Technical Tip: ARP table & Forwarding database in Transparent mode

In transparent mode, the Address Resolution Protocol (ARP) table is used in the following situations:

1. For IP traffic received or originated by the FortiGate itself, and in destination of the management device or next hop.
2. When IPsec is used, the FortiGate uses its ARP table to forward the traffic from the IPsec tunnel to the local
   destination host(s).
   All other forwarding decision is based on the Forwarding Database (FDB) table or optional settings

To view all instances of the forwarding database (FDB), use the following CLI command:

diagnose netlink brctl list

FGT # diagnose netlink brctl list
list bridge information
1. root.b fdb: size=256 used=6 num=7 depth=2 simple=no
2. mgmt.b fdb: size=256 used=5 num=4 depth=2 simple=no
Total 2 bridges

To dump the L2 forwarding table for each VDOM bridge instance, use:

diagnose netlink brctl name host <vdom_name>.b