Here is a link to freeware to get going on this
http://www.webattack.com/f
remember DHCP uses port 67.
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detecting a rogue DHCP server
In my college environment, we recently had a student set up a DHCP server in their dorm room. The student's 'rogue' dhcp server handed out bad IP addresses to several of the lab computers instead of our main DHCP server handing out valid IPs.
I am looking for a utility to find those rogue dhcp servers, but am having difficulty finding one. Any recommendations?
It seems that it should not be difficult to have a utility that sends a DHCP request and then displays to me all replies (preferably by MAC address, but at least by IP address). In a long internet search, the only thing I can find is the DHCPLOC.exe utility in NT4 Resource Kit which showed me only my main DHCP server, not the rogue that I set up myself for testing purposes nor the student's rogue. I also found that Windows 2000 is supposed to have some utilities, but I need a stand alone utility, not an entire operating system.
Jim
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Answers
http://www.net.princeton.e
For linux
Craig
Go to any of the client that has ip address assigned by the bad DHCP Server and type
ipconfig /all
You will get the IP address of the DHCP Server.
Just ping the IP address of the DHCP Server atleast once.
Run arp -a <ipaddress> or just arp -a command and it will show the MAC address of the DHCP Server. Then Kick it off from your network.
If you have access to something like Sniffer, you could capture network packets and filter for DHCP packets.
Specifically, look for DHCP OFFER packets. When a client asks for a DHCP address, the RFC allows for multiple DHCP servers to respond. It is up to the client to decide which lease offer to take.
You should be able to see DHCP OFFER packets coming from your own DHCP server and from the offending student's address. You'll know the IP and MAC address of the offending device.
Depending on how your network is organized and managed, you could conceivably do many things at that point. If you have 100% switched bandwidth, you could find out the physical port that is associated with the MAC address and disable the port.
IamJimbo:
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I've been using this tool in a student housing network...
http://www.sqlsecurity.com
It's called DHCP Sentry and it will run on a server or client PC and wait for a rogue broadcast. It will identify the rogue servers by MAC address of the NIC card and will email a report if you wish. It can also launch a batch process and pass the IP and MAC to the process. It is command line based and runs in a command window. No GUI.
It's inexpensive and works. It helped me find and eliminate a server that had taken down my network.
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by: MishouPosted on 2002-12-12 at 12:52:36ID: 7574556
Hello,
a DHCP server is listening on UDP 67 (I think ) , so it should be easy to spot the rogue DHCP server bad configured running a simple scanning tool for all the inernal ip and looking only for this port only (to speed up the scanning).
You will find it but how you will be able to shut it down that's another story. Now the DDOS can be handy if you can flood that ip.
Mishou
Mishou