usdPimMRouteGRPMask 1.3.6.1.4.1.4874.2.2.43.1.1.12.1.19

The mask of the group-to-RP mapping being used to get the RP for this entry. It is set to 255.255.255.255 (with usdPimMRouteGRPAddr set to 0.0.0.0) if there is no group-to-RP mapping available or if entry is <*, *, RP>.