Loading an IOS on a switch via Xmodem

[Aninda Chatterjee]

A very good evening to all!

There are times when the IOS on a switch may crash and (as a last resort) you need to use the painfully slow Xmodem transfer to save your life. I bought a 3550 a while back and that is precisely what happened with me. Without much else to try, I decided to give Xmodem a shot. I want to share how this can be used and I hope that this may be useful to others.

Since the device is in ROMMON, there’s not much that you can do.  There is, however, a method to transfer another IOS using a direct  console connection with a PC (the transfer is over your console cable itself). This wonderful little thing is called  Xmodem. Now the rate of transfer depends on the baud rate that you set  for your console connection. I tried this with baud set to 9600 and man,  it seemed like it would take over 3 hours for the transfer to complete.  With a little trial and error, I found that the maximum baud rate I  could set it up to work perfectly with was 57600. You can set the baud  rate in ROMMON using the set BAUD <value> command. See below:

switch: set BAUD 57600

This MUST also match on the terminal program setting as well. So (I’m  using TeraTerm) under Setup -> Serial Port, set the baud rate to  match whatever you set it as in ROMMON. Now we’re ready to transfer the  file. The command is very straight forward:

switch: copy xmodem: flash:c3550-ipservicesk9-mz.122-44.SE6.bin

Once you press enter, you see the following:

Begin the Xmodem or Xmodem-1K transfer now…
C

At this point, you need to choose the file location from the terminal  program. Go under File -> Transfer -> Xmodem -> Send and  choose the file that you wish the transfer. The transfer will start and  you will see a transfer window pop up like this:

Once completed, you should get a prompt back to your ROMMON:

Begin the Xmodem or Xmodem-1K transfer now…
C…………………………………………………………………….                                                                                                 ……………………………………………………………………..                                                                                                 ……………………………………………………………………..                                                                                                 ……………………………………………………………………..                                                                                                 ……………………………………………………………………..                                                                                                 ……………………………………………………………………..                                                                                                 ……………………………………………………………………..                                                                                                 ……………………………………………………………………..                                                                                                 ……………………………………………………………………..                                                                                                 ……………………………………………………………………..                                                                                                 ……………………………………………………………………..                                                                                                 ……………………………………………………………………..                                                                                                 ……………………………………………………………………..                                                                                                 ……………………………………………………………………..                                                                                                 ……………………………………………………………………..                                                                                                 ……………………………………………………………………..                                                                                                 ……………………………………………………………………..                                                                                                 ……………………………………………………………………..                                                                                                 ……………………………………………………………………..                                                                                                 ……………………………………………………………………..                                                                                                 ……………………………………………………………………..                                                                                                 ……………………………………………………………………..                                                                                                 ……………………………………………………………………..                                                                                                 ……………………………………………………………………..                                                                                                 ……………………………………………………………………..                                                                                                 ……………………………………………………………………..                                                                                                 ……………………………………………………………………..                                                                                                 ……………………………………………………………………..                                                                                                 ……………………………………………………………………..                                                                                                ……………………………………………
File “xmodem:” successfully copied to “flash:c3550-ipservicesk9-mz.122-44.SE6.bin”

Now from ROMMON, boot from flash using the following command:

switch: boot flash:c3550-ipservicesk9-mz.122-44.SE6.bin

This will try to boot the IOS specified and if the transfer was good, then this should go smoothly.

Loading  “flash:c3550-ipservicesk9-mz.122-44.SE6.bin”…#########################                                                                                                 ################################################################################                                                                                                 ################################################################################                                                                                                 ################################################################################                                                                                                 ################################################################################                                                                                                 ################################################################################                                                                                                 ################################################################################                                                                                                 ################################################################################                                                                                                 ################################################################################                                                                                                 ################################################################################                                                                                                 ################################################################################                                                                                                 ################################################################################                                                                                                 ################################################################################                                                                                                 ################################################################################                                                                                                 ################################################################################                                                                                                ########

File “flash:c3550-ipservicesk9-mz.122-44.SE6.bin” uncompressed and installed, entry point: 0×3000
executing…

All’s good again!! The switch runs a POST, once everything checks out, you’re back into the familiar territory!

        — System Configuration Dialog —

Would you like to enter the initial configuration dialog? [yes/no]: no

I hope this was informative.

[anongcheng]

wonderfull, this lesson can troubleshoot my issue, it's useful

thank you for sharing

[gusmedin]

Thanks for sharing, very useful, it helped me a lot.

[dirtydevv]

Super helpful! Thank you!

[adarshane_ISE]

Fantastic !! Followed for the Cisco 2960-X and works the similar way. 

[MattGorzka99290]

It worked flawlessly. Thank you very much!

[jeremiah.guzman]

Worked for me on a 3560cg. Thank you!

[arahmanar7]

Hi, 

I was about to dump the switch!! Fortunately I came across your post, and it works smoothly..

Thanks mate!!

[martin parkinson]

Thank you for your knowledge article on recovery, I would like to add that, as with 000node000 and anybody else, I've always used 115200 in the past (successfully) but wondered what the maximum could be.

So I tried various settings on a Cisco 2960x and the switch finally accepted 230400 baud, but it did not transfer anything.

So the fastest speed you can set for your console is 115200.

Tera Term allows you to XMODEM files over 115200 and it has default baud settings of 921600, 460800 & 230400, I tried all of these and it only accepted 230400.

[marcelaoliveira]

Thank you very much!

[CISCO171346]

But there is one thing, which Cisco employees @Aninda Chatterjee and Cisco TAC will never tell you if you do not have a valid service contract or you have reached the End of Support. Or probably they do not know even if you have these both.

Never Never apply this change of baud rate to 57600 on your switch (if this switch is an Integrated EtherSwitch Service Module) without knowing the options of baud rate which are available on your Router tty line associated to this Switch.

because if you change "that" switch baud rate to 57600 and router do not have it then you will get garbage data because of this mis-match and as this switch is integrated so you do not have any mode button or direct console port on it to reset.