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Ben_LockeFlag for United Kingdom of Great Britain and Northern Ireland asked on

IP Conflict

A number of computer in my office has suddenly started getting IP conflict errors.

All these machines have static IPs which I know are not being used by any other PCs.

If I click diagnose then it says that DHCP is not enabled, I don't want DHCP enabled as they have static IPs.

If I do switch it to the DHCP then they get internet connection but it does not resolve the domain, it just says 'unidentified network'. This has not been an issue before.

This problem started with one user the other day and now 'seems' to be spreading to more people in the office.

Please note the IP settings on each PC are definitely correct.

Any ideas would be greatly appreciated?
TCP/IPDNSNetwork Management

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Ben_Locke

8/22/2022 - Mon
SOLUTION
Prashant Shrivastava

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Prashant Shrivastava

for More information please find this link : this will help you with that - http://blogs.technet.com/b/teamdhcp/archive/2009/07/03/rogue-dhcp-server-detection.aspx
SOLUTION
omarfarid

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ASKER
Ben_Locke

Thanks for the responses guys, we only have one DHCP server, is the DHCP issue going to also cause the issue with static IPs?

No we haven't added any new devices.
omarfarid

Have you experienced any DHCP crash or restart? If you do a DHCP lease renew (from command line run ipconfig /renew) on the client do you still see the problem on the client?
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ASKER
Ben_Locke

Omarfarid, I tried that with no success.

I have installed wireshark on the server and captured some data, could you help me with what I need to look for to give me a clue as to what is going on?
omarfarid

I am not familiar with that. Are the static IPs excluded from the IP range on the DHCP server? if not then your DHCP server is allocating them to other systems.

You may reserve these IPs on your DHCP server and assign them by DHCP server based on the MAC addresses of your system.
ASKER
Ben_Locke

The static ips are in the range 192.168.3.1-219 and the dhcp is 192.168.3.220-250.

When i try and use the DHCP it gives me an IP address 172.27.128.34.

Also in the lease view on the DHCP server every address is a BAD_ADDRESS.
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ASKER
Ben_Locke

Thanks for all your suggestions.

I have discovered that it is a Netgear GS748TS switch.

I realise the setup isn't ideal but i have a Ethernet cable connecting that to the main network switches which are GS700TS.

This solution has worked fine in the past as I have two other switches connected like that without any issues.

How ever with this one, if I unplug it everything goes back to normal. As soon as I plug it back in it starts again.

Ideas?
Surrano

So which switch the clients are connected to and which switch provides the (wrong) DHCP addresses? It'd be nice to see the switch configurations...

also please check whether you properly follow the guidelines explained here:
http://kb.netgear.com/app/answers/detail/a_id/136
omarfarid

So the other switch was also working as DHCP server?
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ASKER
Ben_Locke

The switches are not acting as the DHCP server, we have a DC that does the DHCP server role also.

This morning i have tried to stack this problem switch correctly with a HDMI cable but cannot get it work with my other 2.
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ASKER
Ben_Locke

My comment contains the fix for the problem