RFC 4601, "Protocol Independent Multicast - Sparse Mode (PIM-SM): Protocol Specification (Revised)", August 2006
Note: This RFC has been obsoleted by RFC 7761Source of RFC: pim (rtg)
Errata ID: 1119
Status: Held for Document Update
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 4.5.1 says:
The action "Send PruneEcho(*,*,RP)" is triggered when the router stops forwarding on an interface as a result of a prune. A PruneEcho(*,*,RP) is simply a Prune(*,*,RP) message sent by the upstream router on a LAN with its own address in the Upstream Neighbor Address field. Its purpose is to add additional reliability so that if a Prune that should have been overridden by another router is lost locally on the LAN, then the PruneEcho may be received and cause the override to happen. A PruneEcho(*,*,RP) need not be sent on an interface that contains only a single PIM neighbor during the time this state machine was in Prune-Pending state.
Forged PruneEcho messages could operate as a form of Denial-of-Service (effectively the same as a Prune(*,*,RP) in this context). The issue is resolved by using AH, but it is not listed as one of the forged message types in section 6.1.1.