What is a link-local IPv6 address (fe80::/10) and how is it used?

A link-local address is auto-generated on every IPv6 interface for communication on the local link only — routers never forward it off the segment.

* Field layout of an fe80::/10 link-local address. — Michel Bakni, CC BY-SA 4.0, via Wikimedia Commons. *

• Range: fe80::/10 (in practice you see fe80::/64)
• Every IPv6 interface always has one, generated automatically the moment IPv6 comes up — even with no router or DHCP present
• Scope is the single link: packets with a link-local source/destination are never routed beyond the local segment
• Essential for bootstrapping: Neighbor Discovery, Router Solicitation, and SLAAC all happen over link-local before a global address exists

Tip: Because the same fe80:: prefix is reused on every link, you often must specify the interface too — e.g. ping6 fe80::1%eth0 — otherwise the OS doesn't know which link you mean (the %zone is the "zone ID").

Go deeper:

• Link-local address — IPv6 (Wikipedia) — fe80::/10, why routers never forward it, and its role in Neighbor Discovery.
• RFC 4862 §5.3 — IPv6 SLAAC — how the link-local address is formed at interface bring-up.