What is aut-num?

An aut-num is the RPSL object describing an autonomous system in an Internet Routing Registry: its number, name, contacts and routing policy.

The object's key is the AS number itself, written like AS64500. Typical attributes are as-name: (a short label), admin-c: and tech-c: (references to contact objects), mnt-by: (the maintainer allowed to change it), and member-of: (as-sets the AS asks to join). Policy is expressed with import: and export: lines, or mp-import: and mp-export: for IPv6 and other address families. An export line such as "to AS64501 announce AS64500:AS-CUSTOMERS" documents which as-set a neighbour should expand to build a filter for you.

When a Regional Internet Registry assigns an ASN, it creates the aut-num in its own database, usually maintained jointly by the RIR and the holder, so you will normally edit an existing object rather than create one. In practice, few networks keep detailed import and export policy accurate, and almost nobody generates router configuration from it. What still matters is the export towards upstreams and peers, because that is where they look up your as-set name, and correct contact details so other operators can reach you during an incident. A common confusion is to expect an aut-num to list the prefixes an AS announces: it doesn't. That is the job of route and route6 objects, which name the AS in their origin: attribute. The IRR, RPSL and AS-SETs lesson shows aut-num objects alongside the other RPSL classes.