On June 8th (the World IPv6 Day) you’ll see Facebook, Google and a number of other web sites reachable over IPv4 and IPv6 (more accurately: the DNS records for their web sites will have both A and AAAA records). No problem … unless your users have misconfigured workstations and you haven’t deployed IPv6 throughout your network yet (not many have).
Users with broken IPv6 connectivity will experience long delays connecting to major public web sites. Their workstations will try to reach the content over IPv6 first and will have to experience a TCP-level timeout before retrying to get the same content over IPv4. Guess whose phone will ring … and what the problem description will be 😉
June 8th: the day your phone won’t stop ringing