A firewall upgrade at Optus that caused Triple Zero calls to fail for 13 hours did not follow internal traffic routing guidance and processes.

CEO Stephen Rue said that the playbook for a “successful upgrade”, drawn from past experience, was not followed.

Specifically, he said that an initial step “to divert calls away from the relevant part of the core network to a separate part of the core network” did not occur.

“The issue occurred because there was a deviation from established processes,” Rue said.

After traffic is diverted, Rue said the process is to “lock” the equipment behind the firewall; “safely upgrade the firewall; with the final step being to unlock and re-divert the traffic back.”

The upgrade, which was scheduled to run across two nights, appeared to be rolled back aft

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