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genehack
Asked: 2010-03-30 13:12:18 +0800 CST

How to get access to console to reset Cisco 3750?

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I acquired two Cisco 3750 switches from another part of my organization.

I was able to complete the standard password/config reset procedure on one without any issues -- boot it, put it into express config mode, telnet in, reset the passwords, etc.

The second one doesn't ever boot to the point where it displays anything on the console. When power cycled, the 'SYST' light flashes green a few times, then comes on a solid green and stays lit. None of the other lights ever flash or light up. Holding down the 'MODE' button for up to 30 seconds produces no noticeable effects. Nothing ever comes out on the console.

Since I was able to configure the first one without any problems, I know my connectinon is good -- console port configured right, good cable, etc. Is this just a hardware problem with the switch? Is there any way I can recover from this and get the switch back into a state where I can configure it?

networking cisco configuration

3 Answers

  1. Best Answer

    If booting while MODE is held down doesn't produce any output via the serial console, and you have the right cable and terminal settings for your device (which you should be able to find from cisco), then I would tend to blame a hardware issue.

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  2. If you get locked out of the switch, you have to :

    1. Unplug the second switch, if you have one stacked, since it still had the start-up config in it.
    2. Unplug the first switch, hold down the mode button, then plug the switch back in holding the mode button in.
    3. Wait for the syst light to go solid green before you release the mode button.

    You will be in the flash entry mode:

    1. Type "flash_init"
    2. Type "load_helper"
    3. Type "dir flash:", then there will be some flash files displayed.
    4. Type "rename flash:config.text flash:config.old". The password is stored in the config.text file and you are moving it so the switch won't load with it.
    5. Type "boot" it should boot up and ask to continue autoinstall. Just say no to all the questions.
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  3. There's a few more things to try. Sometimes, people reconfigure the console speed and that's read as part of the boot process, so you wouldn't necessarily see anything on the screen on boot. If the switch actually switches packets, it may still have CDP enabled on one (or more) ports and you should be able to see what it considers to be its management IP by looking at the CDP packets. Leave a packet sniffer attached to a working switch port for a few minutes and you'll be able to see what come sthrough.

    Alternatively, try a few different speed settings and see if anything actually produces any results.

    Of course, if it's not switching packets when on, it's probably bust, but from a brief reading, I would've thought that changed console port speed would be enough to explain the problems you've seen.

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