双路由器组网端口转发失效求助：Dir-809 D-Link与HG8121H Huawei

Hey there, let's work through why your port forwarding isn't kicking in across these two routers—this is a super common setup issue, so we'll break it down step by step.

First: Understand the Double NAT Problem #

When you cascade two routers (old one connected to the new ISP router), you're creating two separate NAT layers. That means external traffic hits your Huawei HG8121H first, but unless you route it correctly through to the D-Link Dir-809, it'll get stuck. Let's fix that.

Step 1: Verify Router IP Segments & Topology #

• Check your Huawei HG8121H LAN IP (usually found in its admin panel; common defaults are 192.168.1.1 or 192.168.0.1).
• Confirm your D-Link Dir-809 WAN IP is assigned by the Huawei router (it should be in the same subnet as the Huawei's LAN, e.g., 192.168.1.100).
• Critical: Make sure the D-Link's LAN IP is in a different subnet than the Huawei. For example, if Huawei uses 192.168.1.x, set D-Link to 192.168.2.x—this avoids IP conflicts and routing loops.

Step 2: Fix Double NAT (Two Options) #

Option A: Convert D-Link to Access Point (Simplest Solution)

If you don't need a separate subnet for the D-Link, turn it into an AP to eliminate the second NAT layer:

• Log into the D-Link Dir-809 admin panel.
• Disable its DHCP server (this lets the Huawei router handle all IP assignments).
• Unplug the cable from the D-Link's WAN port, and plug it into any LAN port on the D-Link.
• Now all devices connected to the D-Link are in the Huawei's LAN subnet—you only need to set up port forwarding on the Huawei router, pointing directly to your target device's IP.

Option B: Keep Dual Routing (Double Port Forwarding)

If you need the D-Link to maintain its own subnet, you'll need to forward ports twice:

1. On the Huawei HG8121H: Create a port forwarding rule that sends traffic for your target port(s) (e.g., 80, 443) to the D-Link's WAN IP (e.g., 192.168.1.100).
2. On the D-Link Dir-809: Create another port forwarding rule for the same port(s), pointing to the actual device's LAN IP on the D-Link's subnet (e.g., 192.168.2.5).

Step 3: Check Firewall Settings #

• Router Firewalls: Ensure both routers have their port forwarding rules enabled (look for a checkbox like "Enable Rule" in each rule). Also, check if either router has a separate "External Access" or "Firewall Block" setting that's blocking your ports.
• Device Firewall: Don't forget the target device's local firewall (Windows Defender Firewall, macOS Firewall, etc.). Add an inbound rule to allow traffic on your target port(s)—this is a super common oversight!

Step 4: Test Port Forwarding Correctly #

• Avoid LAN Testing: Most routers don't support "hairpin NAT" (accessing your public IP from inside your own LAN). Test using a mobile device on cellular data, or ask someone outside your network to test.
• Terminal Test: Use tools like telnet [your-public-ip] [port] or curl http://[your-public-ip]:[port] (run these from an external network) to verify if the port is open.

Step 5: Confirm You Have a Public IP #

• Some ISPs use CGNAT (Carrier-Grade NAT) which gives you an internal ISP IP instead of a true public IP. To check:
  1. Find the Huawei HG8121H's WAN IP in its admin panel.
  2. Compare it to the IP you see when searching "my IP" from a device connected to the router.
• If they don't match, you're on CGNAT—contact your ISP to request a public IP (this is required for port forwarding to work).

内容的提问来源于stack exchange，提问作者Alpha