CCNA Course in Urdu Lab 2 Part 1 Cisco Internetworking Operating System (IOS)

 

CCNA Course in Urdu Lab 2 Part 1 Cisco Internetworking Operating System (IOS)

LAB 02

MANAGING A CISCO INTERNETWORK

 

THE INTERNAL COMPONENTS OF A CISCO ROUTER

 

COMPONENTS	DESCRIPTION
Bootstrap	Brings up a router and loads the IOS. It is present inside the microcode of ROM of router
POST (Power on self test)	Checks the hardware and presence of interfaces, present inside the microcode of ROM
ROM monitor	Used for manufacturing, testing and troubleshooting, present inside the microcode of ROM
Mini-IOS (RXBOOT, boot loader)	Small IOS present in ROM, used to bring up an interface and loads IOS into flash
RAM	Hold packet buffers, ARP Cache, routing tables, running-config.
Flash Memory	EEPROM used to hold Cisco IOS
NVRAM (Non volatile RAM)	Used to store the startup-config of routers & switches
Configuration register	Controls the booting of router. It is stored in NVRAM. Its default value is 0x2102, which tells the router to load IOS from NVRAM

 

THE ROUTER BOOT SEQUENCE

 

1. First of all the router performs POST
2. Bootstrap loads the Cisco IOS software. By default the Cisco IOS is present in the Flash.
3. IOS looks for a valid configuration in NVRAM. This is called startup-config.
4. If the startup-config is not present in the NVRAM, then the router will copy this file and place it in RAM, call it running-config. Now the router must be operational. If the startup-config isn’t present in the NVRAM then router will broadcast out any interface looking for a TFTP host which has startup-config present in it.

 

MANAGING CONFIGURATION REGISTER

The configuration register is a 16bits (0 to 15) software register that is written into the NVRAM. By default the configuration register is set to load the Cisco IOS from flash memory and to look for and load the startup-config from NVRAM.

 

à The 6^th bit of configuration register is used to ignore the contents of NVRAM; this is used in password recovery.

à The bits (0 to 3) are used as Boot field.

  

 

THE BOOT FIELD (Configuration Register Bits 00-03)

Boot Field	Meaning	Use
00	ROM monitor mode	Set config-register to 2100, you must manually boot the router using b command, the router will show the rommon> prompt
01	Boot image from ROM	Set config-register to 2101 to boot an image stored in ROM, the router will show Router(boot)> prompt
02-F	Specifies a default boot file name	Any value from 2102 to 210F tells the router to use the boot commands specified in NVRAM

 

CHECKING THE CURRENT CONFIGURATION REGISTER VALUE

 

Router#show version

 

The last line of the output of this command will give you the information about the contents of configuration register. By default, the contents of configuration register is 0x2102

 

CHANGING THE CONFIGURATION REGISTER

 

Following are the reasons for which we may change the contents of configuration register:

1. To force the system into the ROM Monitor mode.
2. To select a boot source and default boot filename.
3. To enable or disable the Break function.
4. To control broadcast addresses.
5. To set the console terminal baud rate.
6. To load operating software from ROM.
7. To enable booting from TFTP server.

 

 

Click Here To View Video Lecture in Urdu:

 

Lab 2 Video

 

COMMAND TO CHANGE THE CONTENTS OF CONFIG-REGISTER

 

Router(config)#config-register 0x2101

Router(config)#^Z

 

Now check,

Router#sh ver

 

[output cut]

 

Configuration register is 0x2102 (will be 0x2101 at next reload)

 

After reloading, we get

Router(boot)#sh ver

 

Cisco IOS Software, 2800 Software (C2800NM-ADSECURITYK9-M), Version 12.4(12), RELEASE SOFTWARE (fc1)

[output cut]

 

Configuration register is 0x2101

 

 

 

Now reset original settings of the router

 

Router(boot)#config t

Router(boot)(config)#config-register 0x2102

Router(boot)(config)#^Z

Router(boot)#reload

 

 

RECOVERING PASSWORDS

 

As we know that the passwords are stored in the NVRAM, therefore, if we forget it then we have to by pass the NVRAM in order to log on to the router, Ignoring NVRAM requires turning on the bit 6 of configuration register. After turning on bit 6, the contents of configuration register become 0x2142.

 

Click Here To View Video Lecture in Urdu:

 

Lab 2 Video

 

STEPS TO RECOVER PASSWORD

 

1. Boot the router and interrupt the boot sequence by performing a break, which will take the router into ROM monitor mode.
2. Change the configuration register to turn on bit 6 (0x2142)
3. Reload the router.
4. Enter privileged mode.
5. Copy the startup-config file to running-config.
6. Change the password.
7. Reset the configuration register to the default value.
8. Save the router configuration.
9. Reload the router (optional).

 

à Ctrl+Break key combination is applied during Boot, you get into rommon1>

à rommon1>confreg 0x2142

     rommon1>reset

à Now since the NVRAM is bypassed, now perform the following commands

     Router>en

     Router#copy start run

     Router#config t

     Router(config)#enable secret farhan

     Router(config)#config-register 0x2102

     Router(config)#copy run start

 

In this way the newly set password is overwritten in the NVRAM i.e. from running-config to startup-config

 

Click Here To View Video Lecture in Urdu:

 

Lab 2 Video