Bogons are legitimate IP addresses that have not yet been allocated or delegated by the Internet Assigned Numbers Authority (IANA) or a delegated Regional Internet Registry (RIR). This includes:
- IPv4 fullbogons: Which encompasses the traditional IPv4 bogon prefixes, as well as prefixes that have been allocated to RIRs but have not yet been assigned to mailbox providers or end users.
- IPv6 fullbogons: Which includes all IPv6 prefixes that have not been allocated to RIRs and that have not been assigned by RIRs to mailbox providers or end users.
Mailbox providers typically block bogons because they are assumed to be caused by accidental or malicious misconfiguration.