Local networking, explained
Most file transfer problems are really networking problems in disguise. These pages explain the parts that matter: what a local network is, how devices find each other on it, and what quietly stops them. No prior knowledge assumed.
What is a local network?
Your router, and everything connected to it, makes up a small private network that the rest of the internet can't reach into.
Wi-Fi vs Ethernet for file transfer
Both handle local transfers fine. The differences show up with large files, and one of them catches people out.
Why can't my devices see each other?
It's almost always one of eight things. They're listed here in the order that fixes the most cases fastest.
Guest network vs main network
A guest network is designed to stop devices talking to each other. That's the feature, and it's why file transfer fails on one.
What is mDNS, and how do devices find each other?
There's no directory of what's on your network. Devices find each other by shouting into the room and listening for answers.
Why is my file transfer slow?
A transfer is a chain: source disk, network, destination disk. The slowest link sets the speed, and it's usually not the one you suspect.