In the current situation there are two routers which are connected to each other directly. The first router has the following IPv6 settings:
IP: 2a02:XXXX:8600:2700:ce35:40ff:fe2f:d7e3/64
Prefix: 2a02:XXXX:8600:2700::/57
The second router (running RouterOS) is configured with DHCP prefix delegation in client mode. It receives the following settings from the DHCP server:
Prefix: 2a02:XXXX:8600:2770::/60
Pool: 2a02:a212:8600:2770::/60 with prefix length 64
The DHCP-PD client is instructed to set the default routes based on the received config. It created the following router table:
Dst: ::/0 Gateway: fe80::XXXX:40ff:fe2f:d7e3%ether1-wan
Dst: 2a02:XXXX:8600:2770::/60 Gateway: None
Without setting an ip address on the bridge from the pool the router should already be able to forward global addresses to the link local gateway. However, any ping results in a timeout and when trying to ping the link local address nothing happens. The link local address does show up in the neighbor list, so should be reachable. All neighbor discoveries are disabled and firewall rules are turned off.