[J65nko]

fe80::/10 addresses are IPv6 link local addresses. They are derived from the MAC address (lladdr in the ifconfig output) of the NIC.

See http://en.wikipedia.org/wiki/Link-local_address#IPv6 why they are needed and automatically assigned.

In case you want to get rid of it:

$ ifconfig re0
re0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
        lladdr 00:19:db:47:b0:4c
        priority: 0
        groups: egress
        media: Ethernet autoselect (100baseTX full-duplex,rxpause,txpause)
        status: active
        inet 192.168.222.20 netmask 0xffffff00 broadcast 192.168.222.255
        color=blue]inet6 fe80::219:dbff:fe47:b04c%re0 prefixlen 64 scopeid 0x2[/color]

$ sudo ifconfig re0 -inet6 ; ifconfig re0
re0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
        lladdr 00:19:db:47:b0:4c
        priority: 0
        groups: egress
        media: Ethernet autoselect (100baseTX full-duplex,rxpause,txpause)
        status: active
        inet 192.168.222.20 netmask 0xffffff00 broadcast 192.168.222.255