Find the speed of your Ethernet card in Linux

For logging on to the net or for attaching as a node on a LAN, your computer needs a network card. The network card forms the interface between your computer and the network. There are different kinds of network cards available in the market depending on its speed and other features. Here is a tip to find out the characteristics of your network card.

If you want to find what type of network card is used, its speed, on which IRQ it is listed, and the chip type used, you use the following command :

# dmesg |grep eth0

Here eth0 is the first network card. If you have additional cards, it will be named eth1, eth2 and so on. And here is the output of the above command :

divert: allocating divert_blk for eth0
eth0: RealTek RTL8139 at 0xd800, 00:80:48:34:c2:84, IRQ 9
eth0:  Identified 8139 chip type 'RTL-8100B/8139D'
divert: freeing divert_blk for eth0
divert: allocating divert_blk for eth0
eth0: RealTek RTL8139 at 0xd800, 00:90:44:34:a5:33, IRQ 9
eth0:  Identified 8139 chip type 'RTL-8100B/8139D'
eth0: link up, 100Mbps, full-duplex, lpa 0x41E1
eth0: no IPv6 routers present
...

The important things to note here are those highlighted in colour. As you can see from the above listing, my ethernet card is a RealTek RTL8139 chipset based card on IRQ 9 (Interrupt Request). Its speed is 100 Mbps and is a full-duplex card. And the link is up.

As is the philosophy of Linux, there is more than one way of finding the same information. Linux also comes with a cute sounding tool called mii-tool which can also be used to get the same information about your network card.

# mii-tool -v eth0

eth0: negotiated 100baseTx-FD, link ok
product info: vendor 00:00:00, model 0 rev 0
basic mode:   autonegotiation enabled
basic status: autonegotiation complete, link ok
capabilities: 100baseTx-FD 100baseTx-HD 10baseT-FD
             10baseT-HD
...

Here -v is verbose mode. From the above listed output, one can see that the ethernet card is working as a 100baseTX, FD (Full Duplex) card which can work in the following modes :

• 100 Mbps Speed (Full duplex or half duplex ) or
• 10 Mbps speed (Full duplex or half duplex).
  

And it uses autonegotiation to bring up the link. You can call the above device as a 10/100 NIC.

Another tool which also does the same thing is ethtool. Try the following command on your machine to see the output.

# ethtool eth0

Settings for eth0:
  Supported ports: [ TP MII ]
  Supported link modes:   10baseT/Half 10baseT/Full
                          100baseT/Half 100baseT/Full
  Supports auto-negotiation: Yes
  Advertised link modes:  10baseT/Half 10baseT/Full
                          100baseT/Half 100baseT/Full
  Advertised auto-negotiation: Yes
  Speed: 100Mb/s
  Duplex: Full
  Port: MII
  PHYAD: 32
  Transceiver: internal
  Auto-negotiation: on
  Supports Wake-on: pumbg
  Wake-on: p
  Current message level: 0x00000007 (7)
  Link detected: yes

Here full duplex, half duplex and auto-negotiation have the following meanings.

Full Duplex - Logic that enables concurrent sending and receiving. This is usually desirable and enabled when your computer is connected to a switch.

Half Duplex - This logic requires a card to only send or receive at a single point of time. When your machine is connected to a Hub, it auto-negotiates itself and uses half duplex to avoid collisions.

Auto-negotiation - This is the process of deciding whether to work in full duplex mode or half duplex mode. An ethernet card supporting autonegotiation will decide for itself which mode is the optimal one depending on the network it is attached to.