Fix: ConnectionRefusedError Errno 111 Connection Refused

What is the Errno 111 Error?

The ConnectionRefusedError with error number 111, or Errno 111 for short, indicates that the connection attempt to a remote server or service was denied or refused by that system.

Some key things to know:

• It occurs when an application on one device tries to connect to a server process on another device, but the server process is not running or not accepting connections on the port being requested.
• The error number 111 corresponds to the POSIX error constant ECONNREFUSED, which specifically means “Connection refused.”
• It’s a generic TCP/IP network error that can happen in any programming language, but we’ll focus on causes and fixes within Python applications.
• Other systems may refer to it by different names like Connection refused, Connection reset by peer, or ECONNREFUSED. But they all refer to the same underlying issue.

In summary, Errno 111 tells you that the remote server or service denied the connection request, usually because it’s not running or listening on the port being accessed. Now that we understand the problem, let’s dig deeper into possible root causes.

Common Causes of Errno 111 Errors

There are a few main reasons why a connection may be refused, resulting in Errno 111:

1. Incorrect Port Number – The most straightforward cause is trying to connect to the wrong TCP port number on the remote system. Make sure the port your code is using matches the port the server process is configured to listen on.

2. Firewall Blocking Traffic – Network firewall software could be filtering or blocking traffic to the port in question. Check firewall rules and open ports if a firewall is in use.

3. Process Not Running – The server process or service you’re attempting to connect to may simply not be running on the remote system. Start the process before connecting.

4. Bind Error – It’s possible the server process is running but failed to bind to the expected port/address, so it can’t accept incoming connections on that port.

5. Local Configuration Error – Issues with local network configuration, DNS resolution, or other local factors could prevent the connection from even being sent.

6. Authentication Required – Some servers require authentication before allowing client connections. If authentication isn’t provided, the connection will be refused.

The first steps in troubleshooting are usually to verify the port number, check if the server process is running, and examine firewall rules. Let’s explore these checks in more detail.

Diagnosing Errno 111 Errors

When an Errno 111 occurs, carefully diagnosing the root cause is essential before attempting fixes. Here are some effective diagnosis techniques:

Verify Port Number:
Use netstat or a port scanning tool to check if anything is listening on the expected port on the remote server. Confirm the port number in server configuration matches what client code is using.

Check Process Status:
Use a process monitoring tool like ps to ensure the server daemon or service process is actually running. Try restarting it if not.

Examine Firewall Rules:
Check firewall software rules for any policies blocking traffic on the port. Temporarily disable the firewall as a test.

Test Network Connectivity:
Try using ping or telnet to ensure basic network connectivity and that name resolution is working as expected.

Check Logs:
Review server logs, debugger output, or stderr for any errors or clues. Enable more verbose logging if needed.

Isolate the Problem:
Temporarily simplify the client code to focus just on connecting. Rule out local code as the issue before assuming a remote problem.

Being thorough in diagnosis is key, as the error could be caused by any number of local or remote configuration problems. The next section explores solutions after accurately identifying the root cause.

Fixing Errno 111 Connection Errors

Once you’ve diagnosed the underlying problem, there are several effective approaches for resolving Errno 111 errors:

1. Use the Correct Port

Double check the port number configured on the server matches what the client code is specifying. Hardcode the port into client code as a test if still uncertain.

2. Start the Server Process

If the process simply isn’t running, start it using the appropriate init script, service manager or by manually running the executable.

3. Allow Traffic through Firewalls

Open ports in any firewalls, including software, router/modem, and host-based firewalls like iptables. Temporarily disable as a test.

4. Fix Bind Errors

Check server logs for bind failures and address configuration issues preventing it from listening on the expected socket.

5. Confirm DNS/Network Settings

Troubleshoot any local DNS, routing, interface, or IP address configuration preventing the connection request packet from being sent.

6. Provide Authentication

If required, update client code to handle authentication using the proper credentials before establishing a connection.

7. Refactor Code for Simplicity

Remove unnecessary layers of abstraction or complexity that could be obscuring the true source of the error.

8. Use Troubleshooting Tools

Leverage network utilities like netstat, tcpdump and ifconfig to deep dive on packet flows and pinpoint issues.

9. Check Error Messaging

Print or log more details from exceptions to aid debugging problematic connections and configuration problems.

10. Double Check Assumptions

Re-diagnose from scratch without assumptions to catch any missed issues around ports, firewalls, processes or configurations.

The key is finding the root cause whether it’s due to client code, server configuration, or problems in between. With patience and a methodical approach, Errno 111 errors can always be resolved.

Common FAQs about Errno 111

Q: I’m getting Errno 111, but the server process is definitely listening. What else could it be?

A: Some possibilities are incorrect IP addresses, firewall filtering, mismatched client/server protocols, or authentication requirements not being met. Thoroughly check configs and sniff network traffic.

Q: I restarted everything but still get the error. How can I further debug this?

A: Try simplified client code, add more logging, run server in foreground/debug mode, and use tcpdump/netcat to inspect actual packets. Comparison against a working configuration may also reveal overlooked differences.

Q: Will enabling debug-level logs on the server expose more details?

A: Yes, very verbose logging configured on the server process can provide invaluable clues! It may reveal lower-level errors occurring before the connection is even accepted, like bind failures or missing dependencies.

Q: What could cause Errno 111 errors intermittently?

A: Intermittent errors can be tricky to pin down but possibilities include temporary network issues,race conditions during process startup/binding, flaky firewall rules, or resource exhaustion under high load. Adding retry logic and ample debugging may help track it down.

Q: Is there a way to check if it’s a code issue or configuration problem from the error alone?

A: No, the error itself doesn’t provide that level of context. Errno 111 simply means the connection was refused, which could be due to many factors. Thorough testing and debugging is required to disambiguate code bugs from misconfigurations.

With care and diligence, the true root cause behind even puzzling Errno 111 errors can be uncovered. Now let’s look at some example Python code that might produce this error.

Python Code Examples Causing Errno 111

Here are a few simple Python programs that attempt TCP connections in ways that could result in ConnectionRefusedErrors:

# Incorrect port number
import socket

HOST = '127.0.0.1'  
PORT = 8080 

with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as sock:
  sock.connect((HOST, PORT))

# Process not running
import socket

HOST = 'localhost'
PORT = 5678

with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as sock:
  sock.connect((HOST, PORT))

# Firewall blocking port 
import socket

HOST = '192.168.1.100'
PORT = 80

with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as sock:
  sock.connect((HOST, PORT))