IP Addresses

An IP (Internet Protocol) address uniquely identifies a device on a network. It's like a postal address for your computer.

IPv4 Addresses

  • Format: Four numbers separated by dots (dotted decimal notation)
  • Range: 0.0.0.0 to 255.255.255.255
  • Example: 192.168.1.100
  • Size: 32 bits (4 bytes)
  • Total addresses: ~4.3 billion

IPv4 Address Classes

  • Class A: 1.0.0.0 to 126.255.255.255 (large networks)
  • Class B: 128.0.0.0 to 191.255.255.255 (medium networks)
  • Class C: 192.0.0.0 to 223.255.255.255 (small networks)
  • Private ranges (used in LANs):
  • 10.0.0.0/8
  • 172.16.0.0/12
  • 192.168.0.0/16

IPv6 Addresses

  • Format: Eight groups of four hexadecimal digits
  • Example: 2001:0db8:85a3:0000:0000:8a2e:0370:7334
  • Size: 128 bits (16 bytes)
  • Total addresses: ~340 undecillion (virtually unlimited)
  • Simplified: Leading zeros can be omitted, consecutive zeros can be ::

Example: 2001:db8:85a3::8a2e:370:7334

Special IP Addresses

  • 127.0.0.1 (localhost): Your own computer (loopback)
  • 0.0.0.0: All interfaces, any address
  • 255.255.255.255: Broadcast address (all devices on network)

IP Address Types

  1. Public IP: Unique on the Internet, routable
  2. Private IP: Used within LAN, not routable on Internet
  3. Static IP: Permanently assigned
  4. Dynamic IP: Assigned by DHCP (changes periodically)

Ports

A port is a 16-bit number (0-65535) that identifies a specific process or application on a host. Think of it as an apartment number in a building (the building is the IP address).

Port Ranges

  • Well-known ports (0-1023): Reserved for system services
  • Port 80: HTTP
  • Port 443: HTTPS
  • Port 22: SSH
  • Port 25: SMTP
  • Port 53: DNS

  • Port 21: FTP

  • Registered ports (1024-49151): For registered applications

  • Port 3306: MySQL
  • Port 5432: PostgreSQL

  • Port 8080: HTTP (alternative)

  • Dynamic/Private ports (49152-65535): For temporary use, client-side

Common Ports for Socket Programming

Port Protocol Purpose
80 HTTP Web browsing
443 HTTPS Secure web browsing
22 SSH Secure shell
25 SMTP Email sending
53 DNS Domain name resolution
3306 MySQL Database
5432 PostgreSQL Database
27017 MongoDB Database

Port Binding

  • Server: Binds to a specific port (listens on that port)
  • Client: Uses an ephemeral (temporary) port assigned by OS
  • Multiple sockets: Can't bind to the same port on the same interface simultaneously

Socket Address

A socket address combines IP address and port number: - Format: IP_ADDRESS:PORT - Example: 192.168.1.100:8080 - Example: 127.0.0.1:3000

This uniquely identifies an endpoint for network communication.

Network Address Translation (NAT)

NAT allows multiple devices with private IPs to share a public IP: - Router has public IP (visible to Internet) - Devices on LAN have private IPs - Router translates between private and public IPs - Important for socket programming when connecting through routers

Domain Names vs IP Addresses

  • Domain name: Human-readable (e.g., www.google.com)
  • IP address: Machine-readable (e.g., 142.250.191.14)
  • DNS (Domain Name System): Translates domain names to IP addresses
  • Socket programming often uses IPs directly, but can use domain names (DNS resolution happens automatically)

In Socket Programming

When Creating a Server

# Bind to all interfaces on port 8080
server.bind(('0.0.0.0', 8080))

# Bind to localhost only
server.bind(('127.0.0.1', 8080))

# Bind to specific interface
server.bind(('192.168.1.100', 8080))

When Creating a Client

# Connect to server at specific IP and port
client.connect(('192.168.1.100', 8080))

# Connect using domain name
client.connect(('example.com', 80))

Checking Your Network Information

Linux/macOS

# Show IP addresses
ifconfig
# or
ip addr show

# Show listening ports
netstat -tuln
# or
ss -tuln

Windows

# Show IP addresses
ipconfig

# Show listening ports
netstat -ano

Common Issues

  1. "Address already in use" - Port is already bound by another process - Solution: Choose different port or stop the other process

  2. "Connection refused" - Nothing listening on that port - Solution: Start the server first

  3. Firewall blocking - Firewall prevents connections - Solution: Configure firewall rules

  4. Wrong IP address - Using private IP to connect from outside LAN - Solution: Use public IP or use port forwarding

Key Takeaway: IP addresses identify devices, ports identify applications. Together they form a socket address that uniquely identifies a network endpoint.