Cisco Systems (CSCO) 10-Q 2003 Q1 Quarterly report

Exhibit 99.1

CERTIFICATION PURSUANT TO
18 U.S.C. SECTION 1350
AS ADOPTED PURSUANT TO SECTION 906
OF THE SARBANES-OXLEY ACT OF 2002

I, John T. Chambers, President and Chief Executive Officer of Cisco Systems, Inc. (the “Company”), do hereby certify, pursuant to 18 U.S.C. Section 1350, as adopted pursuant to Section 906 of the Sarbanes-Oxley Act of 2002, that, to my knowledge:

• the Quarterly Report on Form 10-Q of the Company for the quarter year ended October 26, 2002, as filed with the Securities and Exchange Commission (the “Report”), fully complies with the requirements of Section 13(a) or 15(d) of the Securities Exchange Act of 1934; and

• the information contained in the Report fairly presents, in all material respects, the financial condition and results of operations of the Company.

Date: November 20, 2002

/s/  John T. Chambers  John T. Chambers
President and Chief Executive Officer
(Principal Executive Officer)