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LOGICMONITOR BLOG

Is the Internet Ready for L4S?

Catchpoint tested 330,000+ internet paths in 80+ countries and found ECN bleaching in 12%. See why that puts L4S, gaming, and streaming at risk for users.

6–9 minutes
Denton Chikura

NEWSLETTER

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The quick download

The Internet is 88% ready for L4S, but ECN bleaching still breaks low-latency traffic on the paths users actually travel.

  • Catchpoint’s 2024 campaign found ECN bleaching on 12% of observed paths, roughly 42,000 cases.

  • A single device that clears congestion markings anywhere on the path is enough to break L4S.

  • Bleaching rates varied widely by region, highest in Australia and Oceania at 31%, Europe at 23%, and North America at 15%.

  • Measure L4S readiness across the real networks and transit paths your users depend on, not from the endpoints alone.

L4S (Low Latency, Low Loss, and Scalable Throughput) is designed to reduce congestion-related delay across the Internet. As more operating systems, devices, applications, and access networks support L4S, its benefits increasingly depend on what happens across the entire path between client and server.

That creates an end-to-end readiness challenge. A device and server may support L4S, but a single ISP, transit provider, router, or other intermediary can clear Explicit Congestion Notification (ECN) markings, a problem known as ECN bleaching. When that happens, L4S cannot receive the congestion signals it needs to work.

In 2024, Catchpoint, a LogicMonitor company, conducted a global measurement campaign to understand how often ECN bleaching occurred across observed Internet paths. The results found that 88% of the measured paths were ready for L4S. The 88% figure represents the share of observed paths where ECN bleaching was not detected during the campaign. This article revisits those findings as a baseline for teams evaluating L4S adoption in 2026, troubleshooting inconsistent results, or deciding where additional testing is needed.

The results are a point-in-time snapshot of the paths and vantage points included in the campaign. They remain useful because they show why L4S readiness must be evaluated across the real networks, regions, and transit paths that users depend on.

How L4S depends on ECN

Explicit Congestion Notification (ECN) is a longstanding mechanism in the IP stack that lets routers signal congestion by marking packets instead of dropping them. Rather than waiting for packets to be lost, a router that’s close to congestion can mark traffic so the endpoints slow down in time and avoid the loss.

L4S builds on that mechanism. Routers mark packets with congestion information, the endpoints echo that information back, and the sender adjusts its rate almost immediately. For that feedback loop to work, the ECN markings have to survive every device on the path. A network counts as L4S-ready only when ECN works correctly from end to end.

L4S is a set of Internet protocols and specifications defined through the IETF, including RFC 9330. It aims to reduce latency by enabling faster congestion feedback. For ultra-low latency use cases like VR, multiplayer gaming, and streaming, the impact is significant. Major companies including Apple, Google, Comcast, Nokia, and Deutsche Telekom have shown interest in its implementation.

Why ECN bleaching breaks L4S

ECN bleaching happens when a device along the path clears those markings before they arrive. If bleaching occurs at any point between client and server, the endpoints never see the congestion signal, and L4S becomes unusable. A single bleaching hop anywhere in the path is enough to break it.

ECN and L4S need support from the client and server, but also from every device in between. A single device that clears the ECN bits can prevent the endpoints from receiving the congestion feedback L4S depends on.

Example of ECN bleaching (identified by Catchpoint)

How the measurement campaign worked

The findings come from a global measurement campaign that Catchpoint ran across its global monitoring network. Using Pietrasanta Traceroute, an enhanced traceroute tool, the team ran more than 330,000 traceroutes from over 500 nodes in more than 80 countries. The dataset was last updated May 3, 2024, and was originally prepared for RIPE 88. The campaign tested pairs of nodes in the same region, though not always the same country, and each result logged where congestion markings survived and where a device cleared them.

These findings describe the paths and vantage points included in the campaign. They are not a complete measurement of every Internet path. The results reflect a partial view at one moment in time, and the intent is to prompt collective action to strengthen global networks, not to single out any provider.

ECN bleaching findings

Across the campaign, 12% of observed paths showed ECN bleaching, approximately 42,000 cases out of more than 330,000 traceroutes. Bleaching appeared in every region the campaign measured.

Results from Catchpoint’s ECN bleaching measurements campaign as of May 3, 2024 (Catchpoint)

  • The region with the highest rate of bleaching was Australia and Oceania at 31%, followed by Europe at 23%, then North America at 15%.
  • The three countries with the highest bleaching rates, in order, were Estonia, Israel, and New Zealand.
  • ECN bleaching doesn’t happen on every transit through a given ISP. That means only some devices perform ECN bleaching, either on purpose or by accident.
  • The ISPs introducing bleaching most frequently were Workonline in Africa, Arelion (Telia) in Asia, Europe, North America, and South America, and Vocus in Oceania.

The location and number of vantage points in a region strongly affect these percentages. With only a few probes, traceroutes tend to cross the same incumbent ISP, which shows either 100% or 0% bleaching. This is especially visible in Oceania and Europe, where most of the observed bleaching traced back to two incumbent ISPs, Vocus and Telia.

ECN Bleaching Rates by Region

The charts below break the results down by region, showing how often ECN bleaching appeared on paths within each one. Reading them side by side shows where L4S has room to run today and where bleaching still stands in the way.

Rates in Africa

ECN bleaching percentage across observed paths in Africa during the May 2024 campaign.

Rates in Asia

ECN bleaching percentage across observed paths in Asia during the May 2024 campaign.

Rates in Europe

ECN bleaching percentage across observed paths in Europe during the May 2024 campaign.

Rates in South America

ECN bleaching percentage across observed paths in South America during the May 2024 campaign.

Rates in North America

ECN bleaching percentage across observed paths in North America during the May 2024 campaign.

Rates in Oceania

ECN bleaching percentage across observed paths in Oceania during the May 2024 campaign.

Detailed results: ISPs where ECN bleaching first appears, by continent

This detailed section lists, per continent, the ISPs the campaign found introducing ECN bleaching, along with how many times each one caused it. Counting follows a first-to-bleach rule: an ISP is credited when it’s the first to clear markings on a traceroute, at any hop. The point is to map where bleaching enters the path, not to rank providers.

Rates: ISPs in Africa

AS nameASNCounts
Workonline3727127
TWELVE99 Arelion fka TeliaCarrier129924
MTNNS-AS1663721
LEVEL333568

ISPs introducing ECN bleaching in Africa

Rates: ISPs in Asia

AS nameASNCounts
TWELVE99 Arelion fka TeliaCarrier12993914
LEVEL33356500
CHINANET-BACKBONE No.31 Jin-rong Street4134435
AS64536453353
GLOBE-TELECOM-AS Globe Telecoms4775341
CHINAMOBILE-CN China Mobile Communications Group Co. Ltd.9808333
CHINA169-BACKBONE CHINA UNICOM China169 Backbone4837319
ZEN-NET4229140
GTT-BACKBONE GTT3257125
CMI-INT-HK China Mobile International Limited5845374
IIT-TIG-AS-AP True International Gateway Co. Ltd.3808255
HURRICANE693953
PARTNER-AS1240043
LEONIX-TELECOM Leonix Telecom5062834
BTN-ASN349132
COGENT-17417420
OPENTRANSIT551112
UNICOM-NM-WULANCHABU-IDC UNICOM InnerMongolia province network13900710
GLOBALNET-AS315008
VIETEL-AS-AP Viettel Group75524
OMANTEL-AS ZOI – Zain Omantel International85292
MF-MGSM-AS PJSC MegaFon311332
M1NET-SG-AP M1 NET LTD175472
SKB-AS SK Broadband Co Ltd93182
FLAG-AS Flag Telecom Global Internet AS154122
HOTNET-IL HOTmobile128491
JASTEL-NETWORK-TH-AP JasTel Network International Gateway456291
SINGTEL-AS-AP Singapore Telecommunications Ltd74731
SUMMITCOMMUNICATIONS-BD Summit Communications Ltd587171
CHINATELECOM-CHONGQING-IDC Chongqing Telecom1344201
INDOSAT-INP-AP INDOSAT Internet Network Provider47611
TTNET-MY TIME99301

ISPs introducing ECN bleaching in Asia

Rates: ISPs in Europe

AS nameASNCounts
TWELVE99 Arelion fka TeliaCarrier129916110
IOMART-AS208601395
VODANET International IP-Backbone of Vodafone3209668
NTK IPv6 customers31200656
COGENT-174174374
HURRICANE6939235
ACONET ACOnet Backbone1853159
BITE Bite IP Network13194132
LEONIX-TELECOM Leonix Telecom50628124
ROSTELECOM-AS12389112
M2479009109
ASN-ORANGE-ROMANIA895377
DTAG Internet service provider operations332051
LDCOMNET1555748
CW Vodafone Group PLC127346
ASN-TELENERGO ul. PERKUNA 47 WARSZAWA2080443
GLOBE-TELECOM-AS Globe Telecoms477537
LEVEL3335635
GTT-BACKBONE GTT325726
OPENTRANSIT551125
SEABONE-NET TELECOM ITALIA SPARKLE S.p.A.676224
IONOS-AS856017
CONVERGENZE-AS ISP services in Italy3912010
LIBERTYGLOBAL Liberty Global formerly UPC Broadband Holding aka AORTA68309
Online SAS128766
QUICKLINE Quickline AG156006
AS-BENESTRA Bratislava Slovak Republic55786
NEO-ASN legacy Neotelecoms82186
ARTNET1971555
BTN-ASN34915
RETN-AS90023
BELPAK-AS BELPAK66973
NTL50891
TRANSTELECOM Moscow Russia204851
RCS-RDS 73-75 Dr. Staicovici87081
VTC-AS Russia Vladivostok89201

ISPs introducing ECN bleaching in Europe

Rates: ISPs in North America

AS nameASNCounts
TWELVE99 Arelion fka TeliaCarrier12996675
TWC-12271-NYC12271774
ATT-INTERNET47018754
TWC-10796-MIDWEST10796474
TWC-20001-PACWEST20001456
AS-WHOLESAIL20055455
Alestra S. de R.L. de C.V.11172120
GTT-BACKBONE GTT325779
LEVEL3335676
ZAYO-6461646128
HURRICANE693920
NTT-LTD-2914291417
COGENT-17417412
COMCAST-7922792211
UNITAS18287
SWITCH-LTD230056
Axtel S.A.B. de C.V.65036
Operbes S.A. de C.V.187342
TWC-7843-BB78431
TELX-LEGACY360861

ISPs introducing ECN bleaching in North America

Rates: ISPs in Oceania

AS nameASNCounts
VOCUS-BACKBONE-AS Vocus Connect International Backbone4826305
ASN-TELSTRA Telstra Limited122148
AAPT AAPT Limited276411

ISPs introducing ECN bleaching in Oceania

Rates: ISPs in South America

AS nameASNCounts
TWELVE99 Arelion fka TeliaCarrier129957
TELXIUS TELXIUS Cable1295612
EPM Telecomunicaciones S.A. E.S.P.134895

ISPs introducing ECN bleaching in South America

How LogicMonitor fits in

LogicMonitor Synthetics and Internet Performance Monitoring provide outside-in visibility into the Internet paths that connect users to applications. This type of measurement can help teams investigate reachability and performance conditions across regions, networks, and transit providers. Paired with LM Envision infrastructure and cloud telemetry, it provides additional context for understanding how Internet conditions relate to application performance.

Find the ECN bleaching hiding on your paths before it undermines L4S.

LogicMonitor combines path-level internet measurements with deep infrastructure and application telemetry, exposing where congestion signals drop off so you can intervene before performance degrades.

FAQs

What is ECN bleaching?

ECN bleaching happens when a network device clears the Explicit Congestion Notification flags carried in a packet. Once those flags are stripped, the endpoints lose the congestion signal ECN was meant to deliver. A single bleaching instance anywhere on the path is enough to remove the benefit.

Why does ECN bleaching matter for L4S?

L4S (Low Latency, Low Loss, Scalable Throughput) is an internet standard defined in RFC 9330 that relies on ECN to detect congestion early and keep latency low. If ECN flags get bleached along the way, L4S can’t sense congestion, and applications like gaming, streaming, and VR lose the low-latency experience the standard promises.

How ready is the Internet for L4S today?

Catchpoint’s 2024 measurement campaign found that 88% of observed paths were ready for L4S, with no bleaching detected. The remaining 12% showed bleaching, roughly 42,000 cases, and rates varied widely by region and country. Because a single hop can break L4S, readiness has to be measured across the real networks and transit paths users depend on.

By Denton Chikura

Technical Writer

Denton Chikura is a technical writer and longtime observability advocate focused on helping site reliability engineers and engineering teams discover the tools and capabilities that strengthen internet resilience. He works at the intersection of monitoring, performance, and infrastructure to make complex systems more understandable and usable, bridging the gap between deep technical detail and real‑world operations. His goal is to help teams build faster, detect issues earlier, and recover smarter, ultimately making the internet a better, more reliable place for everyone.

Disclaimer: The views expressed on this blog are those of the author and do not necessarily reflect the views of LogicMonitor or its affiliates.

© LogicMonitor 2026 | All rights reserved. | All trademarks, trade names, service marks, and logos referenced herein belong to their respective companies.

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