Squid caching takes me back. I was dealing with a network for a large car dealership (2006), and they were having issues with pages appearing out of date, as well as sales people who couldn't help themselves from looking at adult websites. I had to figure out the entire network (was put in place before I ever showed up to provide support), which included both the physical and software layers. Not only was I on ladders in the service area, using a network tone device (for those that don't know, you can connect a cable to a device that pushes a tone down the line, and then pick up that tone on a device that lets you run the device down the line and hear the one if you have the correct wire), but I also had to figure out this server using a Squid cache that stood in front of everything.

Eventually I got all the devices marked from origin to their patch cables in the server room, and I started looking into the Squid cache. It turns out that they were caching everything, as well as blocking websites. I figured out what websites they needed to do their job, and turned off caching, while also learning the ACLs for blocking websites. Anything else was allowed, but the Squid cache would hold a copy for some set amount of time (I think it was 24 hours, so if it was legitimate they only had to wait a day, but it also saved on bandwidth by quite a bit - although think this was used more to monitor user activity).

It was frustrating as someone new to large LANs, as well as to in-house caching, but had been using Linux since an early version of Slackware in the later 1990's. Even to this day, as someone that writes software and does DevOps, that knowledge has helped my debugging skills tremendously. Dealing with caching is a skill I feel you need to be burned by in order to finally understand it, and recognize when it's occurring. I cut my teeth on Linux through a teacher that set up a web server in 1997, and not only gave students access to upload their web files, but also a terminal to message each other and see who was online.