IP address conflict / duplicate computers with same IP w/ DHCP server

By spiralingcrazies ·
I am running a network of about 10 PCs and 10 VOIP phones.

Every once in a while I am getting "duplicate use detected" errors where one machine already has a DHCP address and another is given that address and I get the error of duplicate IPs, seems like the system overflows and it can't dish out more DHCP addresses or the network card of the machine is showing as already connected and won't connect it again.

The message I am getting is:

The system detected an address conflict for IP address <for example> with the system having network hardware address <for example 00:10:00:77:25:70>. Network operations on this system may be disrupted as a result.

This happening basically locks up the whole systems and everything needs to be rebooted.

I found something in this article but it seems related to older OSes:

Thanks for your help in advance.

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All Answers

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by Wizard-09 In reply to IP address conflict / dup ...

How long is it before ip address are released and reused again, you seem to have a very small network to be running DHCP, if i was you i would just use static ip.

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Have you added a wireless router lately?

by 1bn0 In reply to IP address conflict / dup ...

A wireless router may have a DHCP server running in conflict with your network Servers DHCP function.

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More info about DHCP

by LarryD4 In reply to IP address conflict / dup ...

A liitle more info please

What is your DHCP server?

What is the scope of your DHCP server?

What is the assignable address pool for your DHCP scope?

Is their any other device on your network that could have a DHCP server running other then your "known" server?

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Need the DHCP

by spiralingcrazies In reply to More info about DHCP

I need to keep the DHCP as the VOIP phones need it, so I can't hard code everything there.

I am on a RV042 Linksys router which doesn't have wireless. I added a Netgear wireless router as an extra node just for wireless clients and DHCP on it is disabled. Checked it - DHCP is still disabled. TO be on the safe side I shut it down, keeping it off until I find the culprit.

There was also a print server (another Netgear) - one of these little gizmos that let you network your laserjet, shut this down and it is staying off.

So for now only one Linksys router with DHCP server on it enabled and a phone server (Shoretel) that handles the phone system.

This network was running happily for the last year or probably a bit longer until we had a remote office doing IPSEC router to router VPN. That's when the crashes started happening but at the same time we also went to a new antivirus/firewall (McAfee) on each PC and most users need to log in via VPN to another site. I've also disconnected the remote office.

The only other thing that has changed that I can think of is that there are a few Vista laptops with TCP/IP ver 6 enabled and most users are doing VPNs to another site and also carrying these machines home. I am thinking somehow the Subnet Mask from their home connection on one or more of these laptops is acting up and not releasing properly. That's just a hunch.

The router is at the latest firmware and the only thing that seems a bit blurry to me is the phone system as it seems to be running on a Dell appliance server, although it looks like it is configured not to dish out DHCP addresses.

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IP reservation....

by ---TK--- In reply to Need the DHCP

I'm not sure how IP phones are but if its IP based it should have a MAC... I would try (for the time being) gather up all the MAC address and start Reserving them. Then limit the amount of IP's that are being handed out.

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by ---TK--- In reply to IP reservation....

I would also find out how the VPN is set up on the other end... If the VPN server is assigning 192.168.1.X -, I would be tempted to say switch your network to 192.168.2.X based.... It shouldn't cause I have scene weirder issues....

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MACs reserved, DHCP changed

by spiralingcrazies In reply to IP reservation....

I started reserving the MAC addresses like you guys suggested before I even posted here, made a map of anybody on the network as well, including the ip phones. I also changed the DHCP to dish out addresses starting at .150 to .225 as it was previously at .100 to .200 and no dice, it still comes up occasionally.
It looks like it is an offending VIsta laptop that is coming in and out of the office, or maybe even a Mac (there is a single iBook in there).

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Any other suggestions / ideas?

by spiralingcrazies In reply to MACs reserved, DHCP chang ...

I am open to more suggestions. For the meantime the problems seem to have stopped but it doesn't seem like a solution to me as long as I know what is really causing this.

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