Linux Advanced — Networking Practice Exercises

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Practice Exercises

Exercise 1 — Network Discovery

Find your machine’s IP address, default gateway, and DNS servers using command-line tools.

💡 Show Answer 
# IP address
ip -br addr
# or
hostname -I

# Default gateway
ip route | grep default
# default via 192.168.1.1 dev eth0

# DNS servers
cat /etc/resolv.conf
# nameserver 8.8.8.8
# nameserver 8.8.4.4

# All in one:
echo "IP: $(hostname -I | awk '{print $1}')"
echo "Gateway: $(ip route | awk '/default/ {print $3}')"
echo "DNS: $(grep nameserver /etc/resolv.conf | awk '{print $2}' | tr '\n' ' ')"

Exercise 2 — Port Investigation

Find all services listening on TCP ports, then check specifically if anything is running on ports 22, 80, and 443.

💡 Show Answer 
# All listening TCP ports
sudo ss -tlnp

# Check specific ports
for port in 22 80 443; do
  result=$(sudo ss -tlnp | grep ":$port ")
  if [ -n "$result" ]; then
    echo "Port $port: OPEN"
    echo "  $result"
  else
    echo "Port $port: CLOSED"
  fi
done

Exercise 3 — DNS Investigation

For the domain github.com, find its A record, MX records, and name servers. Then do a reverse lookup on one of its IP addresses.

💡 Show Answer 
# A record (IPv4)
dig +short github.com
# 140.82.121.3

# MX records
dig +short github.com MX
# 1 aspmx.l.google.com.
# ...

# Name servers
dig +short github.com NS
# dns1.p08.nsone.net.
# ...

# Reverse lookup
dig -x 140.82.121.3
# 3.121.82.140.in-addr.arpa. ... PTR lb-140-82-121-3-iad.github.com.

Exercise 4 — SSH Key Setup

Generate an Ed25519 SSH key pair and create an SSH config entry for a server called myserver at 192.168.1.50 with user deploy on port 2222.

💡 Show Answer 
# Generate key pair
ssh-keygen -t ed25519 -C "deploy-key" -f ~/.ssh/deploy_key

# Create SSH config entry
cat >> ~/.ssh/config << 'EOF'

Host myserver
    HostName 192.168.1.50
    User deploy
    Port 2222
    IdentityFile ~/.ssh/deploy_key
EOF

# Set correct permissions
chmod 600 ~/.ssh/config
chmod 600 ~/.ssh/deploy_key

# Copy key to server (when server is reachable)
# ssh-copy-id -i ~/.ssh/deploy_key myserver

# Now connect with just:
# ssh myserver

Exercise 5 — File Transfer Challenge

Download a file from https://example.com/data.csv, then transfer it to a remote server at 192.168.1.10:/tmp/ using two different methods. Show how to verify the transfer.

💡 Show Answer 
# Download the file
curl -O https://example.com/data.csv
# or
wget https://example.com/data.csv

# Method 1: scp
scp data.csv user@192.168.1.10:/tmp/

# Method 2: rsync (better for large files)
rsync -avz data.csv user@192.168.1.10:/tmp/

# Verify — check file exists and size matches
# Local:
ls -l data.csv
md5sum data.csv

# Remote:
ssh user@192.168.1.10 'ls -l /tmp/data.csv && md5sum /tmp/data.csv'
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