Static and Dynamic IP Addresses

Every device on a network needs an IP address so that packets reach the right destination. That address can be given to a device in one of two ways: static or dynamic.

Static IP addresses

A static IP address is set by hand and stays the same every time the device connects. Because it never changes, other devices can always rely on finding that device at the same address. Network managers use static addresses for equipment that must be easy to locate, such as a file server, a shared printer or the router itself.

Dynamic IP addresses

A dynamic IP address is given out automatically when a device joins the network, usually by a DHCP server. It is taken from a pool of free addresses and can be different each time the device connects. When the device leaves, its address returns to the pool for someone else to use. This saves addresses, because a network only needs enough for the devices online at once, not for every device that might ever join.

For example, the school's CCTV recorder is set to the static address 172.16.8.5, so the office computers always know where to look for the camera footage. A tablet from the computing trolley, though, might pick up 172.16.8.60 when it is switched on before lunch, then rejoin the same network after lunch as 172.16.8.77, because the DHCP server handed out whichever addresses were free at that moment.

An IP address is not a permanent label for the hardware: it belongs to the connection a device is using, and it is handed back when that connection ends.