The link-local addresses are defined by RFC4291 and have a fix format, hence we do not need to configure the prefix length. 2.5.6. Link-Local IPv6 Unicast Addresses.
Explanation: Link-local addresses refer only to a particular physical link and are used for addressing on a single link for purposes such as automatic address IPv6 Address Types & Format Explained with Examples IPv6 link-local addresses are similar to IPv4 link-local addresses defined in RFC 3927 that use the 169.254.0.0/16 prefix. The use of IPv4 link-local addresses is known as Automatic Private IP Addressing (APIPA) in Windows Vista, Windows Server 2008, Windows Server 2003, and Windows XP. The scope of a link local address is the local link. Use IPv6 link local addresses on server side of a load
Link-local IPv6 addresses have a smaller scope as to how far they can travel: only within a network segment that a host is connected to. Routers will not forward packets destined to a link-local address to other links. A link-local IPv6 address must be assigned to every network interface on which the IPv6 protocol is enabled.
Link-local IP address ranges. Link-local addresses may be assigned manually or automatic operating system procedures. They are assigned most often via autoconfiguration. They are normally only used to assign IP addresses when no mechanism of address configuration exists, such as DHCP, or when another configuration method has failed. Understanding IPv6 Link Local Address - Cisco Apr 14, 2020 ip - What is Link-local addressing? - Network Engineering
Ipv6 link-local - Cisco Community
What is a Link-Local IP Address? Link-local IP address ranges. Link-local addresses may be assigned manually or automatic operating system procedures. They are assigned most often via autoconfiguration. They are normally only used to assign IP addresses when no mechanism of address configuration exists, such as DHCP, or when another configuration method has failed. Understanding IPv6 Link Local Address - Cisco Apr 14, 2020