FAQ
TL;DR: To expose services behind a UPC Horizon + Asus RT‑N18U, use 1 DMZ on Horizon and 2 port rules on Asus; “DMZ to Asus’s WAN address and do redirection on Asus.” Test via DDNS:port from outside. [Elektroda, makosuu, post #17238431]
Why it matters: This helps UPC Horizon and Asus RT‑N18U/Tomato users fix NO‑IP DDNS access and reach LAN services without bridge mode.
Quick Facts
- Workaround: Set Horizon DMZ to the Asus WAN IP, then create port forwards on Asus/Tomato. [Elektroda, makosuu, post #17238431]
- RFC1918 private IPv4 ranges: 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16; these aren’t Internet‑routable. [“RFC 1918 — Address Allocation for Private Internets”]
- Testing: Leave “Src Address” blank; verify from an external network using hostname:port (e.g., yourhost.no‑ip.org:81). [Elektroda, makosuu, post #17238574]
- Some services need both TCP and UDP; adding a second UDP rule made it work in this case. [Elektroda, Tomis, post #17238605]
How do I fix DDNS not working with UPC Horizon + Asus RT‑N18U?
Use this sequence. 1) Note the Asus WAN IP. 2) On Horizon, set DMZ to that Asus WAN IP. 3) On Asus/Tomato, create port forwards to your device. “In Horizon only DMZ to Asus’s WAN address and do redirection on Asus.” [Elektroda, makosuu, post #17238431]
How do I test that my NO‑IP DDNS and port forwards actually work?
Test only from outside your LAN. On a mobile network or off‑site, open http://yourhost.no‑ip.org:PORT in a browser. Do not rely on local tests. “You have to check from the external network by typing in the DDNS browser.” [Elektroda, makosuu, post #17238574]
Which IP should I enter in the Horizon DMZ field?
Enter the WAN IP of your Asus RT‑N18U (from its status page). DMZ on Horizon must target that exact WAN address so inbound traffic reaches Asus. [Elektroda, makosuu, post #17237791]
What do I put in Tomato’s Ext Ports, Int Port, and Int Address?
Set Ext Ports to the public port you’ll use (e.g., 81). Set Int Port to the device’s service port (e.g., 81). Set Int Address to the device’s LAN IP. This maps external 81 to internal 10.x.x.x:81. [Elektroda, makosuu, post #17238488]
Do I need to fill the “Src Address” field in Tomato?
No. It’s optional and restricts who can connect. Leave it blank while testing. Verify from an external network using hostname:port to confirm reachability. [Elektroda, makosuu, post #17238574]
It still doesn’t work after setting DMZ—what am I missing?
Create port forwards on the Asus too. Forward the needed TCP ports, and add UDP if required. In this case, 2 rules (TCP + UDP) were needed before DDNS:port worked. [Elektroda, Tomis, post #17238605]
Is it normal that Horizon’s Internet Status IP matches my NO‑IP hostname?
Yes. That’s expected. It shows your hostname resolves to the same public IP Horizon reports, which is correct for DDNS. [Elektroda, makosuu, post #17237932]
Do I need IPv4 for this, and what about IPv6?
The working setup used IPv4. Prioritize IPv4 for these port‑forward steps. As one expert asked, “Got IPv6 or IPv4?” Check what your ISP provides before configuring. [Elektroda, makosuu, post #17237932]
Should I also forward ports on Horizon if DMZ is enabled?
No. DMZ already forwards all inbound ports from Horizon to the Asus. Create per‑service port forwards only on the Asus. [Elektroda, makosuu, post #17237932]
Does pinging my DDNS hostname prove the setup works?
Not necessarily. ICMP ping can fail even when the service is reachable. Test the actual service by opening hostname:port in a browser. [Elektroda, Tomis, post #17238381]
What if my Asus WAN IP is private (e.g., 10.x.x.x or 192.168.x.x)?
DDNS will update, but inbound connections won’t reach your LAN. Use Horizon’s DMZ to the Asus WAN or request a public IP from your ISP. [Elektroda, makosuu, post #17237775]
Edge case: My ISP uses CGNAT (100.64.0.0/10). Will this work?
No. CGNAT blocks unsolicited inbound connections. You’ll need a public IPv4, a VPN, or IPv6 with proper firewall rules. 100.64.0.0/10 is the CGNAT space. [“RFC 6598 — Shared Address Space for Carrier‑Grade NAT”]
How do I reach my device’s web page externally?
Forward its port on Asus, ensure Horizon DMZ points to Asus, then browse http://yourhost.no‑ip.org:PORT. Example: internal 10.0.66.11:81 becomes external yourhost.no‑ip.org:81. [Elektroda, Tomis, post #17238454]
. You have (optional) in brackets. You have to check from the external network by typing in the DDNS browser: 81 or what ext port you have chosen
