How to change "Ethernet" card's speed in Linux.

Check the NIC cards speed and other attributes.

#ethtool eth0


Settings for eth1:
 Supported ports: [ TP ]
 Supported link modes: 10baseT/Half 10baseT/Full
 100baseT/Half 100baseT/Full
 1000baseT/Full
 Supports auto-negotiation: Yes
 Advertised link modes: 10baseT/Half 10baseT/Full
 100baseT/Half 100baseT/Full
 1000baseT/Full
 Advertised auto-negotiation: Yes
 Speed: 1000Mb/s
 Duplex: Full
 Port: Twisted Pair
 PHYAD: 0
 Transceiver: internal
 Auto-negotiation: on
 Supports Wake-on: pumbg
 Wake-on: g
 Current message level: 0x00000033 (51)
 Link detected: yes

                        // Supported link must be 1000 for Gigabit support. 

To force a speed change to 1000Mbps, full duplex mode, run:

# ethtool -s eth0 speed 1000 duplex full autoneg off

== Permanent  solutions =

vi /etc/sysconfig/network-scripts/ifcfg-eth0:

   ETHTOOL_OPTS="speed 1000 duplex full autoneg off"     //Set ETHTOOL_OPT value.






Restart the interface to apply changes:
# ifdown eth0 && ifup eth0

check:

https://iperf.fr                 //you will get testing tool. 

==========Check from windows Windows ==============


Check windows ethernet speed:

C:\Users\Administrator.LDC13>wmic NIC where NetEnabled=true get Name, Speed
Name Speed
Realtek PCIe GBE Family Controller 1000000000