# ip -6 route add default via 2002:4340:3:2b12:FF:FF:FF:FF dev eth0
RTNETLINK answers: Invalid argument
We cannot add a route whose gateway is an invalid IP address.
The network address is always the first IP address in a subnet.
In the above example, the first four blocks
2002:4340:3:2b12 represent the IP, and the next four blocks
FF:FF:FF:FF represent the subnet.
The first IP in that block would be: