Todd Hollmann brought the Facebook IPv6 story into the data center and the different stages of IPv6 deployment. Facebook’s current data center fabric is all IPv6, but a few years ago, the team faced an interesting and unexpected dilemma: We had run out of 10.0.0.0/8 space! Assigning large prefixes to each rack made all the tooling and summarization easier, but it was wasteful. Facebook tried to model IPv6 like IPv4 where possible, but it turns out it wasn’t really possible because of the lack of proper support throughout the protocols. Further, Facebook decided to allocate a /64 network per rack, which seems a little excessive but winds up being efficient in terms of routing table lookups in ASICs and ECMP implementation for IPv6. Finally, Todd covered the challenges on the management plane with IPv6; traceroute, ping, SNMP, SSH, and other tools all initially had significant bugs with their IPv6 implementation.