By David Uberti and Steven Rosenbush

The Christmas Day bombing in Nashville hit a weak point in telecommunications infrastructure, disrupting phone and internet service for days and underscoring a key risk for increasingly digitized businesses.

A recreational vehicle exploded in front of an AT&T Inc. switching station, knocking out a central node that directs data from users and businesses across telecom systems. The incident, information technology experts and executives say, highlights how a terrorist attack, natural disaster or cyber incident can do widespread economic damage should it hit such a location.

"The way the networks are developed across the U.S. leads them to be susceptible to this type of event," said Nick Enger, chief technology officer of Advanced Technology Consulting Inc., an IT advisory firm.

Telecom networks in particular cities or regions converge at these so-called central offices. While AT&T said Monday that it restored most service in Nashville, the incident illustrates how a problem at one of these physical locations can send ripple effects across an entire region's digital infrastructure. Law-enforcement officials have considered whether the AT&T facility was targeted in the attack.

"This event creates an opportunity for all of us to review our backup and resiliency planning not only for our technology and non-office facilities, but also to identify and assess the physical and technological resilience of our critical partners," Edward Wagoner, chief information officer, digital, at commercial real-estate service firm Jones Lang LaSalle Inc., said in an email. The company has a presence in Nashville, but Mr. Wagoner said he couldn't discuss specific clients.

AT&T customers in states beyond Tennessee, including Kentucky and Alabama, suffered disruptions to service in recent days. The Kentucky Department of Education reported internet trouble at many of its facilities until Monday morning, and Tennessee state officials said in a statement that outages disrupted services such as the state's child abuse hotline and online Medicaid portal.

The issues also forced some planes to reroute their approaches to or takeoffs from Nashville International Airport, causing delays.

"All of us in town are struck by the extent to which this attack affected so many things across the region," Tom Jurkovich, vice president of strategic communications and external affairs for the Metropolitan Nashville Airport Authority, said in an interview.

Hundreds of AT&T workers and first responders have worked to get the downtown Nashville facility up and running, putting out fires, running the facility on generator power and pumping 3 feet of water out of the building's basement, the company said.

The company added Monday morning that 11 portable cell sites continued running throughout the region and "nearly all home internet and video customers have been restored."

The bombing underscores the need for businesses to build redundancies into their networks, allowing one service to take over if another goes down, IT experts say.

"There may be different levels of disruption that businesses face, as witnessed by the shift to remote work due to the pandemic, disruptions caused by natural disasters or this latest event in Nashville," said Vineet Jain, chief executive of Egnyte Inc., of Mountain View, Calif., which provides online file synchronization, sharing and other services. Egnyte uses multiple internet service providers that are designed to take over for one another in the event of an outage, he said. The use of multiple tech vendors at various levels minimizes risk, he said.

Mr. Enger, whose firm advises businesses on IT resilience, said dozens of clients from Tennessee, Kentucky, Indiana and Alabama lost their primary connection following the Nashville bombing.

While lining up contingency plans requires upfront investment, Mr. Enger added, "If you don't have a plan in place [during an incident], it's too late at that point."

Over time, networks should become more secure as software replaces physical infrastructure, said Dan Bieler, principal analyst for innovation, future of work and digital strategy at Forrester Research.

The shift to so-called software-defined networking has been under way for years but is only about one-third complete, he said. Such systems can route data across networks in a more efficient way and might be more resilient to disruptions.

The timetable for these innovations is difficult to forecast, and deployment varies from carrier to carrier as older infrastructure ages out, Mr. Bieler said.

"Companies don't want to rip out equipment that they invested in if it is still doing its job," he said. "It is a gradual process."

--Angus Loten contributed to this article.

Write to David Uberti at david.uberti@wsj.com and Steven Rosenbush at steven.rosenbush@wsj.com

(END) Dow Jones Newswires

12-28-20 1748ET