AS21928
Operated by T-MOBILE-AS21928 - T-Mobile USA, Inc..
Summary
- // analyst note
- US mobile subscriber traffic; CGNAT means a single IP maps to many subscribers and is dynamically reassigned — avoid per-IP attribution. Home Internet/Fiber are also CGNAT.
- // security note
- CGNAT mobile network — one IP commonly maps to many subscribers and is dynamically reassigned; Home Internet/Fiber also use CGNAT.
About this ASN.
AS21928 is T-Mobile USA's autonomous system, registered under ARIN, with the IRR as-name "TMobileUSA" and the description "T-Mobile USA IP Backbone." It carries the company's US cellular handset traffic and, increasingly, its fixed-wireless and fiber consumer products — T-Mobile Home Internet and T-Mobile Fiber. The network holds roughly 12–13 million IPv4 addresses (prefix counts vary widely across aggregators) plus a sizable IPv6 footprint, and historically takes transit from carriers including Level 3/Lumen (AS3356), AS3549, and AS6461. After the 2020 Sprint merger, Sprint's legacy ASNs — notably AS1239 and AS6296 — folded into the T-Mobile family, so analysts may still see those numbers in historical paths. The central triage caveat is carrier-grade NAT on the mobile side: a single public IP routinely represents many subscribers and is dynamically reassigned, defeating point-in-time IP-to-user attribution. T-Mobile Home Internet and T-Mobile Fiber also sit behind CGNAT, which compounds the shared-IP ambiguity for what looks like fixed-line traffic. Sprint Corporation and T-Mobile US completed their all-shares merger on April 1, 2020, with T-Mobile as the surviving brand.
- Operator
- T-Mobile USA, Inc. [Confirmed] — ARIN RDAP/WHOIS
- Country / RIR
- US, ARIN [Confirmed] — ARIN RDAP
- Allocated
- 2002-06-12 (ARIN RegDate; updated 2012-02-24) [Confirmed] — ARIN RDAP
- Org status
- active; Sprint + T-Mobile US merger (~$26B, announced 2018-04-29, closed 2020-04-01), T-Mobile surviving brand — en.wikipedia.org
Security/abuse context
CGNAT mobile network — one IP commonly maps to many subscribers and is dynamically reassigned; Home Internet/Fiber also use CGNAT, compounding shared-IP ambiguity. Third-party mobile/bittorrent/crawler tags reflect a large consumer pool. No notable distinct public abuse-dataset ranking found as of 2026-06-06 — ipinfo.io
Network & routing
- Network type
- mobile-carrier [Confirmed] — operator + IRR (RADB "T-Mobile USA IP Backbone")
- Size
- ~491–1,848 IPv4 prefixes (sources disagree; ~12.2M–13.1M addrs), ~410 IPv6 — bigdatacloud.com / ipqualityscore.com / bgp.he.net (2026-05/06)
- Routing/peering
- largely a leaf eyeball network (~11–12 IPv4 peers); historical upstreams AS3356, AS3549, AS6461 (RADB); PeeringDB record exists (net/3592) but sparse; RPKI unknown — bgp.he.net, ipinfo.io
- Notable usage
- T-Mobile USA's mobile/IP backbone; also carries T-Mobile Home Internet (FWA) and T-Mobile Fiber (FTTH) — t-mobile.com
- Related ASNs
- AS1239 (Sprint, legacy), AS6296 (Sprint PCS, legacy), plus other T-Mobile ASNs
- Analyst note
- Encountered as US mobile subscriber traffic; CGNAT means a single IP maps to many subscribers and is dynamically reassigned, so avoid per-IP attribution. Home Internet/Fiber are also CGNAT.
What this network routes.
- 100.128.0.0/9
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Who it talks to.
| ASN | Operator | Role |
|---|---|---|
| AS6461 | ZAYO-6461 - Zayo Bandwidth | upstream |
| AS3356 | LEVEL3 - Level 3 Parent, LLC | upstream |
| AS174 | COGENT-174 - Cogent Communications, LLC | upstream |
| AS6939 | HURRICANE - Hurricane Electric LLC | upstream |
| AS58453 | CMI-INT-HK - China Mobile International Limited | upstream |
| AS9002 | RETN-AS RETN Limited | upstream |
| AS35280 | F5 F5 Networks SARL | upstream |
| AS4230 | AS4230 - CLARO S.A. | upstream |
| AS137409 | GSLNETWORKS-AS-AP - GSL Networks Pty LTD | upstream |
| AS37468 | Angola Cables - Angola Cables | upstream |
| AS60068 | CDN77 Datacamp Limited | upstream |
| AS18678 | AS18678 - INTERNEXA S.A. E.S.P | upstream |
| AS33891 | CORE-BACKBONE Core-Backbone GmbH | upstream |
| AS7195 | AS7195 - EDGEUNO S.A.S | upstream |
| AS1031 | PEER1-1031 - PEER 1031 LLC | upstream |
| AS6057 | AS6057 - Administracion Nacional de Telecomunicaciones | upstream |
| AS32621 | TCV-511 - Twin City VoIP, Inc. | upstream |
| AS394256 | CLOUDSINGULARITY - Tech Futures Interactive Inc. | upstream |
| AS64126 | AS64126 - DOMINICAN TELECOM PRIME, DTP, S.R.L. | upstream |
| AS6424 | EDGOO EDGOO NETWORKS UNIPESSOAL LDA | upstream |