GRE tunnels support unicast and multicast IP packets as payload. From a multicast prospective, a GRE tunnel IP interface (associated with a private tunnel SAP) can be configured as an IGMP interface or as a PIM interface; MLD is not supported. The following multicast features are supported:
IGMP versions 1, 2 and 3
IGMP import policies
IGMP host tracking
static IGMP membership
configurable IGMP timers
IGMP SSM translation
multicast CAC
per-interface, per-protocol (IGMP/PIM) multicast group limits
MVPN support (draft-rosen)
MVPN support (BGP-MPLS)
PIM-SM and SSM operation
PIM BFD support
configurable PIM timers
configurable PIM priority
PIM tracking support
PIM ECMP (bandwidth or hash-based)
static multicast route