Cases2 cases

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1. IL-0394 A Cloudflare router in Miami leaked IPv6 BGP routes to peers and providers for 25 minutes, congesting the backbone

   Cloudflare2026

   Symptoms

   On 22 January 2026 from 20:25 UTC, a Cloudflare edge router in Miami sent unintended BGP advertisements of IPv6 prefixes to its transit providers and peers. External networks' traffic was funnelled into the Miami data center, the backbone between Miami and Atlanta became congested, and some Cloudflare customer traffic saw elevated loss and higher latency.

   Packet lossHigh latency

   Trigger

   At 20:25 UTC Cloudflare's policy automation pushed a change, merged at 19:52 UTC, that removed the BGP announcements from Miami for a data center in Bogotá, Colombia, by deleting the prefix-list 6-BOG04-SITE-LOCAL from several export policy terms.

   Root cause

   Configuration change

   Component

   BGP routingBackbone network (WAN)

   Contributing factor

   No configuration tests

   Detection

   The network team began investigating unintended route advertisements from Miami at 20:40 UTC, and an incident was raised at 20:44 UTC.

   Remediation

   • A network operator reverted the bad configuration change on the Miami router by hand
   • Paused the automation for the router so it could not run again
   • Reverted the triggering change in the network automation code repository
   • Unpaused the automation on the Miami router after confirming it ran without the routing policy bug

   Action items

   • Patch the failure in the routing policy automation that caused the leak
   • Add BGP community-based safeguards that reject routes received from providers and peers on external export policies
   • Add automatic routing policy evaluation to the CI/CD pipelines that looks for empty or erroneous policy terms
   • Detect problems in network configurations and the effects of automated changes earlier
   • Validate routing equipment vendors' implementations of RFC9234 before rolling out BGP roles and the Only-to-Customer Attribute
   • Encourage long-term adoption of RPKI Autonomous System Provider Authorization (ASPA)

   Lessons

   Removing only the prefix lists from export policy terms left terms that were too permissive, because a match on route-type internal accepts IBGP routes as well. Cloudflare states that route leaks are easy to cause by accident and that RFC9234 is the only way, independent of routing policy, to prevent route leaks caused at the local AS.

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2. IL-0341 Traffic between Cloudflare and AWS us-east-1 had high latency, packet loss and origin failures for almost four hours

   Cloudflare2025

   Symptoms

   From 16:27 UTC on 21 August 2025, users connecting to Cloudflare from servers in AWS us-east-1, or receiving connections from Cloudflare there, saw high latency, packet loss and failures to reach origins. Cloudflare's network team was alerted to internal congestion in Ashburn (IAD) at 16:44 UTC.

   Packet lossHigh latencyIntermittent timeouts

   Trigger

   At about 16:27 UTC a single customer began sending many requests from AWS us-east-1 to Cloudflare for objects in Cloudflare's cache, doubling the total traffic from Cloudflare to AWS.

   Root cause

   Capacity exhaustion

   Component

   Transit gateway or network interconnectBGP routingCDN and edge network

   Contributing factor

   No headroomHarmful manual actionExcessive blast radius

   Detection

   Cloudflare's network team was alerted to internal congestion in Ashburn (IAD) at 16:44 UTC, and an incident was raised for customer impact at 17:45 UTC.

   Remediation

   • Rate limited the single customer whose traffic caused the surge
   • Took further traffic engineering actions that fully resolved the congestion
   • Asked AWS to revert its BGP prefix withdrawals, which AWS finished at 20:07 UTC

   Action items

   • Build a mechanism to deprioritise a customer's traffic when it congests the network enough to affect others
   • Speed up the Data Center Interconnect upgrades to add network capacity
   • Work with AWS so the two companies' BGP traffic engineering actions do not conflict
   • Build a traffic management system that gives each customer a network resource budget and automates the manual actions used here

   Lessons

   Cloudflare concludes that it must isolate customers better so that no single customer can take over shared network resources and degrade the platform for others, and that its network needs enough capacity to meet demand. It describes the outage as the result of insufficient network congestion management during an unusual high-traffic event.

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