I'm curious what the technology behind it is. There have been some standards based things recently (VXLAN) as well as some non-standards based (OTV, F5 DCI).

I'm curious what the technology behind it is. There have been some standards based things recently (VXLAN) as well as some non-standards based (OTV, F5 DCI). It sounds like VXLAN. VXLAN in short is encapsulating a L2 packet inside a UDP-VXLAN packet and then using multicast to route the packet to multiple switches. The same concepts of subnets still exist, it's just hacking together multiple L2 domains by multicasting between configured switches. The VXLAN header allows for identification between the different networks to specify which actual VLAN it should be mapped to. What's interesting is there are more potential VXLANs than multicast addresses so there is not a mapping between multicast address and VXLAN. As well, the actual VLAN the messages are sent to don't need to match on the other side of the VXLAN. This is all of course assuming Amazon didn't homebrew their own L2 over L3 extension protocol. VXLAN shows promise, so it would be cool, but it is layered with multicast and broadcast complexities.