i have a dhcp server on valn 3 and somebody has put somekind of vmware software on pc with dhcp on that... am not able to find that dhcp server now.. I have the macaddress of that server... i am not able to ping that server too..please let me know how to find that another server
If you have the mac-address of that server, at the switch issue: show mac-address-table and should point to the switchport this device is connected to.
If the switchport listed is connected to another switch, hop onto that switch and execute the same command until you find the culprit device.
I also recommend configuring dhcp snooping if you switch supports it. What type of switch do you have ?
You need to configure DHCP snooping on all switches in your network for it to be effective.
You would have trusted and untrusted ports. Trusted ports will be the ones connected to valid DHCP servers and inter-switch links. Untrusted ports will be the ones connected to every device in your network.
For more information in general configuration on this feature see:
We already gave you the suggestion. I understand that's a huge task given the size of your network. That's the reason features such as DHCP snooping were implemented, to avoid this kind of headaches. I'm afraid you will have to rally up the troops and hop onto each switch until you find the culprit.
After that, formulate a plan and deploy DHCP snooping.