Cases2 cases

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1. IL-0400 Public sector sites across Wales lost connectivity for over 8 hours as a PE router wrongly advertised a default route

   PSBA2026

   Symptoms

   On 25 March 2026 from about 16:40, public sector organisations on the PSBA network across Wales lost connectivity at their sites. The Service Desk saw about 400 alerts at 16:58, when a Major Incident was declared, about 1,500 at 17:05 and about 5,000 across Wales at 17:08, while councils, a fire and rescue service and Natural Resources Wales phoned in to report sites down.

   Network unreachableIntermittent connection failuresLink flapping

   Trigger

   At 16:30 a route map change was applied, outside formal change control, on a PSBA core Provider Edge (PE) router to leak MPLS VPN routes, so that legacy Capita-operated UPS devices in a /16 subnet could be managed by BT/PSBA. The change was removed at 16:40.

   Root cause

   Configuration change

   Component

   BGP routing

   Contributing factor

   Ineffective rollbackMissed in reviewLimited debug accessOverlapping failures

   Detection

   At 16:57 Mid Wales Fire & Rescue Service phoned in a loss of connectivity at its Presteigne site, and at 16:58 a case was opened in Service Now for a group of about 400 alerts and a Major Incident was declared.

   Remediation

   • Removed the route map change from the PE router at 16:40
   • Changed QoS on the BGP to bring back the management links, after which alarms cleared
   • Cleared routes and reset inbound BGP advertisements, which did not stop the default route being advertised
   • Corrected the configuration issue affecting the internet learned route at 01:02
   • Performed a controlled reload of the affected router at 01:10, which restored customer services and management connectivity

   Action items

   • Reinforce change control requirements with an internal briefing on formal change submission, the risks of unplanned changes and roles during planned and emergency changes
   • Create a dedicated Microsoft Teams channel as the single real-time communication point for all live P1 and Major Incidents
   • Explore disaster recovery and business continuity test exercises for major or P1 incidents
   • During loss of management access, have all technical teams assess customer impact from what reporting organisations provide, captured and shared in real time by the Service Desk and Incident Management
   • Investigate a fixed link between Capital Quarter and the PSBA management racks in Vantage Data Centre at Newport, with dedicated management terminals and two-factor authentication for access outside the secure management platform
   • Improve initial triage with stronger probing questions when incidents are reported and keep reassessing and communicating impact throughout the incident
   • Review the P1 and Major Incident process so escalation criteria and timeframes are clearly defined, and train the Service Desk to recognise and escalate them early
   • Review the PSBA estate for legacy configuration, set processes and timeframes for removing it and add controls so it is not introduced again
   • Review email and SMS distribution lists and processes and reinforce Service Desk training on customer communications during P1 and Major Incidents

   Lessons

   The report names eight lessons: a change was made outside PSBA change control; internal communication during the Major Incident was slow and fragmented; the organisation was not ready for a network-wide incident; losing management access stopped the resolver groups from seeing the network state and customer impact; the resolver groups did not understand customer impact in enough detail, which delayed finding the root cause; escalation to PSBA management was slow; legacy configuration left in the network contributed; and email and SMS communications did not reach some customers in time.

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2. IL-0339 Azure Front Door and Azure CDN users saw intermittent connection errors, timeouts and latency spikes for hours

   Microsoft Azure2024

   Symptoms

   From 11:45 UTC on 30 July 2024, a subset of customers got intermittent connection errors, timeouts and latency spikes when connecting to Microsoft services that use Azure Front Door (AFD) and Azure Content Delivery Network (CDN). The Azure Portal team saw the first service degradation at 11:47 UTC.

   Intermittent connection failuresIntermittent timeoutsHigh latencyPacket loss

   Trigger

   Around 11:45 UTC the Azure network DDoS protection service was disengaging after a routine DDoS mitigation and returning traffic to its default routing to AFD, but the routes at one site in Europe could not be updated because the network control plane could not reach that site during a local power outage.

   Root cause

   Configuration change

   Component

   CDN and edge networkDDoS protection serviceNetwork control plane (SDN)Data center power and cooling

   Contributing factor

   Overlapping failuresExcessive blast radiusMonitoring blind spot

   Detection

   The Azure Portal team detected service degradation at 11:47 UTC and began to investigate. At 12:10 UTC network monitoring correlated the Portal incident to a network issue at one site in Europe, and networking engineers joined.

   Remediation

   • Rerouted traffic under the standard congestion playbook, which removed most of the impact by 13:58 UTC
   • Ordered the network control plane to reissue its commands to the misbehaving device, which could not be reached
   • Removed the device that kept attracting traffic from the network and scanned the network for other issues

   Action items

   • Add the missing configuration on network devices so a DDoS mitigation issue in one geography cannot spread to another
   • Improve validation and monitoring in the Azure network to detect invalid configurations
   • Improve monitoring for when the DDoS protection service is unreachable from the control plane but still serving traffic

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