Arista Networks, Inc. v. Cisco Sys., Inc., 17-1525 On November 9, 2018, the Federal Circuit ruled that assignor estoppel does not apply in the IPR context. A former employee of Cisco assigned the entire right of the ‘597 patent to Cisco under his employment agreement and later left Cisco to become a founding member of Arista. Arista then instituted an IPR against the ‘597 patent. Cisco contended that the former employee’s assignment of the ‘597 patent to Cisco should have barred the institution of an IPR, because assignor estoppel is a well-established common law principle that Congress was presumed to intend to apply to §311(a). The court disagreed and found that assignor estoppel did not bar institution of the IPR due to the clear words of Congress under §311(a) which allows for any person “who is not the owner of the patent” to file an IPR.