SAN FRANCISCO — Arista Networks is lashing back at a suit filed earlier this month by one of the company’s co-founders, calling it a “Hail Mary” attempt by Silicon Valley billionaire David Cheriton to rejuvenate his private software company.

Cheriton, a Stanford computer engineering professor, helped found Arista in 2004 with longtime business partner Andreas Bechtolsheim. The same year Cheriton launched Optumsoft Inc. and the two companies entered a licensing agreement, which allowed Arista, a supplier of cloud networking solutions, to employ Optumsoft’s proprietary software development tool.