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Disabling NetBIOS through DHCP

By JLA ·
TechFolks:

I am attempting to clean up a network environment that is currently fairly clogged with NetBIOS broadcast traffic on a single subnet. We have a Win2K DC, and a mixed environment of win2KPro, XP, NT4, and one W98 machine. As I have noticed that NB traffic accounts for more than 60% of our network traffic, I wanted to set the DHCP server to disable NetBIOS for my Win2KPro stations only, per the advanced settings, but I am hesitant to do so, as I am not entirely sure what functionality I might lose when the W2K clients stop speaking NB. Is there any clear or easy way to assess what the impact might be for making this change without just pulling the trigger and hoping for the best? Any advice or guidance would be appreciated.

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Disabling NetBIOS through DHCP

by Ann777 In reply to Disabling NetBIOS through ...

Here's a very good article on the subject (pros and cons) and it takes you to a link that tells you specifically how to do this via your DHCP server:

http://www.petri.co.il/disable_netbios_in_w2kxp.htm

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Disabling NetBIOS through DHCP

by JLA In reply to Disabling NetBIOS through ...

Thank you, but I know *how* to do it; the question I asked is how to assess the actual impact on my client machines without going to each one and searching for shares on downlevel clients, printers, etc. My understanding is that if DNS is functional and all needed shares, etc. for those Win2K clients are located on Win2K or XP boxes, I should be okay. However, "should" isn't enough, I need to KNOW before I implement it.

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Disabling NetBIOS through DHCP

by timwalsh In reply to Disabling NetBIOS through ...

Hate to tell you this, but anytime you get something that "should" work, what is really being said is "This should work in most normal situations. However, we have no way of testing every possible permutation that you are likely to experience. Therefore, we leave it up to you to test this in your specific environment. Good luck!"

Therefore that would be my suggestion: Set up a small test environemtn and see how this change affects that environment before going live on your entire network. That will be you ONLY surefire way to asses the impact on YOUR environment.

Good luck.

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Disabling NetBIOS through DHCP

by JLA In reply to Disabling NetBIOS through ...

Semantic content of reply: none. Why would you even answer this question if your suggested answer is "try testing it"?? My question was, what unobvious needs for NetBIOS does a Win2K AD mixed-mode domain with heterogenous clients have that might disrupt operations? I'm looking for a technical answer, not moral support and encouragement. But thanks anyway.

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Disabling NetBIOS through DHCP

by Joseph Moore In reply to Disabling NetBIOS through ...

Since you have a mixed environment, you shouldn't disable NetBIOS for the Win2K clients.

It will take a little explanation as to what is going on and why. I have the time, so here we go:

Win2K has NetBIOS on by default. What that means is thatwhen you try and access a shared resource (shared printer, shared folder) on another machine from a Win2K client, the Win2K machine communicates on TCP port 139 & TCP port 445. Now, whichever port answers the ACK first is the one that Win2K uses forits File and Print Sharing communication.

139 is supported on all modern Windows machines (Win95 onward). 445 is new to Win2K (and XP); it is NOT used by Win 95/98/ME or NT4.

Now, as you can guess, when a Win2K client talks to a NT4 machine, the communication is gonna use TCP port 139, since that is all NT4 had. And that summarizes your problem. Since you have all these down-level clients (NT4 and the 98 box), if you disabled "NetBIOS Over TCP/IP" for Win2K, then your Win2K machines wouldNEVER be able to hit a shared folder on the NT4 machines or 98 machine. They could talk to themselves all they want (and the XP machines), but never the older ones.

So, until you are all Win2K/XP, you cannot remove NetBIOS.

Here is a nice article on port 445 and how it is replacing port 139:
http://ntsecurity.nu/papers/port445/

hope this helps

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Disabling NetBIOS through DHCP

by JLA In reply to Disabling NetBIOS through ...

So if I read the documentation and your answer correctly, if I do *not* have any need to access shares or printers mapped to downlevel cleints, I ought to be safe in doing this. Thanks. Now jsut have to doublecheck the whole environment. What fun!

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Disabling NetBIOS through DHCP

by ewgny In reply to Disabling NetBIOS through ...

Bottom line is that any win2k pc that has NetBios over TCP/IP disabled will not be able to browse /communicate with a WINNT/Win98 PC.
I have tested it!! If your 2000 boxes have no need to communicate with your downlevel OS's (as microsoft likes to call them) then there is no problem. In my case a few users require a drive mapped to a 98 box, so they are unable to have netbios disabled at this time. I have manually disabled NetBios over TCP/IP on many other win2k boxes and have not had any problems at all. Good luck

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Disabling NetBIOS through DHCP

by JLA In reply to Disabling NetBIOS through ...

But if there aren't any shares on local clients (thanks to our brand-spanking-new NAS setup), it shouldn't matter. Thanks for the assistance.

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Disabling NetBIOS through DHCP

by JLA In reply to Disabling NetBIOS through ...

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