IntroToLinux

4. Network Basics

Network Information:

# Show network interfaces
ip addr show
ip a                   # Short form
ifconfig              # Traditional command (may need installation)

# Show routing table
ip route show
route -n              # Traditional command

# Show network connections
netstat -tuln         # TCP/UDP listening ports
ss -tuln              # Modern replacement for netstat
ss -tup               # Show process names

# DNS lookup
nslookup google.com
dig google.com
host google.com

# Test connectivity
ping google.com
ping -c 4 google.com   # Send 4 packets
traceroute google.com  # Show network path

Network Configuration:

# Temporary IP configuration
sudo ip addr add 192.168.1.100/24 dev eth0
sudo ip route add default via 192.168.1.1

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

# Check network manager status
systemctl status NetworkManager
nmcli device status    # NetworkManager command line

Network Services:

# SSH service
sudo systemctl status ssh
sudo systemctl start ssh

# Check SSH connections
who
w
last

# Basic firewall (ufw)
sudo ufw status
sudo ufw enable
sudo ufw allow ssh
sudo ufw allow 80/tcp
sudo ufw deny 23/tcp

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