Support Forum
The Forums are a place to find answers on a range of Fortinet products from peers and product experts.
New Contributor

Question about connecting devices (Catalyst Switches)



I have a Fortigate 401F that I currently have access to via the mgmt interface. This interface is connected to one of my core switches (catalyst 9300) via cat6 and I can reach it at 10.Y.X.115/25. The Fortigate and my switches are all in the same subnet 10.Y.X.0/25

I can ping the Fortigate from every switch in my network, so I know that all the switches can reach the fortigate.


My question comes into play because I am attempting to use the x3 interface (with an SFP transceiver from Fortinet) to connect to one of my switches (for example, SW-30). I have fiber run from SW-30 to the MDF in my primary server room, and when I plug in my NetScout, the interface on SW-30 comes up.

When I insert the fiber into x3 on the Fortigate, the interface on SW-30 goes down, and x3 continues to stay down.

At first I thought this was because x3 does not have an IP assigned to it, but when I attempt to put it on 10.Y.X.31 /25 it says I can have it on the same subnet as mgmt.

I will admit I am new to Fortigate products (and firewall configuration as a whole) but I am wondering what I am missing, and I'm not sure why x3 is not coming up.


Any suggestions would be appreciated.

1 Solution

1G with 10G cannot bring your link up unless you set it to auto or 1G.

You can change X interface speed on FG via CLI. Or better, you can use 1G port, since 10G port is expensive so it is a waste to use it for 1G.

Regarding IP conflict, check if your management port is "dedicated to management". You should find this on GUI or on CLI.


View solution in original post


There is no STP info available on the Cisco for that interface. The interface (Te1/1/2) is not in the blocked port list.

The interface itself is in trunk mode for the vlan that all of my switches live on (10.Y.X.0 /25).



Select Forum Responses to become Knowledge Articles!

Select the “Nominate to Knowledge Base” button to recommend a forum post to become a knowledge article.

Top Kudoed Authors