Understanding the Network Connectivity Issue
When you encounter the error message “Failed to connect to xx.xx.xx.xx port xx: No route to host,” it can be quite frustrating, especially when you’re confident that your network setup is correct. This article will guide you through the process of diagnosing and resolving this issue on your Oracle Cloud (OCI) Ubuntu 20.4 virtual machine.
Let’s start by understanding the environment in which this issue typically arises. You’re using an Oracle-provided Ubuntu image to set up your virtual machine instance. To ensure that your network services run smoothly, you’ve configured the firewall and security lists according to Oracle’s specifications. You’ve also set up your web server, such as Nginx, and allowed connections on critical ports like 80 and 443.
Despite these configurations, you’re unable to connect to external IP addresses. Here’s a breakdown of the steps you’ve taken so far:
| Step | Description |
|---|---|
| 1 | Configured the virtual machine instance using an Oracle Ubuntu image. |
| 2 | Set up the firewall (ufw) to allow connections on ports 80 and 443. |
| 3 | Configured the security lists to accept incoming connections on ports 80 and 443. |
| 4 | Set up your web server (e.g., Nginx) and tested the internal and external connectivity. |
After completing these steps, you attempted to send an HTTP request using the curl command, such as `curl http://130.xxx.xxx.xxx/`. However, you received the error message “curl: (7) Failed to connect to 130.xxx.xxx.xxx: No route to host.” This indicates that there is no route to the specified external IP address.
Diagnosing the Issue
To resolve this issue, you need to diagnose the root cause. Here are some steps you can follow:
1. Check the iptables rules: The Oracle virtual machine instance comes with pre-configured iptables rules. These rules might be blocking the connection to the external IP address. To check the rules, run the following command:
sudo iptables -L
If you find any rules that might be blocking the connection, you can modify or delete them using the `iptables` command.
2. Verify the routing table: Ensure that your system has a route to the external IP address. You can check the routing table using the `route` command:
sudo route -n
If you don’t see an entry for the external IP address, you need to add a route to it. Use the following command to add a route:
sudo route add -net xx.xx.xx.xx netmask xx.xx.xx.xx gw xx.xx.xx.xx
Replace `xx.xx.xx.xx` with the actual IP address, `xx.xx.xx.xx` with the subnet mask, and `xx.xx.xx.xx` with the gateway IP address.
3. Check the DNS settings: Ensure that your system has the correct DNS server configured. You can check the DNS settings using the `cat` command:
sudo cat /etc/resolv.conf
If the DNS server is not set correctly, you can update it using the `nmcli` command:
sudo nmcli con mod eth0 ipv4.dns "8.8.8.8"
Replace `eth0` with your network interface name and `8.8.8.8` with the desired DNS server IP address.
4. Test connectivity: After making the necessary changes, test the connectivity to the external IP address again using the curl command:
curl http://130.xxx.xxx.xxx/
If the connection is successful, you’ve resolved the issue. If not, you may need to investigate further or consult with your network administrator.
Conclusion
In this article, we’ve discussed the steps to diagnose and resolve the “Failed to connect to xx.xx.xx.xx port xx: No route to host” error on your Oracle Cloud (OCI) Ubuntu 20.4 virtual machine. By following the steps outlined above, you should be able to identify and fix the issue, ensuring that your network connectivity is restored.
