It seems like when dhclient runs on eth0 I get an IPv4 address from the DHCP server and a Scope:Link IPv6 address attached to eth0:
inet6 addr: fe80::a00:27ff:fed0:4d41/64 Scope:Link
But I can't see from dhclient-script how that address is being added. On another interface with a static IP address, I'd like to add a link local IPv6 address, and I was wondering if there was a generic command to do that without knowing the mac.
Edit:
It looks like the kernel assigns the link local address when you do "ip link set dev ethX up" or "ifconfig ethX up". However, in my case I had a cable plugged in to the interface that was DHCP'ing and no cable plugged into the interface I was setting up statically. Can't verify until Monday but I'm guessing the kernel does not assign link local addresses to the interface if there's no link.
Answer
Link local addresses are derived from the MAC address of the device. They are auto-generated as a part of bringing the interface up. Auto-configuration includes a discovery process to ensure that the address is unique on the network.
A similar process is used to auto-configure routable addresses when a router advertisement is available. These addresses may be regenerated periodically to provide privacy.
RFC 4862 specifies the processes to be followed.
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