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Two DHCP servers on my network

3D2K asked

My Windows 2008 R2 system is configured on the 192.168.1 subnet and DHCP is offering up valid IP addresses to clients fine.

The end user has an IP Phone system so I decided to use the external IP interface on the telephone handsets to wire up my Windows clients. I connected the telephone system switch to the Windows switch and off we went.

First problem is that the telephone system has its own DHCP server offering IP addresses up on the 192.168.91 subnet.

Any newly connected clients get a 192.168.91 address but if I do an ipconfig /release followed by a /renew they then magically switch over to the 192.168.1 network.

Today the on-site IT support decided to accidentally take down the DHCP server and all clients are now picking up 192.168.91 addresses.

He's now disconnected the connection to the telephone system and is going round connecting directly into the computer network to pull up 192.168.1 addresses again.

I've researched the issue but it doesn't appear possible to elect a preferred DHCP server so has anyone any idea of best practices for this environment as it is handy to use the telephone network?

Watch Question

One of the DHCP servers had to go.  Having two give out IP's in different subnets is sure to cause even greater issues in the long run.

1) Is there no way you can turn off the DHCP server on the phone system and have it on the same network?
2) If you have a switch, you might be able to separate the phone system on it's on VLAN which would isolate DHCP broadcasting to just that VLAN
3) If you can't do any of the above, it might be better just to utilize the DHCP functions of the phone system since you now you can turn off DHCP on the server.  The only drawback would be not being able to fully control your DHCP scope unless the phone system gives you that option (doubtful).  This would mean, however, that any devices with static IP's currently assigned, would have to be changed to reflect the new subnet.


Feared as much.

Call me old-fashioned but I prefer not to use DHCP and assign IP addresses statically albeit my record keeping has to be kept up to date.

I have a request for help from the telephone company pending.