T-Mobile exec explains Monday's network outage was not a DDoS attack

Cal Jeffrey

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On Monday, social media went into a tailspin with unsubstantiated reports that the US was suffering a large scale DDoS that crippled all major cell service providers for about 10 hours. Some reports even claimed that platforms like Instagram, Facebook, and others were also under attack. As it turns out, it was only T-Mobile that was affected, and it was not a distributed denial of service attack that caused the outage.

On Tuesday, T-Mobile's President of Technology Neville Ray explained that the problem occurred because a leased third-party fiber circuit in the southeastern part of the country broke down. This is a common enough occurrence in mobile networks that companies have built redundancies to prevent interruptions. However, this time T-Mobile's backup failed as well.

"This redundancy failed us and resulted in an overload situation that was then compounded by other factors," said Ray. "This overload resulted in an IP traffic storm that spread from the Southeast to create significant capacity issues across the IMS (IP Multimedia Subsystem) core network that supports VoLTE calls."

While some customers from other carriers were also reporting outages, these providers have said that their systems were and remain functional.

On Monday, shortly after the outages began, Cloudflare CEO Matthew Prince denied the problem was caused by distributed denial of service attacks and pinpointed T-Mobile as the cause of the interruptions. He did not address why customers from other carriers were also having trouble.

Verizon later explained that it was only experiencing issues when its users were trying to reach T-Mobile customers.

"Verizon's network is performing well. We're aware that another carrier is having network issues. Calls to and from that carrier may receive an error message," a Verizon spokesperson told CNN Business. "We understand Downdetector is falsely reporting Verizon network issues."

The outage began around noon pacific time on Monday. By 10pm PDT, T-Mobile reported it had fixed the problem and apologized for the interruption in service.

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