Quote:
same IP address is sometimes used by two computers
That means that you did not set up your network properly. Likely, there are still some computers still using fixed IP addresses instead of IP addresses from the DHCP server. So your problems are not a MySQL problem but a network configuration problem.
Normally a DHCP server can be told which addresses it can assign automatically, and which addresses are reserved. Look thru all computers and other devices (e.g. printers) in your network, make sure they get their addresses from the DHCP server, or their fixed IP address falls into the reserved range (and is unique).