Chapter 4 discusses the fundamentals of routers, detailing their components including processors, memory types, and the boot sequence. It explains the role of the Cisco Internetwork Operating System (IOS) which facilitates interaction between the user and the hardware. Additionally, it covers how to connect to a Cisco router and the command line interface (CLI) used for configuration and management.

1. Chapter – 4
ROUTER FUNDAMENTALS
BY :- Gurwinder Singh

2. 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.

3.  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.

4. 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 IOS
Software makes routing decisions and maintains
Routing tables using the processor.

5. 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 :-
POST
Bootstrap Program
Mini-IOS
ROM monitor

6.  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

7.  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.

8. 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 .

9. 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.

10. 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.

11.  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 .

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

13.  IOS
The operating system provides an interface between the user
And 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.

14. The different features of the IOS are follow :-
 Support for different technologies
Scalability
Security

15.  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 port
Auxiliary port

16. 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:-

17.  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

18. 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.

19. 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 access
User 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 level
Privileged 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

20. 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

21.  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

22. COMMAND HISTORY

23. THE END