Modem and Router Can't Share a Subnet

[ImranNasir123]

Despite having set up dozens of networks like the attached simple home installation for a friend, I realized I don't actually know why the modem and router can't sit on the same subnet. In other words, why is the intermediate 10.0.0.1/24 network necessary? Why can't the modem and the router both sit on 192.168.50.1/24?

[Georg Pauwen]

Hello,

the link between the modem and the router seems to be a layer 3 link, that's why a separate subnet is required. That said, the modem typically dishes out the IP addresses for that 'subnet', which actually is the LAN subnet.