Comment by inopinatus

Not a counterexample exactly, but your remark reminded me of this eldritch horror: https://blog.cloudflare.com/cloudflare-servers-dont-own-ips-...

TLDR: Cloudflare is using five bits from the port number as a subnetting & routing scheme, with optional content policy semantics, for hosts behind anycast addressing and inside their network boundary.

Filed in my bookmarks under "abominations".