How to display forwarding domain information
Forwarding domains, or collision domains, are used in routing to limit where packets are forwarded on the network. Layer-2 broadcasts are limited to the same group. By default, all interfaces are in group 0. For example, if the FortiGate unit has 12 interfaces, only two may be in the same forwarding domain, which will limit packets that are broadcast to only those two interfaces. This reduces traffic on the rest of the network.
Collision domains prevent the forwarding of ARP packets to all VLANs on an interface. Without collision domains, duplicate MAC addresses on VLANs may cause ARP packets to be duplicated. Duplicate ARP packets can cause some switches to reset.
It is important to know what interfaces are part of which forwarding domains as this determines which interfaces can communicate with each other.
To manually configure forwarding domains in Transparent mode, use the following FortiOS CLI command:
config system interface
edit <interface_name>
set forward-domain <integer>
end
To display the information for forward domains
Use the following command:
diagnose netlink brctl domain <name> <id>
where <name> is the name of the forwarding domain to display and <id> is the domain id.