Summary

  • ARIN's Origin AS field was optional and allowed an address-block holder to list ASNs from which the addresses might originate.
  • ARIN retired the field on 28 July 2025; historical values are not substitutes for current IRR policy, RPKI authorization or evidence of an operating route.

A hint with a defined source

ARIN's own retirement notice preserves the field's original scope. The holder could record one or more ASNs from which the block “may originate.” That wording matters. It describes supplied registration data, not a result observed by ARIN from the control plane.

The distinction was useful even before retirement. An Origin AS value could guide a search or reveal what a holder expected, but it was not a signed authorization and did not establish that the listed ASN was announcing the block. It could be empty, incomplete or stale.

Retirement changes the evidence clock

ARIN removed Origin AS on 28 July 2025 under Policy ARIN-2021-8, explaining that newer routing-security services had reduced its utility. The field can nevertheless persist in historical exports, cached datasets and analyst systems. A value surviving there is evidence about what an older directory record contained, not proof of the current route.

The replacement is not one universal field. ARIN defines a ROA as a cryptographically signed object identifying which ASN is authorized to originate a prefix, with a maximum length. ARIN's IRR stores declared routing-policy objects. Those records answer authorization and declared-policy questions; neither turns the retired Whois value into proof of a live route.

A defensible routing claim

Start by recording the historical Origin AS value, its source snapshot and date. Then query current IRR and RPKI data, preserving their own timestamps and validation states. If the question concerns a live route, say explicitly that the supplied registry, IRR and RPKI records do not by themselves answer it.

Even this combined evidence has limits: a ROA records authorization, an IRR object records declared policy, and the retired field records a holder-supplied possibility. A defensible conclusion keeps those claims separate.

Sources