Autonomous system detail  ·  US flag US

AS4

Announced

Operated by University of Southern California, US flag US.

Summary

// analyst note
Single-digit ASN with outsized historical weight (Postel/IANA/RFC Editor/B-root); still actively routed by ISI behind Los Nettos. AS4 ↔ AS226 ↔ AS47 form the USC/ISI cluster.
// security note
NEUTRAL/DATED: no notable public abuse signal found as of 2026-06-07; clean research network.
IPv4 prefixes
45
~70.7K addresses
IPv6 prefixes
9
announced
Peer networks
11
5 up · 0 down
IANA block
1-1876
Assigned by ARIN
[ 01 ] — Context

About this ASN.

Updated  ·  Confidence: High  ·  4 sources  ·  How this page is checked

AS4 is a legacy single-digit allocation registered under ARIN to the University of Southern California's Information Sciences Institute (ISI), one of the most historically significant institutions on the Internet. ISI was the institutional home of Jon Postel — RFC Editor and director of IANA for roughly three decades until his death in 1998 — ran IANA until ICANN was created in 1998, continued operating the RFC Editor until 2009, developed DNS (Paul Mockapetris), and operates the DNS B-root server. That weight is historical; the current holder is USC/ISI, and AS4 still actively announces about 47 IPv4 prefixes and 7 IPv6 prefixes (~67,000 IPv4 addresses), importing from AS226 (Los Nettos) and announcing to AS-LOSNETTOS. For triage, AS4, AS226 (Los Nettos), and AS47 (USC main campus) form the USC/ISI cluster; encountering AS4 indicates ISI research network space behind Los Nettos. The ARIN RegDate of 1984-02-22 is the registry date and may be an early refresh. RPKI is weak (one valid IPv6, one invalid IPv4, remainder unknown) — a hygiene note. No notable public abuse signal was found as of June 2026.

Operator
University of Southern California / Information Sciences Institute (ARIN OrgId USC-32, Marina del Rey, CA) [Confirmed] — ARIN RDAP
Country / RIR
US, ARIN [Confirmed]
Allocated
ARIN ASN RegDate 1984-02-22 (registry date; may be early refresh; org RegDate 1984-02-22) [Confirmed for shown date]
Org status
active — isi.edu

Security/abuse context (NEUTRAL, DATED)

no notable public abuse signal found as of 2026-06-07; clean research network — bgp.he.net

Network & routing

Network type
research / education [Confirmed]
Size
~47 IPv4 prefixes, 7 IPv6 (~67,072 IPv4 addrs) — bgp.he.net / bgp.tools (2026-06)
Routing/peering
1 IX; actively announcing; imports from AS226 (Los Nettos), announces to AS-LOSNETTOS; RPKI valid 1 (IPv6), invalid 1 (IPv4), remainder unknown — bgp.he.net
Notable usage
[historical] USC/ISI — home of Jon Postel; ran IANA until ICANN (1998); ran the RFC Editor until 2009; developed DNS (Mockapetris); operates DNS B-root. [current] ISI research network routed behind Los Nettos — isi.edu
Related ASNs
AS226 (Los Nettos — upstream/peer); AS47 (USC-AS, USC main campus, OrgId USC-6 — sibling) [Confirmed]
Analyst note
Single-digit ASN with outsized historical weight (Postel/IANA/RFC Editor/B-root); still actively routed by ISI behind Los Nettos. AS4 ↔ AS226 ↔ AS47 form the USC/ISI cluster.
[ 02 ] — Announced prefixes

What this network routes.

54 prefixes total · as observed by RouteViews at 2026-09-20 · one collector view, not a global census
// IPv4 prefixes45
  1. 128.9.192.0/18/18
  2. 128.9.0.0/20/20
  3. 128.9.112.0/20/20
  4. 128.9.128.0/20/20
  5. 128.9.144.0/20/20
  6. 128.9.160.0/20/20
  7. 128.9.176.0/20/20
  8. 128.9.32.0/20/20
  9. 128.9.48.0/20/20
  10. 128.9.64.0/20/20
  11. 128.9.80.0/20/20
  12. 128.9.96.0/20/20
  13. 103.39.120.0/23/23
  14. 128.9.28.0/23/23
  15. 170.79.218.0/23/23
  16. 128.9.113.0/24/24
  17. 128.9.117.0/24/24
  18. 128.9.122.0/24/24
  19. 128.9.123.0/24/24
  20. 128.9.127.0/24/24
  21. 128.9.16.0/24/24
  22. 128.9.17.0/24/24
  23. 128.9.18.0/24/24
  24. 128.9.19.0/24/24
  25. 128.9.26.0/24/24
  26. 128.9.30.0/24/24
  27. 128.9.31.0/24/24
  28. 128.9.34.0/24/24
  29. 128.9.35.0/24/24
  30. 128.9.36.0/24/24
  31. 128.9.37.0/24/24
  32. 128.9.38.0/24/24
  33. 128.9.40.0/24/24
  34. 128.9.43.0/24/24
  35. 128.9.44.0/24/24
  36. 128.9.46.0/24/24
  37. 128.9.47.0/24/24
  38. 165.140.12.0/24/24
  39. 165.140.14.0/24/24
  40. 198.32.16.0/24/24
  41. 206.117.27.0/24/24
  42. 206.117.31.0/24/24
  43. 206.117.37.0/24/24
  44. 206.117.6.0/24/24
  45. 43.240.64.0/24/24
// IPv6 prefixes9
  1. 2606:d5c0::/32/32
  2. 2804:3edc::/32/32
  3. 2c0f:fdd0::/32/32
  4. 2001:1878:401::/48/48
  5. 2001:1878:402::/48/48
  6. 2001:1878:403::/48/48
  7. 2001:1878:404::/48/48
  8. 2001:500:202::/48/48
  9. 2606:d5c0::/48/48
[ 03 ] — Notable peers & upstreams

Who it talks to.

11 observed neighbours
// Notable connections11 of 11 observed

Neighbours observed by RouteViews at 2026-09-20, lowest ASN first. Relationships are inferences from the CAIDA AS Relationships Dataset, 2026-08-01, and establish no commercial arrangement; a dash means the inference did not resolve.

ASNOperatorRole
AS174 Cogent Communications, LLC upstream
AS226 Los Nettos (c/o USC-ITS) upstream
AS567 Los Nettos Regional Network (operated by USC Information Technology Services) upstream
AS10886 — upstream
AS266306 — upstream
AS37358 — —
AS133296 — peer
AS152709 — —
AS266625 — —
AS328434 — —
AS400215 — peer
Neighbours observed via public BGP collectors; not a complete peering list.