Cisco 3750 software recovery

7 06 2007

A colleague of mine just called, having done an “erase flash” on a 3750. He did this because there was only 16MB of flash on the switch and therefore not enough room for two images at the same time. What he didn’t expect was that the switch would subsequently reboot and end up in bootloader mode with no software on it…

So here’s what we did. I thought I’d write this up because I found it a bit difficult locating the information on

The software for these switches comes as a .tar file. Tar is an old Unix file archive type – it actually stands for “tape archive” and was used for archiving things to tape. The .tar file contains the .bin image that the switch needs to boot, and some other stuff (for Cisco View Device Manager etc). When the switch is running normally, you’d use the command “archive download-sw tftp://<ipaddress>/<filename>” – this command copies the .tar file over and extracts it onto the filesystem.

However when you’re stuck in bootloader mode, there’s no such command. So we need to do something different:

1. Use Winzip (or similar) to extract the .bin file from the .tar file on your computer.

2. Connect to the switch using Hyperterminal at 9600 baud, 8 N 1.

3. You should see a prompt that says “switch:”. This is the bootloader mode. If you don’t see that, either you’re booted up, and you don’t need these instructions, your switch is properly broken, or you’ve got your terminal settings wrong. Try power-cycling the Catalyst while holding the “Mode” button on the front in to get the bootloader.

4. Now downloading the .bin file at 9600 baud is going to take a loooong time (about 2 hours), so we will change the baud rate of the console port temporarily. Enter the command “set BAUD 115200″. After you enter this command, you will start to get funny characters in Hyperterminal because its baud rate and the Catalyst’s are now mis-matched.

5. Close Hyperterminal and re-connect using 115200 baud instead. You should get intelligible stuff on the screen once more.

6. Type “flash_init” to initialise the filesystem. (In our case, this wasn’t necessary)

7. Type “load_helper” to load any helper files (in our case there weren’t any since we’d just wiped the flash).

8. Tell the switch to expect a file by Xmodem, and put it on the flash: “copy xmodem: flash:<filename.bin>” The filename should be the same as what you extracted from the .tar file.

9. In Hyperterminal click Transfer | Send File. In the dialogue box, make sure the protocol is XModem and put in the location of your .bin file. Click “Send” and you should see the process start.

10. Once that’s done, issue the command “boot flash:<filename.bin>” and the IOS will load up.

11. When the switch has booted, you may want to install the full .tar file in the correct manner using the “archive” command.

12. Check that you can reboot OK without ending up in the bootloader again.

13. Finally, you’d better set the console baud rate back to 9600, otherwise you or someone else will be really confused when they next try to use it. Go back into the bootloader by power-cycling the switch and holding down the “Mode” button. Enter the command “set BAUD 9600″ Then type “reset” to reboot the switch.

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33 responses

17 07 2008

Thank you for taking the time to write this out. It came in very handy this evening.

28 08 2008

you can save yourself a reboot by setting the baud back to 9600 after you download the image.

3 09 2008

hi, im having issues trying to bopy across a .bin file using xmodem

i type in the following on a 3750 with no IOS

copy xmodem:flash:c3750-i9-mz.121-19.EA1d

this comes up

usage: copy [-b ]

i then try to copy using xmodem and it errors with no response from remote system

pls can you help?

4 09 2008

Hi Stu –
Unless I am mistaken, you don’t have a space between “xmodem:” and “flash:”, and you are also missing the .bin extension from the filename.
Hope that helps,

6 02 2013
Eric B

I am re-imaging one at the moment. The correct formatting for these switches (because I ran into the same problem erroring) is
copy xmodem:c3750e-ipbasek9-mz.150-2.SE1.bin flash:c3750e-ipbasek9-mz.15
0-2.SE1.bin or it will not work…..

7 10 2008

Nice article! Thank you for your contribution to the R& S community! We had occasion in our shop to use this info today and glad that you had published it!


10 10 2008


thx for the detailed procedure,

17 12 2008
Joe Harris

Here is consolidated link which details the password recovery procedures for many of our products Password Recovery Procedures

19 12 2008

Why don’t you set bigger BAUD? Eg set BAUD 921600
Thanks for your guide

22 12 2008

Yeah – I guess that might be an option. I think I just used 115200 because (as far as I know), the serial UART chips on some devices can’t go any faster than that.

31 12 2008

Hey man, this was mega useful. Thank you for taking the time…

29 01 2009

Hey thanks for that, it came in useful.

have another question, if you want to recover a switch from a remote location, how would you do this?? for example, a console management switch is connected to the 3750, there is also a 56k modem attached to the modem….how can u xmodem a file via PSTN line?

29 01 2009

Hmm- good question. I’ve never had to do that, so I can’t say whether it’d work either way. If i have a chance to try it, I’ll post something.

16 06 2009

Thanks a lot.

29 06 2009

Hi… This is my first experience of recovering IOS in Catalyst 3750 PoE switch. But the switch is in “Switch:” (Switch Column mode). I’m confused that how would I get it out of that mode and reload the IOS from TFTP? I’ll be grateful, if anyone can resolve my problem. I’ll be much thankful.

30 06 2009

Thanks for the detailed instructions on setting it to 115k. I tried to do it with 9600 bauds and I gave up.

8 01 2010


Just want to say thanks for the post. this HOW-TO saved me a lot of time.


30 08 2010

Hi-5 for this!

Thanks for helping others!

27 09 2010

if the baud cant set to 9600,use this command

Router(config)#line con 0
Router(config-line)# speed 9600

13 12 2010

Remember if you are emulating serial cable with a terminal server and you know the line (port) you are using:

ts-server#conf t
Enter configuration commands, one per line. End with CNTL/Z.
ts-server(config)#line 5
ts-server(config-line)#speed 115200

Thanks this was an awesome post.

15 01 2012

Thnx for the Great information Guys.

But I am unable to set back BAUD rate to 9600. I gave set BAUD 9600 command.

When I am in bootloader is works on 9600. when the ios is loaded it works only on 115200.

22 02 2012

Interesting – what happens if you do:

conf t
line con 0
speed 9600

Are you still stuck with 115200?

20 03 2012

Thanks. That worked for me

21 02 2012

Thank you so much…you guys are my heros!!!

28 03 2012

Thank you for this, flash_init was the key step I was missing.

25 05 2012

Thank you…Thank you…Thank you :)

18 10 2012
Big Mook

Thanks for putting this out. It’s been years since I’ve had to do this and it was much easier finding your page than searching for the procedure.

By the way, my 17MB+ bin file is going to take about 1 hour, 15 minutes at 115200, so it would take about 15 hours to transfer at 9600.

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27 09 2013

Thank you so much for the article. I was able to bring up the 3120 switch with the help of this article.

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