Chapter – 4

ROUTER FUNDAMENTALS

BY :- Gurwinder Singh

Introduction

A Router is a network device that allows you to direct data traffic to an appropriate destination . Router maintain routing tables that contain IP addresses of computers over the network. A router has different components that enable its proper functioning. The Internetwork Operating System (IOS) acts as an operating system for the network devices. The IOS has many features that allow the user to interact with the devices.

ROUTER COMPONENTS

• A Cisco router does not contain disk storage mechanisms such as hard disks. Therefore , the router requires certain hardware and firmware components for proper functioning. These components allow the router to enter the boot up process , load to operating system and configuration files. A router has six different components.

1. Processor :-

Cisco router has a processor (CPU) that executes the IOS commands using the router components. Cisco routers use two types of processors such as Motorola 68030 and Orion/R4600. The Cisco IOSSoftware makes routing decisions and maintainsRouting tables using the processor.

2. ROM :-

The Read Only Memory (ROM) is a non-volatile memory storage device. ROM does not lose its contents when the power supply is turned off. The ROM consists of the following components :-POSTBootstrap ProgramMini-IOSROM monitor

Bootstrap Program

A bootstrap program is a ROM monitor component that allows you to initialize the processor hardware when the router boots. This component boots the operating system software after initializing the processor hardware.

POST

The Power-ON-Self-Test (POST) component provides a series of diagnostic tests for the router. These tests start when the router is switched on. The Post is a series of 14 tests that run in the reverse numerical order

Mini-IOS

The Mini-IOS is not present in every router. It provides a minimized version of the IOS image file consisting of the IP code.

ROM Monitor

ROM monitor is a program stored in the ROM which is used to debug user programs. The ROM monitor also allows manufacturing , testing and troubleshooting of ROM.

3. RAM :-

The function of Random Access Memory in the router is similar to that of the memory in a computer. The RAM is volatile storage medium that loses data when the device is switched off.The RAM temporarily stores the active configuration files , routing tables and information in the input and output buffers of the router interface .

4. Flash :-

The flash memory in a router is a non volatile storage medium . It is basically EEPROM . The Flash memory may contain IOS image that is loaded when the router boots.

5. NVRAM :-

Non-Volatile RAM (NVRAM) is a type of random access memory that stores configuration files for the router . The startup file and configuration register for the router are present in the NVRAM.

6. Configuration Register :-

Configuration Register is used to hold the configuration of the router or configuration files of a router. The type value of configuration register is hexadecimal 0x2102. Using this value , router loads Internetwork Operating System (IOS) from the flash memory and configuration from the NVRAM.

ROUTER BOOT SEQUENCE

The router boot sequence consists of the following steps :-

Router performs the POST check for testing the hardware components and memory. Bootstrap program is loaded from the ROM and executed. Bootstrap program starts loading the IOS image from the location specified by the boot field of the configuration register. The Cisco IOS then locates the hardware and software components of the router and displays list of components on the console. IOS loads a configuration file present in the NVRAM into the main memory. The configuration commands execute one after the other. If the valid configuration file is not present in NVRAM , the router displays the setup dialog box .

The router boot sequence appears as shown in below figure :-

IOS

The operating system provides an interface between the userAnd the hardware . Similarly , IOS acts as an interface between the network devices and the user . It stored in the flash memory of the router . The Cisco IOS software running on the router requires the processor of the system for configuring and maintaining the network devices.

The different features of the IOS are follow :-

Support for different technologies

Scalability

Security

CONNECTING TO A CISCO ROUTER

The Cisco router runs Internetwork Operating System (IOS) that manages hardware interface and security of the router . You can configure the router , verify its configuration and access Cisco IOS through the router ports and Telnet.

Cisco router have two main ports –

Console portAuxiliary port

Console port – Allow you to obtain local administrative access to the router . This port is located behind the router as an 8 pin holder called RJ-45 .

Auxiliary port – Allow you to connect modem to the router . You can connect the modem using a straight through cable.

The real panel of Cisco router appears as below figure:-

COMMAND LINE INTERFACE

Cisco router provides a command line interface (CLI) that allows manual configuration of the router .you can access router CLI using three following modes:-

User exec mode

Privileged exec mode

Global configuration mode

User exec mode – Allows you to switch to the different modes of the router . The user exec mode is the mode that is loaded the first time boots up.

Privileged exec mode- Allows you to execute high level commands for the router , such as viewing security settings and configuration settings that are not available in user mode.

Global configuration mode- allows you to execute configuration commands for the router . The configuration terminal command enables you to switch user mode to configuration mode.

When accessing a router, a user must login to the router before any other commands are entered. Router must be accessed with a terminal or by remote accessUser EXEC mode – allows the user to check the router status. No router configuration changes are allowed. Only a subset of the commands available at privileged EXEC levelPrivileged EXEC mode – allows the user to change the router configuration. Global configuration mode can be accessed along with other specific modes :

Interface or Sub interface Line Router Route-map

LOGGING INTO A ROUTER

Two commands can be used to set a password used to access privileged EXEC mode: enable password and enable secret. If both commands are used, the enable secret command takes precedence

If a LED is off when the interface is active and is correctly connected, a problem may be indicated

If an interface is extremely busy, its LED will always be on

The green OK LED to the right of the AUX port will be on after the system initializes correctly

ROUTER LED INDICATORS

COMMAND HISTORY

THE END