Back in the late 90s I had my first cable modem, and I wanted to share it with my mom (had moved back in after a 4 year relationship imploded) - I knew nothing about routers, but I was already playing with Linux, and somehow I found a way to share my Internet connection with my mom’s computer with only a single NIC in my machine, and a hub. It was not the modem allowing both, that I was sure of early on, the modem would only allow one mac address at a time, power cycle would let it pair with a new one. Somehow my machine was buffering and natting packets from hers. It worked for months until suddenly it didn’t, and while researching a fix, everything I could find said what I had been doing couldn’t possibly work, that you needed a separate NIC for the internal network.
Back in the late 90s I had my first cable modem, and I wanted to share it with my mom (had moved back in after a 4 year relationship imploded) - I knew nothing about routers, but I was already playing with Linux, and somehow I found a way to share my Internet connection with my mom’s computer with only a single NIC in my machine, and a hub. It was not the modem allowing both, that I was sure of early on, the modem would only allow one mac address at a time, power cycle would let it pair with a new one. Somehow my machine was buffering and natting packets from hers. It worked for months until suddenly it didn’t, and while researching a fix, everything I could find said what I had been doing couldn’t possibly work, that you needed a separate NIC for the internal network.