[londons_explore]

All these things sound to me like their internal network only supports IPV4, and they simply maintain some mapping of which IPV6 address maps to which IPV4 address and they convert packets where needed so the customer sees IPv6 yet all packets flow over the wire as IPv4 with no additional headers (so that MTU doesn't need to be decreased)

[jiggawatts]

To me it feels like the entire thing was engineered with only IPv4 in mind from day one, and a decade into it some customer demanded IPv6 support. So of course, some middle-manager at Microsoft gets assigned the "task" of enabling IPv6, and he dutifully went over to the engineers and asked them to turn it on. Horrified, they tried to explain that it's a ground up re-engineering of their entire network stack, at which point I don't need to have been in the room to play out the conversation that unfolded in that meeting room line by line:

"Just tell me what the minimum set of tasks is to enable IPv6!"

"You don't understand, it's not like turning on a tap! We have to redo all of the infrastructure around networking!"

"Do we need all that? Just tunnel the packets or something!"

"That's not the same thing, that's only supporting IPv6 in a technical sense, it doesn't really mean the same thing as doing it properly, and it won't work long term. It'll have to be ripped out and replaced, but while maintaining backwards compatibility with a jury-rigged IPv6 implementation. It'll be a nightmare!"

"Don't worry about that now, I just need to say that we've enabled IPv6 so I can satisfy this requirement."

"It'll just tick the check box! Nobody will be able to actually use it! Our customers will be confused and support will have to deal with the fallout!"

"Let me deal with that."

Etc, etc...

Translation: I just want my KPIs so that I can get my bonus. I'm quitting before the fallout hits.