Cisco firewall (or switch / router) losing its config on reload

I am making this post to help any one who might have the same problem I did this week.  i.e.  Cisco device (in my case an ASA  5510 firewall) appeared to be losing its config after a reload.  Even though the config was saved.

I got called down to a remote office to deal with a problem on a Cisco ASA 5510.  There was a power cut and it hadn’t come back up. As such the remote office was completely offline.

When I got there and connected to the serial port, the device was in rom-mon mode.  I typed ‘boot’ and the device booted but there was no config.

I retrieved a config from a backup, copied it on, saved and reloaded.  Config was gone again.  I started to wonder if there was some kind of problem with the memory where the config was saved.  I did a ‘show run’ config was there.  I did a ‘show start’ config was there.  When I reloaded, config was gone.

When I thought about it, I reliased config was not quite gone, more like it wasn’t being loaded. This prompted me to check the configuration register setting.  The confreg is a bit like a bios, it tells the device how to boot and where to boot from.

In this case, the confreg was set to 0x40 (or it might have been 0x41).  In either case, a quick look on Google told me it should be 0x01 on an ASA 5510 for a normal boot.

I issued a ‘confreg 0x01’ at the enable prompt, saved and reloaded and all was well.

In summary, if your Cisco firewall, switch or router seems to be losing it’s config each reboot, check the configuration register setting.

What had happened?

I believe what had happened was the previous sysadmin based at that site (he left a few months ago) had carried out a password-reset and failed to reset the confreg setting when he finished.  When the power-cut hit, the device was booting into rommon.  Not sure what happened to the config, maybe he had restored that and not saved it.

If this post has helped you at all, please leave a comment.

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