DHCP Probs

[westbourne]

Hi all,

Hope someone can point me in the right direction.

1) One of my servers IP address keeps conflicting with another device on the network. I can only assume that whatever device it is, the IP was manually put in, thus causing the conflict. I can get the MAC address of the offending device but I cant locate it, mainly because I cant resolve its host name. Any Ideas??

2) I have created 3 subnets. 192.168.0.0 - 192.168.3.254. Now I have only allowed the DHCP to assing addresses from 192.168.1.0 - 192.168.3.254. However Im finding that some PC's are picking up addresses from the 192.168.0.4 onwards range. Why is this & how do I solve this??

Any ideas would be much appreciated.

[bishopsgarthstockton]

Have you tried switching all the machines, AP, network printers off, and then deleting the address leases.

Im probably talking jiberish

[j17sparky]

1. Turn known device off and then try to resolve the hostname of the offending device.
Or change the mac address of the known device.

[kerrymoralee9280]

Have you not installed a new nas box or anything. I can remember when we got ours it conflicted with a server as it already had a set IP. We had to turn the server off to configure the nas then it was all peachy...

[_Bob_]

Put the first half of the mac into:
http://standards.ieee.org/regauth/oui/index.shtml

It will at least let you know the manufacturer of the mystery device which may be a clue.

[Oops_my_bad]

If you have managed switches that display their ARP database you can trace it back to the offending port

A right bollock if you have cascaded switching - it might take you a while to work your way back

[Mr_T]

A quicky to try is when the server is off try poping the the offending ip address into a web browser with http:// before it and if the conflicting device is has web interface you should be able to find out what it is.

Other thoughts are if you run a seperate admin network have they befome joined at some point and the admin server is sending out addresses?
Is it and AP/router sat on the network somewhere with DHCP turned on?

Also if your teachers have full control of their lappys has one of them set it up internet connection sharing at home then pluged it into the school network?

[westbourne]

Cheers guys.

I found out the prob. Turns out a netgear wireless switch i installed as a temp measure has a dhcp server itself automatically on.

Only found the device by turning of the domain controller & stopping dhcp on the 2nd DC & then releasing & renewing an ip on a laptop. The typed the ip conflicting ip into browser which brought up the netgear login box.

School boy error or what!

Still lesson learned & its sorted now.

[Oops_my_bad]

Heheh... dont worry you wouldn't be the first to have that happen

[Joedetic]

That was one of the things i thought of immediately. Mostly because someone in the halls of residence plugged a router into the network in their room the wrong way round and killed ResNET. That might be the reason routers are banned. Also it turns out that they were banned from the network for a month or two

[bandgeekmafia78]

You could have setup a new reservation in DHCP for the offending machine given that you knew its MAC address.