Spanning Tree Settings¶

STP (Spanning Tree Protocol) prevents loops in switched networks. FortiSwitch supports RSTP (Rapid Spanning Tree) and MSTP. By default, RSTP is enabled and should stay enabled — disabling STP on a network with redundant links creates broadcast storms.

Steps¶

View / change STP state per port¶

WiFi & Switch Controller → FortiSwitch Ports → click port.
STP Settings:
- Edge Port — Enable for ports connected to end devices (workstations, printers, APs). Skips the STP listening/learning states for faster link-up.
- STP State — Enable (default).
- STP Cost — leave at auto unless you have a specific reason.
- STP Priority — leave at default.

📸 Screenshot needed

FortiSwitch Port edit dialog with STP Settings section expanded.

Disable STP on a port (rare)¶

Only do this when you're CERTAIN the connected device doesn't create loops:

Servers with bonded NICs (LACP handles redundancy, STP not needed).
Specific test environments.

Globally adjust STP¶

config switch-controller managed-switch
edit "S108EXXXXXXXXX"
    set stp-priority 4096   # lower wins root election; e.g. for designated root switch
    config stp-settings
        set forward-time 15
        set max-age 20
        set hello-time 2
    end
next
end

Verify¶

diagnose switch-controller switch-info stp

Shows root bridge, port states (Forwarding/Blocking/Discarding), and topology.

Common Issues¶

Port stuck Blocking. STP detected a loop. Disconnect the suspected loop or fix port roles.
Slow link-up on end devices. Edge Port not set. Enable on ports facing PCs/APs.
Two switches fight for root. Both have low priority. Pick one as designated root; raise the other's priority.
Network melt-down after disabling STP. Re-enable immediately.