AS3356

AS3356 is one of the largest Tier-1 IP backbones in the world, registered to Level 3 Parent, LLC and operated today by Lumen Technologies. It is the combined backbone that resulted from years of consolidation — Level 3 absorbed Global Crossing, TW Telecom, WilTel, and Broadwing (the old Global Crossing/Level 3 AS3549 was folded into AS3356 around 2013), and Level 3 itself merged with CenturyLink in 2016–2017. As a settlement-free Tier-1, AS3356 sells transit globally and routinely sits in the middle of AS paths rather than originating end-user content. Its scale shows in CAIDA AS Rank, where it is #1 globally: a customer cone of roughly 54,887 ASNs, ~935,384 prefixes, and ~2.28 billion addresses, with a transit degree around 6,549 and thousands of direct customers. Because it is a backbone, abuse signals attach to downstream customers, not to AS3356 itself — seeing AS3356 in a path simply means the traffic crossed Lumen's network. Its peering posture is selective, as is typical for a Tier-1 protecting settlement-free relationships.

Operator

Level 3 Parent, LLC (Lumen Technologies) [Confirmed] — ARIN RDAP/WHOIS

Country / RIR

US, ARIN [Confirmed] — ARIN RDAP

Allocated

2000-03-10 [Confirmed] — ARIN RDAP (the org "Level 3 Parent, LLC" RegDate 2018-02-06 reflects a later Lumen reorg, not the AS allocation)

Org status

Level 3 + CenturyLink merger (Oct 31, 2016 agreement; closed 2017; ~$26.50 cash + 1.4286 CTL shares per Level 3 share); CenturyLink rebranded to Lumen Technologies Sept 2020; absorbed Global Crossing/TW Telecom/WilTel/Broadwing; AS3549 folded ~2013; legacy AS209; agreed to sell consumer fiber (Quantum Fiber) to AT&T — sec.gov, comsoc.org

Security/abuse context

as a transit backbone it originates little end-user content; abuse signals attach to downstream customers, not AS3356. No notable standalone abuse signal as of 2026-06-03

Network & routing

Network type

transit-backbone (Tier-1) [Confirmed] — CAIDA + bgp.tools

Size

CAIDA AS Rank #1 globally — customer cone ~54,887 ASNs / ~935,384 prefixes / ~2,279,334,944 addresses; transit degree ~6,549; ~6,478 customers, ~74 peers — asrank.caida.org/asns/3356 (2026-05)

Routing/peering

selective (Tier-1; restrictive to new settlement-free peers); RPKI validating ROV — bgp.tools

Notable usage

global Tier-1 IP transit backbone (merged Level 3 + CenturyLink); peers with ~6,585 networks — lumen.com

Related ASNs

AS3549 (former Global Crossing/Level 3, folded in); AS209 (legacy CenturyLink/Qwest)

Analyst note

Seen in the MIDDLE of AS paths as transit, almost never as an origin. Its presence means the path traversed Lumen's backbone.