When Register message filtering by source and group address is enabled then: - for groups for which the local router is the RP, it will process received PIM Register messages as normal only if the {source, group} pair of the encapsulated multicast data packet is included in the extended access list corresponding to the list index value configured for this object; if the {source, group} pair is excluded from the extended access list, the local router will send a Register-Stop message, and - on interfaces on which the local router is the DR, it will encapsulate received multicast data packets and forward them in PIM Register messages only if the {source, group} pair of the multicast data packet is included in the extended access list corresponding to the list index value configured for this object. In other words, the extended access list is a whitelist of the {source, group} pairs for which the local router is permitted to Register-encapsulate/decapsulate multicast data packets. rlPimTmEntRegSrcAndGrpFilter defaults to an empty string, which indicates that no access list is specified.