How to find the DHCP server on a network

Simon Hobson dhcp1 at
Tue May 19 22:03:42 UTC 2009

John Tabasz (jtabasz) wrote:

>Can someone suggest a clean way to identify the DHCP servers on a network?

As well as the other suggestions, note that some information is 
provided in your own DHCP server logs.  IIRC, the log entries when a 
client requests an address include the server identifier included by 
the client. Dredging around in the depths of my memory, I think the 
log goes something like :

   ... request for a.b.c.d (w.x.y.z) from .....

where a.b.c.d is the IP address the client wants to use, and w.x.y.z 
is the server it got it from.

So that will tell you the IP address.
You'll then need to start interrogating a device on the network it's 
attached to to get it's MAC address;
and then your switches to find the port it's attached to;
and then your patching records to see the physical location to visit 
with the "rogue server deactivating tool" (a.k.a. big hammer) and 
"user education tool" (a.k.a. piece of clue by four) !

Simon Hobson

Visit for books by acclaimed
author Gladys Hobson. Novels - poetry - short stories - ideal as
Christmas stocking fillers. Some available as e-books.

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