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Bogon

published · September 12, 2026

A bogon is an IP address that should not appear on the public Internet: private, reserved or documentation space, or a block no registry has allocated to anyone.

A bogon is an IP address that should not appear as the source of traffic on the public Internet: private space (10/8, 172.16/12, 192.168/16), loopback, link-local, the carrier-grade NAT block, the documentation ranges, multicast and class E, and, more interestingly, unallocated space — blocks that exist on the map but that no regional Internet registry has handed to any operator. A packet claiming to come from one is forged or misrouted, and a request from one deserves no benefit of the doubt.

What Spaw answers

Two fields cover the two halves. Private, reserved and documentation space answers reason: reserved_range: every other field is null and the lookup is free, because there is nothing to say about it. Unallocated space answers is_unallocated: true, evaluated against the five registries' daily delegated statistics, and it is the heaviest feed signal in the score at +100 — such an address has no legitimate owner to be behaving on behalf of. The flag is null rather than false until every registry file covering that address family is installed, so a partial set of registries never fabricates a negative.

What it does not mean

Unallocated is not the same as unused. Space can be allocated and dark, or reserved by a registry for a future purpose; the flag says only that the registries recorded no allocation or assignment on the day the files were read.

Related

markdown version: /glossary/bogon.md

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