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I would like to know what duplex (half or full) my network card has negotiated with a switch when they are both set to auto configuration in Windows.

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up vote 5 down vote accepted

Without looking at the switch, the only way it seems possible is if the windows driver for your NIC reports this information. To see if it does, go to Control Panel --> Administrator Tools --> Event Viewer. You then want to look at the System logs (in Windows7 this is under the Windows Logs tree). Once you found the System logs, click on Source at the top to use as the sorting criteria. Now look for your NIC driver, mine for example is b57nd60a. Scroll through all the entries that your NIC driver has made and if you're lucky you'll see what speed it negotiated at in the event report.

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This is a pain in the ass, but it works, thanks. I sorted by Source, and found b57w2k (for a BroadCom chip) and then looked at the history of it configuring it self. – Scott Markwell Dec 23 '09 at 23:35
+1. Worked for me. Searched for my NIC brand name (Marvell in this case) and jumped right to it. – DuckMaestro Mar 9 '12 at 5:48

Type the following into command prompt:

wmic NIC where NetEnabled=true get Name, Speed

It should tell you.

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Could you provide sample output? – Insane Oct 31 '15 at 2:40
This worked great for me in Windows 10! Thanks. – user3731622 Dec 18 '15 at 22:16
That doesn't appear to list whether or not it negotiated at full-duplex. Perhaps "get Name,Speed,AutoSense" gives that to you? – Wodin Apr 28 at 8:17

Some cards (Intel for example) have a diagnostic suite that shows this information. This software is often not installed. Usually just the driver is installed and the diagnostic/management app is not. I believe the Intel app is called ProSet

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This works in Windows 7, not sure about lower versions:

  1. Right click on the network card in Network Connections in the Control Panel
  2. Click Configure
  3. Click the Link Speed Tab
  4. Look at the Link status Window.

enter image description here

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This one would work with lower versions of Windows but it is relevant only to certain network card drivers. Basic drivers and most drivers from other manufacturers than Intel will not show the information. – pabouk Jan 24 '14 at 9:36

The easiest way I can think of is to get a switch that has lights on the front or a management interface and simply take a look.

Other than that, I am not really aware of any software able to tell you.

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There is no software-way to report the duplex mode negotiated(especially with a switch) because all of those things happen on the physical layer.

You will need some kind of measurement device to diagnose that electronically.

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I waffled between serverfault and superuser, imo it's suitable for both, if the mod's think otherwise I wouldn't object. – Scott Markwell Dec 23 '09 at 23:38

On my Windows 7 Platform -

  • List item

Type at the Windows 7 search bar Network and Sharing Center. Select - Network and Sharing Center

Change Adapter Settings

Right Click ( The LAN Lannetwrk Adapter) select Status it will show you the speed you have negotiated with the next network device up stream.

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Link speed is unfortunately not the same as Duplex. It is possible to be Half Duplex 100mbps for example. – Scott Markwell Dec 11 '14 at 2:22

NIC Speed duplex settings can found with below command

C:>linkspeed /s

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That command does not appear to be present in a default Windows install. – Jason Aller Apr 10 '15 at 15:17
Please use complete details about what you claim answers the question. Linking to resources is always helpful to backup your claim. – CharlieRB Apr 10 '15 at 18:32

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