Dell OptiPlex 980 (Early 2010) - Manual (Page 25)

Option Description
Random
ID
The IPv6 Interface ID is automatically generated using a random number
as described in RFC 3041. This is the default.
Intel ID The IPv6 Interface ID is automatically generated using the MAC address.
Manual
ID
The IPv6 Interface ID is configured manually. Selecting this type requires
that the Manual Interface ID is set with a valid value.
3. IPv6 Address
Under the Wired LAN IPv6 Configuration, select IPv6 Address and press Enter.
Type the IPv6 Address and press Enter.