Fortiswitch RPVST STP Priority Inconsistent

Question

Hi all,

Setting up a pair of Fortiswitch 108F connected to Cisco Switch. Due to most of the switches are Cisco, so will need to deploy in rpvst. Configured the Fortiswitch interface that connected to Cisco Switch as "set rpvst-port enable" to match with Cisco rpvst.

When the Cisco VLAN priority is higher priority (numerically lower), Fortiswitch will get an error "STP priorities inconsistent" and the port will enter discarding state.
If Fortiswitch configuring same or higher priority, everything was working fine, both sides interfaces are Forwarding and learning the correct root bridge.

Anyone face this issue before? Can advise for this?

Many thanks in advance.

ashishrathee · Answer

It seems like you are experiencing STP priority inconsistencies when configuring a FortiSwitch interface connected to a Cisco switch using RPVST. To resolve this issue, you need to ensure that the VLAN priorities are set correctly on both sides to avoid the "stp priorities inconsistent" error and keep the ports in the forwarding state.

Here are the steps to address this issue:

1. Ensure that the VLAN priorities on the FortiSwitch match or are numerically lower than the priorities set on the Cisco switch for the corresponding VLANs.

2. Verify that the VLAN priorities are consistent across both switches to maintain a stable STP topology.

3. If the FortiSwitch is showing the error "stp priorities inconsistent," adjust the VLAN priorities on the FortiSwitch to align with the priorities on the Cisco switch.

4. After adjusting the priorities, check the STP status to ensure that both sides are forwarding and learning correctly.

By following these steps and ensuring consistency in VLAN priorities between the FortiSwitch and the Cisco switch, you should be able to resolve the STP priority inconsistency issue and maintain a stable network topology.

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