Cisco said it was disappointed by the lawsuit, saying it takes its open source software obligations and responsibilities seriously.
"We are currently reviewing the issues raised in the suit but believe we are substantially in compliance. We have always worked very closely with the FSF and hope to reach a resolution agreeable to the company and the foundation."
Cisco is one of the leading contributors to the Linux kernel. Cisco also is holding a $100,000 contest for Linux developers and uses the open source operating system with its AXP router module as well.