As my ISP is not providing static ip address.
how I access WD myCloud via FTP externly without public static IP address ?
I want to backup my couple of website.
Have you gone to the Dashboard and set up FTP? Settings>Network>Network Services>FTP (On or Off).
You will need to know the broadband side IP address of your internet connection where the My Cloud is being hosted. If that IP address changes constantly (many times IP addresses don’t change unless the router/model releases/renews the broadband side IP address or the router/modem is turned off then back on (or restarted). Perform an internet search for “what is my IP address” and you should get your broadband IP address.
Depending on your router or modem model, it may be possible to use a “DDNS” service that would provide you one web address in instances where IP addresses change. Some consumer routers have an option for using DDNS services for exactly this reason.
As the previous person indicated you will need to enable FTP service within the My Cloud Dashboard settings. Then you probably will have to enable port forwarding (port 21) of your router to the My Cloud. Some broadband providers may block inbound FTP access however in which case you may have to change the port number used to access FTP on the My Cloud.