Technical Note: Forwarding multicast traffic in NAT mode

[Sandeep_FTNT]

Description	This article explains how to configure multicast traffic forwarding on a FortiGate. Multicast enables efficient delivery of data to multiple recipients simultaneously using a single transmission stream. Multicast is commonly used in applications such as real-time video/audio streaming and IPTV.  This feature allows forwarding multicast streams statically between the FortiGate interfaces from the multicast routers and sources to the multicast receivers; however, it is not intended for routing multicast traffic using dynamic multicast routing protocols. Note: Enabling both multicast forwarding and multicast routing simultaneously on the same device or VDOM is not recommended. Multicast forwarding treats the traffic statically, while routing uses dynamic procol decisions such as reverse path forwarding (RPF) checks.
Scope	FortiGate allowing multicast flow from a multicast router or source at port2  to a multicast receiver at port1.
Solution	Step 1:  Enabling multicast forwarding By default, Multicast Forwarding is enabled on FortiGate devices and the multicast-forward setting must be used to enable or disable multicast forwarding. Enable multicast forwarding from CLI using the following commands: config system setting     set multicast-forward enable end Prevent the TTL for forwarded packets from being changed. To preserve TTL values for forwarded multicast packets, use the multicast-ttl-notchange option. Enable it only if packets expire prematurely before reaching the multicast router. config system settings     set multicast-ttl-notchange enable end Step 2:   Configure the multicast policy. In a multicast policy, the source interface refers to the interface where the multicast receiver—such as an IPTV box—is located, while the destination interface is where the multicast router or source resides. The multicast group(s) is selected in the destination field. From the GUI: Navigate to Policy & Objects -> Multicast Policy -> Create New. Select the source and destination interfaces with the source and destination IP addresses. Note: If the Multicast tab is not seen then navigate to System -> Feature Visiblilty, and enable Multicast Policy. From the CLI: config firewall multicast-policy     edit 1         set srcintf  port1         set dstintf  port2         set srcaddr  all         set dstaddr  all     next end