It's not that different to v4. Broadcast domains are an L2 concept and still exist (although L3 broadcast doesn't; there's just multicast). IPsec isn't really b

It's not that different to v4. Broadcast domains are an L2 concept and still exist (although L3 broadcast doesn't; there's just multicast). IPsec isn't really built in, it was just developed for v6 initially. It uses the exact same address-family-agnostic socket and name resolution APIs as v4 does, so for most functionality the same code handles both. You don't need to rearchitect your network either, because v6 fundamentally works in exactly the same way v4 does. All you need to do is deploy a v6 /64 everywhere you have a v4 /24 (or /22 or whatever). There's really not much that's different between them at all... and making v6 64 bits wouldn't have helped either, because that would have the same compatibility issues that v6 does while also not being big enough. It'd be pretty silly to go through all this to deploy a new L3 protocol, only to then have to do it again because we didn't make it big enough the first time.