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                                                                   EXHIBIT 10.66

                             MODIFICATION AGREEMENT
                    (FIRST AMENDMENT TO OPERATIVE DOCUMENTS)

     This MODIFICATION AGREEMENT (this "AGREEMENT") is made as of April 19,
2000, by BNP LEASING CORPORATION, a Delaware corporation ("BNPLC"), BANQUE
NATIONALE DE PARIS ("AGENT") and NETWORK APPLIANCE, INC., a California
corporation ("NAI")

                                 R E C I T A L S

     A. BNPLC and NAI executed a Lease Agreement (Phase V- Improvements) (the
"IMPROVEMENTS LEASE") and a Lease Agreement (Phase V- Land) (the "LAND LEASE"),
each dated March 1, 2000 (collectively, the "LEASES").

     B. BNPLC, Agent and NAI desire to modify certain provisions of certain
Operative Documents as provided below.

     NOW, THEREFORE, in consideration of the above recitals and other good and
valuable consideration, the receipt and sufficiency of which are hereby
acknowledged, the parties agree as follows:

1.   Definitions. Capitalized terms used in this Agreement and not otherwise
     defined herein shall have the meanings given to them in the Leases.

2.   Modifications. The Operative Documents are hereby modified as follows:

     a.   Modifications to Closing Certificate. Section 1(C) of the Closing
          Certificate is amended and restated as follows:

          "(C) Title Insurance. Without limiting NAI's obligations under the
          preceding subparagraph, contemporaneously with the execution of this
          Agreement NAI shall provide to BNPLC a title insurance policy (or
          binder committing the applicable title insurer to issue a title
          insurance policy, without the payment of further premiums) in the
          amount of no less than $55,000,000, in form and substance satisfactory
          to BNPLC, written by one or more title insurance companies
          satisfactory to BNPLC and insuring BNPLC's fee estate in the Land and
          Improvements."

     b.   Modifications to Common Definitions and Provisions Agreement (Phase V-
          Improvements). The definition of "Maximum Construction Allowance" is
          amended and restated as follows:

          "MAXIMUM CONSTRUCTION ALLOWANCE" means an amount equal to $55,000,000,
          less the sum of the Initial Funding Advance under and defined in the
          Other Common Definitions and Provisions Agreement and the Initial
          Funding Advance under and as defined in this Agreement.

     c.   Modification to Participation Agreement.

          i.   The reference to "$51,000,000" on the cover page of the
               Participation Agreement is amended and restated to refer to
               "$55,000,000".

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          ii.  The first sentence of Section 3.2.2 is amended and restated as
               follows:

               "Before 12:00 noon, San Francisco time, on the third Business Day
               prior to any date on which BNPLC expects to make a payment of a
               Construction Advance to NAI under the Construction Management
               Agreement or of costs or expenditures considered as Construction
               Advances pursuant to subparagraph 6(e) of the Phase V
               Improvements Lease, BNPLC shall notify the Participants of the
               amount of such payment, and each Participant shall pay to BNPLC
               such Participant's Percentage times such amount prior to 12:00
               noon, San Francisco time, on such date."

          iii. Section 3.2.3 is amended and restated as follows:

               "LIMITATION ON ADVANCES BY PARTICIPANT. Notwithstanding anything
               herein to the contrary or any adjustment to any Participant's
               Percentage pursuant to Section 4.1, the total of all payments
               required of any Participant to BNPLC by this Section 3.2
               (excluding interest on past due payments required by Section
               3.2.2) because of any Construction Advances made to NAI under the
               Construction Management Agreement (in contrast to costs or
               expenditures considered as Construction Advances pursuant to
               subparagraph 6(e) of the Phase V Improvements Lease after a
               Landlord's Election to Continue Construction, as provided below)
               shall not exceed the amount that would cause such Participant's
               Participation Amount to exceed the Participation Amount specified
               for such Participant in Schedule 1.

               In the event of a Landlord's Election to Continue Construction
               under subparagraph 6(e) of the Phase V Improvements Lease, no
               Participant shall be required to make any payments to BNPLC
               relating to costs incurred by BNPLC to continue or complete the
               Construction Project in excess of its total Participation Amount
               specified for such Participant in Schedule 1, unless such
               Participant has approved of the same in writing to BNPLC."

3.   Ratification. Each of the Operative Documents, as amended by this
     Agreement, are hereby ratified and confirmed in all respects.

4.   Entire Agreement. This Agreement and the documents and agreements referred
     to herein set forth the entire agreement between the parties concerning the
     subject matter hereof and no amendment or modification of this Agreement
     shall be binding or valid unless expressed in a writing executed by both
     parties hereto.

5.   Successors and Assigns. All of the covenants, agreements, terms and
     conditions to be observed and performed by the parties hereto shall be
     applicable to and binding upon their respective heirs, personal
     representatives, successors and, to the extent assignment is permitted
     under the Operative Documents, their respective assigns.

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6.   Execution in Counterparts. To facilitate execution, this Agreement may be
     executed in as many identical counterparts as may be required. It shall not
     be necessary that the signature of, or on behalf of, each party, or that
     the signature of all persons required to bind any party, appear on each
     counterpart. All counterparts, taken together, shall collectively
     constitute a single instrument. It shall not be necessary in making proof
     of this Agreement to produce or account for more than a single counterpart
     containing the respective signatures of, or on behalf of, each of the
     parties hereto. Any signature page to any counterpart may be detached from
     such counterpart without impairing the legal effect of the signatures
     thereon and thereafter attached to another counterpart identical thereto
     except having attached to it additional signature pages.

7.   Recitals. The recitals contained herein are incorporated by this reference.

     IN WITNESS WHEREOF, the parties have executed this Agreement as of the date
first above written.

                                       BNP LEASING CORPORATION,
                                       a Delaware corporation


                                       By:
                                          -----------------------------------
                                       Lloyd G. Cox, Vice President


                                       BANQUE NATIONALE DE PARIS

                                       By:
                                          -----------------------------------
                                       Name:
                                            ---------------------------------
                                       Title:
                                             --------------------------------


                                       NETWORK APPLIANCE, INC., a California
                                       corporation

                                       By:
                                          -----------------------------------

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