The protocol that automatically assigns IP addresses to devices on a network is the Dynamic Host Configuration Protocol, or DHCP.
DHCP uses a client-server model. When a device joins a network, its DHCP client requests configuration information, and a DHCP server can provide an IP address together with settings such as the default gateway, DNS servers, and the lease duration. This avoids configuring every device manually.
The address is often leased rather than permanently assigned. A device can renew the lease, while the server can reclaim the address after it expires and allocate it elsewhere. DHCP servers may run on dedicated systems, routers, or residential gateways.
DHCP is distinct from DNS, which translates names into IP addresses, and ARP, which helps map IPv4 addresses to hardware addresses on a local network. DHCP was first defined in 1993 and also has an IPv6 version called DHCPv6.