A loopback interface is a logical interface that is always up (no physical link dependency) and the attached subnet is always present in the routing table.
The FortiGate's loopback IP address does not depend on one specific external port, and is therefore possible to access it through several physical or VLAN interfaces. Multiple loopback interfaces can be configured in either non-VDOM mode or in each VDOM.
Loopback interfaces still require appropriate firewall policies to allow traffic to and from this type of interface.
A loopback interface can be used with:
- Management access
- BGP (TCP) peering
- PIM RP
Loopback interfaces are a good practice for OSPF. Setting the OSPF router ID the same as loopback IP address troubleshooting OSPF easier, and remembering the management IP addresses (ssh to “router ID”).
Dynamic routing protocols can be enabled on loopback interfaces.
For black hole static route, use the black hole route type instead of the loopback interface.