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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-0256 Basecamp was fully down twice in two days as hardware load balancers crashed and routers lost sync after failover

   37signals2020

   Symptoms

   On Tuesday 1 September 2020 Basecamp could not be loaded at all for 17 minutes, from 9:51am to 10:08am Central Time (14:51–15:08 UTC), and nothing seemed to work. On Wednesday 2 September it happened again for 15 minutes, from 10:50am to 11:05am Central Time (15:50–16:05 UTC).

   Service outageLink flappingHigh latency

   Trigger

   On 1 September the network links between the data centers went offline, and during the recovery a hardware load balancer crashed. On 2 September the primary load balancer in Virginia crashed again, and later its secondary crashed too.

   Root cause

   Software defect

   Component

   On-premises load balancerBackbone network (WAN)

   Contributing factor

   Overlapping failuresNo headroom

   Remediation

   • On 1 September, intervened by hand to get the network routers working with the standby load balancer
   • On 2 September, fixed the same router and load balancer desynchronization by hand

   Action items

   • Find the cause of the load balancer crash with the vendor and apply its bugfix
   • Replace the hardware load balancers
   • Reroute the redundant cross-datacenter network paths for proper circuit diversity
   • Evaluate moving from hardware to software load balancers, which can be deployed in minutes
   • Evaluate decentralizing the load balancer architecture to limit the impact of one failure
   • Assess the systems for resilience, fragility and risk, and review the assessment process itself

   Lessons

   Basecamp plans for failures like these and practises responses to catastrophic failures in its live systems, but three obscure issues in five days chained into overlapping failures. What caught the team by surprise were cascading failures that exposed unexpected fragility and hard paths to recovery, which Basecamp says it can prepare for.

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