I use three Pix firewalls. One at my colocation, one here, and another one to give additional security to servers such as my mail server. The third one just crashed.
I found out because I had 500 emails, which triggered my email monitor that tells me when there's more than 100. Each email was six emails from my monitoring server, telling me that it couldn't contact six of my servers.
I went down to the Data Shed. First I looked at the servers that were out of contact. They were all running fine. Then I looked at the switch, that was OK. And then I looked at the Pix firewall, and it had no lights. Power off. And then I saw it was switching itself on and off, on and off. So I did the first thing one does in this situation, because it's easy to do and it sometimes fixes the problem. I powered it off, waited five seconds, then powered it on. It came back on, and stayed on, and the six servers are back online.
This power cycle cure is embedded in anyone who deals with computers a lot, so much so that it's the first thing we try when *anything* stops working. It's worked for my car, several times, for example.
Pixes never crash, or so I believed. This belief is based on more than ten years of using them. Now the belief is "Pixes hardly ever crash". I'll be putting that Pix onto my power controller, so that if need be, I can cycle the power remotely.
... later ...
It crashed again. So I've put another Pix in it's place.
I opened it up, I can't see anything wrong. I'll leave it running for a while, to see if this is a long-term problem, or can I use it as a spare?