Fed up with patent trolls, Rackspace is going on the offensive.

After successfully defending itself from a patent infringement lawsuit over Linux, the Texas-based cloud infrastructure service provider says it filed a lawsuit today against Parallel Iron and IP Nav, a patent assertion entity (PAE) that Rackspace calls "the most notorious patent troll in America."

Commonly referred to as patent trolls, PAEs are created to extract licensing fees from other companies rather than make products based on the patents.

In a blog post today, Rackspace said Parallel Iron sued it and 11 other defendants in Delaware last week for allegedly infringing on three patents that Parallel Iron said cover the use of the open-source Hadoop distributed file system (HDFS). Since last June, the Delaware-based shell company has filed similar lawsuits against at least 23 defendants, including Amazon, Oracle, and Facebook.

Rackspace said that its battle began in 2010 when IP Nav, acting on Parallel Iron's behalf, accused Rackspace of patent infringement but would not reveal the details of its claims until Rackspace agreed to a "forbearance agreement," which held that either side would give the other 30 days notice before suing.

Rackspace said it agreed to the deal but that Parallel Iron broke the agreement by suing it without giving prior notice. "Parallel Iron willfully ignored its own agreement," Rackspace said in its complaint.

Today, Rackspace fired back with its own lawsuit (see below) filed in U.S. District Court in its hometown of San Antonio for breach of contract and a declaratory judgment that Rackspace does not infringe on the patents in question. The lawsuit comes on the heels of Rackspace winning dismissal of a lawsuit from Uniloc, which alleged Linux infringed on a patent it holds related to processing floating-point numbers.

"We aren't going to take it," Rackspace general counsel Alan Schoenbaum wrote today in a company blog post. "Our goal with this lawsuit is to highlight the tactics that IP Nav uses to divert hard-earned profits and precious capital from American businesses. This time, the patent troll should pay us."

Schoenbaum points out that IP Nav claimed in a Federal Trade Commission filing (PDF) to be a "white hat" entity created to "give the little guy a chance" -- an assertion Schoenbaum called "laughable."

"This is tragic comedy at best," he said. "There are few trolls more notorious than IP Nav, and there is no such thing as a patent troll that has the best interests of small businesses in mind. Instead, IP Nav and Parallel Iron are acting in their own selfish interests and suffocating innovation, while stripping capital away from businesses both large and small."

CNET has contacted IP Nav for comment and will update this report when we learn more.

Rackspace Complaint