gavron wrote: Hello!
What happens in the local network and how do routers/switches and all other equipment behave if we connect two computers/devices with the same MAC address?
From experience, the internet will appear and disappear on computers, connections with servers will disappear and reappear, when you start transferring a larger file, it will fly whole and will not break anything. A flood will start in the network and a lot of packets will fly to such an extent that their number will increase to such an extent that nothing can be done in this part of the network that is under a given switch. Most likely, the flood is caused by the fact that the second machine takes packets from the first one, the first one does not have a matching checksum and asks for a retransmission and the circle closes. As the second machine did the same, then both start to renew the packets, the switch does not assign the MAC table permanently, but updates it quite often, e.g. 3 COM did it every few minutes, the situation returned to normal and, for example, after 5 minutes flood again. Before I checked what and how, I have to admit that I ran around the cages and clients. I had networks several years ago, new networks, taken over, were sometimes built in such a strange way that such eggs were commonplace. I immediately switched to DHCP with blocking, as someone entered a static IP or changed the MAC in the subnet to one that was not entered in the database, it immediately blocked it, only in this way I managed to deal with such users who know better than an amine how the computer should be configured. To sum up, if you get two MAC's in one subnet, the internet will start to disappear on both computers.
P.S. I also had a notification on my e-mail that someone changed their IP or MAC, and I had an SMS notification on the e-mail, so if someone changed it, I immediately received an SMS. And one more thing, when I wanted to have access to the Internet from any computer, I changed his MAC to one of his subnets, but which no one used. Unfortunately, there was no protection for this, it was only a limit of connections in the network, and if someone did not pay, after blocking, he could change the MAC to a neighbor, then only physical disconnection or blocking of his port, but only in managed swiches.
I also think something is going on. I'm just installing 2xw98 on virtualbox and we'll see what happens.. First I'll test on a virtual network and then I'll do bridged and see what my router will do...