Network_diagnostics

Chapter 39: Network Diagnostics Scripts

Overview

This chapter covers network diagnostics scripts for testing connectivity, analyzing network traffic, and troubleshooting network issues - essential skills for DevOps engineers.

---

Network Basics

Understanding Network Tools

# Common network tools
ip          # Modern network configuration
ss          # Socket statistics
ping        # Test connectivity
traceroute # Trace network path
dig         # DNS queries
netstat     # Network statistics
tcpdump    # Packet capture
nmap        # Network scanning

---

Connectivity Testing

Ping Tests

#!/usr/bin/env bash
# ping_test.sh - Test network connectivity

HOST="${1:-google.com}"
COUNT="${2:-4}"

echo "Testing connectivity to $HOST..."
ping -c "$COUNT" "$HOST"

Multiple Host Monitoring

#!/usr/bin/env bash
# monitor_hosts.sh - Monitor multiple hosts

HOSTS=(
    "8.8.8.8"
    "google.com"
    "cloudflare.com"
    "1.1.1.1"
)

echo "=== Network Monitoring ==="
for host in "${HOSTS[@]}"; do
    if ping -c 1 -W 2 "$host" &>/dev/null; then
        echo "✓ $host is reachable"
    else
        echo "✗ $host is unreachable"
    fi
done

---

Port Analysis

Port Scanning

#!/usr/bin/env bash
# port_scan.sh - Scan ports on localhost

set -euo pipefail

HOST="${1:-localhost}"
START_PORT="${2:-1}"
END_PORT="${3:-1024}"

echo "Scanning $HOST ports $START_PORT-$END_PORT..."

for port in $(seq $START_PORT $END_PORT); do
    if timeout 0.1 bash -c "echo >/dev/tcp/$HOST/$port" 2>/dev/null; then
        echo "Port $port: OPEN"
    fi
done

Check Specific Ports

#!/usr/bin/env bash
# check_ports.sh - Check if specific ports are open

set -euo pipefail

HOST="${1:-localhost}"
PORTS=(22 80 443 3306 5432 6379 8080)

echo "Checking common ports on $HOST..."

for port in "${PORTS[@]}"; do
    if timeout 0.5 bash -c "echo >/dev/tcp/$HOST/$port" 2>/dev/null; then
        echo "Port $port: OPEN"
    else
        echo "Port $port: CLOSED"
    fi
done

---

DNS Analysis

DNS Lookup

#!/usr/bin/env bash
# dns_lookup.sh - Perform DNS lookups

set -euo pipefail

DOMAIN="${1:-google.com}"

echo "=== DNS Lookup for $DOMAIN ==="

# A record
echo "A record:"
dig +short "$DOMAIN" A

# AAAA record (IPv6)
echo "AAAA record:"
dig +short "$DOMAIN" AAAA

# MX record
echo "MX record:"
dig +short "$DOMAIN" MX

# NS record
echo "NS record:"
dig +short "$DOMAIN" NS

# TXT record
echo "TXT record:"
dig +short "$DOMAIN" TXT

Reverse DNS

#!/usr/bin/env bash
# reverse_dns.sh - Reverse DNS lookup

set -euo pipefail

IP="${1:-8.8.8.8}"

echo "Reverse DNS for $IP:"
dig +short -x "$IP"

---

Network Statistics

Connection Analysis

#!/usr/bin/env bash
# network_stats.sh - Show network statistics

echo "=== Network Statistics ==="
echo ""

echo "--- Established Connections ---"
ss -tun | grep ESTAB

echo ""
echo "--- Listening Ports ---"
ss -tunl | grep LISTEN

echo ""
echo "--- Connection States ---"
ss -tan | awk '{print $1}' | sort | uniq -c | sort -rn

Interface Statistics

#!/usr/bin/env bash
# interface_stats.sh - Show network interface statistics

set -euo pipefail

INTERFACE="${1:-}"

echo "=== Network Interface Statistics ==="

if [[ -z "$INTERFACE" ]]; then
    ip -s link show
else
    ip -s link show "$INTERFACE"
fi

---

Bandwidth Testing

Speed Test

#!/usr/bin/env bash
# speed_test.sh - Test network speed

set -euo pipefail

# Test download speed
echo "Testing download speed..."
download_speed=$(curl -s -o /dev/null -w '%{speed_download}' https://speed.cloudflare.com/__down?bytes=10000000)
echo "Download: $((download_speed/1024/1024)) MB/s"

# Test upload speed
echo "Testing upload speed..."
upload_speed=$(curl -s -o /dev/null -w '%{speed_upload}' https://speed.cloudflare.com/__up -X POST -d "test")
echo "Upload: $((upload_speed/1024/1024)) MB/s"

---

Troubleshooting Scripts

DNS Troubleshooting

#!/usr/bin/env bash
# troubleshoot_dns.sh - Troubleshoot DNS issues

set -euo pipefail

DOMAIN="${1:-google.com}"

echo "=== DNS Troubleshooting for $DOMAIN ==="
echo ""

# Check if DNS server is reachable
echo "1. Checking DNS server..."
ping -c 1 8.8.8.8 &>/dev/null && echo "✓ DNS server reachable" || echo "✗ DNS server unreachable"

# Test DNS resolution
echo ""
echo "2. Testing DNS resolution..."
if dig +short "$DOMAIN" | grep -q '[0-9]'; then
    echo "✓ DNS resolution working"
    dig +short "$DOMAIN"
else
    echo "✗ DNS resolution failed"
fi

# Test with different DNS servers
echo ""
echo "3. Testing with different DNS servers..."
for dns in "8.8.8.8" "1.1.1.1" "208.67.222.222"; do
    result=$(dig +short @"$dns" "$DOMAIN" A | head -1)
    echo "DNS $dns: $result"
done

Network Path Analysis

#!/usr/bin/env bash
# trace_route.sh - Trace network path

set -euo pipefail

HOST="${1:-google.com}"

echo "=== Traceroute to $HOST ==="
traceroute -m 15 "$HOST"

---

Firewall Rules

List iptables Rules

#!/usr/bin/env bash
# list_iptables.sh - List iptables rules

echo "=== iptables Rules ==="
echo ""

echo "--- Filter Table ---"
sudo iptables -L -n -v

echo ""
echo "--- NAT Table ---"
sudo iptables -t nat -L -n -v

---

HTTP/HTTPS Analysis

Test HTTP Endpoints

#!/usr/bin/env bash
# test_endpoint.sh - Test HTTP/HTTPS endpoints

set -euo pipefail

URL="${1:-http://localhost:8080/health}"

echo "Testing: $URL"
echo ""

# HTTP status code
status_code=$(curl -s -o /dev/null -w "%{http_code}" "$URL")
echo "HTTP Status: $status_code"

# Response time
time_total=$(curl -s -o /dev/null -w "%{time_total}" "$URL")
echo "Response Time: ${time_total}s"

# Content type
content_type=$(curl -s -I "$URL" | grep -i "content-type" | cut -d: -f2 | xargs)
echo "Content-Type: $content_type"

# Check SSL certificate (for HTTPS)
if [[ "$URL" =~ ^https ]]; then
    echo ""
    echo "SSL Certificate:"
    echo "$URL" | openssl s_client -connect "${URL#https://}" 2>/dev/null | \
        openssl x509 -noout -dates -subject
fi

---

Advanced Diagnostics

Packet Capture

#!/usr/bin/env bash
# capture_packets.sh - Capture network packets

set -euo pipefail

INTERFACE="${1:-eth0}"
COUNT="${2:-100}"
OUTPUT_FILE="${3:-/tmp/capture.pcap}"

echo "Capturing $COUNT packets on $INTERFACE..."
sudo tcpdump -i "$INTERFACE" -c "$COUNT" -w "$OUTPUT_FILE"

echo "Capture saved to: $OUTPUT_FILE"

Network Latency Analysis

#!/usr/bin/env bash
# latency_test.sh - Test network latency

set -euo pipefail

HOST="${1:-google.com}"
COUNT="${2:-10}"

echo "Testing latency to $HOST..."
echo ""

# Measure latency
ping -c "$COUNT" "$HOST" | tail -1

# Show RTT statistics
ping -c "$COUNT" "$HOST" | grep "rtt"

---

Summary

In this chapter, you learned:

• ✅ Connectivity testing with ping
• ✅ Port scanning and analysis
• ✅ DNS lookup and troubleshooting
• ✅ Network statistics
• ✅ Bandwidth testing
• ✅ DNS troubleshooting
• ✅ Route tracing
• ✅ Firewall rules
• ✅ HTTP endpoint testing
• ✅ Packet capture
• ✅ Latency analysis

---

Next Steps

Continue to the next chapter to learn about Container Automation Scripts.

---

Previous Chapter: Log Analysis Scripts Next Chapter: Container Automation Scripts