Sorry, I didn't see it was solved.

MichaelSch wrote Access of the mobile through the wifi (Fritzbox connected to the balanced router aka DHCP server) works so I can backup my pictures on the NAS. But I want to access the NAS from...

When WAN1 fails, you mean the policy routing you configure could get access to Internet via WAN2 or not? I need confirm..If it could get online, it is normal.

I agree, TL-ER6120 v2 is nice for me.

Bro, What's the TL-ER6120 hardware and firmware version? Check if the configuration parameters is the same on both router and shrew client.

Hi bro, with TL-R600VPN V4, the NAT throughput is 680Mbps.