How a ‘Cisco Expert’ with Only Three Months’ Experience Blew Up a Customer’s Network

Martin, the only Cisco‑trained staff at a tiny IT‑infrastructure firm, was promoted internally to the title of “Cisco expert” despite having only three months of experience. When his company visited a client that operated Nortel equipment, the client needed a new switch for their network.

During the visit, Martin installed the rack, applied the default configuration, and set up the VLANs discussed over coffee. After testing and confirming everything appeared functional, he prepared to leave.

Just then, the client’s IT team called him back, reporting that over 4,000 AS/400 season data records had disappeared. Martin realized a causal link between the moment he connected the new switch and the loss of sessions. The only way to recover the sessions was for the IT team to manually terminate each one.

Investigation showed the root cause was the new switch’s Spanning Tree Protocol (STP) settings. The AS/400 system relied on TCP/IP emulation to maintain SNA connections between hosts; losing a single packet caused a catastrophic failure.

Martin felt deep embarrassment and blamed his managers for labeling him an “expert” and assigning a critical client to a novice. He noted that senior staff were friendly but the incident caused them significant headaches. Ultimately, his superiors noticed the problem but did not fire him, and Martin walked away with valuable lessons about the risks of over‑promoting inexperienced engineers.