Linux ethtool Examples to Manipulate Ethernet Card (NIC Card)

Ethtool utility is used to view and change the ethernet device parameters.

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

Upon successful connection, the three parameters mentioned above gets appropriate values. i.e Speed is assigned with known value, Duplex become either Full/Half, and the Link detection becomes Yes.

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

Half Duplex, Full Duplex, and Auto-Negotiation

Introduction

The configuration of your Ethernet Card defines how effectively your servers communicate.

It is necessary to understand how Auto-Negotiation, Speed, and Duplex settings affect the transfer of data to maintain network connectivity with minimal effort.

This article will show you how to change Speed, Duplex, and Auto-Negotiation settings in Linux with ethtool commands.

Prerequisites

• Command-line/terminal window
• A user account with root or sudo privileges
• The Ethtool configuration tool installed

Half Duplex, Full Duplex, and Auto-Negotiation

Half-duplex mode allows a device to either send or receive packets in turn. A device set to this mode cannot perform both actions at the same time.

When a device’s mode is at full-duplex, it can also send and receive packets simultaneously.

Auto-Negotiation is a mechanism by which a device automatically chooses the best performing transmission mode based on its counterparts’ characteristics. It is recommended to keep Auto-Negotiation enabled as it allows devices to choose the most efficient means for the transfer of data.

What is a Duplex Mismatch?

When a device, with enabled auto-negotiation, connects to a device that is not using this signaling method, the process does not work. The end of the connection with an active auto-negotiation is still able to detect the speed of the other end, but cannot correctly detect the duplex mode. As a rule, the auto-negotiating end of the connection is going to use half-duplex while the other end might be at full-duplex. This situation is considered a duplex mismatch.

A duplex mismatch does not stop communication completely. Single packets and small amounts of data do not cause immediate issues. However, when a large amount of data is sent from either end, the speed drops significantly. The connection is working, but the performance is reduced as the data transfer rate is asymmetrical and might lead to packet loss.

How to Use Ethtool Command to Configure NIC Settings

Ethtool is a Network Interface Card configuration command that allows you to retrieve information and change your NIC settings. These settings include Speed, Duplex, Auto-Negotiation, and many other parameters.

To proceed, you’ll need to know the name of your network interface card.

To find the name of your network interface card, run the following command from the command terminal:

ifconfig

The command works with both Linux Centos 7 and Ubuntu. The output provides the name of the device interface card.

In the above example, the name of the device is enp0s3.

Now that you have determined the name of the device, check the current Speed, Auto-Negotiation, and Duplex mode settings with the command: ethtool devicename.

In our specific example the command is:

ethtool enp0s3

The output shows that the current speed is 1000Mb/s, that the Duplex is at ‘Full,’ and that Auto-Negotiation is turned on.

Ethtool Command to Change Ethernet Adapter Settings

The ethtool –s command can be used to change the current settings by defining the values for “speed,” “duplex,” and “autoneg” in the following format

sudo ethtool –s [device_name] speed [10/100/1000] duplex [half/full] autoneg [on/off]

For example, to set the speed at 1000Mb/s, the duplex mode to ‘full’ and the auto-negotiation to ‘on’ the command would be:

sudo ethtool –s enp0s3 speed 1000 duplex full autoneg on

The ethtool [device_name] command is necessary to confirm that the changes have been applied.

Ethtool_opt Variable to Permanently Set Ethtool Command Settings

Changes made with Ethtool are by default reverted after a system is re-booted.

To apply custom settings each time a system boots edit the file for the device interface:

vi /etc/sysconfig/network-scripts/ifcfg-enp0s3

Add the desired values as a line at the end of the file using the following syntax:

ETHTOOL_OPTS="speed [100|1000|10000] duplex [half|full] autoneg [on|off]”

For example:

ETHTOOL_OPTS="speed 1000 duplex full autoneg on”

Save the changes and exit the file.

Now the changes are applied after every reboot and are permanent unless the file is altered again.

yum repository for locally-mounted DVD on Red Hat Enterprise Linux 7

• Once you have downloaded a DVD version of your chosen Rhel Version and copied it over to a location on your server.
• Mount the RHEL installation ISO to a directory like /mnt/disc, e.g.:
  
  

  # mkdir -p  /mnt/disc
  # mount -o loop RHEL7.1.iso /mnt/disc
  

  If you use DVD media , you can mount like below.
  
  

  # mkdir -p  /mnt/disc
  # mount /dev/sr0  /mnt/disc
  

• Copy the media.repo file from the root of the mounted directory to /etc/yum.repos.d/ and set the permissions to 0644 or another similar permissions set:

  # cp /mnt/disc/media.repo /etc/yum.repos.d/rhel7dvd.repo
  # chmod 644 /etc/yum.repos.d/rhel7dvd.repo
  

• Edit the new repo file, changing the gpgcheck=0 setting to 1 and adding the following 3 lines

  vi /etc/yum.repos.d/rhel7dvd.repo
  enabled=1
  baseurl=file:///mnt/disc/
  gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-redhat-release
  

  In the end, the new repo file could look like the following

  [InstallMedia]
  name=DVD for Red Hat Enterprise Linux 7.1 Server
  mediaid=1359576196.686790
  metadata_expire=-1
  gpgcheck=1
  cost=500
  enabled=1
  baseurl=file:///mnt/disc/
  gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-redhat-release
  

• Clear the cache and check whether you can get the packages list from the DVD repo

    # yum clean all
    # yum repolist enabled

• It should look like the following if no other repository is enabled.
  To avoid any corruption its recommend to disable any non-redhat repositories.

# yum repolist enabled
Loaded plugins: product-id, search-disabled-repos, subscription-manager
This system is not registered to Red Hat Subscription Management. You can use subscription-manager to register.
repo id                                                                                 repo name                                                                     
InstallMedia                                                                        Red Hat Enterprise Linux 7.7 
repolist: 5,229

• If no errors are returned, the following can be used to update:

  # yum update

Linux Kernel Modules - Load, Unload, Configure

Linux allows the Kernel to be configured at run time, to enable or disable different services as you see fit. This way you don't have to compile a monolithic kernel, and can save some memory usage. Some modules you'll only need for a short time, others you'll need all the time. You can configure your Linux machine to load kernel modules on startup so you don't have to remember to do that when (if) you reboot.

Module Commands

There are a few commands that allow you to maniuplate the kernel. Each is quickly described below, for more information say `man [command]`.

• depmod - handle dependency descriptions for loadable kernel modules.
• insmod - install loadable kernel module.
• lsmod - list loaded modules.
• modinfo - display information about a kernel module.
• modprobe - high level handling of loadable modules.
• rmmod - unload loadable modules.

The usage of the commands is demonstrated below, it is left as an excerise to the reader to fully understand the commands.

Using Module Commands

Below the different kernel module commands are demonstrated

# Show the module dependencies.
depmod -n

# Install some module
insmod --autoclean [modnam]

# This lists all currently loaded modules, lsmod takes no useful parameters
lsmod 

# Display information about module eepro100
modinfo --author --description --parameters eepro100

# Removing a module (don't use the example)
rmmod --all --stacks ip_tables

Module Configuration Files

The kernel modules can use two different methods of automatic loading. The first method (modules.conf) is my preferred method, but you can do as you please.

• modules.conf - This method load the modules before the rest of the services, I think before your computer chooses which runlevel to use
• rc.local - Using this method loads the modules after all other services are started

Using 'modules.conf' will require you to say `man 5 modules.conf`. Using 'rc.local' requires you to place the necessary commands (see above) in the right order.

Sample modules.conf

# modules.conf - configuration file for loading kernel modules
# Create a module alias parport_lowlevel to parport_pc
alias parport_lowlevel parport_pc
# Alias eth0 to my eepro100 (Intel Pro 100)
alias eth0 eepro100
# Execute /sbin/modprobe ip_conntrack_ftp after loading ip_tables
post-install ip_tables /sbin/modprobe ip_conntrack_ftp
# Execute /sbin/modprobe ip_nat_ftp after loading ip_tables
post-install ip_tables /sbin/modprobe ip_nat_ftp

Sample rc.local

#!/bin/sh
#
# This script will be executed *after* all the other init scripts.
# You can put your own initialization stuff in here if you don't
# want to do the full Sys V style init stuff.

/sbin/insmod ip_tables
/sbin/modprobe ip_conntrack_ftp
/sbin/modprobe ip_nat_ftp

Conclusion

You should see/know that modules are necessary. They can be loaded via 'modules.conf' or 'rc.local', but 'modules.conf' load them first and 'rc.local' loads them last. Using the various module commands you can add, remove, list or get information about modules.