Cisco CEO John Chambers speaks during the 2011 International Consumer Electronics Show (CES) in Las Vegas.

Debbie Gross was thrilled when Cisco Systems offered her a $36,000 salary to join as executive assistant in 1991. She didn't know much about the 560-person company, but at age 35 she was up for a new challenge, and the pay amounted to a solid raise from her previous gig.

As Cisco celebrates its 30th anniversary this month, Gross stands among the longest-tenured of the technology company's 74,000-plus employees. And she's spent her 2½ decades there working for a single boss: John Chambers.