Link-local address

In a computer network, a link-local address is a network address that is valid only for communications within the network segment (link) or the broadcast domain that the host is connected to.

Link-local addresses are usually not guaranteed to be unique beyond a single network segment. Routers therefore do not forward packets with link-local addresses.

For protocols that have only link-local addresses, such as Ethernet, hardware addresses that the manufacturer delivers in network circuits are unique, consisting of a vendor identification and a serial identifier.

Link-local addresses for IPv4 are defined in the address block 169.254.0.0/16, in CIDR notation. In IPv6, they are assigned with the FE80::/64 prefix.

Address assignment

Link-local addresses may be assigned manually by an administrator or by automatic operating system procedures. For Internet Protocol (IP) networks, they are assigned most often using stateless address autoconfiguration. In IPv4, they are normally only used to assign IP addresses to network interfaces when no external, stateful mechanism of address configuration exists, such as the Dynamic Host Configuration Protocol (DHCP), or when another primary configuration method has failed. In IPv6, link-local addresses are mandatory and required for the internal functioning of various protocol components.