Techie Traced Cables From Basement To Maternity Ward And Onto A Roof, Before Acar Crash Revealed The Problem

On Call Welcome once again to On Call, The Register‘s Friday column that shares reader-contributed tales of tech support terror and triumph.

This week, meet a reader we’ll Regomize as “Geoffrey,” who told us about the time he was called out to fix a hospital’s access control network – a setup that controlled physical access to different parts of the facility.

“Doors that should be locked were unlocked, cards that should unlock doors wouldn’t register,” Geoffrey told On Call. “It was a closed network, but absolute chaos, and the onsite engineer couldn’t figure out what was going on,” he added.

The job needed boots on the ground, and Geoffrey’s boots were made for walking in to save the day.

On arrival he started in the basement and found a 16 port switch – part of the spine of the access control network.

“A couple of activity lights on the switch were blinking way too fast,” Geoffrey told On Call. He decided to follow the cable that corresponded to the distressed port and found another switch and another pair of rapidly blinking activity lights.

Following another cable led Geoffrey into a maternity ward that incongruously housed a small wall-mounted box within which he found a small switch, power-over-ethernet injectors, and yet more cables that he learned were connected to a pair of wireless bridges on the hospital roof that enjoyed line-of-sight to a carpark.

Because of course it made sense for a switch in a maternity ward to connect to a roof and a car park.

Geoffrey unplugged an injector and the network returned to perfect health.

Which suggested the bridge was the source of the borkage and meant a visit to the roof was in order.

Once he ascended, Geoffrey gazed at the carpark and noticed that one of its exit barriers was working fine but the other was permanently raised.

The onsite engineer explained that someone recently drove their car into the barrier and damaged the wireless bridge, which had been replaced … just before the access control system went bad.

Geoffrey had a hunch that the access control system vendor shipped pre-configured bridges, usually with the same SSID and password.

A little testing proved his hypothesis: the bridges on the roof both shared a name and password. After the accident in the carpark they’d dropped the connection to the Wi-Fi kit down there and connected to each other. The resulting loop flooded the network and caused the access system issues.

Installing new bridges with unique SSIDs and connecting the right cable to the right box soon sorted things out.

Have your debugging efforts taken you on strange journeys into unlikely places? If so, start your trip towards becoming an On Call contributor by clicking here to send us an email. ®

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