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DHCP Subnet Mask Problem

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10 replies

by jim

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On my 150+ machine network, I have two or three that get the wrong subnet mask when they renew their IP addresses via DHCP. (DHCP server running NT 4.0). Instead of renewing 192.168.0.X with a subnet mask of 255.255.255.0, they get the right addressrange, but a 255.255.0.0 mask. Since it only affects a few machines, I suspect it is a client problem, not a server problem. Anyone ever seen this before? Thanks!

10 replies

by hacbmis

The only thing I can see that would make the mask change would be the number of subnets or nodes DHCP is set to, ie.. 192.168.0.0 to 192.168.0.255.

by timwalsh

Is it the same 2 or 3 computers that have the wrong subnet mask?
Is it possible that these computers have more than 1 NIC? Maybe the second NIC has a fixed IP address with the wrong subnet mask defined.
Is it possible you have a rogue DHCP serversomewhere on your network?
Are you running a backup or secondary DHCP server someplace on the network?
Is it possible these particular computers actually have fixed IP address with the wrong subnet mask defined (although I imagine you've checked that)?

by ericryd

Check your lease times, make sure that computers aren't getting new IP's and filling up the address pool.

by jim

All were good ideas... I replaced the two NICs involved and...so far... the problem hasn't recurred. Thanks to all!

by jim

I still think it is some kind of NIC problem... why would it only happen to these two machines? I can't believe it is a system problem or it would happen to some of the others. AAAAARRRRGGGGHHHH!

by apaul4

Have you tried comparing results from ipconfig /all and an arp -a to see if there are any static or stuck addresses that show up?
Or when you do the IP config /all does the DHCP server IP listed match that of machines that get correct address configurations?

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