Hi @FafaG 

Thanks for posting in our business forum.

Not sure if this is a compatibility issue.

However, for LACP, the up and down status is maintained by the packets. Have you tried to Wireshark and monitor the LACP handshake?

There isn't too much to troubleshoot with LACP/LAG. It should work regardless of the mode but if that's a third-party, we recommend Active vs Passive. Not the same mode. ID and priority are local values. Does not affect the link.

Hi @FafaG 

Thanks for posting in our business forum.

FafaG wrote

Hey  @Clive_A 

I found the issue reason...

For anyone who need this information:

I have an Switch with 10G Interfaces, but the fortigate firewall are just 1Gbit interface, so when I connect both, I need to set the interface speed to 1000M in Switch settings, then interface comes up. The problem start when I create a LACP interface and the interface goes down. What you need to do is to set the speed on the new LACP interface instead of hardware interface.

Example how to solve:

Switch(conf)#interface Gi1/0/1

Switch(conf-if)#channel-group 1 mode passive
 

Switch(conf)#interface port-channel 1

Switch(conf-if)#speed 1000

 

To check if LACP is UP, you use this command:
Switch(config)# show interface status Po1

 

In my case, I was using stand alone CLI interface, but you can do it in GUI interface too or in Switch adopt by controller, you just need to overide the LAG interface speed.

Thank's and Best Regards.

What you need to troubleshoot for a LAG is the speed and duplex.

I thought it was a 10G or they auto negotiate the speed. Usually, that should be fine and not manual.

It could be the compatibility with the port negotiation which fails. But I wonder if you can get a link without LAG before? That'd be strange if it could auto negotiate to 1Gb but failed in LAG.