DNS Issues Cause Downtime for Major Sites

Some of the web's most prominent sites experienced downtime and sluggishness Wednesday night due to problems with DNS services. The issues were most pronounced at UltraDNS, which reported that its performance problems were caused by an electronic attack.

The list of sites experiencing problems included Salesforce.com, Amazon Web Services and Walmart.com. DNS is short for the domain name system, which serves as a roadmap allowing users to find web sites. Domain registries like VeriSign provide centralized web lookups through a network of data centers, while commercial DNS service providers like UltraDNS offer additional tools to manage traffic.

UltraDNS told CNet that it was hit by a distributed denial of service attack (DDoS) targeting its west coast infrastructure at data centers in San Jose and Palo Alto. A DDoS attack targets a site or provider with large volumes of traffic in an attempt to overwhelm its ability to serve content.

That logjam at UltraDNS caused ripples across the Internet, causing uptime  problems for several major service providers.

"We can confirm some customers in the West Coast are experiencing issues with resolving DNS," Amazon Web Services reported. The issue was resolved by 6:40 p.m. and affected Amazon's EC2 compute service, S3 storage and CloudFront content delivery network,  Pacific time.

"Due to a global DNS outage, all services at salesforce.com were affected," Salesforce reported on its status dashboard. "We are closely working with our providers to get more details and to isolate the nature of the problem."

The outages marked the third time this year that DDoS attacks on DNS providers had disrupted service for customers:

Successful attacks on DNS providers are not unprecedented, but these services are designed to be resilient. VeriSign has deployed new infrastructure in a $100 million upgrade at multiple data centers, with a goal of expanding its capacity to handle more than 4 trillion DNS requests per day by 2010.