arping

Finding Duplicate IP Addresses

You want to know how to test an IP address on your LAN to see whether it is a duplicate.
Solution

Use arping, like this:
$ arping -D 192.168.1.76
ARPING 192.168.1.76 from 0.0.0.0 eth0
Unicast reply from 192.168.1.76 [00:14:2A:54:67:D6] for 192.168.1.76 [00:14:2A:54:67:
D6] 0.605ms
Sent 1 probes (1 broadcast(s))
Received 1 response(s)

Received 1 response(s) means that this address is already in use, and arping even gives you the MAC address. You may also test with a hostname:

$ arping -D uberpc
ARPING 192.168.1.76 from 0.0.0.0 eth0
Unicast reply from 192.168.1.76 [00:14:2A:54:67:D6] for 192.168.1.76 [00:14:2A:54:67:
D6] 0.590ms
Sent 1 probes (1 broadcast(s))
Received 1 response(s)

You should set a time limit or count limit, or arping will keep running when it gets no response. This example sets a time limit of 10 seconds:

$ arping -w10 -D 192.168.1.100
ARPING 192.168.1.100 from 0.0.0.0 eth0
Sent 11 probes (11 broadcast(s))
Received 0 response(s)

Use -c5 instead of -w10 to tell arping to run for five counts.

if you have intermittent connectivity problems with a particular host , run arping to see if it has a duplicate address

arping will work when ping fails.


source:- carla schroder