I've had 6in4 working well for months with the WAN IP being the public IP. I recently put an Ubiquiti Edgerouter in front of the OpenWRT router to handle the dual wan failover (I was never able to get dual WAN to work with 6in4).
Now the WAN interface of the OpenWRT router (running 18.06.2) has 192.168.0.3 (from the Edgerouter's DHCP at 192.168.0.1).
On the Edgerouter, I have a Source NAT masquerade for each WAN (eth1 and eth2) and a DNAT for each WAN pointing to 192.168.0.3. Both for all protocols (which you'd think includes protocol 41)
Everything works fine on my network: all the ports for devices on the LAN are reachable, per the port forwarding rules in the OpenWRT router. Except for the 6in4 tunnel, which stopped working. TX/RX remains at 0. Local IPv4 address is as before, "empty to use the current WAN address".
Do I have to change the config on my OpenWRT router or should a change be applied to the Edgerouter??
Yep, hence I noted "which you'd think includes protocol 41" in the OP.
Are you saying that
the fact that the WAN on the OpenWRT now has a private IP is not the problem,
everything seems to be configured properly,
(thus) I should find out whether protocol 41 is being passed to the OpenWRT router?