Multicasting (also called IP multicasting) consists of using a single multicast source to send data to many receivers. Multicasting can be used to send data to many receivers simultaneously while conserving bandwidth and reducing network traffic. Multicasting can be used for one-way delivery of media streams to multiple receivers and for one-way data transmission for news feeds, financial information, and so on. Many dynamic routing protocols such as RIPv2, OSPF, and EIGRP use multicasting to share hello packets and routing information.
A FortiGate can operate as a Protocol Independent Multicast (PIM) version 2 router. FortiGates support PIM sparse mode (RFC 4601) and PIM dense mode (RFC 3973), and can service multicast servers or receivers on the network segment to which a FortiGate interface is connected. Multicast routing is not supported in transparent mode.
To support PIM communications, the sending and receiving applications, and all connecting PIM routers in between, must be enabled with PIM version 2. PIM can use static routes, RIP, OSPF, or BGP to forward multicast packets to their destinations. To enable source-to-destination packet delivery, sparse mode or dense mode must be enabled on the PIM router interfaces. Sparse mode routers cannot send multicast messages to dense mode routers. If the FortiGate is located between a source and a PIM router, between two PIM routers, or is connected directly to a receiver, you must manually create a multicast policy to pass encapsulated (multicast) packets or decapsulated data (IP traffic) between the source and destination.
A PIM domain is a logical area comprising a number of contiguous networks. The domain contains at least one bootstrap router (BSR), and if sparse mode is enabled, a number of rendezvous points (RPs) and designated routers (DRs). When PIM is enabled, the FortiGate can perform any of these functions at any time as configured.
A PIM domain can be configured in the GUI by going to Network > Multicast, or in the CLI using
config router multicast. Note that PIM version 2 must be enabled on all participating routers between the source and receivers. Use
config router multicast to set the global operating parameters.
When PIM is enabled, the FortiGate allocates memory to manage mapping information. The FortiGate communicates with neighboring PIM routers to acquire mapping information and, if required, processes the multicast traffic associated with specific multicast groups.
Instead of sending multiple copies of generated IP traffic to more than one specific IP destination address, PIM-enabled routers encapsulate the data and use a Class D multicast group address (188.8.131.52 to 184.108.40.206) to forward multicast packets to multiple destinations. A single stream of data can be sent because one destination address is used. Client applications receive multicast data by requesting that the traffic destined for a certain multicast group address be delivered to them.