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:{{trout}} I SLAPPED YOUR SANDCASTLE WITH A TROUT [[User:Cranloa12n|Cool guy]] ([[User talk: Cranloa12n|talk]] • [[Special:Contributions/Cranloa12n|contribs]]) • he/they 02:32, 1 April 2022 (UTC)

==IP address assignment {{April fools}}==

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

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

The address assigned with DHCP is associated with a ''lease'' and usually has an expiration period. If the lease is not renewed by the host before expiry, 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 the network. A network administrator may configure DHCP by allocating specific IP addresses based on MAC address.

DHCP is not the only technology used to assign IP addresses dynamically. [[Bootstrap Protocol]] is a similar protocol and predecessor to DHCP. [[Dialup]] and some [[broadband networks]] use dynamic address features of the [[Point-to-Point Protocol]].

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

In the absence or failure of static or dynamic address configurations, an operating system may assign a link-local address to a host using stateless address autoconfiguration.

===Sticky dynamic IP address===

{{Unreferenced section|date=January 2021}}

''Sticky'' is an informal term used to describe a dynamically assigned IP address that seldom changes. IPv4 addresses, for example, are usually assigned with DHCP, and a DHCP service ''can'' use rules that maximize the chance of assigning the same address each time a client asks for an assignment. In IPv6, a [[prefix delegation]] can be handled similarly, to make changes as rare as feasible. In a typical home or small-office setup, a single [[Router (computing)|router]] is the only device visible to an [[Internet service provider]] (ISP), and the ISP may try to provide a configuration that is as stable as feasible, i.e. ''sticky''. On the local network of the home or business, a local DHCP server may be designed to provide sticky IPv4 configurations, and the ISP may provide a sticky IPv6 prefix delegation, giving clients the option to use sticky IPv6 addresses. ''Sticky'' should not be confused with ''static''; sticky configurations have no guarantee of stability, while static configurations are used indefinitely and only changed deliberately.

===Address autoconfiguration===

Address block {{IPaddr|169.254.0.0|16}} is defined for the special use of link-local addressing for IPv4 networks. In IPv6, every interface, whether using static or dynamic addresses, also receives a link-local address automatically in the block {{IPaddr|fe80::|10}}. These addresses are only valid on the link, such as a local network segment or point-to-point connection, to which a host is connected. These addresses are not routable and, like private addresses, cannot be the source or destination of packets traversing the Internet.

When the link-local IPv4 address block was reserved, no standards existed for mechanisms of address autoconfiguration. Filling the void, [[Microsoft]] developed a protocol called [[Automatic Private IP Addressing]] (APIPA), whose first public implementation appeared in [[Windows 98]]. APIPA has been deployed on millions of machines and became a [[de facto standard]] in the industry. In May 2005, the [[IETF]] defined a formal standard for it.

===Addressing conflicts===

An IP address conflict occurs when two devices on the same local physical or wireless network claim to have the same IP address. A second assignment of an address generally stops the IP functionality of one or both of the devices. Many modern [[operating system]]s notify the administrator of IP address conflicts. If one of the devices involved in the conflict is the [[default gateway]] access beyond the LAN for all devices on the LAN, all devices may be impaired.