My Cloud Ex2 Ultra, Do i really need to open both 22 and 873 port in order to run the remote backup job?

I have 2 My Cloud Ex2 Ultra OS5 Version 5.15.106 and i wants to setup 1 for storage and 1 for backup.

let’s call My Cloud Ex2 Ultra for storage as “MCStorage” and My Cloud Ex2 Ultra for backup as “MCBackup”

So i have read through and follow the step A in MCBackup and C in MCStorage and i skip B because i am using double NAT. So the part B i configure manually which the ultimate aims is to open port 22 and 873 for WAN IP.

So the part B i configure as below. I am using same WAN (public ip address), in the same location just different routers.
MCBackup → Router 1 → Router 2 → Internet → Router 2 → Router 3 → MCStorage

MCBackup (LAN cable to Router 1 ) IP Address: 192.168.65.199
Router 1 IP Address: 192.168.65.1 ( port forward 22 for IP 192.168.65.199 MCBackup )
Router 2 IP Address: 192.168.66.1 ( port forward 22 for IP Router 1 )
Router 3 IP Address: 192.168.67.1 ( port forward 22 for IP Router 1 )
MCStorage (LAN cable to Router 3 ) IP Address: 192.168.67.199

As in the instruction B said that port 22 and 873 need to be opened in order to backups. But why in my scenario case i just opened port 22 and it will work as usual? Do i really need to open both 22 and 873 port in order to run the remote backup job?

MYStorage has Remote Backups jobs
Backup Type: Synchronize
Recurrence 7:00/Daily

Hi @MichealMing,

As per the details shared, please follow this KBA article, In order to configure the remote backup: My Cloud OS 5: Remote Backups