25 Gbps port (x5) on the FortiGate-600F is not working

[Alfonziino]

Hi, 

we upgraded our core network by replacing the core firewall with FortiGate-600F and Aruba Switch 8360v2.
The issue is with the interconnection between the FortiGate and Aruba switch. The 25 Gbps port (x5) on the FortiGate-600F is not working when the DAC cable is connected to the Aruba switch. There is no link on the port.

We tested several DAC cables – original Fortinet DAC cable, and original Aruba DAC cable – but none of them worked.
Interestingly, if the DAC cable is connected to two interfaces on the same unit, the port starts to work. There is a link on it. We connected the DAC cable to ports x5 and x6 on the FortiGate, creating a loop. Both DAC cables from Fortinet and Aruba were working. Similarly, on the Aruba side, creating a loop brought the interfaces up.
Could you help me to fix this issue and understand why the interconnection between the two network devices is not working?

Thank you 

[AEK]

Hello

Can you ensure both sides are auto negotiate and try again?

[tpatel]

Hello Sir, 
Can you please check speed on aruba switch interface and fortigate interface speed is same.Please click on below link and reference document.
https://community.fortinet.com/t5/FortiGate/Technical-Tip-Changing-the-speed-of-a-FortiGate-interfac...

[Alfonziino]

if the DAC cable is connected to port x5 and x6 (LOOP), then the ports work:

==[x5]
mode: static
ip: 0.0.0.0 0.0.0.0
ipv6: ::/0
status: up
speed: 25000Mbps (Duplex: full)
FEC: cl91-rs-fec
FEC_cap: {cl91-rs-fec,cl74-fc-fec}

==[x6]
mode: static
ip: 0.0.0.0 0.0.0.0
ipv6: ::/0
status: up
speed: 25000Mbps (Duplex: full)
FEC: cl91-rs-fec
FEC_cap: {cl91-rs-fec,cl74-fc-fec}

but if I connect the DAC to the x5 port and the ARUBA port, the communication no longer works:

==[x5]
mode: static
ip: 0.0.0.0 0.0.0.0
ipv6: ::/0
status: down
speed: n/a
FEC: cl91-rs-fec
FEC_cap: {cl91-rs-fec,cl74-fc-fec}

[sw2090]

I ran into similar issue when I connect a 400F to a DELL Switch. The reason im my case were incompatible transceivers. Due to this the transceivers on both ends did not communicate. 

Replacing those with a DELL DAC Cable that came with the DELL Switches made it work.

Maybe this could give you some clue?