Security - bogons

Bogons are bogus or fake IP addresses. Bogons include IP addresses that are not in any range allocated or delegated by the Internet Assigned Numbers Authority (IANA) or a delegated regional Internet registry (RIR). The areas of unallocated address space are called the bogon space.

Bogons also include address ranges reserved for private networks loopback interfaces, and link-local addresses, such as:

Many ISPs and end-user firewalls automatically filter and block bogons, because they have no legitimate use, and usually are the result of accidental misconfiguration or malicious intent.

https://en.wikipedia.org/wiki/Bogon_filtering