Within a local network (also called a Local Area Network, or LAN for short), a router distributes data to various devices. The router is also responsible for IP address assignment – more specifically, the DHCP server integrated in the router is responsible. For example, the DHCP (Dynamic Host Configuration Protocol) automatically assigns free IP addresses to the corresponding devices. Computers, smart TVs, smartphones, or a Raspberry Pi each receive such an address via which they can communicate with other devices. Therefore, all devices are uniquely identifiable via their so-called MAC address.
Since IP addresses in a private network are individually assigned by the DHCP and the coupling of devices to an IP address is only valid within your local network, here we’re talking about private IP addresses. In the default settings, Raspberry Pi also receives its IP address via the DHCP server. The private IP addresses of individual devices can change though, depending on the configuration of the DHCP server.
To be able to reach Raspberry Pi on the same address in your own LAN, you have to provide it with a static, private IP address. One such static IP address for Raspberry Pi can be used, for example, for the remote maintenance of a computer within the network protocol SSH (Secure Shell): If you have an SSH program installed, you can control the Raspberry Pi via another computer using the SSH client. This has the advantage that you don’t have to connect a monitor and input device separately for operation anymore. But if the minicomputer only has a dynamic private IP address, then you have to reselect the current IP address for every SSH access and link it to the SSH client – you bypass this step with a static private IP address.
A static private IP address is essential for your Raspberry Pi if you want to set it up as a server in the LAN. If the Raspberry Pi server is also to continue being available outside of the local network, then you have to assign it another static address via which the server can be accessed on the internet. For example, an internet connection with a static public IP address or a DDNS service.