I recently dealt with a client’s network outage caused by a misconfigured router. I had to dig into the routing tables and found that one static route was pointing to the wrong gateway. Once corrected, the network was restored. Have you encountered similar routing issues in your teaching, and how do you explain routing table troubleshooting to your students?
When I've taught routing, I always started on the whiteboard, building a pseudo table to teach the very basics and move on from there.
I've always taught that if you can avoid a static entry on a routing table, if there's any way, do so - routing protocols are smarter. And if you have to have a static entry, document the heck out of it, so someone that comes behind knows. The way I see it, these days, if you have to use a static entry, you're trying to do something unconventional or weird.
That's where the documentation comes in - because "well, it was a good idea when I put it in there" will turn into "what the heck was this fool thinking?". In the OP's example, I think that entry was correct at one time, that it was working once and then one day, it wasn't working. Perhaps the gateway was changed, but no one bothered to look at the static routes in the other routers.
However, these bugs are also great to teach. Using something like GNS3 to build a network up and test with, has been a mainstay for me over the years.
/r