Subnetting IPv6 addresses/routes

Question

I would like to subnet the default IPv6 route into 2 network routes. The original default route was:

default via fe80::218:74ff:fe27:9640 dev eth0  proto kernel  metric 1024

I tried adding the following 2 routes, which together should be equivalent to the default route:

ip -6 route add ::/1 dev eth0 via fe80::218:74ff:fe27:9640  
ip -6 route add 80::/1 dev eth0 via fe80::218:74ff:fe27:9640

The first command went through, but the second one generated an error:

RTNETLINK answers: File exists

Why is this happening? What's the correct way to specify 2 network routes covering everything?

Answer 1

80:: is 0080::/1, which isn't a valid route - try 8000::/1 instead.

Answer 2

The route should be 8000::/1. It's not a good idea though... All public IPv6 traffic uses 2000::/3, which will use ::/1. All ULA traffic (for example) will use the other route, but if you want that then you should create a default route (::/0) and a route for the ULA addresses (fc00::/7). Splitting on 8000::/1 does not make a lot of sense...