Subscribers of Comcast's Xfinity internet service across the United States suffered an outrage early Monday, Nov. 6, starting around 10:00 a.m. PT and continuing for the next two hours. Major cities including New York and San Francisco were affected.

So far, people have only reported outages for internet service. TV and home phones appear to be unaffected. Comcast confirmed the reports via its customer support account on Twitter, apologized, and promised that it's working on a fix.

Comcast Xfinity Service Down In Major US Cities

The problems vary among Comcast Xfinity users: some reported intermittent or slow connections, while some said they couldn't access the internet entirely. Sites such as Google, some said, were still accessible, but Facebook and Twitter took ages to load.

DownDetector.com offers a clear look at whole outage situation. According to its data, most recent outage reports come from Mountain View, Portland, Denver, Chicago, Seattle, New York, San Francisco, Houston, Minneapolis, and Boston. Check out this live outage map to get a visual overview of which states are suffering from internet problems at the moment and how bad it is.

Comcast said the issue was caused by a configuration error and affected some customers with IP-based services. The service is now functioning normally again, it seems.

"We know how important these services are to our customers. Our technicians were able to restore service within approximately 90 minutes."

While the issue seems to have been resolved for some people, others indicate they're still having internet problems. The comments section at DownDetector.com is still full of complaints and outage reports.

The site also indicates that other ISPs similarly suffered from outages on the same day, including AT&T and Verizon, but both companies told PCMag that they did not experience any major service disruptions.

Why Internet Outages Occurred Across The US

The nationwide outages were a result of a configuration error, according to Comcast, but what exactly happened? There's an internet backbone company called Level 3, as Wired reports, that was responsible for the misconfiguration, which created a ripple effect that caused problems among services such as Verizon, Cox, RCN, Spectrum, and Comcast.

Roland Dobbins, principal engineer at security firm Arbor Networks, said the misconfiguration was a "route leak." ISPs use Autonomous Systems, also called ASes, to determine which IP addresses are on which networks, and route packets of data between them. A route leak causes ASes to malfunction, making them issue incorrect information about IP addresses on their network, which causes failures for all ISPs involved.

Internet outages caused by route leaks have occurred for decades, although they're not that frequent.