I only just now found this thread, so I'm sorry I'm late to the party, but here, I put it on Medium.
https://gushi.medium.com/the-worst-day-ever-at-my-day-job-beff7f4170aa > On Mar 12, 2021, at 10:07 PM, Mark Tinka <mark@tinka.africa> wrote: > > Hardly famous and not service-affecting in the end, but figured I'd share an > incident from our side that occurred back in 2018. > > While commissioning a new node in our Metro-E network, an IPv6 point-to-point > address was mis-typed. Instead of ending in /126, it ended in /12. This > happened in Johannesburg. > > We actually came across this by chance while examining the IGP table of > another router located in Slough, and found an entry for 2c00::/12 floating > around. That definitely looked out of place, as we never carry parent blocks > in our IGP. > > Running the trace from Slough led us back to this one Metro-E device in > Jo'burg. > > It took everyone nearly an hour to figure out the typo, because for all the > laser focus we had on the supposed link of the supposed box that was creating > this problem, we all overlooked the fact that the /12 configured on the > point-to-point link was actually supposed to have been a /126. > > The reason this never caused a service problem was because we do not > redistribute our IGP into BGP (not that anyone should). And even if we did, > there are a ton of filters and BGP communities on all devices to ensure a > route such as that would have never made it out of our AS. > > Also, the IGP contains the most specific paths to every node in our network, > so the presence of the 2c00::/12 was mostly cosmetic. It would have never > been used for routing decisions. > > Mark.
