AS400

AS400 is a legacy autonomous system number registered under ARIN to Air Force Systems Networking (ARIN org handle 7ESG), a U.S. Air Force / Department of Defense network entity based at Maxwell AFB–Gunter Annex, Montgomery, Alabama, with administrative, technical, and abuse contact handled by DISA-Columbus (Defense Information Systems Agency) in Whitehall, Ohio. AS400 does not carry its own discrete RDAP autnum object; an ARIN RDAP query for autnum 400 resolves to the shared block record AFCONC-BLOCK1-AS (handle AS379), which spans AS379–AS508 and was registered on 1989-08-04. AS400 inherits its registrant, contacts, address, top-level registration event, and "active" status from that block record. Unlike some dormant siblings, AS400 is actively routing: RIPEstat and third-party BGP sources show it announcing a single IPv4 prefix, 132.3.104.0/21 (2,048 addresses), with near-full IPv4 RIS visibility (322 of 323 peers) and no IPv6 presence; its historical first-seen prefix was the much larger 143.158.0.0/16 (2000-08-18), so the announced footprint has shrunk/shifted since 2000. It is a single-homed stub reached through the DoD network fabric with a single observed neighbor in the DoD Network Information Center / DISA range (bgp.he.net and the operator-angle pass report AS27064; the community-angle pass reports AS27066 — both DoD NIC handles, so the exact neighbor ASN is left as a small unresolved range). No PeeringDB network record exists for AS400 (asn/400 returns 404) and DoD peering is centrally gated via the DISN connection process rather than published per-ASN. No notable public abuse or reputation signal was found as of 2026-07-02 across Spamhaus, AbuseIPDB, and NANOG archives; search results for the literal string "AS400" are dominated by IBM's unrelated AS/400 server platform, which was carefully excluded. CAIDA AS Rank, customer cone, and RPKI validity could not be assessed (CAIDA timed out; RPKI validation was skipped upstream for lack of a prefix parameter) and are recorded as Unknown rather than guessed.

Operator

Air Force Systems Networking (ARIN org handle 7ESG; U.S. Air Force / DoD), administered by DISA. Community research associates the block with the 754th Electronic Systems Group at Gunter Annex [Confirmed for org/7ESG via RDAP; Likely for the 754th ELSG attribution] — https://rdap.arin.net/registry/autnum/400, https://airforce.togetherweserved.com/unit/11470/754th-Electronic-Systems-Group

Country / RIR

US, ARIN [Confirmed] — RIPEstat abuse-contact-finder (authoritative_rir: arin), https://rdap.arin.net/registry/autnum/400

Allocated

1989-08-04 (ARIN RDAP autnum TOP-LEVEL registration event on the AFCONC-BLOCK1-AS block record covering AS379–AS508; NOT an IEEE date — IEEE publishes no ASN registration dates); last changed 2008-06-06 [Confirmed] — ARIN RDAP autnum top-level events[]

Org status

active per ARIN RDAP status (block record active) and confirmed by active third-party BGP routing of one prefix; no operator-official page confirms or denies current operational use of AS400 specifically

[Confirmed for active routing] — https://rdap.arin.net/registry/autnum/400, https://bgp.he.net/AS400

Contacts

DISA-Columbus, 300 North James Road, Whitehall, OH 43213, US — disa.columbus.ns.mbx.arin-registrations@mail.mil, +1-844-347-2457 ext2 (POC handle REGIS10-ARIN); registrant address 501 East Moore Dr., Bldg 884, Rm 1100, Gunter Annex, Maxwell AFB, AL 36114, US

[Confirmed] — https://rdap.arin.net/registry/entity/REGIS10-ARIN, https://rdap.arin.net/registry/autnum/400

Security/abuse context (NEUTRAL, DATED)

no notable public abuse signal found as of 2026-07-02 — not in Spamhaus, AbuseIPDB (all "AS400" hits were unrelated IBM AS/400 hostname artifacts), or NANOG archives; consistent with a small non-transit government network [Likely — absence-of-evidence, not a certified clean record] — https://bgp.tools/as/400, https://www.abuseipdb.com/, https://www.spamhaus.org/

Network & routing

Network type

U.S. government / military network (DoD, U.S. Air Force), administered by DISA; not a commercial ISP, hosting, content, or transit network [Confirmed] — https://rdap.arin.net/registry/autnum/400

Size

one announced IPv4 prefix, 132.3.104.0/21 = 2,048 addresses; 0 IPv6 prefixes. Historical first-seen prefix was 143.158.0.0/16 (2000-08-18), so the announced footprint has shrunk/shifted since 2000 [Confirmed] — RIPEstat routing-status / announced-prefixes (2026-07-02)

Routing/peering

announced with near-full IPv4 visibility (322/323 RIS peers v4; 0/321 v6); observed_neighbours = 1; single-homed stub via DoD NIC/DISA. Upstream/peer reported as AS27064 (bgp.he.net / operator angle) vs AS27066 (community angle) — both DoD NIC handles; exact neighbor ASN unresolved [Confirmed for stub/visibility; Likely for the specific neighbor ASN] — RIPEstat routing-status, https://bgp.he.net/AS400, https://bgp.tools/as/400

Peering policy

none published; no PeeringDB network record for AS400 (asn/400 → 404); DoD/DISA peering centrally gated via the DISN connection process, not per-ASN [Confirmed] — https://www.peeringdb.com/asn/400

RPKI

not assessed — RIPEstat rpki-validation was skipped (no --prefix supplied); no ROA/validity determination available for 132.3.104.0/21 under AS400 from the data gathered [Unknown]

AS rank / customer cone

Unknown — CAIDA AS Rank lookup timed out and was not independently retried; customer cone not available in the RIPEstat payload [Unknown]

Notable usage

no AS400-specific public-facing service documented on any operator-official page; AS400 is one member of the historical AFCONC-BLOCK1-AS Air Force/DoD block (AS379–AS508). bgp.he.net notes it "announces bogons" — a route-object/registration-hygiene note about its prefix, not a corroborated abuse or hijack event [Confirmed for block membership; Likely for the bogon note as single-source] — https://rdap.arin.net/registry/autnum/400, https://bgp.he.net/AS400

Related ASNs

sibling members of the AFCONC-BLOCK1-AS block AS379–AS508 (e.g. AS379, AS385, AS386, AS389–AS391, AS393, AS397, AS398) [Confirmed for block range] — https://rdap.arin.net/registry/autnum/400

Analyst note

legacy DoD/Air Force block-member ASN. RDAP has no discrete autnum for AS400; identity and the 1989-08-04 registration date come from the parent AFCONC-BLOCK1-AS record (handle AS379, startAutnum 379 / endAutnum 508), which correctly applies to AS400. The security angle's caution about the RDAP redirect was resolved: the canonical fetch and routing angle both read the block-record top-level registration event as the applicable first-party allocated_date, so it is recorded, not nulled. Distinguishing fact vs. dormant siblings: AS400 is actively announcing 132.3.104.0/21.