Home NetworkHere’s a little problem that drove me crazy: How do you determine the Master Browser in a Windows Workgroup?

First of all, lemme explain a bit about how a workgroup works. When you have a LAN set up running Windows machines, each machine can see all the others in Network Neighborhood (or just “Network” in Vista). If you want to see the files on another machine, you just go to Network Neighborhood, click, et voila!

The other method you can use is to open Windows Explorer (keyboard shortcut: Win-E) and in the location/address bar, type:


So, if you want to go to the computer called BALTHAZAR, you’d type:


And hit enter. This is handy to know if Network Neighborhood is not working. And a grumpy Network Neighborhood is exactly the reason why sometimes, you need to find out which computer is the Master Browser.

On a local area network (LAN), each computer “talks” to the others. Each computer has an IP address, like, and also a name. The name is what you call your computer so you and your friends don’t have to remember the IP address. In our example above, the computer name is BALTHAZAR, but the IP address might be Fabulous.

[ad name=”square-r”] So, what happens is that each computer on the LAN must talk to the others. Since we’re only dealing with a workgroup, and there is no domain server, there is no computer to keep track of what machines are active on the network. This is where the Master Browser schtick comes into play.

What happens is that all the computers on your LAN hold an “election”. This election depends on a number of factors, but for the purposes of this discussion, we just have to know that all the computers get together and vote on who will be the Master Browser on the LAN. Once a computer is elected, it will keep track of what machines are connected to the LAN by more or less sending messages to say, “Yo! You still there?”

Of course, you may ask: What happens when the computer that is the Master Browser gets shut down when, say, I go to bed? In that case, you will find that your Network Neighborhood may not work so well. At that point, all the computers on the LAN get together again and they hold another election. As I understand it, there are one or more “Backup Master Browsers” waiting in the wings, but we’ll ignore that for now.

Now, what happens when you have Network Neighborhood turning up blank on you sporadically, or possibly missing several of the computers on your LAN from time to time? Well, in that case, you need to determine who is the Master Browser so that you can narrow down the problem to one computer and see if maybe you need an updated ethernet driver, or there are firewall problems, or whatever.

The “fun” way of doing this is with DOS commands. Here’s how you’d do it:

  1. Open up a command prompt
  2. Type net view and hit enter
  3. Look at the list of computer names. These are the computers on your LAN. Note that the format is \\COMPUTER-NAME like I talked about above.
  4. For each name in the list, type the following command: nbtstat -a COMPUTER-NAME

One of the results from the nbtstat commands will show a row with “_MSBROWSE_” in it. That means that this computer is the Master Browser.

Wasn’t that fun?

No, it wasn’t.

So, I wrote a little script in Ruby to do this for you. I needed to in order to troubleshoot a networking problem on one machine on my LAN, and I didn’t want to type 10-20 commands every time. But as long as I was writing it, I figured I would jack it up a bit. Here’s what it does:

  • net view net view /domain to determine the list of workgroup names
  • net view /domain:[WORKGROUP] to determine the list of puter names for each [WORKGROUP]
  • extracts the individual computer names and sticks them in an array
  • iterates through the array and calls ping -n 1 -4 COMPUTER-NAME on each computer name (we only want to display IPv4 addresses, hence the “-4” switch)
  • iterates through the array of IP addresses and calls nbtstat -A IP-ADDRESS (the “-A” means “I’m giving you an IP address instead of a computer name”. This is a more reliable way of doing things.)
  • After each call to nbtstat, it not only checks for the _MSBROWSE_ string, but it also records the MAC address of the network adapter in the remote computer.
  • iterates through all the data and displays a nicely formatted table, like so:
Scanning LAN...

BERT     00-18-C0-42-A3-B2   CHEESE
RHINOX   00-00-00-00-00-00   WORKGROUP   MASTER
Q        00-28-F6-68-F5-48   WORKGROUP
RADDAR   00-02-0D-74-FC-33   CHEESE
MOP      00-1B-8C-56-01-52   CHEESE      MASTER
AI       00-6A-83-6B-A0-83   WORKGROUP

Press any key to exit...

I wrote this little script in Ruby because it was fast and easy. But I didn’t want to have to call it from a command prompt with ruby all the time, and I wanted others to be able to use it without having to install Ruby on their own computers. So, I compiled it into a self-contained executable using RubyScript2Exe, and I added a pretty icon with Resource Hacker. Now my nifty little 2kB script is a lovely 1.5MB executable. Well, ya know… You can’t have everything. It may be bloated, but at least it works!

You can run it from the command line, or from Windows. It’s best to put the file in your Windows directory. It won’t run properly unless it’s on your boot drive (usually C:). From version 1.6, it will run just fine even from a USB stick. If plopped into the Windows directory itself, it will be executable from any drive or directory on your computer. Anyway, if you run it from Windows, it will just open up a command prompt window and pause before closing it so you can see the results. On my machine, it’s nice and speedy.

Oh, and one last note: it might take 30 seconds or so to scan your LAN. The more machines you have, the more work it was to do.

So, now you have a lovely tool to determine the IP address, MAC address, name, and Master Browser status of all the computers on your LAN.

UPDATE (8 June 2009): My little LANscanner program has been updated to version 1.1. It now supports the x64 flavor of Windows XP, Vista, and 7. Be sure to read the included .TXT file for install instructions!

UPDATE (27 February 2010): LANscanner has been updated to version 1.2. New in this release is the display of the workgroup for each computer, as well as formatting improvements that should make the output easier to read even with long computer/workgroup names.

UPDATE (20 March 2010): LANscanner has been updated to version 1.3. This release is mostly a bug fix for 1.2. In the older version, the only workgroup reported was the one your puter was on. Oops! That didn’t make the feature very useful. Now LANscanner will first scan for all available workgroups, and accurately report all machines on all workgroups, including which puter is the Master Browser for each workgroup. I also optimized some code here and there for good measure.

UPDATE (23 December 2012): Thanks to some adventures by frank in bahia, there is one thing you will want to check if you have problems with LANscanner. As he wrote in his comment below:

Second only to “is the PC turned on” in the obvious fix category is “is Client for Microsoft Networks installed”.

What I’ll never understand is how those things UNinstall themselves!

To make sure Client for Microsoft Networks is installed:

  1. Open Network and Sharing Center
  2. Click “Change adapter settings”
  3. Right-click your ethernet adapter and choose Properties
  4. If “Client for Microsoft Networks” does not appear in the list of items, click the “Install…” button
  5. Choose “Client” for network feature you want to add, and then click the “Add…” button
  6. Find Microsoft’s “Client for Microsoft Networks” in the list, and click OK to install it

That should be about it. Of course, the procedure above varies a little depending on whether you’re using XP, Vista, Win 7, or Win 8, but that’s the gist of it. Thanks, frank!

UPDATE (27 January 2013): Thanks to dennis, it seems the System Error 53 is caused by workgroup and/or puter names with spaces in them. This has been fixed in v1.4. Also, LANscanner is now built using Ocra 1.3.0 and Ruby 1.9.3, since RubyScript2Exe is now rather outdated and nonfunctional. The executable is now 26% smaller.

UPDATE (04 May 2013): Version 1.5 of LANscanner is now available. Changes to this version:

  1. LANscanner now speaks Swedish, French, and English. If you’d like the program to work in your language, please e-mail me the output of the command:  nbststat -A IPADDY,  for any IPADDY on your LAN
  2. If MAC address is detected as 00-00-00-00-00-00, we now use “arp -a IPADDY” to overcome Samba problems and retrieve a valid MAC address
  3. All character encodings are now supported (at the expense of increased EXE file size, but oh well).
  4. To sort the output by IP addy instead of by puter name, pass any argument to LANScanner, like so:  lanscan.exe ip
  5. Improved formatting for shorter IP addresses

Thanks to Mikael G for the “arp -a” tip!

UPDATE (07 May 2013): Version 1.51 is out. Added support for German and Polish Windows.

UPDATE (25 May 2013): Version 1.52 is out. Added support for the following command-line switches:

  1. -ip  =  sort output by IP address. Note that this has changed from the previous version!
  2. -w WORKGROUP  =  Scan only the workgroup called WORKGROUP
  3. -e WORKGROUP  =  Scan all workgroups except WORKGROUP

UPDATE (24 August 2013): Version 1.53 is out. Fixed -ip option so that IPs are properly numerically sorted.

UPDATE (11 November 2013): Version 1.54 is out. Added support for Spanish Windows.

UPDATE (27 April 2014): Version 1.55 is out. Added support for Norwegian Windows, plus the following command-line switches:

  1. -n = suppress the “Press any key to exit…” message at the end
  2. -m = Only display MASTER browsers found

UPDATE (22 October 2014): Version 1.56 is out. Added support for Portuguese, and changed to Ruby v2.0.0 + Ocra 1.3.3. Script is now bigger, but with Ruby 2 goodness!

UPDATE (17 December 2014): Version 1.57 is out. Added support for Japanese.

UPDATE (09 May 2015): Version 1.6 is out. Added support for running on any drive, not just the Windows installation drive. Will also run off a USB stick or any other drive – as long as Windows is installed on the puter.

UPDATE (27 November 2015):  Windows 10 November Update (1511) breaks LANscanner! You’re probably getting: System Error 1231 has occurred. Microsoft is aware of the problem, and will hopefully release a fix soon. SIGH…

UPDATE (25 January 2016): Version 1.61 is out. Added support for Dutch. In Windows 10, supposedly an update that should be released in March will fix the System Error 1231 issue.

UPDATE (02 Feb 2016): Version 1.62 is out. Added support for Czech.

UPDATE (18 Feb 2016): Version 1.63 is out. Fixed detection of Windows drive.

UPDATE (2 Mar 2016): AT LAST! Latest 1 March updates for Windows 10 seem to have fixed the Samba issues that busted LANscanner. So, it finally works again!

UPDATE (1 May 2016): Version 1.64 is out. Fix for puters with multiple network adapters resulting in multiple/incorrect MAC addresses and Master Browser in output

UPDATE (22 May 2016): Version 1.64 has been rebuilt with Ocra 1.3.5. When built using the Ocra 1.3.6 gem, the resulting EXE was detected as malware by a number of antivirus solutions. Should be all better now!

UPDATE (21 Aug 2016): Version 1.65 is out. Fix for Win 10 where nbtstat no longer works to get local WORKGROUP, MSBROWSE status, or MAC addy; Getting IP from PuterName is more reliable and no longer results in entries with IP but no MAC or WORKGROUP after a puter is turned off

UPDATE (24 Aug 2016): Version 1.66 is out. Rebuilt in Ruby 2.0.0 to make it work on 32-bit Windows again, fixed bug introduced in 1.65 related to new “Get IP” function on XP

UPDATE (27 Aug 2016): Version 1.67 is out. Removed fancy IP detection since it broke things… Oops!

UPDATE (28 Oct 2016): Version 1.68 is out. Added option “-nodeip www.xxx.yyy.zzz” for specifying the IPv4 of the network adapter you want to scan from/for in the case of puters with multiple network adapters. Note that VirtualBox adds its own virtual network adapter, which counts as a 2nd adapter. If you have multiple network adapters and you do not use the -nodeip option, your results may be wonky!

UPDATE (30 Jan 2018): ** LAN Scanner no longer works on Windows 10 1709 and above. **
See here for more info:

Time to switch to a HomeGroup on Windows 10

UPDATE (27 Dec 2018): LAN Scanner works again on Windows 10. See here for version 2.0!


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