How to split global ipv6 between subnets?

Question

Computer networks

I decided to learn ipv6 and set up 6to4 at home.
The main local subnet, where all devices receive global ipv6 and everything works as it should.
When I tried to configure ipv6 on the second (test) subnet, which is also connected to the gateway, the ip address was issued correctly, but the prings did not go to the external network.
Found the problem:

2002:xxxx:xxxx:/64 link#2 U 3 1500 em1

All traffic for global addresses is routed to em1 (main network), and nothing to em2 (test).

I tried to break the network 2002:xxxx:xxxx::/64 into smaller /96 so that they could be divided into different subnets, but after that ip was no longer issued even on the main network. I read that for auto-tuning you need a network / 64.

Question:
How can I distribute the /64 global address range to several internal subnets?

Answer 1

6to4 produces /48, cut into several /64 and you will have auto-tuning everywhere.
If you want to target smaller networks than /64 - Route Advertisement will not work, only static setting.
On the main gateway, register the route to the dedicated /96 either via link-local, or select /126 (more is possible if other networks connect through the same link) between the main gateway and the gateway of the second network and register the route through the address in this /126