Fixing Network Connectivity Problems on Alpine Linux

Network connectivity issues can be frustrating, but with the right tools and techniques, you can quickly diagnose and resolve most problems on Alpine Linux. Let’s explore comprehensive troubleshooting methods! 🌐

Common Network Connectivity Issues

Before diving into solutions, let’s identify common problems:

• No Internet Connection: Complete loss of connectivity
• Slow Network Performance: High latency or low throughput
• Intermittent Connectivity: Sporadic connection drops
• DNS Resolution Issues: Can’t resolve domain names
• Specific Service Failures: Certain protocols not working
• Local Network Problems: Can’t reach local devices

Essential Network Troubleshooting Tools

First, let’s install the necessary diagnostic tools:

# Update package repositories
sudo apk update

# Install essential network tools
sudo apk add iproute2 iputils bind-tools tcpdump netstat-nat
sudo apk add mtr nmap iperf3 ethtool wireless-tools curl wget

Step 1: Basic Connectivity Diagnosis

Check Network Interface Status

Start with the basics - verify your network interfaces:

# List all network interfaces
ip link show

# Check interface details and IP addresses
ip addr show

# View routing table
ip route show

# Check interface statistics
cat /proc/net/dev

Verify Interface Configuration

# Check if interface is up
ip link show eth0

# Bring interface up if down
sudo ip link set eth0 up

# Check for DHCP assigned address
sudo dhclient eth0

# Or assign static IP if needed
sudo ip addr add 192.168.1.100/24 dev eth0

Step 2: Test Basic Connectivity

Ping Tests - The Foundation

# Test loopback (should always work)
ping -c 4 127.0.0.1

# Test default gateway
ping -c 4 $(ip route | grep default | awk '{print $3}')

# Test local network connectivity
ping -c 4 192.168.1.1

# Test external connectivity
ping -c 4 8.8.8.8

# Test with specific interface
ping -I eth0 -c 4 8.8.8.8

Advanced Ping Diagnostics

# Continuous ping with timestamps
ping -D 8.8.8.8

# Ping with packet size variation
ping -s 1472 -c 4 8.8.8.8  # Large packets to test MTU

# Ping with flood test (be careful!)
sudo ping -f -c 100 8.8.8.8

Step 3: DNS Resolution Troubleshooting

Test DNS Resolution

# Test DNS resolution
nslookup google.com

# Alternative DNS lookup
dig google.com

# Test specific DNS server
dig @8.8.8.8 google.com

# Check reverse DNS
dig -x 8.8.8.8

Fix DNS Issues

# Check current DNS configuration
cat /etc/resolv.conf

# Add reliable DNS servers
sudo nano /etc/resolv.conf

Add these entries:

nameserver 8.8.8.8
nameserver 8.8.4.4
nameserver 1.1.1.1

Test DNS Performance

# Time DNS queries
time nslookup google.com

# Test multiple DNS servers
for dns in 8.8.8.8 1.1.1.1 208.67.222.222; do
    echo "Testing $dns:"
    time dig @$dns google.com +short
done

Step 4: Route and Gateway Diagnosis

Examine Routing

# Show routing table
route -n

# Show detailed routing information
ip route show table all

# Check for multiple gateways
ip route show | grep default

Trace Network Path

# Trace route to destination
traceroute google.com

# Better trace with MTR (combines ping and traceroute)
mtr google.com

# MTR with report mode
mtr --report --report-cycles 10 google.com

Fix Routing Issues

# Add default gateway
sudo ip route add default via 192.168.1.1

# Delete incorrect routes
sudo ip route del default via 192.168.1.2

# Add specific route
sudo ip route add 10.0.0.0/8 via 192.168.1.1

Step 5: Check Network Services and Ports

Test Port Connectivity

# Test specific port connectivity
telnet google.com 80

# Test with netcat
nc -zv google.com 80

# Test multiple ports
nmap -p 22,80,443 google.com

# Test local service ports
netstat -tlnp

Monitor Network Connections

# Show active connections
ss -tuln

# Show processes using network
lsof -i

# Monitor connections in real-time
watch -n 1 'ss -tuln'

Step 6: Wireless Network Troubleshooting

Diagnose Wireless Issues

# Check wireless interface
iwconfig

# Scan for available networks
iwlist wlan0 scan | grep ESSID

# Check wireless connection quality
iwconfig wlan0 | grep Quality

# View wireless information
iw dev wlan0 info

Fix Wireless Connectivity

# Restart wireless interface
sudo ip link set wlan0 down
sudo ip link set wlan0 up

# Connect to wireless network
sudo wpa_supplicant -B -i wlan0 -c /etc/wpa_supplicant/wpa_supplicant.conf

# Get IP address via DHCP
sudo dhclient wlan0

Configure Wireless Network

# Create wireless configuration
sudo nano /etc/wpa_supplicant/wpa_supplicant.conf

Add network configuration:

network={
    ssid="YourNetworkName"
    psk="YourPassword"
    key_mgmt=WPA-PSK
}

Step 7: Bandwidth and Performance Testing

Test Network Speed

# Install iperf3 for bandwidth testing
sudo apk add iperf3

# Test bandwidth to server (if available)
iperf3 -c iperf.example.com

# Test local network bandwidth
# On server: iperf3 -s
# On client: iperf3 -c server_ip

Monitor Real-time Traffic

# Monitor interface traffic
iftop -i eth0

# Simple traffic monitoring
watch -n 1 'cat /proc/net/dev'

# Bandwidth monitoring with vnstat (install first)
sudo apk add vnstat
vnstat -i eth0

Step 8: Advanced Packet Analysis

Capture and Analyze Packets

# Capture packets on interface
sudo tcpdump -i eth0

# Capture specific traffic
sudo tcpdump -i eth0 host 8.8.8.8

# Capture and save to file
sudo tcpdump -i eth0 -w capture.pcap

# Analyze HTTP traffic
sudo tcpdump -i eth0 -A port 80

Filter Network Traffic

# Monitor DNS traffic
sudo tcpdump -i eth0 port 53

# Monitor SSH connections
sudo tcpdump -i eth0 port 22

# Monitor specific source
sudo tcpdump -i eth0 src host 192.168.1.100

Step 9: Hardware-Level Troubleshooting

Check Ethernet Interface

# Check link status
ethtool eth0

# View detailed interface information
ethtool -i eth0

# Check for errors
ethtool -S eth0 | grep -i error

# Test different speeds
sudo ethtool -s eth0 speed 100 duplex full

Examine Network Hardware

# Check network hardware
lspci | grep -i network

# View kernel messages
dmesg | grep -i eth

# Check for hardware errors
dmesg | grep -i error

Step 10: Create Automated Diagnostic Script

Create a comprehensive network diagnostic script:

# Create diagnostic script
sudo nano /usr/local/bin/network-diag.sh

Add the diagnostic script:

#!/bin/sh

echo "=== Alpine Linux Network Diagnostic Script ==="
echo "Timestamp: $(date)"
echo

# Basic interface information
echo "=== Network Interfaces ==="
ip addr show
echo

# Routing information
echo "=== Routing Table ==="
ip route show
echo

# DNS configuration
echo "=== DNS Configuration ==="
cat /etc/resolv.conf
echo

# Test basic connectivity
echo "=== Connectivity Tests ==="
echo "Testing loopback..."
ping -c 2 127.0.0.1 > /dev/null && echo "✓ Loopback OK" || echo "✗ Loopback FAILED"

GATEWAY=$(ip route | grep default | awk '{print $3}' | head -1)
if [ ! -z "$GATEWAY" ]; then
    echo "Testing gateway ($GATEWAY)..."
    ping -c 2 $GATEWAY > /dev/null && echo "✓ Gateway OK" || echo "✗ Gateway FAILED"
fi

echo "Testing external connectivity..."
ping -c 2 8.8.8.8 > /dev/null && echo "✓ External IP OK" || echo "✗ External IP FAILED"

echo "Testing DNS resolution..."
nslookup google.com > /dev/null 2>&1 && echo "✓ DNS OK" || echo "✗ DNS FAILED"

# Active connections
echo
echo "=== Active Connections ==="
ss -tuln | head -10

# Recent network errors
echo
echo "=== Recent Network Errors ==="
dmesg | grep -i "network\|eth\|wlan" | tail -5

echo
echo "=== Diagnostic Complete ==="

Make it executable:

sudo chmod +x /usr/local/bin/network-diag.sh

# Run the diagnostic
/usr/local/bin/network-diag.sh

Common Fixes for Specific Issues

Issue: No Internet Connection

Solution Steps:

1. Check physical connection
2. Verify interface is up: sudo ip link set eth0 up
3. Get new IP: sudo dhclient eth0
4. Check routing: ip route show
5. Test DNS: nslookup google.com

Issue: Slow Network Performance

Solution Steps:

1. Test bandwidth: iperf3 -c server
2. Check interface errors: ethtool -S eth0
3. Monitor traffic: iftop -i eth0
4. Check MTU size: ip link show eth0
5. Adjust network settings if needed

Issue: Intermittent Connectivity

Solution Steps:

1. Monitor with continuous ping: ping -D 8.8.8.8
2. Check for hardware issues: dmesg | grep eth
3. Monitor interface: watch -n 1 'ip addr show eth0'
4. Check power management: ethtool eth0

Issue: DNS Not Working

Solution Steps:

1. Check /etc/resolv.conf
2. Test different DNS servers
3. Flush DNS cache: sudo rc-service dnsmasq restart
4. Use alternative DNS: dig @1.1.1.1 google.com

Prevention and Monitoring

Set Up Network Monitoring

# Create monitoring script
sudo nano /usr/local/bin/network-monitor.sh

Add monitoring script:

#!/bin/sh

# Log file
LOG="/var/log/network-monitor.log"

# Test connectivity and log results
TIMESTAMP=$(date)
if ping -c 1 8.8.8.8 > /dev/null 2>&1; then
    echo "$TIMESTAMP: Network OK" >> $LOG
else
    echo "$TIMESTAMP: Network DOWN - Running diagnostics" >> $LOG
    /usr/local/bin/network-diag.sh >> $LOG
fi

Set Up Automatic Recovery

# Create recovery script
sudo nano /usr/local/bin/network-recovery.sh

Add recovery logic:

#!/bin/sh

# Simple network recovery script
if ! ping -c 2 8.8.8.8 > /dev/null 2>&1; then
    echo "Network down, attempting recovery..."
    
    # Restart network interface
    ip link set eth0 down
    sleep 2
    ip link set eth0 up
    
    # Request new IP
    dhclient eth0
    
    # Wait and test
    sleep 5
    if ping -c 2 8.8.8.8 > /dev/null 2>&1; then
        echo "Network recovered successfully"
    else
        echo "Network recovery failed - manual intervention required"
    fi
fi

Conclusion

You now have a comprehensive toolkit for diagnosing and fixing network connectivity problems on Alpine Linux! Remember that network troubleshooting is often a process of elimination - start with the basics and work your way up to more complex issues.

Key takeaways:

• Always start with basic connectivity tests
• Use systematic approaches to isolate problems
• Keep diagnostic tools handy
• Monitor your network proactively
• Document solutions for future reference

With these skills and tools, you’ll be able to quickly identify and resolve most network connectivity issues! 🚀

Happy networking and troubleshooting! 🔧