I'm playing with IPv6, and I know that FE80::/10 are link-local addresses. I believe that means that they are only known on the links that they're attached to. (If I'm wrong, please correct me.) I'm running OSPF between two routers, and I'm noticing that the only addresses that get put into the routing table are global addresses 2000::/3, but NONE of the FE80:: addresses are put into the routing table. FEC0:: addresses are put in the routing table, but I thought these addresses are obsolete?
So, what are the FE80 addresses really good for, and in what situations?
site local are routable because there is a 16-bit subnet field that can be different on link to link allowing 65535 /64 prefixes.
unique local are similar use fc00::/7 but expands the available space.
Cisco routers still support site local there was a thread about this few days ago.
To give an idea ipv4 multicast 224.0.0.X are said link local: they cannot be forwarded by a router from an interface to another interface.
ipv6 link local are the unicast counterpart of the same:
on a given ipv6 link = L2 broadcast domain each ipv6 host can send and receive ipv6 packets using link local.
Think of them as ipv4 packets with TTL=1 they cannot go in another subnet.
Hope to help