MANAGING CISCO IOS
Anil Kumar Vishwakarma
The router boot sequence
Locating IOS software
The configuration register
Backing Up the Cisco IOS
Restoring or Upgrading the Cisco Router IOS
Backing Up Router Configuration
Restoring Router Configuration
Cisco Discovery Protocol (CDP)
ROUTER BOOT SEQUENCE
1. The router performs a POST. The POST tests the hardware to
verify that all components of the device are operational and
present. For example, the POST checks for the different interfaces
on the router. The POST is stored in and run from ROM (read-only
2. The bootstrap looks for and loads the Cisco IOS software. The
bootstrap is a program in ROM that is used to execute programs.
The bootstrap program is responsible for finding where each IOS
program is located and then loading the file. By default, the IOS
software is loaded from flash memory in all Cisco routers.
3. The IOS software looks for a valid configuration file stored in
NVRAM. This file is called startup-config and is only there if an
administrator copies the running-config file into NVRAM.
4. If a startup-config file is in NVRAM, the router will load and run this
file. The router is now operational. If a startup-config file is not in
NVRAM, the router will start the setup-mode configuration upon
It is 16-bit software register that’s written into NVRAM.
Used to control how the router boots up.
The default configuration setting on Cisco routers is 0x2102.
To know what is the current value of configuration register, use show
You can change the default value by using this command.
Notice that bit 6 can be used to ignore the NVRAM contents. If it is enabled.
Here are the main steps to password recovery:
1. Interrupting the Router Boot Sequence by pressing the Ctrl+Break
key combination when using HyperTerminal and while the router first
reboots. The command prompt will be like that.
rommon 1 >
2. Changing the Configuration Register to ignore NVRAM contents by
using this command
rommon 1 > confreg 0x2142
3. Reloading the Router and Entering Privileged Mode by this
rommon 1 > reset
The router will reload and ask if you want to use setup mode answer
4. Copy startup-config to running-config in Privileged Mode by using
Router#copy start run
5. Change password by setting new password
Router(config)#enable secret kkkk
6. Change the value of configuration register to enable NVRAM contents
7. Save your work
Router#copy run start
8. Reload router to activate changing of configuration register
BACKING UP THE CISCO IOS
Before you upgrade or restore a Cisco IOS, you really should copy
the existing file to a TFTP or FTP host as a backup just in case the
new image crashes and burns.
To back up the Cisco IOS to a TFTP server, you use this command
Router#copy flash FTP OR
Router#copy flash TFTP
This command requires only the source filename and the IP address
of the TFTP or FTP server.
You can get the source filename by using Show flash command.
The key to success in this backup routine is to make sure that you’ve
got good, solid connectivity to the TFTP server. Check this by pinging
the device from the router.
RESTORING OR UPGRADING ROUTER IOS
You can download the file from a TFTP or FTP server to flash memory
by this command
Router#copy FTP flash
This command requires the IP address of the FTP server and the name
of the file you want to download.
You are prompted to make sure that you really want to proceed with
erasing flash memory.
BACKING UP ROUTER CONFIGURATION
To copy the router’s configuration from a router to a FTP server, you can
use these commands.
Router#copy run FTP
Router#copy start FTP
Copying the Current Configuration to NVRAM
Router#copy run start
RESTORING ROUTER CONFIGURATION
If you did copy the router’s configuration to a TFTP server
as a second backup, you can restore the configuration
Router#copy tftp run
This command ask you about FTP_IP address, Source
filename and destination filename.
CISCO DISCOVERY PROTOCOL
CDP is a proprietary protocol designed by Cisco to help administrators
collect information about both locally attached and remote devices.
By using CDP, you can gather hardware and protocol information about
neighbor devices, which is useful info for troubleshooting and
documenting the network.
The show cdp command gives you information about two CDP global
parameters that can be configured on Cisco devices:
how often CDP packets are transmitted to all
the amount of time that the device will hold
packets received from neighbor devices.
Global CDP information:
Sending CDP packets every 60 seconds
Sending a holdtime value of 180 seconds
Use the global commands cdp holdtime and cdp timer to configure the CDP
holdtime and timer on a router:
Router(config)#cdp timer 90
Router(config)#cdp holdtime 240
Gathering Neighbor Information by using this command Router#sh
Gathering Interface Traffic Information including the number of CDP packets
sent and received and the errors with CDP.
Router#sh cdp traffic
Gathering Port and Interface Information including CDP status on router
interfaces or switch ports.
Router#sh cdp interface
To turn off CDP on one interface on a router,
Router(config-if)#no cdp enable
CISCO DISCOVERY PROTOCOL (CDP)