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Ignored subnetmask

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7 replies

by filip_declercq

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Hello

since recently I got a weird problem. Let me explain my setup first. I use a Win2k server that is connected to the company LAN and to a lab-setup LAN. The server is DHCP client on the company LAN and NAT-router/DHCP server on lab-side. The lab network is 192.168.0.0/24, gateway is the server, with fixed IP address 192.168.0.1

That's all concerning the setup which works fine, normally.

Now I get this strange result: suddenly it seems that the subnetmask of the lab side is ignored (or is set at 0.0.0.0): every IP address you try to reach, is searched for in the lab-LAN: the server even makes ARP requests to any webserver on the net you try! When I take a look at the settings, they seem OK. Just changing the settings and putting them back as they were, solves the problem, for about half an hour.

I think this could be a virus, but I cannot find a thing with an updated McAfee viruscan.

Any ideas?

with kind regards

F. Declercq

7 replies

by edlockett

There is a DHCP option for 'all subnets are local'. If this option were set it would produce the effect you describe. Check your DHCP options, on both of the DHCP servers.

Hope this helps :-)

by bfilmfan

Ed is correct. It is Scope Option 027.

Open up DHCP administrator.
Choose the DHCP server.
Choose the Scope.
Expand it.
Choose Scope Options.
Right click in the right side pane.
Choose Configure Options.
Scroll down and choose 027.

by filip_declercq

I checked the DHCP settings. This does not apply. By the way: when this odd behaviour occurs, re-entering the same subnetmask settings on lab-side solves the problem.

by voldar

Subnet mask = 0.0.0.0 means you have a duplicated IP address in your segment. Check if this is not the case to solve your problem.

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