Link local addresses have a scope limited to the network segment of the holding interface. In IPv4, link local range is 169.254/16 and in IPv6 range is fe80::/10.

IPv4 link local addresses are used in most cases when automatic IP addresses is desired for a specific interface, but there is no DHCP server to assign IP addresses.

IPv6 link local IP addresses have a broader usage specially in data center network segments where routing protocols such as OSPFv3 and RIPng can run between link local addresses instead of global/organization addresses.

Another use case for link local addresses is as next-hops for static routes.

List ipv6 neighbors in Junos CLI

> show ipv6 neighbors 
IPv6 Address                 Linklayer Address  State       Exp Rtr Secure Interface
2001:470:1f15:72b:1:0:22:2   00:0c:29:6b:1a:15  stale       1113 no no      vlan.22     
2a02:2f0f:27::22:2           00:0c:29:6b:1a:15  stale       972 no  no      vlan.22     
2a02:2f0f:27:26::2           00:0c:29:e9:71:60  stale       1066 no no      vlan.26     
fe80::1                      00:15:63:40:4c:40  stale       780 yes no      ae1.5       
fe80::20c:29ff:fe03:a588     00:0c:29:03:a5:88  stale       686 no  no      vlan.8      
fe80::20c:29ff:fe6b:1a15     00:0c:29:6b:1a:15  stale       836 no  no      vlan.22     
fe80::20c:29ff:fee9:7160     00:0c:29:e9:71:60  stale       1052 no no      vlan.26 

IPv6 static route to a link local next-hop in Junos

In order to use a link local address as next-hop for an IPv6 static route, the interface is a mandatory parameter of the static route due to the nature of link local addresses. Interfaces next-hop can be specified only for qualified (alternate) next hops.

> configure 
Entering configuration mode
# set routing-options rib inet6.0 static route ::/0 qualified-next-hop fe80::1 interface ae1.5