You need to use the ethtool command to display or change Ethernet card settings. It is used for querying settings of an ethernet device such as
=> Link speed
=> Auto negotiation
=> Coalescing settings
=> Change the rx/tx ring parameters
=> Setup new speed and much more
Most intelligent network devices use an autonegotiation protocol to communicate what media technologies they support, and then select the fastest mutually supported media technology.
How do I determine ethernet connection speed?
Type the following command to get speed for eth0:
$ ethtool eth0 | less
$ ethtool eth0 | grep -i speed
You can also use the following two commands:
$ dmesg | grep eth0 | grep up
$ dmesg | grep bond0 | grep up
OR use the command line utility called mii-tool to checks or sets the status of a network interface’s Media Independent Interface (MII) unit:
$ mii-tool -v eth0