FIXED: Zyxel router DDNS error “Error validating DYNDNS svr answer. Check usr,pass,hostname!”

This is a quick post to hopefully help others suffering with this issue.

I setup DDNS (Dynamic DNS) on my Zyxel router, connected to a hostname that I had setup. No matter what I did with the configuration, I couldn’t get it to work.

In the end, I setup what I thought was right in the Dynamic DNS Configuration page, and used telnet to get into the router. I then ran the following command (obviously replace (with your email address), 123456 (with your password), and (with your hostname)):
inadyn -u -p 123456 --update_period_sec 3600 --dyndns_system --alias

This worked!
I:INADYN: IP address for alias '' needs update to 'x.x.x.x'
I:INADYN: Alias '' to IP 'x.x.x.x' updated successful.

At this pointed, I closed the telnet window, and turned off the router for a while, restarting a while later, and getting a new IP address. To my surprise, the DDNS function updated!

I’m assuming something was not being picked up from the Zyxel Dynamic DNS Configuration page correctly, and so running it manually in the router fixed it. Either way, this seemed to worked.

Leave a comment if this works for you, as I don’t want to leave misleading advice here, but wanted to share as I struggled to find a fix online.

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