Cisco Systems Inc. notched a victory on Tuesday in its legal battle against rival Arista Networks Inc., winning a ruling from a federal agency that could lead to a halt on imports of Arista's networking hardware.

David Shaw, an administrative law judge for the International Trade Commission, found that Arista infringed three Cisco patents that cover software features used in the company's switching systems. His ruling, called an initial determination, is a step toward a possible ITC import exclusion order against Arista products.

Such rulings are subject to a final determination by the commission, a ruling Arista said it expects in June. Any exclusion order may be blocked by the president or overruled by an appeals court.

Still, the ruling is bad news for Arista, a fast-growing Silicon Valley company founded in 2004 and led by former Cisco executives. The company's stock fell 2.5% in after-hours trading following the news.

Cisco, the biggest maker of networking gear, accused Arista of violating its patents and copyrights in December 2014 in federal court as well as at the ITC. Some of the allegations involve the method used to type commands to program Cisco hardware -- known as the command line interface, or CLI -- that is used by Arista and some other competitors.

Write to Don Clark at don.clark@wsj.com

(END) Dow Jones Newswires

February 02, 2016 17:15 ET (22:15 GMT)