Cisco Systems Inc. promoted Donald Listwin to the post of executive vice president, solidifying his position as heir apparent to Chief Executive John Chambers at the No. 1 computer networking company. Cisco also said it adopted a "poison pill" plan designed to thwart a hostile takeover, though the company said it had not faced such a bid in its 12-year history. Listwin, 39, joined Cisco in 1990 and most recently was senior vice president in charge of the company's corporate marketing and its carrier business, which sells equipment to phone companies and Internet service providers. In his new role, Listwin will add to his current duties by taking charge of Cisco's new product line for consumers. The San Jose-based company is looking for sales to consumers and telecommunication carriers to drive revenue growth as sales to its traditional corporate customers slow. Chambers has stated he expects more than 50% of Cisco's revenue to come from carriers by 2002. Cisco spokesman Doug Wills said Listwin, as the company's sole executive vice president, is its "heir apparent." Cisco shares fell 6 cents to close at $79.06 on Nasdaq.