Project

General

Profile

Using ethtool to troubleshoot your physical NIC/network connectivity issues

User documentation
12/05/2017

  • Last Updated: 08/10/2018

Use the ethtool command to check your physical connections. You may have plugged a cable into eth1 when intended to be in eth0 and vice versa.

ethtool eth0
ethtool eth1

If you are connected to a gigabit network you will see these relevant settings:

    Speed: 1000Mb/s
    Duplex: Full
    Link detected: yes

NOTE: Some 100M network connections will display no for Link Detected even though the connection is up and working. The PHY adapater sense settings for 100M are older and non-standard versus 1G so this problem may happen.

You can also use the ip link command to see if your link status is healthy - check the state for UP:

ip link | grep eth0

Sample ip link output:

2: eth0: <BROADCAST,MULTICAST,SLAVE,UP,LOWER_UP> mtu 1500 qdisc mq master bond0 state UP mode DEFAULT group default qlen 4096

Sample ethtool output for a 1G network connection:

Settings for eth0:
    Supported ports: [ TP ]
    Supported link modes:   10baseT/Half 10baseT/Full 
                            100baseT/Half 100baseT/Full 
                            1000baseT/Half 1000baseT/Full 
    Supported pause frame use: No
    Supports auto-negotiation: Yes
    Advertised link modes:  10baseT/Half 10baseT/Full 
                            100baseT/Half 100baseT/Full 
                            1000baseT/Half 1000baseT/Full 
    Advertised pause frame use: Symmetric
    Advertised auto-negotiation: Yes
    Link partner advertised link modes:  10baseT/Half 10baseT/Full 
                                         100baseT/Half 100baseT/Full 
                                         1000baseT/Full 
    Link partner advertised pause frame use: Symmetric Receive-only
    Link partner advertised auto-negotiation: Yes
    Speed: 1000Mb/s
    Duplex: Full
    Port: Twisted Pair
    PHYAD: 1
    Transceiver: internal
    Auto-negotiation: on
    MDI-X: off
    Supports Wake-on: g
    Wake-on: d
    Current message level: 0x000000ff (255)
                   drv probe link timer ifdown ifup rx_err tx_err
    Link detected: yes

Files