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Strange Win2k/AD DHCP problems

By rcsoar4fun ·
I manage a network of about 400 hosts out of a very large enterprise network. Recently we have been having some strange DHCP and DNS issues. It seems to have become a problem since the machines where migrated to AD from an NT domain. The machines are "locked down" Win2k on Ethernet, connected via Cisco 3500 switches and a 2600 router. The DHCP server is 5 router hops away in a different state. The issue we have run into is if a machine is left off for several weeks and turned on it will have an IP address conflict with another machine. It will refuse to release its IP address. The users do not have the right to run ipconfig /release or renew. It does not appear to work under administrator either. After a short time of being on the network both machines will complain about duplicate IP addresses and refuse to see the network. In several cases the only fix has been to leave the domain and rejoin. Also the IP addresses will resolve to different machine names, depending on which part of the building (i.e. switch) you are plugged into. My guess is that a DHCP request is being sent to the server which is timing out. It then assumes the IP is free and assumes its old IP. At this point should they request new IP addresses? If the security on the machine will not allow the IPCONFIG command to be run can the machine still request a new one? I do not have any sort of access to anything outside of my router, including the DHCP server. The "experts" in corporate say there is no problem and its something on our end.



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slow WAN link

by CG IT In reply to Strange Win2k/AD DHCP pro ...

you can change the lease duration, which might help with the problem. Check the settings for DHCP to see if clients update automatically.

I would say your assumption that DHCP discover times out or is to slow due to distance is probably correct.

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More DHCP Servers

by julie.schneider In reply to Strange Win2k/AD DHCP pro ...

If this is a large network, is there a reason why the DHCP server is 5 router hops away?

I would ideally have a DHCP server at your site, if possible. 5 hops is a lot and is not a great network design, IMO. There might be enough of a delay to cause a problem. Did this problem just start recently? How are the sites connected? Could it be a DSL or T-1 problem? --especially if it just started up recently.

Are there not enough addresses to lease out? It might be an issue if the scopes aren't large enough.

Hope this helps.

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I agree

by rcsoar4fun In reply to More DHCP Servers

I agree this is not a great network design, but one I am stuck with. I do not have the ability to install a DHCP server locally either.

We are currently using about 450 of about 700 addresses. Until about 2 months ago we only used about 250 of those addresses. I suspect the recent increase has caused a little more churn than before.

We are using 384K T-1, recently updated from a 256K line. All appears to be well on that side.


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Please consider this.......

by SysAdminTech In reply to Strange Win2k/AD DHCP pro ...

WOW ! this is a good one because you did all the proper steps that I would take. My questions might enlighten an answer to your problem. Have you checked your scope? You may need to extented the rage of your scope. Is it the same machine it keeps conflicting with. If so try reimaging that PC.

Last but not least it sounds like you have a Dynamic IP address in your network, you may want to consider going from Dynamic IP to static IP's it may consume some of your time but it will resolve the IP conflict.

Good Luck !

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