One of the first things I do after a reported network outage is to check the uptime of the network equipment.
Many times a device reboot could explain what happened. WHY it rebooted is a whole other article.
I've been using Fluke Network's Optiview XG lately and like its feature to report if I device rebooted in the past 5 days. I can also change the number of days for different scenarios.
In this video, I investigate a Cisco switch and why it rebooted using my XG, but the methodology is still relevant and can be performed manually.