240.0.0.0/4

This block is reserved by the IPv4 protocol and is not assigned for normal networks. Historically it was held aside for future use, and many operating systems and network devices still treat it as unusable.

This block is not publicly routable. It should not be used for ordinary unicast traffic on the Internet or inside production networks unless a very specific platform and lab plan says otherwise.

A system administrator is most likely to see it in malformed logs, scans, packet captures, old examples, or experiments. In normal operations it is usually a sign of bad input, a parser issue, or intentionally synthetic test data.

Firewall tip: reserved 240.0.0.0/4 addresses are normally treated as bad IPv4 addresses. If they appear as source, destination, or forwarded traffic on an Internet-facing firewall, the usual action is to drop them.