Catalyst 3750X IOS update questions

Tilman Schmidt · ‎10-18-2013

The C3750X-24T-S I recently posted about still doesn't offer a usable Web GUI. With no solution in sight, I would like to try a software update.

Currently the unit has installed 12.2(55)SE5 universal. I decided to go for the latest 15.2(1)E which should also give me the sorely missing SSH public key authentication.

Now I encounter a few complications:

The new tar image is 28.610.560 bytes which won't fit into the 64 MB flash alongside the current one, let alone be able to be unpacked.
No web interface, so I'll have to use the command line.
I don't have a TFTP server around, either.

#1 is perhaps not that bad as the flash memory currently contains both tar and bin images of 12.2(55)SE5, which looks redundant. Without the old tar image, the new one as such would fit. #2 wouldn't scare me as I'm used to the command line anyway. However it also means no HTTP upload, so in conjunction with #3, the only remaining option for getting the new image onto the machine is SCP. Now I'm routinely using SCP for configs anyway and it works perfectly fine. However, all the instructions for updates from the command line I found so far are based on TFTP only.

Which leads me to a couple of questions on how to cope with that situation:

Is the archive download command, which is the documented way for installing the new software image, limited to TFTP as source, or does it work with SCP too?
How much free flash space do I actually need? The size of the tar image? Twice that size so it can be unpacked?
Can I delete the tar image of the currently running software version 12.2(55)SE5 from the flash without ill effects? (After backing it up to my SCP server of course.)
In case that doesn't free up sufficient flash space, can the current image be deleted to make space for the new one while it is still running?
What is the failure mode if flash space is insufficient for an update? Will it fail gracefully or catastrophically?

Thanks in advance for any help!

Tilman

Leo Laohoo · ‎10-18-2013

I don't have a TFTP server around, either.

Use TFTPd32/TFTPd64. Download from here.

#1  is perhaps not that bad as the flash memory currently contains both tar  and bin images of 12.2(55)SE5

You do not need the TAR file in the switch.

Is the archive download  command, which is the documented way for installing the new software  image, limited to TFTP as source, or does it work with SCP too?

TFTP, FTP, SCP, HTTP, etc.

How much free flash space do I actually need?

Wrong question. The question I should be asking you is this: Have you TESTED 15.2(1)E on a non-production switch? If you haven't, make sure you do. I know of one person who loaded this IOS into his 3750X and it does nothing but crashes. Read this.

Can  I delete the tar image of the currently running software version  12.2(55)SE5 from the flash without ill effects? (After backing it up to  my SCP server of course.)

You can delete the old IOS but "backup" the old IOS??? Why? If you want a "backup" to the old IOS, go to the Cisco website and download the IOS. That's is the best method.

In  case that doesn't free up sufficient flash space, can the current image  be deleted to make space for the new one while it is still running?

I do this all the time. Make sure while you are un-packing the IOS, the appliance doesn't loose power or crashes.

What is the failure mode if flash space is insufficient for an update? Will it fail gracefully or catastrophically?

"failure mode"? Care to elaborate?

I recently posted about still doesn't offer a usable  Web GUI

What you are doing, i. e. upgrading the IOS to get a "usable GUI" is an exercise of futility. CLI is the best way to go down the path.

Tilman Schmidt · ‎10-19-2013

Thanks a lot, Leo, for your elaborate answer.

Leo Laohoo schrieb:

You do not need the TAR file in the switch.

Good. Though I wonder why it's there then, but that question's moot.

Is the archive download command, which is the documented way for installing the new software image, limited to TFTP as source, or does it work with SCP too?

TFTP, FTP, SCP, HTTP, etc.

Perfect.

How much free flash space do I actually need?

Wrong question. The question I should be asking you is this: Have you TESTED 15.2(1)E on a non-production switch? If you haven't, make sure you do. I know of one person who loaded this IOS into his 3750X and it does nothing but crashes. Read this.

Good point, though that thread seems actually to be about a corrupted image. However, once I've tested the image on another switch, the question remains: How much free flash space do I need in order to install it successfully on the production switch? The update instructions just tell me to make sure there's "sufficient space" but not how much that is.

Can I delete the tar image of the currently running software version 12.2(55)SE5 from the flash without ill effects? (After backing it up to my SCP server of course.)

You can delete the old IOS but "backup" the old IOS??? Why?

Cisco's upgrade instructions explicitly recommend it, and it is no big effort, just a single command.

In case that doesn't free up sufficient flash space, can the current image be deleted to make space for the new one while it is still running?

I do this all the time. Make sure while you are un-packing the IOS, the appliance doesn't loose power or crashes.

Fine. I'd still prefer to keep the previous IOS image available like I do on the routers and small business switches, but if that isn't possible on the Catalyst then so be it.

What is the failure mode if flash space is insufficient for an update? Will it fail gracefully or catastrophically?

"failure mode"? Care to elaborate?

If the update fails because of insufficient free flash, which state will the unit be in? Same as before the attempt, ie. running normally with the old software image still in the flash so that I have all the time in the world to think about what went wrong? (graceful failure) Crashed and without any usable software image in the flash so that I have to reinstall the old software via Xmodem under combat conditions? (catastrophic failure) Something in between?

I recently posted about still doesn't offer a usable Web GUI

What you are doing, i. e. upgrading the IOS to get a "usable GUI" is an exercise of futility. CLI is the best way to go down the path.

Of course the CLI is essential. Still the GUI is sometimes nice to have, too. But, as I wrote, that's not my only reason for upgrading.

Leo Laohoo · ‎10-20-2013

How much free flash space do I need in order to install it successfully on the production switch?

The IOS itself would need >16 mb of free flash space. Besides, no need to worry. If you use the "archive download-sw" or "archive tar /x" command, if the flash space is not enough, the process will tell you.

Cisco's upgrade instructions explicitly recommend it, and it is no big effort, just a single command.

It's an outdated "recommendation" before the age of "the internet". Download the IOS from the Cisco website and compare the MD5 hash values of the file you've just downloaded vs the values found in the Cisco download site. This is a MUST. You have no idea how many people uploaded a corrupt TAR file into a production switch.

The outdated recommendation is exactly as outdated the recommendation to recover a corrupted IOS on 3750E/X, 2960S/X, 3560E/X, 3850 and 3650 switches using XModem. It's outdated because the XModem process takes about a minimum of 45 minutes while the USB process takes about 10 minutes.