What is inetnum?

An inetnum is the database object a Regional Internet Registry uses to record who holds a range of IPv4 addresses; its IPv6 equivalent is inet6num.

Both are RPSL objects, used by RIPE NCC, APNIC, AFRINIC and other databases in the same family; ARIN's database uses its own format. The key of an inetnum is a range written as two addresses, such as 192.0.2.0 - 192.0.2.255, while an inet6num uses prefix notation, such as 2001:db8::/32. Typical attributes are netname:, country:, org:, contact references (admin-c:, tech-c:), a status: describing how the space was given out (for example allocated to a provider or assigned to an end user), and maintainer references. mnt-by: names the maintainer who may change the object itself, mnt-lower: controls who may create more-specific inetnums inside it, and mnt-routes: controls who may create route objects for it.

That last point is why inetnums matter for routing. In an authoritative registry, creating a route or route6 object needs authorisation from the maintainer of the address space, so a route object there means the space holder agreed to that origin AS. Non-authoritative IRRs have no inetnums to check against, which is how stale or unauthorised route objects end up in them. Engineers also meet inetnums whenever they run whois on an address: the answer is the inetnum (or ARIN's equivalent), showing which organisation holds the range and how to contact it. It is registration data only and does not say where the range is routed. The IRR, RPSL and AS-SETs lesson explains how inetnum maintainers control route object creation.