| Description |
This article describes how multicast works within a FortiSwitch managed by FortiGate when IGMP-snooping is configured. |
| Scope | FortiSwitch managed by FortiGate (FortiLink). |
| Solution |
The following architecture has been built in a lab environment:
Host05 will send a report to join the multicast group 225.1.2.3.
To configure the IGMP-snooping:
FortiGate # config system interface FortiGate (interface) # edit TEST-60 set ip 192.168.60.1 255.255.255.0
In this example, enable the igmp-snooping for the VLAN 60 names TEST-60. Enabling igmp-snooping in the VLAN interface will automatically enable switch-controller-igmp-snooping-fast-leave.
If no multicast routing is enabled on the FortiGate, it is necessary to set a querier by overriding the configuration. This can be seen just below.
FortiGate # config switch-controller managed-switch config vlans
Regarding the querier-addr: If the traffic is local to the switch, it is possible to set the value to 1.1.1.1 for example, this means that the switch will act locally as the querier.
This querier address can be any value; it does not represent the actual IP address. It plays a role in an election process, as only one querier can be active in a network. In the case where multiple queriers are configured then an election process will take place. The switch with the lowest configured IP address in the querier-addr field will be elected as the active querier.
If multicast traffic passes through different switches, using the FortiGate as a querier is recommended. The VLAN interface IP on the FortiGate can be set as a querier. It will require that multicast routing be enabled on the FortiGate.
More information about FortiGate as an IGMP querier on the following documentation: Technical Tip: How to configure the FortiGate as an IGMP querier on a FortiSwitch topology.
Multicast behavior with igmp-snooping enabled:
On Host05: From CLI: mcjoin. With this, a report is sent by the device to inform that the host wants to join the group 225.1.2.3. From a sniffer on the switch, it is possible to see this packet: 186.669487 sp5 -- 802.1Q vlan#60 P0 -- 192.168.60.2 -> 225.1.2.3: ip-proto-2 8.
The host05 sends a packet to inform that it wants to join group 225.1.2.3.
On Host06: From CLI: mcjoin -s -c 10 (-s allows to send the multicast traffic, -c 10 to send 10 packets).
On Host05: The progress bar at the top right-hand corner will display the number of packets sent. As 10 packets have been sent from host06, 10 packets should be received.
On Host07:
root@host07:/home/fortinet# tcpdump -i eth1 -f "host 225.1.2.3" tcpdump: verbose output suppressed, use -v[v]... for full protocol decode
No packet is received. This means that IGMP has been successfully configured, and the switch does not flood all the ports with multicast traffic.
Related articles: Technical Tip: Multicast / IGMP behavior with FortiSwitch Technical Tip: How to configure the FortiGate as an IGMP querier on a FortiSwitch topology |
