Technical Tip: Create a static IGMP group entry

[akileshc]

Description

This article describes how to use static-group (multicast-flow) entries on the specific interface to have static multicast IGMP group entries on Firewall.

Scope

FortiGate.

Solution

Overview.

• When an IGMP-enabled networking unit (FortiGate) gets a join request for a specific group, it sends all IP multicast traffic it receives for that group through the port on which the join request was received.
• When the user is ready to leave the multicast group, it sends a 224.0. 0.2 IGMP Leave Group message to the network and no longer belongs to the group. When a leave request is detected, the relevant IGMP device stops transmitting traffic for the specified multicast group via the port where the leave request was received (if there are no other current members of that group on the affected port.).
• Creating a static IGMP group entry ensures that FortiGate will preserve this IGMP group information for a given group and interface and will continue to deliver the multicast stream over the designated interface.

CLI syntax.

config router multicast-flow

edit "static-group"

config flows

edit 1

set group-addr 239.0.0.1
set source-addr 10.120.7.230

next

end

next

end

config router multicast

    set multicast-routing enable
        config interface

            edit "port1"

                set pim-mode sparse-mode
                set static-group "static-group"

            next

        end

end

It is only necessary to specify the source address, if the source transmitter IP is known, if multiple sources is transmitting to the same group and only want to perform the join to a specific source, or if using Source Specific Multicast (SSM). Otherwise do not specify the source.

If using SSM, it also needs to be specified under config router multicast, and the interfaces must be configured to use IGMP version 3:

config router multicast
    set multicast-routing enable
        config pim-sm-global

            set ssm enable

        end

        config interface

            edit "your interface"

                set pim-mode sparse-mode

        end

        config igmp

            set version 3 (default)

end

To verify the entry.

get router info multicast igmp groups 239.0.0.1
IGMP Connected Group Membership
Group Address Interface Uptime Expires Last Reporter
239.0.0.1 port1 00:18:40 stopped(static) 0.0.0.0 <- Statically Added IGMP group Info