The advertised speed and the actual speed of the link can be different
sudo ethtool enp1s0
Settings for enp1s0:
Supported ports: [ TP ]
Supported link modes: 10baseT/Half 10baseT/Full
Advertised link modes: 10baseT/Half 10baseT/Full
This reports the actual link speed as negotiated between both devices on each end of the link. My laptops network card the local switch I connect to.
Whereas the actual speed reported by these tools is
sudo mii-tool enp1s0
enp1s0: negotiated 100baseTx-FD flow-control, link ok
sudo ethtool enp1s0 | grep -i speed
I will only ever reach the link speed when I download something connected in the same LAN at the same speed.
If I download a file from a server on the same LAN. I will get the full 100Mb/s.
So where I connet to will make a difference to the speed I get.