OSPF Dynamic Routing on FortiGate

Why dynamic routing

Static routes do not scale and do not adapt when a path fails. OSPF (Open Shortest Path First) is a link-state IGP that lets routers discover each other, share topology, and recompute best paths automatically.

Core concepts

• Areas — OSPF divides the network into areas to limit flooding; Area 0 is the backbone all other areas connect to.

• Adjacencies — neighbors form relationships and exchange link-state advertisements (LSAs).

• Cost — OSPF picks paths by cumulative cost (lower is better), derived from interface bandwidth.

config router ospf
    set router-id 10.0.0.1
    config area
        edit 0.0.0.0
        next
    end
    config ospf-interface
        edit "port1"
            set interface "port1"
            set network-type point-to-point
        next
    end
end

Redistribution

FortiGate can redistribute connected, static, or BGP routes into OSPF so the rest of the network learns them. Be deliberate — uncontrolled redistribution can create routing loops or black holes.

What it means for you

OSPF is the backbone of most enterprise internal routing. Knowing how areas, adjacencies, and cost interact lets you design resilient topologies and troubleshoot why a route is (or is not) in the table.