown (old value of RP(G) may be used instead to
          improve behavior in routers implementing older versions of
          this spec).  Set the Join Timer (JT) to expire after
          t_periodic seconds.

Notes:

Sending the Prune(*,G) may help state issues, but if the change in MRIB was spurious or there was a situation where a difference of opinion in lower route costs exists, some traffic may be dropped until the MRIB becomes consistent again.

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