How to Troubleshoot NoValidConnectionsError: Network Connectivity and Server Reachability in Paramiko

NoValidConnectionsError means Paramiko cannot connect to the server. This often indicates network or server issues. This tutorial explains how to troubleshoot it.

Understanding NoValidConnectionsError

This error occurs when Paramiko fails to establish a connection. This can be due to various network or server problems. This is a common connectivity issue.

Common Causes

Incorrect hostname or IP address is a common cause. Network connectivity problems can also cause this. Server downtime is another possibility.

Handling the NoValidConnectionsError

Use try-except blocks to catch the NoValidConnectionsError. This prevents your program from crashing. It allows for proper error handling.

import paramiko

try:
    ssh = paramiko.SSHClient()
    ssh.set_missing_host_key_policy(paramiko.AutoAddPolicy())
    ssh.connect("incorrect_hostname", username="your_username", password="your_password") # Intentionally incorrect
    ssh.close()
except paramiko.ssh_exception.NoValidConnectionsError as e:
    print(f"Connection Error: {e}")
except Exception as e:
    print(f"Other error: {e}")

Verifying Hostname or IP Address

Double-check the hostname or IP address for typos. Use ping to verify basic network connectivity. This helps ensure correct addressing.

Checking Network Connectivity

Test network connectivity to the target server. Use ping, traceroute, or telnet. This helps diagnose general network problems.

# Example using ping (in a separate shell or using subprocess)
# ping your_hostname

Firewall Rules

Ensure firewalls are not blocking SSH traffic. Check both client and server firewall rules. Port 22 (default) must be open.

Server Status

Verify that the SSH server is running on the target machine. Contact the server administrator if needed. This rules out server-side issues.

Port Number Verification

Ensure you are using the correct SSH port number. The default is 22. If it’s different, specify it in the connect() call.

import paramiko

try:
    ssh = paramiko.SSHClient()
    # ...
    ssh.connect("your_hostname", username="your_username", password="your_password", port=2222) # Example port 2222
    ssh.close()
except paramiko.ssh_exception.NoValidConnectionsError as e:
    print(f"Connection Error: {e}")
except Exception as e:
    print(f"Other error: {e}")