(Generic Routing Encapsulation) A tunneling protocol used to encapsulate a wide variety of protocol packet types inside IP tunnels, creating a virtual point-to-point link to firewalls or routing devices over an IP Internetwork.

(Protocol Independent Multicast) One of two PIM operational modes:

• PIM sparse mode (PIM-SM) tries to constrain data distribution so that a minimal number of routers in the network receive it. Packets are sent only if they are explicitly requested at the RP (rendezvous point). In sparse mode, receivers are widely distributed, and the assumption is that downstream networks will not necessarily use the datagrams that are sent to them. The cost of using sparse mode is its reliance on the periodic refreshing of explicit join messages and its need for RPs.

• PM dense mode (PIM-DM) assumes all downstream routers and hosts want to receive a multicast datagram from a sender and floods multicast traffic throughout the network. Routers without downstream neighbors prune unwanted traffic. To minimize repeated flooding of datagrams and subsequent pruning, PIM DM uses a state refresh message sent by routers directly connected to the source.

  The firewall can be configured only as a multicast proxy so multicast traffic can be passed through the up-/downstream interface. The firewall cannot act as a PIM router.