AS51

AS51 is a legacy U.S. government allocation registered under ARIN to Headquarters, USAISC (the US Army Information Systems Command), administered under the ARIN org HEADQU-3 at Fort Huachuca, AZ, with the DNIC-AS naming convention denoting the Defense Network Information Center lineage. It is one of a very large pool of legacy US Army/DoD ASNs held by HEADQU-3, which administers several hundred ASNs including AS13, AS54, the AS523-series, and AS1450–1546. The ASN appears dormant in 2026: no prefix origination is observed. The ARIN RDAP RegDate is 1985-10-09. For triage this is a dark military legacy ASN — like AS48, an AS51 origin appearing in live BGP would be unexpected, and its registry presence should be treated as administrative only. No notable public abuse signal was found as of June 2026.

Operator

Headquarters, USAISC (US Army Information Systems Command; ARIN OrgId HEADQU-3, Fort Huachuca, AZ 85613) [Confirmed] — ARIN RDAP

Country / RIR

US, ARIN [Confirmed]

Allocated

ARIN RDAP RegDate 1985-10-09 [Confirmed] — ARIN RDAP

Org status

legacy/dormant (registered, not announcing)

Security/abuse context (NEUTRAL, DATED)

no public abuse signal; dormant — bgpview.io

Network & routing

Network type

government / military (US Army) [Confirmed]

Size

appears dormant; no observed prefix origination — bgpview.io / networksdb.io (2026-06)

Routing/peering

dormant; RPKI n/a — bgpview.io

Notable usage

[historical] one of several hundred legacy US Army/DoD ASNs under HEADQU-3 (incl. AS13, AS54, AS523-series, AS1450–1546) — army.mil

Related ASNs

AS13 (US Army USAISC), AS54, AS1501/AS1544 and other HEADQU-3 ASNs [Confirmed]

Analyst note

A dark military legacy ASN. Like AS48, an AS51 origin in live BGP would be unexpected; treat registry presence as administrative only.