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Bizarre Subnet Mask Behavior with DHCP

By Val_K ·
I have been battling this issue on my 35 node Windows 2000 with various Win 9x client network for over a year and it's driving me crazy. No one I talk to has an answer or has ever seen it before.

When some clients try to renew their leases, for some reason the subnet mask goes from 255.255.255.0 to 255.255.0.0 or 255.0.0.0 and the PC will not connect to its network resources even though it has a valid IP address (the address pool is 192.168.0.110 - 192.168.0.250).

This happened over threedifferent DHCP servers (WinNT 4.0, FreeBSD, Win 2K) We are using a Cisco Catalyst 3500 Series XL switch that I suspect may be playing at least some role in the problem. Most of the NICs are Kinston KNE 100, but there are a smattering of other NICs that are affected as well. Most of the affected clients are running Windows 98 SE but a few are still Windows 95.

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Bizarre Subnet Mask Behavior with DHCP

by srespd In reply to Bizarre Subnet Mask Behav ...

Firstly, The problem definitely has to do with your router (that is responsible for renewing the leases). However, i wouldn't rule out the fact that Windows 98 and definitely Windows 95 are partly responsible. It would be helpful to know which settings you have for the network your using and what the router is set to. All machines need to be on the same subnet to be connected to each other. Theoretically, you could have different machines connected to a different subnet to cluster certain machines together. I would look into the settings that your router has for renewing leases (somewhere in the script). You can set up ip local pool setup_pool 192.x.x.x 192.x.x.x (range). and specify subnets. Look at the Software config guide that came with the router or go online at www.cisco.com Hope this helps

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Bizarre Subnet Mask Behavior with DHCP

by Val_K In reply to Bizarre Subnet Mask Behav ...

Isn't it the DHCP server that's renewing leases? What does the router have to do with that? We are using a Cisco 1720 router. I mentioned the switch earlier because equipment that's plugged into our hub never have this problem.

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