Technical Tip: Auto-negotiation speed for SFP fiber ports on 90G/91G series

[skrymi]

Description	This article describes the behavior on 90G/91G for SFP fiber ports speed connected with switch device.
Scope	FortiGate 7.2.9 OS.
Solution	FortiGate 90G/91G Series have 2x 10/5/2.5/GE RJ45 or 10GE/GE SFP+/SFP shared media ports. If FortiGate is linked up with SFP fiber ports to a switch 1000-auto, the speed options on the FortiGate are as follows: FGT91G-2 (wan1) # set speed 1000auto 1000M auto-negotiation. 2500auto 2500M auto-negotiation. 5000auto 5000M auto-negotiation. 10000auto 10G auto-negotiation. If RJ45 or other cable is used for connection to 1G speed switch port, the link is UP at any speed. If SFP_fiber is used to connect to a 1G speed FortiGate SFP port, the link will be DOWN at 10000auto speed. FGT91G-2 # show system interface wan1 | grep speed set speed 1000auto FGT91G-2 # get system interface physical wan1 == [onboard] ==[wan1]                  mode: dhcp                  ip: 0.0.0.0 0.0.0.0                  ipv6: ::/0                  status: up                  speed: 1000Mbps (Duplex: full)<<===port up at 1000auto                  FEC: none                  FEC_cap: none If the speed port is changed to 10000auto, the status becomes down: FGT91G-2 # show system interface wan1 | grep speed <- Change to 10000auto. set speed 10000auto FGT91G-2 # get system interface physical wan1 == [onboard] ==[wan1]                   mode: dhcp                   ip: 0.0.0.0 0.0.0.0                   ipv6: ::/0                   status: down <- Port change to down, Status is Down.                   speed: n/a                   FEC: none                   FEC_cap: none For SFP fiber, when 'set speed 10000auto' is in place, it can only link up with 10G speed. When 'set speed 5000auto/2500auto/1000auto' is configured, it can only link up with 1G speed. This is a hardware limitation because 90G/91G SFP ports do not support Auto-negotiation.