#sudo ifconfig eth0 inet6 add 2001:3c8:a702::4/64

#sudo ip -6 address show eth0

eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qlen 1000
    inet6 2001:3c8:a702::4/64 scope global
       valid_lft forever preferred_lft forever
    inet6 fe80::221:5aff:fe50:d794/64 scope link
       valid_lft forever preferred_lft forever

OK WORK