Router

🧭 Introduction to Routers: The Heart of Networking

A router is an internetworking device that connects multiple logical networks. It operates at Layer 3 (Network Layer) of the OSI model and determines the best path for data packets. In a LAN, a router usually acts as the Default Gateway, enabling internal devices to reach external networks like the internet.

⚙️ Router Hardware Components & Memory Types

• Console Port (RJ45–RS232): Used for direct configuration using a terminal.
• RAM: Temporarily holds the running configuration.
• NVRAM: Stores the startup configuration persistently.
• Flash Memory: Stores the IOS (Internetwork Operating System).

💡 Understanding Router Modes

Prompt	Mode
Router>	User Mode (limited access)
Router#	Privilege Mode (full access) — use enable or en to enter
Router(config)#	Global Configuration Mode

Other Modes

• User Mode: Basic access, can’t make changes.
• Setup Mode: Assists with initial configuration.
• ROMmon Mode: Recovery environment used for:
  • IOS recovery
  • Password reset
  • Flash issues
  Access via: Ctrl + Pause/Break (real device) or Ctrl + C (Cisco Packet Tracer)

🧩 Types of Routers

1. Based on Platform

• Hardware Routers: Cisco, Juniper, D-Link, HP, etc.
• Software Routers: Microsoft Server, Linux Server

2. Based on Modularity

• Fixed (Non-Modular) Routers: Non-upgradable, ports fixed to motherboard.
• Modular Routers: Allow for interface upgrades using LAN/WAN cards via available slots.