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                                                                    EXHIBIT 23.1

               CONSENT OF ERNST & YOUNG LLP, INDEPENDENT AUDITORS


We consent to the reference to our firm under the captions "Selected
Consolidated Financial Data" and "Experts" and to the use of our report dated
March 2, 2000, in the Registration Statement (Form S-1 No. 333-35938) and
related Prospectus of CoSine Communications, Inc. for the registration of
10,000,000 shares of its common stock.


                                         Ernst & Young LLP

Palo Alto, California



The foregoing consent is in the form that will be signed upon the completion of
the reincorporation of CoSine Communications, Inc. in Delaware as described in
Note 11 of the Notes of the Consolidated Financial Statements.



                                        /s/  Ernst & Young LLP

Palo Alto, California
August 23, 2000