You need to specify the port number when attempting to access Home Assistant as you are forwarding 8123 → 8123. If you used 443 (external) → 8123 (internal) you could leave off the port number as 443 is the default port for https.
Although port forwarding on your router should retain the value as it traverses to your LAN (normally it would change), you might try something called 1:1 NAT or NAT Passthrough (which might be protocol/port-specific). Some routers have specific settings for DDNS or a DMZ. Have you explored these? FYI: Before you change too many settings, you should make a backup of your router configuration.
Just open the port(s) you need, otherwise you’ll be more vulnerable to a network attack. My router will accept a comma separated list, but I avoid port forwarding if I can.
Stating the obvious, make sure the encryption is working and you have a strong password.
If you can’t get DDNS to work, there’s always Nabu Casa, which requires no open ports.
I had a similar issue and it was related to my ISP. my isp was using one public ip address but had another router after that ip address to manage different clients. Assume that 1.2.3.4 is your public address but you are not the only one assigned to this by your ISP. I am paying 3 euros per month to get a dedicated and fix ip address so i don’t need to worry about this shared pool.
Hey man. I have been reading your conversation regarding your question on this page. I have faced the same problem you stated and I have been trying the suggestions and still doesn’t work. Have you fixed the problem? If yes please share me your solution.
Thanks.