Network Protocols

DHCP (Dynamic Host Configuration Protocol)

  • Simplifies IP address management
  • Administrators don’t need to manually assign IP addresses to each client in the network

Reference: Oracle DHCP Documentation

Middleware

RPC (Remote Procedure Call)

  • REST: Representational State Transfer
  • SOAP: Simple Object Access Protocol

Web Server

Virtual Host

  • One computer hosting multiple domains
  • Implementation methods:
    • Specify host name and domain name in URI
    • Specify host header field

Proxy Types

  • Cache Proxy: Uses cached responses
  • Transparent Proxy: No changes, just redirects requests

WebSocket

Use Case

When a server needs to push values to a browser.

Example: In Jira, when a value is changed elsewhere, the Jira page open in the browser automatically refreshes.

STOMP over WebSocket

  • STOMP: Simple Text Oriented Messaging Protocol
  • Provides a frame-based protocol on top of WebSocket

Mesh Network

Features

  • Censorship resistant: No central control point
  • Decentralized: Civilian network
  • Ubiquitous: Essential for home networking

How it Differs

Traditional networks require a central system for communication, but mesh networks allow direct communication between devices.

Network Speed Check

Tools

Use webpagetest.org to check which layer is causing slow performance.

This tool helps identify:

  • DNS lookup time
  • Connection time
  • Time to first byte
  • Content download time

OSI Model Overview

Understanding the OSI (Open Systems Interconnection) model helps you reason about where problems occur in networking.

Layer Name Protocol Examples Description
7 Application HTTP, FTP, SMTP, DNS User-facing protocols
6 Presentation SSL/TLS, JPEG, ASCII Data formatting and encryption
5 Session NetBIOS, PPTP Session management
4 Transport TCP, UDP Reliable/unreliable data delivery
3 Network IP, ICMP, ARP Routing and addressing
2 Data Link Ethernet, Wi-Fi Frame delivery on local network
1 Physical Cables, Radio waves Physical signal transmission

TCP vs UDP

Feature TCP UDP
Connection Connection-oriented Connectionless
Reliability Guaranteed delivery Best-effort delivery
Ordering Maintains order No ordering guarantee
Speed Slower (overhead) Faster (minimal overhead)
Use Cases Web, email, file transfer Video streaming, gaming, DNS

TCP uses a three-way handshake (SYN, SYN-ACK, ACK) to establish connections, ensuring both sides are ready to communicate. UDP skips this process, making it faster but less reliable.

Port Numbers

Common port numbers every developer should know:

Port Service Protocol
20/21 FTP TCP
22 SSH TCP
25 SMTP (email) TCP
53 DNS TCP/UDP
80 HTTP TCP
443 HTTPS TCP
3306 MySQL TCP
5432 PostgreSQL TCP
6379 Redis TCP
8080 HTTP (alternate) TCP

Network Debugging Tools

ping

Tests basic connectivity to a host:

ping google.com

traceroute / tracert

Shows the route packets take to reach a destination:

traceroute google.com    # Linux/Mac
tracert google.com       # Windows

netstat / ss

Shows active network connections:

netstat -an | grep LISTEN    # Show listening ports
ss -tuln                     # Modern alternative on Linux

tcpdump

Captures and analyzes network packets:

tcpdump -i eth0 port 80     # Capture HTTP traffic on eth0

These tools are essential for diagnosing network issues such as connectivity problems, slow responses, or unexpected traffic patterns.