Troubleshooting Backend External Access Failure

## Verify Intranet Access First

Before troubleshooting external access, confirm that intranet access to the backend is working normally.

1. On the server, open a browser locally.
2. Visit `http://<intranet-ip>:8182`.
3. Confirm that the backend login page opens successfully.

If intranet access also fails, resolve that issue first by following the intranet access troubleshooting document.

## Common Causes and Solutions

### 1. External Port Is Not Open

**Symptom**  
Accessing `http://<public-ip>:8182` from an external network times out or fails to connect.

**Solution**

- **Router or NAT device:** Log in to the router management interface and configure port forwarding to map external port `8182` to internal server port `8182`. Depending on the device, this setting is usually under **Advanced Settings**, **Port Forwarding**, or **NAT**.
- **Cloud server security group:** In the cloud platform console, such as Alibaba Cloud, Tencent Cloud, or AWS, allow inbound TCP traffic on port `8182`. In most cases, the rule should allow access from `0.0.0.0/0` or a restricted source IP range, depending on your security policy.

### 2. Server Firewall Blocks External Requests

**Symptom**  
The service is reachable from the intranet, but external requests are blocked.

**Solution**

Run the appropriate firewall command on the server:

```bash
# Linux (firewalld)
firewall-cmd --zone=public --add-port=8182/tcp --permanent
firewall-cmd --reload

# Linux (ufw)
ufw allow 8182/tcp

# Windows (run as administrator)
netsh advfirewall firewall add rule name="LarkXR_Admin_External" dir=in action=allow protocol=TCP localport=8182
```

### 3. Public IP or DNS Resolution Is Incorrect

**Symptom**  
Access by domain name fails, but access by public IP succeeds.

**Solution**

1. Verify that the domain resolves to the correct public IP address.
2. Use one of the following commands:
   ```bash
   nslookup <domain>
   # or
   dig <domain>
   ```
3. If a cloud load balancer is used, check that the listener and forwarding configuration are correct.

## Quick Verification

### Test External Connectivity

Run these commands from a device outside the local network:

```bash
telnet <public-ip> 8182
curl -v http://<public-ip>:8182
```

If `telnet` connects successfully or `curl` returns a response, the port is reachable externally.

### Check Port Mapping

Review the router, NAT gateway, or cloud platform settings to confirm that external port `8182` is correctly mapped to the target internal server.

## Additional Notes

- Disable local VPN or proxy software before testing to avoid misleading results.
- If the server is deployed in Mainland China and accessed through a domain name, confirm that the domain has completed ICP filing, because missing compliance requirements may affect public accessibility.