I think I have followed the instructions as per the OpenWRT docs, but I am getting an error trying to enable dyndns.
My provider is namecheap and that is the OpenWRT supplied script I use (via luci interface). I have replaced the real ip's with xx's and the real name of my site with mysite. The ip is the ip I am currently on wan side.
The log error I am getting on starting the script is
134534 : Detect registered/public IP
134534 : #> /usr/bin/khost -t A mysite.com >/var/run/ddns/mysite_dyndns.dat 2>/var/run/ddns/mysite_dyndns.err
134534 : Registered IP '127.0.0.1' detected
134534 info : Starting main loop at 2019-08-30 13:45
134534 : Detect local IP on 'network
134534 : Local IP '100.72.xxx.xxx' detected on network 'wan'
134534 : Update needed - L: '100.72.xxx.xxx' <> R: '127.0.0.1'
134534 ERROR : No or private or invalid IP '100.72.xxx.xxx' given! Please check your configuration
134534 ERROR : No update send to DDNS Provider
You have hit the nail on the head. My ISP, I found out, is unfortunately deploying CGNAT.
I have requested them to opt me out of this but I am not sure of they will, yet.
I may have to look around for another ISP which is a pity as they are possibly the fastest around here with no downgrade in speed at peak times. But hey, they are selling me the full monty!