how to find out other dhcp server in my network?

[CHUN FAI LAW]

i have my own network with dhcp pool already, how can i find that if there is some client connection their own dhcp server to my network?

how can i find that though my router? i know it can be prevent by dhcp snooping. but due to some of our switch not support this function.

Is there any suggestion or anything i can check the problem through my router?

[Paul Preston]

Hi Chun,

I can't think of a specific command on the IOS router to discover dhcp servers - I don't believe there is one.

Why don't you simply setup "ip address dhcp" on the interface connected to that network and check whether you have received an ip address?

Regards,

--
Paul Preston
Proxar IT Ltd. Registered in England and Wales: 6744401- VAT: 942985479
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[CHUN FAI LAW]

may be i can simply check the client computer, and find the source mac with arp -a

and then search the mac address in switch mac address table to find where is the source dhcp server...haha

[SOcchiogrosso]

There are many different ways:

1. Packet capture looking dhcp offer packets
2. Configure dhcp snooping on your LAN switches
3. So an ipconfig /all on the client (windows) PC to see the IP address of the dhcp server or received its address from


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[CHUN FAI LAW]

Thankyou for your advice, i think capture program is one of the good tools to get the rogue dhcp.

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[SOcchiogrosso]

It will also be very time consuming unless you trigger the dhcp process manually


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