What will happen if two computers on the network are having same MAC and IP address? Assume 20 to 25 computers are present in the network and they are accessing the internet through single gateway. Is any security risk there for both the computers which are having same MAC and IP? In this scenario HTTPS connection is secure or not? Can traffic of one computer monitored by other?
Usually, if you have duplicate IP addresses on a network, your computer will give you a warning that the IP you are using is already in use. When two devices somehow wind up with the same IP address, this is detected and the network interface on both on them gets disabled, causing each system to lose its connectivity until the conflict is resolved.
You can refer here for the duplicate MAC situation.