Docker Network Connectivity Issues with RingLink

This guide will help you resolve Docker network connectivity issues that may occur when using RingLink.

Overview

When using Docker with RingLink, you may encounter network connectivity issues where containers lose their ability to communicate with external networks. This typically manifests as:

Failed ping attempts to external addresses
Unable to pull Docker images
Connection timeouts in containerized applications

Root Cause

The primary cause of this issue is related to MTU (Maximum Transmission Unit) configuration:

RingLink network interface uses an MTU of 1350
Docker's default MTU may be higher than this value
When packets exceed the MTU limit, they are discarded by the system
This mismatch leads to network connectivity problems

Solution

1. Checking Current MTU

First, verify your current Docker MTU setting:

docker network inspect bridge | grep -i mtu

2. Modifying Docker MTU Configuration

Follow these steps to adjust the Docker MTU setting:

Open the Docker daemon configuration file:

sudo vim /etc/docker/daemon.json

Add or modify the MTU configuration:

{
    "mtu": 1350
}

If you have other Docker daemon configurations, make sure to preserve them and only add/modify the MTU setting.

3. Apply Changes

After modifying the configuration, you need to reload and restart Docker:

# Reload the daemon configuration
sudo systemctl daemon-reload
 
# Restart Docker service
sudo systemctl restart docker.service

Restarting Docker will stop all running containers. Make sure to save any important data and plan for downtime.

4. Verify the Changes

Confirm that the changes have been applied successfully:

# Check the new MTU setting
docker network inspect bridge | grep -i mtu
 
# Test network connectivity
docker run --rm alpine ping -c 4 google.com

Troubleshooting

If you continue to experience issues after applying these changes, check the following:

Common Problems

Ensure you have proper permissions:

# Check Docker group membership
groups ${USER}
 
# Add user to Docker group if needed
sudo usermod -aG docker ${USER}

Diagnostic Commands

Use these commands to gather more information:

# Check Docker service status
sudo systemctl status docker
 
# View Docker daemon logs
sudo journalctl -u docker.service
 
# Inspect Docker network configuration
docker network inspect bridge

If you need additional help, please check our community forums or open an issue on GitHub.