IP Address Assignment

IP addresses are assigned to hosts either dynamically as they join the network, or persistently by host hardware or software configuration. Persistent configuration is also known as using a static IP address. Conversely, when a computer's IP address is assigned each time it is restarted, this is known as using a dynamic IP address . 

Dynamic IP addresses are assigned by the network using the Dynamic Host Configuration Protocol (DHCP). DHCP is the most frequently used technology for assigning addresses. This avoids the administrative burden of assigning specific static addresses to each device on the network. It also allows devices to share a limited address space on a network if only a few of them are online at any given time. Usually, dynamic IP configuration is enabled by default in modern desktop operating systems. 

Addresses assigned with DHCP are associated with leases and usually have an expiration date. If the lease is not renewed by the host before it expires, the address may be assigned to another device. Some DHCP implementations attempt to reassign the same IP address to a host, based on its MAC address, each time it joins a network. Network owners can configure DHCP by allocating specific IP addresses based on MAC addresses. 

DHCP isn't the only technology used to dynamically assign IP addresses. Bootstrap Protocol is a protocol and predecessor similar to DHCP. Dialup and some broadband networks use the dynamic addressing feature of the Point-to-Point Protocol. 

Computers and equipment used for network infrastructure, such as routers and mail servers, are typically configured with static addresses. 

In the absence or failure of static or dynamic address configuration, the operating system can assign link-local addresses to hosts using stateless address autoconfiguration.