How to upgrade Cisco Router IOS using TFTP Server


This document covers IOS up gradation step by step process on Cisco Router. The Router should be up and running whose image needs to be upgraded and this document not intended for password recovery. 

You make sure that new IOS image supports hardware, software features, Router has enough Flash memory to run the image and other memory & processor related specifications. If you do sure, go to the SoftwareCenter in the Technical Support area at and use the Hardware-Software compatibility matrix to determine the version of software which is suited.

Any IOS up gradation or backup process first we will need to have TFTP server. This can be downloaded from Internet. There are several versions of TFTP available free

(Free TFTP can be downloaded from )

Step 1

 a)     Copy from CD or Download the Cisco IOS software image to your workstation or PC.

b)     Install the new Cisco IOS software image in the outbound / root directory of the TFTP serve. The TFTP server looks for the image in this directory

c)     Memory requirements for each image are also in the outbound directory of the TFTP server. Verify that you have enough memory on Router using the show version command

Router# show version

Cisco Internetwork Operating System Software

IOS ™ C2845-4V Software (C2845V-Y6-M), Version



Copyright (c) 1986-2000 by cisco Systems, Inc.

Compiled Mon 10-Apr-00 13:45 by phanguye

Image text-base: 0x80013170, data-base: 0x8067D780

ROM: System Bootstrap, Version 12.1(1r)XB1, RELEASE


Router uptime is 0 minutes

System returned to ROM by reload

System image file is “flash:c2845v-y6-mz.121-1.XB”

CISCO C2845-4V (MPC855T) processor (revision 0x502)

with 15360K/1024K bytes of memory.

Processor board ID JAD043100FS (1979977378), with

hardware revision 1987

CPU rev number 5

Bridging software.

4 POTS Ports

1 Ethernet/IEEE 802.3 interface(s)

1 ATM network interface(s)

128K bytes of non-volatile configuration memory.

8192K bytes of processor board System flash


Configuration register is 0x2102

Step 2

 Establish a console session to the router.

This can be done with a direct console connection or a virtual TELNET connection. A direct console connection is preferred because a TELNET connection is lost during the reboot phase of the software installation . The console connection is made with a rolled cable (flat black or blue cable), and connects the console port of the router to the COM-port of the PC.

(Serial to USB converters are available incase we want to use LAPTOPs. Nowadays modern LAPTOPS are not equipped with DB 9 ports)

Launch HyperTerminal on the PC, and use the following settings:

9600 bits per second

8 data bits

0 parity bits

1 stop bit

No Flow Control

(These are Restore Default settings)

Hyperterminal settings for Cisco Router











Step 3 

Verify that the TFTP server has IP connectivity to the router.

The TFTP server must have a network connection to the router and must be able to ping the IP

address of the router targeted for a TFTP software upgrade. To achieve this, the router interface

and the TFTP server must have:

An IP address in the same range, or

A default gateway configured.

After verifing network connectivity with your TFTP server, write all the changes to memory by issuing a write memory command on the router.

Router# write memory

Building configuration…



Step 4

Issue the show flash command to check the available space in the Flash memory.

Router# show flash

System flash directory:

File Length Name/status

1 3802992 c2845v-y6-mz.121-1.XB

[3803056 bytes used, 4585552 available, 8388608 total]

8192K bytes of processor board System flash (Read/Write)

We should ideally have enough Flash memory to install the new Cisco IOS software image alongside with existing image. If we do not have the required memory available, ensure that the total amount of system flash is enough to accept the required new IOS image and then the upgrade process will overwrite your existing IOS image, leaving you with just the new image.

Step 5

It is highly recommended that we should always back up existing IOS image (incase of revert back if we deleted or over write existing image)

Router# copy flash tftp

Source filename []? c2845v-y6-mz.121-1.XB

Address or name of remote host []?

Destination filename [c2845v-y6-mz.121-1.XB]?






3802992 bytes copied in 27.276 secs (140851 bytes/sec)

Step 6

It is also recommended to back up running configuration.

Router# copy startup-config tftp

Address or name of remote host []?

Destination filename [startup-config]?


676 bytes copied in 0.100 secs

(We can also take manual backups in text mode)

Step 7

Enter the show version command to verify that the configuration register setting is set to 0x2102. This setting is required so that the router boots from Flash.

If the router’s configuration register is not set to 0x2102, record the current value, and use the following commands to set it to the required value.

Router# configure terminal

Router(config)# config-reg 0x2102

Router(config)# exit


Step 8

Copy the Cisco IOS software image from the TFTP Server to Flash in the router. Under NO circumstances we should halt the copy process or power off your router or the TFTP server. If you do so, you will not be able to recover from the situation. (Unless, X modem transfer via ROM MON mode)

Router# copy tftp flash

Address or name of remote host []?

Source filename []? c2845v-y6-mz.121-1.XB

Destination filename [c2845v-y6-mz.121-1.XB]?

%Warning:There is a file already existing with this name

Do you want to over write? [confirm]

Accessing tftp://…

Erase flash: before copying? [confirm]

Erasing the flash filesystem will remove all files!

Continue? [confirm]

Erasing device…



ee …erased

Erase of flash: complete

Loading c2845v-y6-mz.121-1.XB from (via

Ethernet0): !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!






[OK – 3802992/7605248 bytes]

Verifying checksum… OK (0x1ABC)

3802992 bytes



Step 9

Confirm the router upgrade by issuing the following command:

Router>show flash

 Make sure the Cisco IOS software image name in the show flash command output is the name of the upgrade image.



Filed Under: Router General


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