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Subnet Mask

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by scopo

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I have a windows 2000 server on my class C network running DHCP. My clients about 50 machine are running win98. What is happening is that the client machine's subnet mask keeps changing from 255.255.255.0 to either 255.0.0.0 or 255.255.0.0. When this happen they cannot see other machines on the network and they receive a message that "no domain controller was available to validate the passowrd". what is causing this problem and how can I resolve it? I thought the problem was caused by my network class. I had a class A address with a class C subnet. But I have since changed to a straight class C and the problem is still occuring on some of the clients. Is this a problem with the clients or a settings on the DHCP Server?
Thank you foryour assistance.

6 replies

by radiic

Sorry I dont have a definitive answer for you, but I did experience this problem at the last company i worked at. We had 2 workstations out of 200 that did exactly as you described. On boot up they would suddenly get a class b subnet on our class cnetwork. We would log on to the machine and run winipcfg and do a release all, renew all and it would get its proper class c sub. They would only do it once in awhile, but it was the same 2 machines. They were loaded in the same manner as over 100 other machines. We never figured out why those 2 did that. I suspect now that I think about it maybe they had flakey nic's in them. And this was on a NT4 sp6 DHCP network. I really dont think it is your server settings. On my current Network Ihave not encountered this problem.

by ann777

It sounds as if part of the problem may be in the registry. It sets a DHCP assignment and will keep on incrementing and adding to it until it finds an address that has worked before.

In Win98 go to Start --> Run --> regedit --> HKEY_LOCAL_MACHINE --> System --> CurrentControlSet --> Services --> VxD --> DHCPInfo00 and delete the entire key.

You may see DHCPInfo01 ... 02 ... 03 etc as these increment.

You might also want to delete the DHCP key as well. Then exit out of the registry. reboot. run winipcfg and release all ... renew all. You should be fine if your DHCP server is properly setup and operational.

This might also happen if all the ip addresses are assigned and there are none on the proper subnet to assign... but it should not see any of the older subnets after clearing out the registry. What might start happening is if everything is taken, you might get a local assignment of ip=169.254.x.x subnet=255.255.0.0

by ann777

There's a registration/expiry time of DHCP leases. If your scope does not have extra ip addresses for your 50 computers, you may be running into these types of problems. If the lease has not yet expired and the computer is shutdown, that ip address is still assigned and taken by that computer. When that computer is powered up, and finds that ip address available for use it will take it. If another powered up computer has grabbed that ip, then it starts backtracking through the registry for previous assignments to see if they are available. If there's none there, it should go bach to the DHCP server and request an available one.

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