Dear all,

I have a network that contains a lot of computers.
They are using fixed IP.

I want to know if two computers are set to the same IP address, what will be happened?

And, how could I detect whether two computers(or more computers) are using the same IP address?

Thanks,
Barry

You will know if two devices have the same IP address because one of them will not work. Linux doesn't seem to notice duplicate IPs, but Windows and Mac will both complain if you configure duplicates.

You should have an IP database documenting who has what and it should be controlled by an individual or at least by one department. If you don't have such a thing then you will need to produce one.

You can check every machine manually. You could pull the arp table off a router if there is one on your subnet. You could use a subnet scanner to ping all available addresses on your subnet and collect what responds. There are lots of windows programs that do this, and I'm sure someone here can suggest Linux programs to match.

Alternatively if you leave a traffic analyser running on your subnet it should spot any IP addresses that appear to change their mac addresss (any IP who's mac address flips from one to another and back has obviously been duplicated). This might be the easiest approach as it should collect all of your IP and mac address bindings. Don't forget that the first 3 bytes of the mac address is an OID which you can lookup on the internet, should give you an idea as to what mac addresses are. Some analysers can reverse DNS lookup the IPs thay find so giving you IP-MAC-NAME lists which should come in handy for the future.

Whats the best Linux traffic analyser anyone?

Just spotted nmap, looks like a good option as a subnet scanner.
something called arpwatch might also help as it logs arps