Cases4 cases

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1. IL-0509 SourceHut was down for 170 hours after a DDoS led its upstream network to null-route the PHL datacenter's subnet

   SourceHut2024

   Symptoms

   At about 06:00 UTC on 10 January 2024, SourceHut's monitoring raised the alarm as a layer 3 DDoS attack hit its infrastructure in the PHL datacenter, and at about 09:00 UTC SourceHut lost all access to its PHL network. PHL was the primary datacenter, and the network became unreachable for SourceHut staff and the general public alike.

   Network unreachableService outage

   Trigger

   A layer 3 DDoS attack against SourceHut's PHL infrastructure that began at about 06:00 UTC on 10 January 2024 and broadened to more of the PHL subnet on 11 January.

   Root cause

   Dependency failure

   Component

   ISP and transit networksBGP routing

   Contributing factor

   Single point of failureLimited debug accessUntested backup

   Detection

   SourceHut's monitoring systems noticed that something was wrong and raised the alarm from about 06:00 UTC on 10 January.

   Remediation

   • Got Cogent, through the colocation provider, to narrow the null route from the /24 to the targeted /32, which mostly restored service on 10 January
   • Moved DNS to an external DNS provider
   • Brought up a new primary database in AMS
   • Restored backups from FRE to AMS
   • Applied the difference between production data and the last backups by hand
   • Provisioned a new mail system and configured the mail services for it
   • Set up an OVH box that NATs traffic through OVH's DDoS-resistant network to the production subnet in AMS
   • Used a temporary subnet from the PHL network provider for out-of-band access to the PHL servers
   • Served pages.sr.ht through an out-of-band link to PHL while its object storage was migrated
   • Emailed pages.sr.ht users whose apex records pointed at the PHL subnet with instructions
   • Ran build workers on dedicated bare-metal OVH servers

   Action items

   • Provision a new standby database
   • Configure backups from AMS to FRE
   • Install a new monitoring system
   • Retire the PHL datacenter installation and ship its servers to AMS
   • Move build service back onto SourceHut-operated servers once the build servers are shipped from PHL to AMS
   • Research and implement a way to run SourceHut in an on-premise Kubernetes cluster
   • Plan a second production-ready datacenter to load balance against, able to take over full service in a datacenter outage

   Lessons

   The operational plans SourceHut kept for failures up to the loss of a whole datacenter proved important in this incident. The incident exposed a known shortcoming in redundancy and resilience that the team was working on but had not finished, and the response of the upstream network to the attack did more damage than anything else.

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2. IL-0267 Wikimedia's eqsin cache site went unreachable when both of its transport links to the core data centers were down

   Wikimedia Foundation2023

   Symptoms

   On 10 January 2023 at 16:37 UTC Icinga reported "BGP status on cr3-eqsin is CRITICAL: BGP CRITICAL - AS1299/IPv6: Active - Telia, AS1299/IPv4: Active - Telia", and from 16:45 the hosts in Wikimedia's eqsin site went DOWN with "PING CRITICAL - Packet loss = 100%". Users normally directed to eqsin, mostly in the APAC region, could only read Wikipedia pages already cached in eqsin.

   Network unreachable

   Trigger

   Planned maintenance by the transport provider took down eqsin's second transport link while the first was still down from a long fiber cut.

   Root cause

   Dependency failure

   Component

   Backbone network (WAN)BGP routingCDN and edge network

   Contributing factor

   Single point of failureIgnored early signal

   Detection

   Automated monitoring: Icinga BGP status alerts for cr3-eqsin at 16:37 and cr2-eqsin at 16:44, followed by a flood of host-down alerts and three pages at the same time.

   Remediation

   • Depooled eqsin from DNS
   • Repooled eqsin

   Action items

   • Create a backup GRE tunnel for eqsin (T327265)
   • Ensure the long-down transport link comes back up properly once it is fixed (T322529)
   • Automatically parse maintenance notifications and alert on conflicting maintenance (T230835)

   Lessons

   The site was depooled quickly, and "depool first, investigate later" was the right attitude. A flood of host-down alerts usually means a network problem. eqsin stayed too long on a single working transport link, SREs did not catch that the downtime of the two transport links overlapped, and the provider's planned maintenance was not recorded in a task or reminder.

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3. IL-0358 Packet Public Cloud locations had high latency and unreachable paths from routing loops and blackholed traffic

   Packet2019

   Symptoms

   At about 08:49 UTC on 2 June 2019, Packet's internal network monitoring alerted on serious reachability and performance problems in several of Packet's global datacenter locations. The first investigation found routing loops and traffic being blackholed to specific internal and Internet destinations.

   Network unreachablePacket lossHigh latency

   Trigger

   A trans-continental US backbone link in the network of Packet's upstream provider Zayo had a hardware failure and blackholed IP traffic routed over it.

   Root cause

   Dependency failure

   Component

   Backbone network (WAN)BGP routingNetwork control plane (SDN)

   Contributing factor

   –

   Detection

   Packet's internal network monitoring alerted at 08:49 UTC on reachability issues in several global datacenter locations, and engineers confirmed them at 08:52.

   Remediation

   • Migrated traffic to an alternative network and removed Zayo from the provider mix
   • Applied route filters to return service to normal
   • Optimised specific routing policies to improve latency across the backbone with the new traffic mix

   Action items

   • Expand internal connectivity monitoring and alerting of on-call operations teams
   • Expand network automation and routing so traffic can be balanced across all available backbone paths and an operator can trigger automated re-routes across all Packet datacenters in a major provider incident
   • Make Packet's provisioning systems less dependent on third party network providers and inter-datacenter connectivity

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4. IL-0258 FastMail was unreachable for almost two hours when the GRE tunnels carrying its traffic from Level 3 went down

   Fastmail2016

   Symptoms

   At 4.50am Melbourne time on Sunday 7 February (evening of 6 February UTC), FastMail became unavailable and stayed unreachable for almost two hours. Traffic to FastMail's public IP range never made it into FastMail's own network.

   Service outageNetwork unreachable

   Trigger

   The GRE tunnels between Level 3 and NYI, which carried FastMail's filtered traffic into its network, went down.

   Root cause

   Dependency failure

   Component

   DDoS protection serviceBGP routing

   Contributing factor

   Limited debug access

   Detection

   NYI, the datacentre provider, noticed the failure quickly.

   Remediation

   • NYI escalated with Level 3's support until FastMail's public IP ranges were pointed back to NYI

   Action items

   • Go back to DDoS protection from Black Lotus under NYI's explicit control
   • Build nginx frontends in the Los Angeles datacentre that reach NYI over the secondary network, and point DNS to them if NYI's primary network fails
   • Add hardware in Amsterdam and change the delivery system so it depends less on NYI
   • Work with NYI to understand its processes for detecting and responding to network faults

   Lessons

   Much of FastMail's and NYI's reliability had come from NYI controlling its own infrastructure. With protection always on at Level 3, NYI could not restore the routes itself, and FastMail calls the resulting delay in restoring service unacceptable.

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