When Core Switches Fail: A Network Engineer’s Close Call and Lessons Learned

Hello, I’m Xiao Le, a regular network engineer. Recently, news reported large‑scale network outages in Japan and Canada, which reminded me of a bizarre network failure I experienced that almost caused a major incident.

I work for a large state‑owned enterprise, handling network maintenance. Our network supports many services with high real‑time and reliability requirements, using legacy equipment from a foreign vendor (referred to as "S" devices) that relies on a proprietary spanning‑tree protocol, making a full hardware replacement difficult.

During a pandemic‑era shift change with few staff on duty, I was performing a routine inspection when the monitoring system flooded with alarms. One alert indicated that the IP address of a core switch (model 9, unit B) was unavailable.

Rushing to the equipment room, we found the switch completely dark except for the power LED. Connecting a console cable yielded only a ">" prompt with no normal command interface. The paired A unit was still operational, confirming our redundancy tests had been worthwhile.

After contacting the warranty provider, we collected logs and configuration data for a case submission. While awaiting a response, the paired A unit also failed with identical symptoms. Using the experience from the B unit, we performed a power‑cycle restart, and the A unit recovered after about ten minutes.

The vendor’s case analysis revealed a known bug: the SSD used in the switch engine locks after 28,224 cumulative operating hours (approximately 3.2 years), regardless of power cycles. This “time bomb” caused the engine to hang, leading to a full switch outage.

We discovered other switches of the same series approaching the same hour count, meaning simultaneous failures could occur, posing a catastrophic risk to our business.

The vendor offered two remediation options: upgrade the NX‑OS operating system or upgrade the SSD firmware. Because a full shutdown of critical switches was impractical, we chose the SSD firmware upgrade.

After the firmware upgrade, the switches continued to operate normally beyond the critical hour threshold, confirming the fix’s effectiveness.

This incident highlights the severe impact of hardware bugs in core network equipment, especially when devices are deployed for years without firmware updates. It also underscores the responsibility of vendors to proactively inform customers of such defects and to establish recall or tracking mechanisms similar to those in the automotive industry.

Upgrade the NX‑OS system.

Upgrade the SSD firmware.

In summary, the outage was caused by an SSD firmware bug that triggers after a specific runtime, and the timely firmware upgrade prevented further disruptions.