Changing Intel X710 fiber NIC speed

I have a optical X710 NIC which runs in 10000Mb/s speed (SFP+). I use "ethtool" to show its capabilities:

    ethtool enp1s0f0
Settings for enp1s0f0:
    Supported ports: [ FIBRE ]
    Supported link modes:   10000baseT/Full 
                            1000baseX/Full 
                            10000baseSR/Full 
                            10000baseLR/Full 
    Supported pause frame use: Symmetric
    Supports auto-negotiation: Yes
    Supported FEC modes: Not reported
    Advertised link modes:  10000baseT/Full 
                            1000baseX/Full 
                            10000baseSR/Full 
                            10000baseLR/Full 
    Advertised pause frame use: No
    Advertised auto-negotiation: Yes
    Advertised FEC modes: Not reported
    Speed: 10000Mb/s
    Duplex: Full
    Port: FIBRE
    PHYAD: 0
    Transceiver: internal
    Auto-negotiation: off
Cannot get wake-on-lan settings: Operation not permitted
    Current message level: 0x00000007 (7)
                   drv probe link
    Link detected: yes

As you can see, 1GE is supported. But, when I try to change its speed, I get this error:

    sudo ethtool -s enp1s0f0 speed 1000
Cannot set new settings: Operation not supported
  not setting speed

Do you have any idea about the problem? How can I change the speed mode?

Solution 1:

From the Intel adapter guide:

Fiber-based adapters operate only in full duplex at their native speed. You cannot change the speed or duplex of Intel adapters that use fiber cabling

The NIC will autonegotiate settings with the link partner down to 1GB/s.