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I plug my Windows PC into the network and get the message "Windows System Error - A duplicate name exists on the network". What do I do?



Last revision November 9, 2004

First, this answer assumes that your Windows PC has been properly registered on the Earth Sciences network or is registered elsewhere on the Stanford network with the "roaming" attribute, so it will get a temporary IP address in Earth Sciences.

The problem here is the failure to align network names used by different protocols on the same computer so they match.

Your only valid unique computer network name is the one you use when you register the computer on the Stanford network. This is the IP hostname that is listed in the campus nameservers and maps to the static unique IP address assigned to your computer.

When designing Windows, Microsoft combined standard internet TCP/IP protocols, which all must use your registered IP hostname and address, with its own special file and print sharing protocols. Then Microsoft, in its infinite wisdom (folly?), decided that it would be cool to let you use a different name, like "Mary's Great Laptop", for Windows file and print sharing, instead of being stuck with your boring IP hostname, which can't use any fancy characters or blanks.

So a Windows PC on the network can have two names: its IP hostname, which it acquires automatically from the campus DHCP servers when it connects to the network; and its "Windows" network name, which is used for Windows file and print sharing and can be set by the user if the computer is not part of a centrally managed Windows domain. The possibility of setting these names differently leads to confusion and this error message.

Most Windows PCs on campus and in Earth Sciences are not part of a managed Windows domain, so it is possible for their standard IP hostname to differ from their Windows network name, which is the name that shows up when browsing for file or print shares in Network Neighborhood or My Network Places.

There is no way to guarantee that a user-selected Windows network name is unique, as these names are not registered in any central location. Your one true IP hostname is registered and is unique in all the world (when used in the fully-qualified format with the ".stanford.edu" suffix). Because Windows network names are not registered, Windows does a broadcast lookup on the local network segment only to see if the name you have selected is already in use. That may be fine on the network segment where you first set your Windows network name, but then cause a conflict when you move the computer to another network segment. Or it may be OK one day, but then lead to a conflict another day when someone else puts a new PC on the network and picks the same Windows network name that you were using (while your computer happened to be off the network).

So, when you see the error message "Windows System Error - A duplicate name exists on the network", it means that another Windows PC already on that network segment has selected the same Windows network name, even though both of you have completely unique IP hostnames. This error message is not completely disabling. Standard internet protocols like email, web access, ftp, telnet and ssh will all still work because they all use your one true IP hostname. But it does mean that your PC would not be able to share files or printers to other Windows PCs on the network, which is not recommended anyway, due to security issues.

What can you do about this?

The only way to avoid this naming confusion is if everyone follows the same rule: use one and only one name, your officially registered IP hostname, for all purposes.

First of all, make sure that your PC's Windows network name is set exactly equal to your official IP hostname. This will solve your problem if the Windows name was formerly different from the IP hostname, and will make sure that you do not contribute to making the problem worse. To set this name, right-click on My Computer and select Properties. When the System Properties window opens, click on the Computer Name tab. You can then set your Windows network name to match your IP hostname. You don't need the ".stanford.edu" suffix, just the main name.

But what if you forgot your IP hostname that you picked when you registered your PC on the network? In this case, you will have to look it up using the campus nameservers.

First, you need the IP address that your PC is using while plugged into its "home" network. If you registered in Earth Sciences, then your home network is any of the network jacks in Earth Sciences. If you registered in your on-campus residence, then your home network is there. You must be connected to your home network to find your registered static IP address; if you are "roaming" to another network, or using wireless, you are getting a temporary IP address that will not map to your one true IP hostname.

Look up your IP address using one of these methods:

  • Windows 95, 98, and ME:

    Select Run from the Start menu. Enter the command winipcfg and press the RETURN or ENTER key. When the winipcfg windows opens, make sure that the actual ethernet adapter is selected in the drop-down menu at the top. Sometimes, this menu will start with the PPP (modem) adapter, and you have to select the real ethernet adapter from the menu. Your current IP address should be displayed.

  • Windows NT, 2000, XP, and 2003:

    First, open a command-line (DOS-style) window to type commands by running the cmd program from the Run item in the Start menu. Inside the command-line window that it opens, type the command ipconfig /all and press the RETURN key. Information about your ethernet adapter(s) will be displayed. If you have more than one, make sure you are looking at the information for the local area connection that is active. It will show your IP address.

Once you have your static assigned IP address (from your home network), you can then lookup the official IP hostname assigned to your computer. You can do this using the host program from a pangea command-line login. For example, typing this command from a pangea login will look up the IP address for pangea:

host 171.64.168.31

This gives the not surprising result

Name: pangea.Stanford.EDU
Address: 171.64.168.31
Aliases: pangea

Another way to look up your assigned IP hostname using your IP address is to use one of the many web sites offering DNS (domain name system) lookups. For example, you can use the Reverse DNS lookup form (near top of center column) on the DNS Stuff website.

But what if your Windows network name is already set equal to your registered IP hostname and you still get that error message about duplicate name on the network? This means that there is a trespasser on the network, who has cavalierly entered your registered IP hostname as his Windows network name, even though it is not the same as his own IP hostname. Perhaps he is jealous that your registered name is so much better. Or perhaps he is just careless. Anyway, what can you do?

Your first choice is to ask the network manager to help you track down this miscreant and force him to change his Windows network name to match his own registered IP hostname. This is a tedious and difficult process. You will get faster results with your second choice, which is to pick an entirely new name, not yet in use for either an IP hostname or a Windows network name, and then ask the network manager to change your registered IP hostname to this new name, which you enter in your Windows System Properties.

If you opt to pick a new name, first verify that it is not in use as an IP hostname. You can use the host program on pangea, or enter your proposed name in the Host name checking form that is available on pangea's network registration web page.

Next, after verifying that your proposed new name is not in use as an IP hostname, enter it on your PC as your Windows network name in the System Properties window to make sure it is not already taken by some rebel on the local network.

After your proposed new name passes both tests, send it, along with your existing IP hostname or address (so your computer can be identified in the network database) to the network manager and ask him to change your IP hostname to this new name.

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