Even worse, there are often huge bugs in routers or switches with regards to IPv6 that aren't often discovered because IPv6 is so rarely used. I remember readi

Even worse, there are often huge bugs in routers or switches with regards to IPv6 that aren't often discovered because IPv6 is so rarely used. I remember reading about Facebook's migration as a great case study. One example problem they had was that their switches couldn't handle getting a BGP feed with IPv6 addresses when they had not been configured for IPv6. In other words, when they added IPv6 to their BGP feeds they crashed an entire network segment worth of switches. This is another massive headache w.r.t IPv6 switchover: all the bugs and edge cases we've found with IPv4 thirty years ago are all brand new wild country problem with IPv6.