Network Diagnostics Toolkit

Intermediate10 min

Diagnose network connectivity, DNS resolution, port availability, and routing issues using standard Linux networking tools.

Prerequisites

-Linux shell access

Steps

Check network interfaces and IP addresses

View all network interfaces and their assigned IP addresses.

$ ip -brief addr

Test DNS resolution

Verify that DNS is resolving domain names correctly.

$ dig google.com +short

Use 'dig @8.8.8.8 domain.com' to test against a specific DNS server.

Check if a remote port is reachable

Test TCP connectivity to a specific host and port.

$ nc -zv example.com 443 -w 5

The -w flag sets a timeout. Use -u for UDP ports.

Trace the network path to a destination

See each network hop between you and the destination to identify where packets are being dropped.

$ traceroute -n example.com

Check listening ports

View all ports that are currently listening for connections.

$ ss -tlnp

-t for TCP, -l for listening, -n for numeric ports, -p for process names.

Full Script

full-script.sh

#!/bin/bash
# Network Diagnostics Toolkit
set -euo pipefail

echo "=== Network Interfaces ==="
ip -brief addr

echo ""
echo "=== Default Route ==="
ip route | grep default

echo ""
echo "=== DNS Configuration ==="
cat /etc/resolv.conf | grep -v '^#'

echo ""
echo "=== DNS Resolution Test ==="
dig google.com +short 2>/dev/null || nslookup google.com 2>/dev/null | grep Address

echo ""
echo "=== Listening Ports ==="
ss -tlnp | head -20

echo ""
echo "=== Active Connections ==="
ss -tn state established | head -10

echo ""
echo "=== Diagnostic Commands ==="
echo "Ping:         ping -c 4 <host>"
echo "DNS:          dig <domain> +short"
echo "Port check:   nc -zv <host> <port>"
echo "Traceroute:   traceroute -n <host>"
echo "Listening:    ss -tlnp"
echo "Connections:  ss -tn state established"

FAQ

Discussion

Loading comments...

#!/bin/bash # Network Diagnostics Toolkit set -euo pipefail echo "=== Network Interfaces ===" ip -brief addr echo "" echo "=== Default Route ===" ip route | grep default echo "" echo "=== DNS Configuration ===" cat /etc/resolv.conf | grep -v '^#' echo "" echo "=== DNS Resolution Test ===" dig google.com +short 2>/dev/null || nslookup google.com 2>/dev/null | grep Address echo "" echo "=== Listening Ports ===" ss -tlnp | head -20 echo "" echo "=== Active Connections ===" ss -tn state established | head -10 echo "" echo "=== Diagnostic Commands ===" echo "Ping: ping -c 4 <host>" echo "DNS: dig <domain> +short" echo "Port check: nc -zv <host> <port>" echo "Traceroute: traceroute -n <host>" echo "Listening: ss -tlnp" echo "Connections: ss -tn state established"