CN's internal upgrade cut its own internet link and halted Toronto's GO trains

On 3 October 2023 a network-wide system failure at Canadian National Railway halted GO Transit service across all corridors and shut UP Express in Toronto. CN told employees the outage 'was attributed to an internal system upgrade and affected CN's ability to connect to the internet.' GO and Via trains both require an internet connection to CN's systems to operate through Union Station.

Trains only resumed gradually through the evening after CN worked with GO to take over train dispatching temporarily, allowing partial resumption of GO and Via services. A Via passenger's London-to-Toronto trip left at 10:50 a.m. due at 1:10 p.m. and arrived at 4:20 p.m. — more than three hours late, missing meetings with Ontario MPPs and the premier. The shutdown also produced surge pricing on ride-hailing apps and pushed the TTC to add subway service.

CN said its own trains experienced no delays and no data was affected, and that there was no indication of a cybersecurity issue. Its website and customer portal were themselves offline for part of the afternoon. CN apologized for the impact, said the cause remained under investigation, and promised a review with GO Transit.

All GO corridors and UP Express halted for most of 3 Oct 2023; Via trains hours late; one trip took 3+ hours extra; resumption only by evening

CN ran an internal upgrade whose failure mode was the loss of internet connectivity for its network-wide systems.

GO Transit and Via depend on live connectivity to CN systems for dispatching, so CN's failure stopped their trains across Toronto.

The failure also took CN's own website and customer portal offline for part of the day.

Recovery required improvising a handover of GO's dispatching to CN before normal operations could resume.

When one railway's systems carry everyone else's dispatching, an upgrade that can sever connectivity takes the region down with it — failover needs testing before maintenance, not during it.

Service resumed with 'minimal disruptions' by the morning of 4 October 2023. CN said it would work with GO to review the incident and put processes in place to avoid further disruptions; no root cause was published at the time of the report.