Winston Lawrence

Project Manager & Occasional developer

Troubleshooting a NetBIOS Network Mapping problem

This post is a write-up of a networking problem that I just helped to resolve. The name of the sysadmin has been changed and the messages which actually span a 10 day period, have been condensed and edited to fit into this post. This was an interesting experience for several reasons: the network is some 3400 miles away; I never actually logged on to the network; I didn't know Markel, the sysadmin, before we started troubleshooting the problem network.

Markel: We've just upgraded from a Windows 2003 to a Windows 2008 domain. After the upgrade, a number of applications using the network neighborhood services stopped working. There are two sites involved: computers in SITEA can only locate and work with computers and servers in SITEA; computers and servers in SITEB can only locate and work with computers and servers in SITEB.

Winston: This sounds like it might be a NetBIOS browsing problem as you haven't mentioned  problems with login, authentication or permissions issues which might have pointed to an Active Directory problem and you haven't mentioned any internet access problems which might have pointed to DNS configuration issues. Can you verify that all of the Windows services that should be running, are actually running?

Markel: All of the services appear to be running correctly I added a WINS server on each site when I first saw the problem and I have WINS replication going between both sites.

Narrowing down the problem NetBIOS or WINS?

Winston: Can you give me a better picture of the network configuration at SITEA and SITEB e.g. do you have any firewalls between the sites and are you running any rules on said firewalls/routers that may be blocking NetBIOS traffic? Also could you edit the LMHOST file on just one site and add a a computer/server on the other site and let me know what happens?

Markel: We do not have the firewall switched on and there is no filtering or port blocking on the routers. We have approx 50 servers 300 desktops site a, 10 servers 100 desktops site b. I will try the LMHOST file test this morning and let you know the outcome.

Winston: Okay, You may need to do the Notepad runas administrator trick to edit the LMHOSTS file.

Markel: I have added servers to the LMHOSTS file but this has not made a difference. I can do NSLOOKUP and the information is correct. I can ping, map drives and access the computer \computer etc. from any computer on either site to any computer on the other site with no problems. Its just the network neighbourhood that is showing the single sites only.

Winston: What does your IP address structure look like (Class A or B or C) and what does your subnet mask look like at Site A and Site B? Is your PDC on site A or Site B? I'm leaning towards Site B being on a different subnet from Site A, the domain master browser is whichever site your PDC is located and the other site (being on a different subnet) does not have its own master browser configured and that your browse list is not being populated properly by the Domain Master Browser. Apologies though for handing you more questions instead of answers.

Markel: Winston any help will do mate. PDC is on SITEA a 10.49.*.* ip address range along with the helpdesk server. subnet mask second site (SITEB) is 172.31.., sm full dns running no stub zones. I also have the 2 remaining 2003 servers (dc) running on this site.

NetBIOS over the WAN

Winston: With that IP address configuration you essentially have two different sites that are trying to browse across a WAN and that all of the required services (netbios over TCP/IP) being routed across the WAN with NAT translation on both sides (see: NETBIOS - A twisted history). I'm going to have to think about this one (browsing across a WAN) as its a little different than what I thought you were trying to do - it also explains your DNS configuration which was puzzling me. Can you run browstat.exe on site a and site b and post the results? The Domain Master browser should be the PDC on Site A. I'm betting that when you run this on site B it does not show a Master browser on that subnet. Anyway post the results of browstat.exe.

Markel: Is browstat.exe part of Windows Server 2003 or 2008?

Winston: You get browstat.exe as part of the Microsoft support tools from Microsoft download center if you dont already have a copy, Ive run it on XP, Vista,Windows 2000 and 2003 and It runs just fine on 2008 (Ive seen reports from 2008 runs) and should give you enough information about the actual computer browser configuration to resolve the issue.

Markel: I'll have to run this from a windows xp machine, browstat.exe is not compatible with windows 7 or server 2008 rc2. I'll have ago with the windows compatibility mode first and let you know how I get on.

Winston: Okay, just ignore the error message about different version of Windows and run it - it should be okay.

Markel: Got it! Computer browser is disabled by default on server 2008 rc2. Enable it and it works -  THANK YOU!

Winston: Glad you got it working Markel, You should probably put at least one copy of browstat.exe on a machine in each domain as this would have solved (this problem) in a minute or two.

Winston Lawrence

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