Facebook makes extensive use of IPv6 internally. As you suggested, EC2's lack of support is the issue. Edit: here are the slides from Facebook's presentation

Facebook makes extensive use of IPv6 internally. As you suggested, EC2's lack of support is the issue. Edit: here are the slides from Facebook's presentation to the IPv6 World Congress in March about their internal IPv6 use. If IPv6 interests you, they're definitely worth a read: http://www.internetsociety.org/deploy360/wp-content/uploads/2014/04/WorldIPv6Congress-IPv6_LH-v2.pdf http://www.internetsociety.org/deploy360/wp-content/uploads/...