Falsehoods Programmers Believe About LANs

Programmers commonly make incorrect assumptions about Local Area Networks (LANs) across multiple categories including NAT configuration, network protocols, MAC addresses, reachability, and DHCP operations. The article lists numerous falsehoods—such as assuming LANs are always behind a single NAT, that MAC addresses are globally unique, or that devices on the same subnet can always reach each other—highlighting how reality is often more complex than typical programmer assumptions. Many of these statements are sometimes true and sometimes false depending on specific network configurations and implementations.