DHCP

DHCP (Dynamic Host Configuration Protocol) makes sure a device joining a network automatically receives a free IP address, the matching subnet mask, the gateway, and usually DNS servers too. Without DHCP, every address would need to be entered manually, which quickly becomes unmanageable past a handful of devices. This job is handled by a DHCP server, often built into a router or run as a dedicated service.

In practice, a device broadcasts a request for an address when it starts up, and the DHCP server answers with a free address from a defined range known as the pool. That assignment is a lease — borrowed for a set period and renewed automatically for as long as the device stays on the network. Some devices, such as printers or servers, get a fixed reservation instead, so their address never changes.

A classic problem is two DHCP servers running on the same network — for instance a private router that's accidentally still active: devices then get addresses from whichever server answers first, and connectivity becomes unreliable. Just as common is an address pool that's too small, running out the moment more devices are on the network than originally planned for.