Autonegotiation Tutorial


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Autonegotiation Tutorial

Autonegotiation Tutorial

Q. How do I find out my NIC speed in Linux ?
A. Use ethtool or mii-tool to display or change ethernet card settings.

ethtool

To display duplex speed of eth0, type the following command

# ethtool eth0


Sample outputs

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: pumbg Wake-on: g Current message level: 0x00000001 (1) Link detected: yes

mii-tool

To display duplex speed of eth0, type the following command

# mii-tool -v eth0

Sample outputs

SIOCGMIIREG on eth0 failed: Input/output error eth0: negotiated 100baseTx-FD, link ok product info: vendor 00:50:43, model 11 rev 1 basic mode: autonegotiation enabled basic status: autonegotiation complete, link ok capabilities: 100baseTx-FD 100baseTx-HD 10baseT-FD 10baseT-HD advertising: 100baseTx-FD 100baseTx-HD 10baseT-FD 10baseT-HD flow-control link partner: 100baseT4 100baseTx-FD 100baseTx-HD 10baseT-FD 10baseT-HD

Where,
100baseTx-FD: 100Mbps full duplex (FD)
100baseTx-HD: 100Mbps half duplex (HD)
10baseT-FD: 10Mbps full duplex (FD)
10baseT-HD: 10Mbps half duplex (HD)

The communications in most enterprise networks are realized by connecting network adapters with twisted pairs, and usually the speed of these twisted pairs is 100MB, but the transmission speed is diverse in different network cards. We usually use a 10Mbps/100Mbps fast network adapter (or HUB), viz its speed is auto-negotiated between 10MB and 100MB. For this net card, theoretically a small file like a 12MB file would finish the transmission within a few seconds, but it takes a longer time actually. The reason for slow speed is that before transmission the net card needs to decide in which speed to perform this action, so if the network adapter can skip over this negotiation, speed will get faster.

We need to choose the speed (10M or 100M) depending on practical needs. If most computers in your LAN are using 10M/100M fast network adapters or 100M adapters, well then I strongly recommend taking the 100MB full-duplex; if some 10M cards are still in use or the network connection is unstable, that you can slow down the speed to 10MB to ensure a stable networking. Below I will show you how to change the speed of your HUB easily:

Step 1 Right-click My Network Places and select Properties to open the Network Connections sheet.

Step 2 Right-click your Local Area Connection and choose Properties.

Step 3 In the General tab, you will find your net card's brand and model under Connection using.

Step 4 Click Configure to open your network adapter's Properties sheet

Step 5 Switch to Advanced tab, and then choose Connection Type or Speed and Duplex. Usually its default value is Auto Negotiation and in the normal situation you can choose 100 Mbps Full Duplex.

If you have to wait for a long time to transmit files and your networking is neither stable nor smooth, you can try this method above.

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