Incident Library
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Cases6 cases

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  1. IL-0539 KT's internet service failed nationwide for about 89 minutes as wrong routes spread from one router in Busan
    KT2021
    Symptoms

    On 25 October 2021 from about 11:16, traffic to the DNS servers in KT's network rose sharply, and then KT's internet service failed across the whole country. KT recognised the internet outage at 11:20, and the outage lasted about 89 minutes until KT finished recovery at about 12:45.

    Network unreachableService outage
    Trigger

    During the replacement of an enterprise network router at KT's Busan office, worked on remotely from the Busan communication center, a worker entered a routing configuration script that lacked the 'exit' command that should have ended the IS-IS part of the configuration.

    Root cause
    Configuration change
    Component
    Interior routing (IGP)BGP routing
    Contributing factor
    Missed in reviewNo configuration testsChange during peak hoursExcessive blast radius
    Detection

    KT recognised the internet outage at 11:20, four minutes after DNS traffic began to surge at 11:16. The Ministry of Science and ICT saw the traffic increase in its own monitoring, and KT reported the outage to the ministry at 11:40.

    Remediation
    • Isolated the router where the faulty routing configuration was entered
    • Logged in to each regional router, deleted the faulty processes and restarted them
    Action items
    • Check the network management of major carriers, including their work procedures and the systems that stop technical errors from spreading
    • Consider having major carriers introduce simulation systems that diagnose errors from network work in advance
    • Have the NMS center and network operations center of each major carrier check technically that approved work plans are followed
    • Strengthen safeguards in routing work, such as limiting the number of route entries updated at once below a set level
    • Strengthen the monitoring of carriers' outages and develop technology, including AI-based preventive diagnosis, for network stability and resilience
    • Prepare structural measures for a stable network architecture and network survivability
    • Let carriers notify users of outages through SNS, text messages and other means, not only the website
    Lessons

    The investigation named management problems and technical problems. On the management side, work approved for the night was done during the day, partner company workers did the routing work without a work manager, and the work was done with the network still connected. On the technical side, the two pre-verification steps were people reading the script and missed the missing 'exit', there was no virtual testbed for trying the work on a disconnected network, and nothing stopped an error in one region from spreading to the whole country.

    View case
  2. IL-0228 IPv4 routing across OVHcloud's global network broke after a router change put the full internet routing table into OSPF
    OVHcloud2021
    Symptoms

    At 09:20 CET on 13 October 2021, during a planned change on a router, IPv4 traffic across OVHcloud's whole network stopped being routed, while all IPv6 traffic stayed reachable. The team detected a problem with the router's performance at 09:21 CET and escalated at once.

    Network unreachableService outage
    Trigger

    A planned change to a router in the Vint Hill datacentre in the United States, meant to strengthen anti-DDoS protection, included a command to regulate the redistribution of BGP into OSPF, and the router did not interpret that command correctly.

    Root cause
    Configuration change
    Component
    Interior routing (IGP)BGP routingBackbone network (WAN)
    Contributing factor
    Ineffective rollbackExcessive blast radius
    Detection

    At 09:21 CET the team detected a problem with the router's performance and started the escalation process.

    Remediation
    • Disconnected the optical equipment to isolate the router's connectivity
    • Powered off the faulty router
    • Stabilised connectivity to restore the remaining services
    Action items
    • Re-evaluate the change procedure for this type of equipment, which applies the command line natively
    • Strengthen the related change process
    View case
Check your cluster for this

These 6 cases involve BGP routing and Backbone network (WAN). kubegap audits a Kubernetes cluster for gaps like these, read-only, from Claude Code or Codex; its checks cite public reports like the ones in this library.

Open kubegap

By root cause1

Configuration change6 cases

Component
BGP routing6Backbone network (WAN)3Interior routing (IGP)3
Contributing factor
Excessive blast radius3No configuration tests3Ineffective rollback3Missed in review2Unverified assumption1Change during peak hours1Limited debug access1Harmful manual action1Overlapping failures1
Organisation
Cloudflare1KT1Microsoft Azure1OVHcloud1PSBA1Wikimedia Foundation1
  1. IL-0400 Public sector sites across Wales lost connectivity for over 8 hours as a PE router wrongly advertised a default route
    PSBA2026
  2. IL-0394 A Cloudflare router in Miami leaked IPv6 BGP routes to peers and providers for 25 minutes, congesting the backbone
    Cloudflare2026
  3. IL-0225 An IGP purge command made every Microsoft WAN router recompute routes, causing global latency, timeouts and packet loss
    Microsoft Azure2023
  4. IL-0266 Eqiad routers looped traffic between each other after a BGP MED change and could not reach other sites' public IPs
    Wikimedia Foundation2021
  5. IL-0539 KT's internet service failed nationwide for about 89 minutes as wrong routes spread from one router in Busan
    KT2021
  6. IL-0228 IPv4 routing across OVHcloud's global network broke after a router change put the full internet routing table into OSPF
    OVHcloud2021