Ethtool utility is used to view and change the ethernet device parameters.
To change the Maximum Transmission Unit (MTU), refer to our ifconfig examples article.
After the above changes, if the Link Detection still says “No”, check whether there are any issues in the cables that runs from the switch and the system, you might want to dig into that aspect further.
To capture and analyze packets from a specific network interface, use tcpdump utility.
Use ethtool option -p, which will make the corresponding LED of physical port to blink.
On ubuntu, you have to modify /etc/network/interfaces file and add all your changes as shown below.
On SUSE, modify the /etc/sysconfig/network/ifcfg-eth-id file and include a new script using POST_UP_SCRIPT variable as shown below. Include the below line as the last line in the corresponding eth1 adpater config file.
1. List Ethernet Device Properties
When you execute ethtool command with a device name, it displays the following information about the ethernet device.# ethtool eth0
Settings for eth0:
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: 100Mb/s
Duplex: Full
Port: Twisted Pair
PHYAD: 1
Transceiver: internal
Auto-negotiation: on
Supports Wake-on: d
Wake-on: d
Link detected: yes
This above ethtool output displays ethernet card properties such as speed, wake on, duplex and the link detection status. Following are the three types of duplexes available.
- Full duplex : Enables sending and receiving of packets at the same time. This mode is used when the ethernet device is connected to a switch.
- Half duplex : Enables either sending or receiving of packets at a single point of time. This mode is used when the ethernet device is connected to a hub.
- Auto-negotiation : If enabled, the ethernet device itself decides whether to use either full duplex or half duplex based on the network the ethernet device attached to.
2. Change NIC Parameter Using ethtool Option -s autoneg
The above ethtool eth0 output displays that the “Auto-negotiation” parameter is in enabled state. You can disable this using autoneg option in the ethtool as shown below.# ifdown eth0
eth0 device: Broadcom Corporation NetXtreme II BCM5709 Gigabit Ethernet (rev 20)
eth0 configuration: eth-bus-pci-0000:0b:00.0
# ethtool -s eth0 autoneg off
# ethtool eth0
Settings for eth0:
Supported ports: [ TP ]
Supported link modes: 10baseT/Half 10baseT/Full
100baseT/Half 100baseT/Full
1000baseT/Full
Supports auto-negotiation: Yes
Advertised link modes: Not reported
Advertised auto-negotiation: No
Speed: Unknown! (65535)
Duplex: Unknown! (255)
Port: Twisted Pair
PHYAD: 1
Transceiver: internal
Auto-negotiation: off
Supports Wake-on: g
Wake-on: g
Link detected: no
# ifup eth0
After the above change, you could see that the “link detection” value changed to down and auto-negotiation is in off state.3. Change the Speed of Ethernet Device
Using ethtool you can change the speed of the ethernet device to work with the certain network devices, and the newly assign speed value should be within the limited capacity.# ethtool -s eth0 speed 100 autoneg off
# ethtool eth0
Settings for eth0:
Supported ports: [ TP ]
Supported link modes: 10baseT/Half 10baseT/Full
100baseT/Half 100baseT/Full
1000baseT/Full
Supports auto-negotiation: Yes
Advertised link modes: Not reported
Advertised auto-negotiation: No
Speed: Unknown! (65535)
Duplex: Unknown! (255)
Port: Twisted Pair
PHYAD: 1
Transceiver: internal
Auto-negotiation: off
Supports Wake-on: g
Wake-on: g
Link detected: no
Once you change the speed when the adapter is online, it
automatically goes offline, and you need to bring it back online using
ifup command.# ifup eth0
eth0 device: Broadcom Corporation NetXtreme II BCM5709 Gigabit Ethernet (rev 20)
eth0 configuration: eth-bus-pci-0000:0b:00.0
Checking for network time protocol daemon (NTPD): running
# ethtool eth0
Settings for eth0:
Supported ports: [ TP ]
Supported link modes: 10baseT/Half 10baseT/Full
100baseT/Half 100baseT/Full
1000baseT/Full
Supports auto-negotiation: Yes
Advertised link modes: Not reported
Advertised auto-negotiation: No
Speed: 100Mb/s
Duplex: Full
Port: Twisted Pair
PHYAD: 1
Transceiver: internal
Auto-negotiation: off
Supports Wake-on: g
Wake-on: g
Link detected: yes
As shown in the above output, the speed changed from 1000Mb/s to 100Mb/s and auto-negotiation parameter is unset.
To change the Maximum Transmission Unit (MTU), refer to our ifconfig examples article.
4. Display Ethernet Driver Settings
ethtool -i option displays driver version, firmware version and bus details as shown below.# ethtool -i eth0 driver: bnx2 version: 2.0.1-suse firmware-version: 1.9.3 bus-info: 0000:04:00.0
5. Display Auto-negotiation, RX and TX of eth0
View the autonegotiation details about the specific ethernet device as shown below.# ethtool -a eth0 Pause parameters for eth0: Autonegotiate: on RX: on TX: on
6. Display Network Statistics of Specific Ethernet Device
Use ethtool -S option to display the bytes transfered, received, errors, etc, as shown below.# ethtool -S eth0
NIC statistics:
rx_bytes: 74356477841
rx_error_bytes: 0
tx_bytes: 110725861146
tx_error_bytes: 0
rx_ucast_packets: 104169941
rx_mcast_packets: 138831
rx_bcast_packets: 59543904
tx_ucast_packets: 118118510
tx_mcast_packets: 10137453
tx_bcast_packets: 2221841
tx_mac_errors: 0
tx_carrier_errors: 0
rx_crc_errors: 0
rx_align_errors: 0
tx_single_collisions: 0
tx_multi_collisions: 0
tx_deferred: 0
tx_excess_collisions: 0
tx_late_collisions: 0
tx_total_collisions: 0
rx_fragments: 0
rx_jabbers: 0
rx_undersize_packets: 0
rx_oversize_packets: 0
rx_64_byte_packets: 61154057
rx_65_to_127_byte_packets: 55038726
rx_128_to_255_byte_packets: 426962
rx_256_to_511_byte_packets: 3573763
rx_512_to_1023_byte_packets: 893173
rx_1024_to_1522_byte_packets: 42765995
rx_1523_to_9022_byte_packets: 0
tx_64_byte_packets: 3633165
tx_65_to_127_byte_packets: 51169838
tx_128_to_255_byte_packets: 3812067
tx_256_to_511_byte_packets: 113766
tx_512_to_1023_byte_packets: 104081
tx_1024_to_1522_byte_packets: 71644887
tx_1523_to_9022_byte_packets: 0
rx_xon_frames: 0
rx_xoff_frames: 0
tx_xon_frames: 0
tx_xoff_frames: 0
rx_mac_ctrl_frames: 0
rx_filtered_packets: 14596600
rx_discards: 0
rx_fw_discards: 0
7. Troubleshoot the Ethernet Connection Issues
When there is a problem with the network connection, you might want to check (or change) the ethernet device parameters explained in the above examples, when you see following issues in the output of ethtool command.- Speed and Duplex value is shown as Unknown
- Link detection value is shown as No
After the above changes, if the Link Detection still says “No”, check whether there are any issues in the cables that runs from the switch and the system, you might want to dig into that aspect further.
To capture and analyze packets from a specific network interface, use tcpdump utility.
8. Identify Specific Device From Multiple Devices (Blink LED Port of NIC Card)
Let us assume that you have a machine with four ethernet adapters, and you want to identify the physical port of a particular ethernet card. (For example, eth0).Use ethtool option -p, which will make the corresponding LED of physical port to blink.
# ethtool -p eth0
9. Make Changes Permanent After Reboot
If you’ve changed any ethernet device parameters using the ethtool, it will all disappear after the next reboot, unless you do the following.On ubuntu, you have to modify /etc/network/interfaces file and add all your changes as shown below.
# vim /etc/network/interfaces post-up ethtool -s eth2 speed 1000 duplex full autoneg off
The above line should be the last line of the file. This will change speed, duplex and autoneg of eth2 device permanently.
On SUSE, modify the /etc/sysconfig/network/ifcfg-eth-id file and include a new script using POST_UP_SCRIPT variable as shown below. Include the below line as the last line in the corresponding eth1 adpater config file.
# vim /etc/sysconfig/network/ifcfg-eth-id POST_UP_SCRIPT='eth1'
Then, create a new file scripts/eth1 as shown below under /etc/sysconfig/network directory. Make sure that the script has execute permission and ensure that the ethtool utility is present under /sbin directory.
# cd /etc/sysconfig/network/ # vim scripts/eth1 #!/bin/bash /sbin/ethtool -s duplex full speed 100 autoneg off
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