I agree (irony warning!) those IPv4 addresses would be best used for Hue lamps or something, no?

On a more serious note, I've been watching IPv6 "rolling out" since 2004 (which is when I had an active role in mobile network planning), and I'm somewhat saddened that we haven't yet been able to switch over completely (even if it is somewhat more awkward to shout IPv6 addresses across the room, which was one of the arguments one of my colleagues had against it.)

thats why we use DNS more effectively. A tool is only useful is if it implemented correctly. it would be easier and faster with well thought out DNS to yell a name across the room. (would have been my response to that silly argument)

Yeah, well, DNS can't be used for core network configs - only to expose them to lesser networks :)

To clarify those of you who haven't worked in a telco core: You can't rely on DNS to configure core network gear. EVERYTHING of consequence is done using IP addresses, DNS is a convenience/comfort service for outer layers and end users.

and there are ... so many obscure and strange problems that are caused by a hiccup or simply misconfigured DNS... not saying you shouldn't use it, just ... don't claim it's the ultimate cool-aid that resolves everything.

You can configure with DNS but it just needs to resolve and store the resolved address rather than storing the hostname

Correct me if my understanding of internet routing is wrong, but the IP blocks were not out of service during the experiment. Only that a router(s) was advertising that it would accept traffic for those addresses. It would cause traffic to be sent through AS15562 during the time, which may have been suboptimal at times, but eventually would have reached the destination without visitors being aware of the game being played behind the scenes.

Your understanding is mostly correct. Whether or not traffic directed to any of the /24s involved "would have eventually reached the destination" is undetermined (and possibly irrelevant), meaning it's both possible and not possible. We simply don't know. Speaking strictly about "internet routing" (BGP in this case), it is 100% possible for an announcement to send traffic through an AS which literally dumps it on the floor -- it's happened many times over the years (the Pakistan/Youtube one was noticed by many): https://en.wikipedia.org/wiki/BGP_hijacking#Public_incidents

The question is whether or not the /16 (of which most of the advertised/withdrawn /24s make up) was used by actual devices, or if it's address space NTT has yet to use. If it is assigned to NTT but unused space, then effectively no harm done. If it's actually used IP space, then that would be very inappropriate.

Why not both? (which is actually what happened here)