They don't
have to give it back, of course.
If anything, the first organization to have netblocks yanked out from under them should be the US DoD. As I mentioned a few days ago [0]:
> There are also large portions of the 13 /8s (218 million IPs!) assigned to the US Department of Defense [5] that you wouldn't need to scan since there are no routes to them at all: the 11.0.0.0/8, 22.0.0.0/8, 26.0.0.0/8, 28.0.0.0/8, 29.0.0.0/8, 30.0.0.0/8, and 33.0.0.0/8 networks are, for all intents and purposes, "missing" from the public Internet.
> Additionally, there are only four /24s in 21.0.0.0/8 that are reachable from the public Internet. Out of the 16,777,216 IP addresses that make up 7.0.0.0/8, only 255 are reachable (7.7.7.0/24) [6].
Just because we can't "see" them or get to them doesn't mean they aren't using them, though.
Yes, it sucks that we're out of IPv4 addresses but we've known this was coming for, what, 20+ years? The quicker we all get moved over to IPv6, the quicker we can forget about it.
(Disclosure: I've had a static IP from 44/8 for ~25 years and I don't wanna give it back.)
[0]: https://news.ycombinator.com/item?id=16893669
If anything, the first organization to have netblocks yanked out from under them should be the US DoD. As I mentioned a few days ago [0]:
> There are also large portions of the 13 /8s (218 million IPs!) assigned to the US Department of Defense [5] that you wouldn't need to scan since there are no routes to them at all: the 11.0.0.0/8, 22.0.0.0/8, 26.0.0.0/8, 28.0.0.0/8, 29.0.0.0/8, 30.0.0.0/8, and 33.0.0.0/8 networks are, for all intents and purposes, "missing" from the public Internet.
> Additionally, there are only four /24s in 21.0.0.0/8 that are reachable from the public Internet. Out of the 16,777,216 IP addresses that make up 7.0.0.0/8, only 255 are reachable (7.7.7.0/24) [6].
Just because we can't "see" them or get to them doesn't mean they aren't using them, though.
Yes, it sucks that we're out of IPv4 addresses but we've known this was coming for, what, 20+ years? The quicker we all get moved over to IPv6, the quicker we can forget about it.
(Disclosure: I've had a static IP from 44/8 for ~25 years and I don't wanna give it back.)
[0]: https://news.ycombinator.com/item?id=16893669