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Router Components, Boot process and Types of router ports

In this tutorial, we will learn about introduce you to router components, Router boot process and types of router ports.
Submitted by Mahima Rao, on November 19, 2018

Introduction to Router Components

A router is made up of several types of components. For example, in any Cisco router, you will get 4 types of memory and 2 types of ports. The basic components of any Cisco router are as follows.

  • Memory
    1. ROM
    2. FLASH
    3. RAM
    4. NV-RAM
  • Ports (Interfaces & lines)
  • Command Line Interface

ROM has a bootstrap program called ROM Monitor. When the router is turned on, it performs the bootstrap program hardware diagnostic called Power On Self Test. If this diagnostic is successful, then the bootstrap program loads and loads the IOS from the flash memory. Flash memory can be rewritten. This gives Cisco router the ability to upgrade IOS.

If the bootstrap is not found in IOS Flash Memory, then the ROM is loaded with the temporary version of the IOS. ROM cannot be rewritten or erased. You need to upgrade the device, then you can change the ROM.

If IOS is found in flash memory then it is loaded into RAM. After that bootstrap finds the Startup-Configuration file in NV-RAM. NV-RAM is non-volatile RAM, so its contents are not erased.

If IOS does not find the startup configuration file, it tries to load the configuration file from the TFTP server. If TFTP server also does not respond, then the IOS is entered in the initial configuration mode. In this mode, users are asked questions which allow the router to be quickly configured.

If IOS gets a startup configuration file in NV-RAM, then it is loaded into RAM and it becomes a running configuration file.

1) Memory

There are 4 types of memory in Cisco IOS, which are being given below:

  • ROM
    This is read-only memory. It is hardwired in the router. Inside the ROM is a bootstrap program that performs power on self-test. This is called a ROM monitor mode. When the router can not find IOS, it boots from ROM itself.
  • FLASH
    By default First, the router only searches for flash memory for IOS and boots the IOS. This is the electronically erasable programmable read-only memory.
  • RAM
    It is also called dynamic random access memory. RAM is the working area of the Cisco router CPU. In this memory, running configuration file and routing tables are stored.
  • NV-RAM
    It is called non-volatile random access memory. In NV-RAM the startup configuration file is stored, which is used to start the system.

2) Ports

Cisco IOS has interfaces and lines 2 types of ports. These are being given below,

Interfaces connect the router to other devices such as routers and switches. Data in the network travels through these ports. The names of some common interfaces are being given below:

  • Serial interface
  • Ethernet interface
  • Fast Ethernet interface

Interfaces are identified by their name and number. For example, the first ethernet interface is known as Ethernet0. Some router families are modular, so interfaces in them have been organized in slots. Therefore, along with the interface number, the slot number is written as well. You can type 2 interfaces of the first slot in this way.

i) Ethernet0/2

You can configure the router by connecting with other types of ports. These are called lines. The names of some such ports are being given below:

  • Console ports
  • Auxiliary ports
  • VTY ports

Similar to interfaces, lines are also identified by line type and line number. So if the first console port will be written something like this.

Console0

3) Command Line Interface (CLI)

IOS provides a command line interface to interact with the Cisco router. The command line interface is the first option to configure and manage Cisco devices. You can access it via console, modem and telnet connection. In this, you can type the commands and execute them.

Router Booting Process

Every Cisco passes through a booting process, this process is being explained below:

  1. The power of the router is switched on.
  2. Bootstrap program is loaded from the ROM.
  3. Bootstrap runs program POST (Power On Self Test).
  4. Bootstrap tries to load IOS from flash memory -
    1. If IOS is not available in flash memory, then loads basic IOS from bootstrap ROM.
    2. If IOS is found in flash memory it is loaded in RAM.
  5. IOV NV-RAM tries to load startup config file-
    1. If the startup configuration file is not found in NV-RAM, then IOS tries to load a configuration file from the TFTP server.
    2. If TFTP server does not respond then the router enters the initial configuration mode.
    3. If the startup config file is found in NVRAM then it is loaded into RAM.
  6. Running configuration is created in the startup configuration RAM.





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