The Port That Does Not Exist
Summary
The Port That Does Not Exist investigates port 0 in TCP/UDP, a socket API concept rather than a real network port. The piece documents a broad, curious scan of port 0 across the IPv4 space, revealing a surprising mix of devices and services (routers, alarms, industrial gear, surveillance, and more) that respond or are misconfigured to appear on port 0. It highlights the practical quirks of ephemeral port allocation, testing results, and the potential security/visibility implications of port 0 traffic.