Diagnosing Network Issues with Linux Tools

Connectivity Testing

ping — Basic Reachability

# Test connection
ping -c 4 google.com

# With timestamp
ping -D -c 4 google.com

traceroute — Path Analysis

# Shows each hop to destination
traceroute example.com

# TCP traceroute (bypasses ICMP blocks)
sudo traceroute -T -p 443 example.com

# MTR — combines ping + traceroute (live updating)
mtr example.com

DNS Troubleshooting

# Quick lookup
dig +short example.com

# Full query with timing
dig example.com

# Query specific record type
dig MX example.com
dig TXT example.com

# Query specific nameserver
dig @8.8.8.8 example.com

# Trace delegation chain
dig +trace example.com

Port Testing

# Check if port is open on remote host
nc -zv example.com 443

# Check multiple ports
nc -zv example.com 80 443 22

# Using nmap
nmap -p 22,80,443 example.com

Connection Analysis

# All listening ports
ss -tlnp

# All established connections
ss -tnp

# Connections to specific port
ss -tnp sport = :443

# Connection count by state
ss -s

Bandwidth Testing

# Install iperf3
sudo apt install -y iperf3

# On server
iperf3 -s

# On client
iperf3 -c server-ip

# Test download speed from internet
curl -o /dev/null -w "Speed: %{speed_download} bytes/sec\n" https://speed.cloudflare.com/__down?bytes=100000000

Common Issues and Fixes

Tip When reporting network issues to support, include the output of mtr -r -c 100 your-server-ip — it gives us everything we need to diagnose the path.