The day was Tuesday, August 12th 2014. I arrived home, only to find an almost unusable internet situation in my home. Some sites such as AnandTech and Google worked fine, but large swaths of the internet such as Microsoft, Netflix, and many other sites were unreachable. As I run my own DNS servers, I assumed it was a DNS issue, however a couple of ICMP commands later and it was clear that this was a much larger issue than just something affecting my household.
Two days later, and there is a pretty clear understanding of what happened. Older Cisco core internet routers with a default configuration only allowed for a maximum 512k routes for their Border Gateway Protocol (BGP) tables. With the internet always growing, the number of routes surpassed that number briefly on Tuesday, which caused many core routers to be unable to route traffic.