I have checked it for all interfaces. Below the result.

Any update on this matter? What can I do to help?

Oh I forgot to mention. When making config changes in the network equipment. Disconnect and reconnect the network cable. Otherwise the firewall remembers what was negotiated and may give a false idea that it works.

I have setup a test case at home where I have the same firewall as in the office and have a couple of ports to spare. In the office i am interrupting operations.
I have connected a laptop to a cisco switch which is connected to the firewall running opnsense. I have configured the firewall to 100 Mbit Full duplex.
The Cisco switch is also configured to 100 Mbit Full duplex.

!
interface gi1
!
interface gi2
  speed 100
  duplex full
!

In rGbceec3d80a3caf9249e24247fb937674bf5b46b5#723276, @fbsd_opal.com wrote:

In rGbceec3d80a3caf9249e24247fb937674bf5b46b5#723018, @jeroen.steinvoorte_mep-info.com wrote:

I noticed that even though it is configured to Fixed 100Mbit full duplex, it does auto negotiation and falls back to 100 Mbit half duplex, as the ISP has auto negotiation switched off.

If you're using 1000 LX/SX/Y, 100TX or 10T the auto-neg code advertises only one setting (what you set); there is no possibility of it "falling back" to half duplex if full duplex is what was set.
For 100FC or 10FL the code does not do any negotiation.

Since i recently updated my opnsense firewall i am encountering a lot of collisions on the WAN configuration.
I noticed that even though it is configured to Fixed 100Mbit full duplex, it does auto negotiation and falls back to 100 Mbit half duplex, as the ISP has auto negotiation switched off.
For 10 and 100 Mbit connections auto negotiation is disabled when it is set to fixed 10/100 half/full duplex.
All network equipment behaves this way. This is the second time i am forced to take action changing network equipment which is caused by a dodgy network cable.

Is this also tested with a device connected to a network switch that is set to 100 Mbit Full Duplex without auto negotiation?