169.254.0.0/16

Link-local addresses are automatically chosen by a host when it needs an IPv4 address but did not receive one from DHCP (Dynamic Host Configuration Protocol). They are valid only on the local network segment.

This block is not publicly routable. Routers should not forward it, so it cannot be used to reach hosts across the Internet or even across normal routed subnets.

A system administrator is likely to see 169.254.x.x when DHCP is broken, a cable or VLAN (virtual local area network) is wrong, or a device is isolated from the expected network. Some systems also use link-local addressing for local discovery or metadata-style services, but for ordinary desktops and servers it is often a clue that address assignment failed.

Firewall tip: link-local IPv4 belongs only on the local link. Internet-edge and inter-VLAN firewalls usually drop it when it appears as routed traffic, because it should not cross routers.