Autonomous system detail  ·  US flag US

AS104

Announced

Operated by University of Colorado at Boulder, US flag US.

Summary

// analyst note
Active university network with ~2 peers and 2 upstreams; appears in traceroutes through Boulder. Legacy institutional, low risk. ARIN RDAP RegDate 1987-04-09 (Confirmed).
// security note
NEUTRAL/DATED: no notable public abuse signal found as of 2026-06-09; clean R&E network.
IPv4 prefixes
21
~95.2K addresses
IPv6 prefixes
4
announced
Peer networks
3
2 up · 0 down
IANA block
1-1876
Assigned by ARIN
[ 01 ] — Context

About this ASN.

Updated  ·  Confidence: High  ·  2 sources  ·  How this page is checked

AS104 is a legacy spring-1987 allocation registered under ARIN to the University of Colorado at Boulder (Information Technology Services, Boulder, CO; abuse contact abuse@colorado.edu), carrying the handle "COLORADO-AS." It is the campus AS for CU Boulder, announcing the legacy 128.138.0.0/16 Class B network among others (also 198.11.16.0/20 and 192.12.238.0/24), with roughly two peers and two upstreams and about 77 hosted domains across 36 IPs. This is a flagship research-university allocation from the original AS block and appears in traceroutes through Boulder. The ARIN RDAP RegDate is 1987-04-09 (Confirmed). For triage this is an active university network — a clean, low-risk legacy institutional allocation. No notable public abuse signal was found as of June 2026.

Operator
University of Colorado at Boulder (Information Technology Services, Boulder, CO) [Confirmed] — ARIN RDAP
Country / RIR
US, ARIN [Confirmed]
Allocated
ARIN RDAP RegDate 1987-04-09 [Confirmed] — ARIN RDAP
Org status
active

Security/abuse context (NEUTRAL, DATED)

no notable public abuse signal found as of 2026-06-09; clean R&E network — ipinfo.io

Network & routing

Our research recorded 3 IPv4 prefixes; RouteViews currently observes 21.
Network type
research / education (university) [Confirmed]
Size
includes 128.138.0.0/16, 198.11.16.0/20, 192.12.238.0/24; ~77 hosted domains across 36 IPs — IPinfo (2026-06)
Routing/peering
active; ~2 peers, ~2 upstreams; RPKI unknown — ipinfo.io
Notable usage
[current] The campus AS for the University of Colorado Boulder, announcing the legacy 128.138.0.0/16 Class B network; a flagship research-university allocation from the original AS block — colorado.edu
Related ASNs
none specifically confirmed for this profile
Analyst note
Active university network with ~2 peers and 2 upstreams; appears in traceroutes through Boulder. Legacy institutional, low risk.
[ 02 ] — Announced prefixes

What this network routes.

25 prefixes total · as observed by RouteViews at 2026-09-20 · one collector view, not a global census
// IPv4 prefixes21
  1. 128.138.0.0/16/16
  2. 129.19.192.0/18/18
  3. 129.19.240.0/20/20
  4. 198.11.16.0/20/20
  5. 146.5.20.0/22/22
  6. 192.12.238.0/24/24
  7. 192.12.240.0/24/24
  8. 192.12.241.0/24/24
  9. 192.12.242.0/24/24
  10. 192.12.244.0/24/24
  11. 192.12.245.0/24/24
  12. 198.59.51.0/24/24
  13. 198.59.52.0/24/24
  14. 198.59.54.0/24/24
  15. 198.59.55.0/24/24
  16. 198.59.7.0/24/24
  17. 198.59.70.0/24/24
  18. 198.59.81.0/24/24
  19. 198.59.82.0/24/24
  20. 198.59.83.0/24/24
  21. 204.228.80.0/24/24
// IPv6 prefixes4
  1. 2620:18f::/32/32
  2. 2401:eee0:1c0::/42/42
  3. 2401:eee0:200::/42/42
  4. 2001:468:501::/48/48
[ 03 ] — Notable peers & upstreams

Who it talks to.

3 observed neighbours
// Notable connections3 of 3 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
AS3356 Level 3 Parent, LLC (Lumen Technologies) upstream
AS14041 — upstream
AS149433 — —
Neighbours observed via public BGP collectors; not a complete peering list.