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DNS Duplicate IP Address

Posted on 2003-12-02
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Last Modified: 2012-02-15
How can i stop duplicate ip address on our DNS server???
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Question by:agbor1960
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JammyPak earned 500 total points
ID: 9858998
can  you give a little more information?

Someone is conflicting with the address of your DNS server? or someone is registering a bad address in the DNS zone?

Either way you need to discover who is causing the conflict. DNS won't help much unless it's a dynamic registration and you can see the computer name with who did it.

If it's a Windows machine, try "ping -a <ip address>" and see if it returns the computer name to you. Or, if you have WINS, see who's registered the offending address.

Can't really guess much else without more info....
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Author Comment

by:agbor1960
ID: 9859164
The clients get ip address from a DHCP server but some how there's a problem with the configuration of DNS maybe ....like the same ip address for two (2) different workstation...
Thanks
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by:JammyPak
ID: 9859720
You may have an ip address conflict, but I don't think it's a DNS problem.

If you're using dynamic DNS, then clients are registering their addresses in DNS - so the problem is with the client, not DNS.

If you're not using dynamic DNS, then the host addresses are entered manually and you can just re-type the correct address.

In the properties of your DHCP server you can enable conflict detection - this means the server does a test ping for an address before giving it out. This should help prevent the problem. In the meantime, you need to find out who's causing the conflict.

try ping -a
look in the WINS database
try capturing network traffic with a sniffer

these may help you find the culprit.
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Expert Comment

by:riouxnick
ID: 9862062
Do you have any networking hardware, such as a firewall, that has DCHP serving abilities?
If you do, this device might be giving out ip addresses on the same range as your DHCP server.

If this is the case, turn off the DHCP server on the networking device.
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by:stevenlewis
ID: 9863384
In addition to the good advice above, do you have ICS enabled on your network? If so, ICS also has a dhcp server. Really, if using dhcp, the only way for this to happen would be a second dhcp server, or someone has statically assinged and ip that is in the scope of the dhcp server
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Author Comment

by:agbor1960
ID: 9864757
JammyPak- Could this be the reason of a duplicate if the conflict detection is set to 0?? cause ours is 0... the network traffic sniffer, is this for free?? what can the sniffer do for troubleshooting??


stevenlewis- What's ICS...

Thanks guys.....
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by:stevenlewis
ID: 9865718
Internet connection sharing
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by:agbor1960
ID: 9865730
no we don't have it enabled i guess...
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by:JammyPak
ID: 9866903
Having DHCP conflict detection turned off is not the reason you have a conflict, but if it had been on it might have avoided the conflict.

As stevenlewis said, with DHCP, there's two ways you could be getting a conflict - either you've got a rogue DHCP server out there, or someone has given themselves a static address.

Network Monitor is a free MS sniffer - the lite version comes with Server, the full version comes with SMS. If you can't find out who the offender is using these tools, you may just have to pay a visit to each and every computer... :(
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Author Comment

by:agbor1960
ID: 9867175
I don't think there's somebody giving themselves a static address though, cause of (GPO) but i will try to find out if we have other firewall DHCP or something...

Thanks...
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Expert Comment

by:rafamvc
ID: 9870734
Question: -> The problem always happens with same machines?
If yes,
What is your NIC? IF your NIC is something cheap like Realtek you may have NICs with the same MAC Address, then there is the problem. When the machine broadcast for a IP the DHCP server conclude that they are the same machine.

I hope i helped u.
[]´s
Rafael Cardoso
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Author Comment

by:agbor1960
ID: 9872671
They are different workstation though but i will try to investigate the NIC...

Thanks
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by:stevenlewis
ID: 9908406
So how did it happen?
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Author Comment

by:agbor1960
ID: 9910302
I did not try it yet, but i will keep you guys posted...

Thanks
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Expert Comment

by:tomfontanilla
ID: 37601699
I have the same problem. On my DNS server, I see duplicated IP add on the same client. I tried scavenging but did not help. Any thoughts?
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