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It can be quite useful to be able to load an IOS image through a serial connection, particularly if you don’t have access to a TFTP server, or if the router doesn’t have any accessible LAN interfaces. Although this feature is rarely used, Cisco does support xmodem and ymodem file transfers through a serial connection.
We also recommend enabling the CRC checksum feature when you use xmodem to download an IOS image through a serial connection. This will help ensure the integrity of the file transfer.
This video will show you how to upgrade IOS on Cisco Switch. For this video, I am using Cisco Catalyst 2950 but same method can be applied to Catalyst 2960, 3550, 3650, 3750 as well as chassis switch.
We should stress that this process can be extremely slow. Don’t even attempt to download an IOS image at the default speed of 9,600 bps unless you have an entire day to kill. We highly recommend increasing the speed to the highest value that your terminal emulation package will support. We have found that 115,200 bps provides the maximum throughput with the most reliability. The speed command allows you to change the speed of an asynchronous serial port:
In this example, we used Hyperterminal because it is included with the Windows operating system. However, almost any terminal emulation program that supports xmodem or ymodem protocols will work. In fact, we have found significant differences in download times between the various emulation packages, and Hyperterminal tends to be one of the slowest. Other packages such as ProComm tend to be somewhat faster. But they all work.
Even after we increased the speed of the Aux port to 115,200 bps, the file transfer took nearly 25 minutes to complete. By comparison, loading the same IOS version via TFTP through an Ethernet connection took less than four minutes. So, in general, we don’t recommend using this method unless you can’t use TFTP for some reason.
The first step, once you have a copy of the IOS image on your computer, is to connect to the router’s AUX port. Set the line speed to 115,200 bps on both the console port and the terminal emulator, and issue the copy command. The router will prompt you to begin the file transfer with the text “Ready to receive file.”
At this point, you should begin your file transfer protocol. If you are using Hyperterminal, select the “Transfer” drop-down menu, and then click on “Send-file.” It will prompt you for the file name and location, and protocol type. Enter the name of the IOS image, and then select “Xmodem” to start the file transfer.
During the file transfer, the connection is busy transferring the file, so the router can’t display any messages. This is normal. However, most terminal emulator programs provide a status window to let you keep track of the file transfer.
When the transfer is complete, the terminal emulator will drop out of the file transfer mode and the router will put up its normal prompt again. At this point, we highly recommend checking the new IOS image to make sure that it copied successfully. You can verify the file size as follows:
In this case, we loaded the image into the PCMCIA device in slot 1. If you put the image somewhere else, such as the internal flash memory, you would use the command show flash: instead.
If the file size is correct, check the image’s checksum by using the verify command:
Anytime Cisco releases a new IOS image for its network switch (or router), it is recommended that you upgrade it.
This article explains 7 easy steps to upgrade IOS image on a cisco switch or router.
Since you’ll be upgrading the IOS image, make sure you have physical access to the switch and you are in front of it. Use a console cable to connect to the switch.
Please note that the steps given below will be similar to both switches and routers. However this examples shows how to upgrade ios image on a cisco catalyst switch.
Please note that the steps given below will be similar to both switches and routers. However this examples shows how to upgrade ios image on a cisco catalyst switch.
1. Verify Current IOS Version
After you login, go to enable mode, by entering the enable password. This example uses two cisco catalyst 3750 switches configured in stack mode as shown below. So, while upgrading you should upgrade the image on both the flash cards.
If you have only one cisco catalyst switch (non stack mode), follow all the steps mentioned in this document, but you’ll be doing it only on one flash card.
![Switch Switch](/uploads/1/2/5/8/125850447/345840421.jpg)
First, verify the content of the flash cards, using “dir flash1:” command.
As you see above, both the flash cards contains the current IOS image file, which is version “122.35.SE5”
Verify what version of IOS image your switch is currently running. Most likely this will be same as the current IOS image file that you see in your flash card. As you see below, it is using “12.3(35)SE5”
2. Download Latest IOS Image from Cisco Website
Download the latest IOS image for your cisco website
Go to cisco.com -> IOS Software -> Select your Siwtch (for example: Cisco Catalyst Switch 3750G-24T) -> Click on “Download IP BASE” -> Select the latest version that you want to download (for example: 12-2.55.SE1).
Go to cisco.com -> IOS Software -> Select your Siwtch (for example: Cisco Catalyst Switch 3750G-24T) -> Click on “Download IP BASE” -> Select the latest version that you want to download (for example: 12-2.55.SE1).
While you are on this download page, copy/paste the MD5 given to your system. After we download the IOS image and move it to the switch, we’ll verify the MD5 checksum before installing the image.
3. Delete Old IOS Software Image from Flash
Since we’ll be downloading the new ISO image and moving it to the flash card, we need some space. So, delete the current old image from the flash card.
In the above delete command, /f stands for force, and /r stands for recurssive.
On a side note, you should be using some software to monitor your switch status. If you are not doing it install Nagios, and monitor your switches.
4. Copy the IOS image to Cisco Switch
To transfer the IOS image from your laptop to Cisco Switch, you should run a TFTPserver on your laptop (or on the system where you’ve downloaded the IOS image).
If you are running a TFTPserver on your laptop, and connected to the switch using a console cable, assign a ip-address to your laptop, and put your laptop on the same network as the switch.
Copy the ISO image to the flash as shown below using the “copy command”. This will ask you to enter the address of the remote host (which is your laptop in this case), and the source filename that needs to be transferred (which is the ISO image you downloaded from cisco website).
Once you’ve copied it, make sure the file is there on the flash card.
Just to make sure nothing went wrong during the copy, do a MD5 check-sum on this, and compare with the MD5 that you noted down from cisco website while downloading the IOS image. To create MD5 checksum of a file in Cisco catalyst switch, use the “verify” command as shown below.
If you are running two switches in stack configuration, do the same on the second flash card.
5. Modify Switch Boot path-list
Now it is time to tell switch cisco to use the new ISO image to boot from. Before changing the boot information, verify the current configuration, and change it using the “boot system” command as shown below.
6. Save Config and Restart the Switch
Verify the current boot information, save the current configuration, and reboot the cisco switch as shown below.
7. Final Verification after IOS Upgrade
Finally verify the current IOS version of the switch, after the upgrade, it should display the new version as shown below.
Make sure to verify your interface and vlan status, to make sure everything is running properly without any issues.
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