[Day 5] 3. Cisco Router Overview

Cisco routers are a popular brand of routing equipment used in various network environments. Many other vendors offer similar router functionality.
Cisco routers come in both fixed and modular configurations. Fixed-configuration routers have a set number of ports, while modular routers allow for adding additional modules for more flexibility.

Important Ports:
- WIC (WAN Interface Card): Used for serial connections (e.g., S0/0, S0/1).
- FastEthernet Port: For data transfer, not configuration.
- Console Port: Used to configure routers via command-line interface (CLI).

Router Memory Types:
1. ROM (Read-Only Memory): Contains the BIOS, POST (Power-On Self-Test), and ROMMON (ROM Monitor), a minimal OS for recovery.
2. Flash Memory: Stores the Cisco IOS and other files. It is non-volatile and retains data even when powered off.
3. NVRAM (Non-Volatile RAM): Stores the startup configuration that the router reads during boot-up.
4. DRAM (Dynamic RAM): Stores the running configuration and routing tables while the router is operational. It is volatile, meaning data is lost when the router is powered off.

Working of ROM, NVRAM, and DRAM:
- ROM: Manages the initial boot-up process, running POST and loading the MiniOS or ROMMON if necessary.
- NVRAM: Stores startup configurations that are loaded into DRAM during boot-up.
- DRAM: Holds the active running configuration and routing information, which are lost if the router is turned off without saving to NVRAM.