Yes, MR 550 is TP-Link Archer MR550 I do not want to give MR550 a different IP address as I will NEVER plug it in my network at the same time as my fiber box (livebox). I do not want to change any...

@Vincent-TP Hi, Thank you for your answer. I do not need need to connect to both routers (livebox and MR550) at the same time. I do not need a multi-wan setup. I would like only a manual link backup....

Hi, Config 1 (I remove MR550 from the network) works well (Livebox with fixed IP 192.168.123.254), all wired clients with fixed IP, DHCP for wifi clients Config 2 (I remove Livebox from the network),...