Conflicting DHCP server locator under Linux

cable-ethernetIn order to locate conflicting DHCP server in your LAN execute the following command:

sudo dhcpdump -i eth4 | awk '/IP:/{SRC=$2 " " $3} /OP:.*BOOTPREPLY/{ print "DHCP server found:", SRC; }'

The restart your PC network (use DHCP to get new IP). If you see more than one IP address here:

DHCP server found: 192.168.4.1 (0:9:6b:a3:fc:4a)
DHCP server found: 192.168.1.1 (f8:d1:11:9e:1d:8b)
DHCP server found: 192.168.4.1 (0:9:6b:a3:fc:4a)
DHCP server found: 192.168.1.1 (f8:d1:11:9e:1d:8b)
DHCP server found: 192.168.4.1 (0:9:6b:a3:fc:4a)

Then you have two, conflicting DHCP servers in your network. You can use http://www.coffer.com/mac_find/ tool to locate the device type that causes the problems.

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