Cases8 cases

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1. IL-0225 An IGP purge command made every Microsoft WAN router recompute routes, causing global latency, timeouts and packet loss

   Microsoft Azure2023

   Symptoms

   From 07:08 UTC on 25 January 2023, customers saw long network latency and timeouts when connecting to resources in Azure regions and to other Microsoft services such as Microsoft 365 and Power Platform. Microsoft's monitoring detected DNS and WAN issues from 07:11 UTC.

   High latencyIntermittent timeoutsIntermittent connection failuresPacket lossNetwork unreachable

   Trigger

   A network engineer adding capacity to the global WAN in Madrid ran a step of a recently changed standard operating procedure that purged the IGP database; on the router manufacturer involved, that command runs on all IGP-joined routers instead of only the local one.

   Root cause

   Configuration change

   Component

   Backbone network (WAN)Interior routing (IGP)BGP routing

   Contributing factor

   No configuration testsUnverified assumptionExcessive blast radiusHarmful manual action

   Detection

   Monitoring detected DNS and WAN issues from 07:11 UTC and alerted the on-call engineers within 5 minutes of the command being run. The team reviewed all recent changes and identified the command by 08:20 UTC. The engineer making the change was not informed of the alerts because of the unqualified changes to the SOP.

   Remediation

   • Restarted by hand the paused WAN health and traffic engineering systems, which ended the remaining packet loss

   Action items

   • Audit and block similar widespread-impact commands across all three vendors for all WAN router roles
   • Give on-call engineers real-time visibility of approved and unqualified activity on network devices
   • Run regular mandatory operational training and attestation of following all SOPs
   • Have the Change Advisory Board review all SOPs still pending qualification within 30 days

   View case
2. 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.

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3. 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
4. IL-0222 Google Cloud US regions had heavy packet loss and some went unreachable after the network control plane was descheduled

   Google Cloud2019

   Symptoms

   On Sunday 2 June 2019, with user impact beginning between 11:47 and 11:49 US/Pacific, Google Cloud projects in several US regions saw elevated packet loss from network congestion, and some regions became unreachable. Customers saw higher latency, intermittent errors and lost connectivity to instances in us-central1, us-east1, us-east4, us-west2, northamerica-northeast1 and southamerica-east1, while us-west1, Europe and Asia had no regional congestion.

   Packet lossNetwork unreachableHigh latencyHigh error rateMonitoring outage

   Trigger

   At 11:45 US/Pacific a relatively rare type of datacenter maintenance event started in one physical location, and the automation that runs it descheduled logical clusters that also held network control plane jobs in other physical locations.

   Root cause

   Software defect

   Component

   Network control plane (SDN)BGP routingBackbone network (WAN)

   Contributing factor

   Excessive blast radiusCircular dependencyLimited debug accessIneffective rollback

   Detection

   Google engineers were alerted to the failure two minutes after it began and started the incident process used for the most serious production incidents. The first customer notice appeared on the status page at 12:53 US/Pacific.

   Remediation

   • Lowered the priority of less critical network traffic classes to reduce congestion
   • Halted the datacenter automation software responsible for the maintenance event
   • Rescheduled the network control plane and its supporting infrastructure in each location
   • Rebuilt and redistributed the lost network control plane configuration, rolling it out from 14:03
   • Directed service traffic away from the affected regions
   • Moved the Cloud VPN control plane in three regions out of its fail-safe state

   Action items

   • Keep the maintenance automation off until safeguards stop it descheduling jobs in several physical locations at once
   • Harden the cluster management software to reject such requests whatever their origin
   • Reconfigure the network control plane to reject maintenance requests of the type involved
   • Make the network control plane in each location persist its configuration
   • Let the network stay in fail static mode longer when the control plane is lost
   • Review, update and test emergency response tooling and procedures, including customer communication tooling, for such network failures
   • Extend continuous disaster recovery testing to this and similarly catastrophic failures

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