Document:

<PAGE>

                                                                 EXHIBIT - 10.64

                                 FIFTH AMENDMENT

         THIS FIFTH AMENDMENT (the "Amendment") is made and entered into as of
the 18th day of November, 2003, by and between CA-THE CONCOURSE LIMITED
PARTNERSHIP, A DELAWARE LIMITED PARTNERSHIP ("Landlord"), and BROCADE
COMMUNICATIONS SYSTEMS, INC., A DELAWARE CORPORATION ("Tenant").

                                    RECITALS

A.       Landlord (as successor by conversion to EOP-The Concourse, L.L.C., a
         Delaware limited liability company, the successor in interest to
         Spieker Properties, L.P., a California limited partnership) and Tenant
         are parties to that certain lease dated December 17, 1999, which lease
         has been previously amended by instruments dated February 16, 2000 (the
         "First Amendment"), August 11, 2000 (the "Second Amendment"), November
         30, 2000 (the "Third Amendment") and November ___, 2003 (the "Fourth
         Amendment") (collectively, the "Lease"). Pursuant to the Lease,
         Landlord has leased to Tenant space currently containing approximately
         271,387 rentable square feet (the "Premises") comprised of (i) all of
         the rentable area, approximately 210,667 rentable square feet
         ("Original Premises"), in the building commonly known as The Concourse
         VI located at 1745 Technology Drive, San Jose, California ("Building
         VI"), (ii) 39,043 rentable square feet (the "Expansion Premises")
         described as Suite Nos. 250, 260, 500 on the 2nd, and 5th floors of the
         building commonly known as The Concourse V located at 1741 Technology
         Drive, San Jose, California ("Building V"), and (iii) 21,667 rentable
         square feet (the "Second Expansion Premises") described as Suite No.
         300 on the 3rd floor of Building V, in the project commonly known as
         The Concourse.

B.       Tenant and Landlord mutually desire that the Lease be amended on and
         subject to the following terms and conditions.

         NOW, THEREFORE, in consideration of the mutual covenants and agreements
herein contained and other good and valuable consideration, the receipt and
sufficiency of which are hereby acknowledged, Landlord and Tenant agree as
follows:

I.       AMENDMENT. Retroactively effective as of the date of the Second
         Amendment, Landlord and Tenant agree that the Lease shall be amended in
         accordance with the following terms and conditions:

         A.       Scheduled Term Expiration Date. The parties agree that the
                  "Scheduled Term Expiration Date", unless sooner terminated in
                  accordance with the Lease, shall mean August 31, 2010.

         B.       Section 1, "Rent", of the Second Amendment, shall be deleted
                  in its entirety and replaced with the following:

                  "A.      RENT. Subject to the provisions of Paragraphs 2.B,
                           Base Rent, net of Operating Expenses per Paragraph 7
                           of this Lease and net of any "additional rent"
                           otherwise due under this Lease, for the Premises
                           shall be as follows:

                           1.       ORIGINAL PREMISES FROM TERM COMMENCEMENT
                                    DATE THROUGH

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                                    SCHEDULED TERM EXPIRATION DATE. As of the
                                    Term Commencement Date, the schedule of Base
                                    Rent payable with respect to the Original
                                    Premises during the Term is the following:

                                                                    MONTHLY
                                             PERIOD                BASE RENT
                                    (09/01/00) - (08/31/01)       $516,159.00
                                    (09/01/01) - (08/31/02)       $531,643.00
                                    (09/01/02) - (08/31/03)       $547,593.00
                                    (09/01/03) - (08/31/04)       $564,020.00
                                    (09/01/04) - (08/31/05)       $580,941.00
                                    (09/01/05) - (08/31/06)       $598,369.00
                                    (09/01/06) - (08/31/07)       $616,320.00
                                    (09/01/07) - (08/31/08)       $634,810.00
                                    (09/01/08) - (08/31/09)       $653,854.00
                                    (09/01/09) - (08/31/10)       $673,470.00

                                    All such Base Rent shall be payable by
                                    Tenant in accordance with the terms of the
                                    Lease.

                           2        EXPANSION PREMISES FROM EXPANSION PREMISES
                                    TERM COMMENCEMENT DATE THROUGH SCHEDULED
                                    TERM EXPIRATION DATE. As of the Expansion
                                    Premises Term Commencement Date, the
                                    schedule of Base Rent payable with respect
                                    to the Expansion Premises during the balance
                                    of the Term is the following:

                                                                    MONTHLY
                                             PERIOD                BASE RENT
                                    (09/01/00) - (08/31/01)       $111,273.00
                                    (09/01/01) - (08/31/02)       $114,611.00
                                    (09/01/02) - (08/31/03)       $118,049.00
                                    (09/01/03) - (08/31/04)       $121,591.00
                                    (09/01/04) - (08/31/05)       $125,238.00
                                    (09/01/05) - (08/31/06)       $128,995.00
                                    (09/01/06) - (08/31/07)       $132,865.00
                                    (09/01/07) - (08/31/08)       $136,851.00
                                    (09/01/08) - (08/31/09)       $140,957.00
                                    (09/01/09) - (08/31/10)       $145,185.00

                                    All such Base Rent shall be payable by
                                    Tenant in accordance with the terms of the
                                    Lease.

                           3        SECOND EXPANSION PREMISES FROM SECOND
                                    EXPANSION PREMISES TERM COMMENCEMENT DATE
                                    THROUGH SCHEDULED TERM EXPIRATION DATE. As
                                    of the Second Expansion Premises Term
                                    Commencement Date, the schedule of Base Rent
                                    payable with respect to the Second Expansion
                                    Premises during the balance of the Term is
                                    the following:

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<PAGE>

                                                                   MONTHLY
                                             PERIOD               BASE RENT
                                    (01/01/01) - (12/31/01)      $104,002.00
                                    (01/01/02) - (12/31/02)      $107,122.00
                                    (01/01/03) - (12/31/03)      $110,335.00
                                    (01/01/04) - (12/31/04)      $113,645.00
                                    (01/01/05) - (12/31/05)      $117,055.00
                                    (01/01/06) - (12/31/06)      $120,566.00
                                    (01/01/07) - (12/31/07)      $124,183.00
                                    (01/01/08) - (12/31/08)      $127,909.00
                                    (01/01/09) - (12/31/09)      $131,746.00
                                    (01/01/10) - (08/31/10)      $135,698.00

                                    All such Base Rent shall be payable by
                                    Tenant in accordance with the terms of the
                                    Lease.

                           4        TENANT'S PROPORTIONATE SHARE OF OPERATING
                                    EXPENSES. For the period commencing on the
                                    Second Expansion Premises Term Commencement
                                    Date and ending on the Scheduled Term
                                    Expiration Date, Tenant shall pay for
                                    Tenant's Proportionate Share of Operating
                                    Expenses in accordance with the terms of the
                                    Lease."

         C.       Deleted Provisions. Section 3, "Rent", of First Amendment of
                  the Lease and Section 1, "Rent", of Second Amendment to Lease
                  are hereby deleted in their entirety and are of no further
                  force and effect.

II.      MISCELLANEOUS.

         A.       This Amendment sets forth the entire agreement between the
                  parties with respect to the matters set forth herein. Landlord
                  and Tenant acknowledge and agree that this Amendment is
                  intended as a clarification of the Base Rent payable under the
                  Lease only and does not in any way modify Tenant's rent
                  obligations under the Lease. There have been no additional
                  oral or written representations or agreements. Under no
                  circumstances shall Tenant be entitled to any Rent abatement,
                  improvement allowance, leasehold improvements, or other work
                  to the Premises, or any similar economic incentives that may
                  have been provided Tenant in connection with entering into the
                  Lease, unless specifically set forth in this Amendment or the
                  Lease.

         B.       Except as herein modified or amended, the provisions,
                  conditions and terms of the Lease shall remain unchanged and
                  in full force and effect.

         C.       In the case of any inconsistency between the provisions of the
                  Lease and this Amendment, the provisions of this Amendment
                  shall govern and control.

         D.       Submission of this Amendment by Landlord is not an offer to
                  enter into this Amendment but rather is a solicitation for
                  such an offer by Tenant. Landlord shall not be bound by this
                  Amendment until Landlord has executed and delivered the same
                  to Tenant.

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         E.       The capitalized terms used in this Amendment shall have the
                  same definitions as set forth in the Lease to the extent that
                  such capitalized terms are defined therein and not redefined
                  in this Amendment.

         F.       Tenant hereby represents to Landlord that Tenant has dealt
                  with no broker in connection with this Amendment. Tenant
                  agrees to indemnify and hold Landlord, its members,
                  principals, beneficiaries, partners, officers, directors,
                  employees, mortgagee(s) and agents, and the respective
                  principals and members of any such agents (collectively, the
                  "Landlord Related Parties") harmless from all claims of any
                  brokers claiming to have represented Tenant in connection with
                  this Amendment. Landlord hereby represents to Tenant that
                  Landlord has dealt with no broker in connection with this
                  Amendment. Landlord agrees to indemnify and hold Tenant, its
                  members, principals, beneficiaries, partners, officers,
                  directors, employees, and agents, and the respective
                  principals and members of any such agents (collectively, the
                  "Tenant Related Parties") harmless from all claims of any
                  brokers claiming to have represented Landlord in connection
                  with this Amendment.

         G.       Each signatory of this Amendment represents hereby that he or
                  she has the authority to execute and deliver the same on
                  behalf of the party hereto for which such signatory is acting.

                       [SIGNATURES ARE ON FOLLOWING PAGE]

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                  IN WITNESS WHEREOF, Landlord and Tenant have duly executed
         this Amendment as of the day and year first above written.

                           LANDLORD:

                           CA-THE CONCOURSE LIMITED PARTNERSHIP, A
                           DELAWARE LIMITED PARTNERSHIP

                           By: EOM GP, L.L.C., a Delaware limited liability
                               company, its general partner

                               By: Equity Office Management, L.L.C., a
                                   Delaware limited liability company,
                                   its non-member manager

                                   By:    /s/ John W. Petersen
                                          --------------------------------------
                                   Name:  John W. Petersen
                                   Title: Regional Senior Vice President

                           TENANT:

                           BROCADE COMMUNICATIONS SYSTEMS, INC., A
                           DELAWARE CORPORATION

                           By:    /s/ Antonio Canova
                                  ----------------------------------------------
                           Name:  Antonio Canova
                           Title: CFO

                                       5<PAGE>

                                                                 EXHIBIT - 10.65

                                 SIXTH AMENDMENT

         THIS SIXTH AMENDMENT (the "AMENDMENT") is made and entered into as of
the 18th day of November, 2003 ("EFFECTIVE DATE"), by and between CA-THE
CONCOURSE LIMITED PARTNERSHIP, A DELAWARE LIMITED PARTNERSHIP ("Landlord"), and
BROCADE COMMUNICATIONS SYSTEMS, INC., A DELAWARE CORPORATION ("TENANT").

                                    RECITALS

A.       Landlord (as successor by conversion to EOP-The Concourse, L.L.C., a
         Delaware limited liability company, the successor in interest to
         Spieker Properties, L.P., a California limited partnership) and Tenant
         are parties to that certain lease dated December 17, 1999 (the
         "ORIGINAL LEASE"), which lease has been previously amended by
         instruments dated February 16, 2000 (the "FIRST AMENDMENT"), August 11,
         2000 (the "SECOND AMENDMENT"), November 30, 2000 (the "THIRD
         AMENDMENT"), November ___ 2003 (the "FOURTH Amendment") and November
         ___, 2003 (the "FIFTH AMENDMENT") (which shall be collectively referred
         to herein as the "LEASE"). Pursuant to the Lease, Landlord has leased
         to Tenant space currently containing approximately 271,387 rentable
         square feet (the "PREMISES") comprised of all of the rentable area
         (approximately 210,667 rentable square feet) in the building commonly
         known as The Concourse VI located at 1745 Technology Drive, San Jose,
         California ("BUILDING VI"), and approximately 60,710 rentable square
         feet described as Suite Nos. 250, 260, 300 and 500 on the 2nd, 3rd and
         5th floors of the building commonly known as The Concourse V located at
         1741 Technology Drive, San Jose, California ("BUILDING V") in the
         project commonly known as The Concourse.

B.       EOP - Skyport I, L.L.C., a Delaware limited liability company (as
         successor in interest to MV Golden State San Jose, LLC, a Delaware
         limited liability company), an affiliate of Landlord ("SKYPORT
         LANDLORD"), and Tenant are also parties to that certain lease dated
         December 1, 2000 (as subsequently amended, the "SKYPORT LEASE").
         Pursuant to the Skyport Lease, Tenant currently leases approximately
         193,977 rentable square feet in the building commonly known as Skyport
         Tower III, and located at 1600 Technology Drive (the "SKYPORT
         PROPERTY").

C.       Skyport Landlord and Tenant have entered into that certain Real Estate
         Sale and Lease Termination Agreement [1600 Technology Drive, San Jose,
         California] dated as of November 18, 2003 ("SKYPORT SALE AGREEMENT"),
         pursuant to which the Skyport Landlord has, concurrent with the date of
         this Amendment, sold the Skyport Property to Brocade Communications
         Systems Skyport LLC, a Delaware limited liability company
         ("Purchaser"), as assignee of certain of Tenant's rights under the
         Skyport Sale Agreement, on the terms and conditions of the Skyport Sale
         Agreement, which terms and conditions include the execution of this
         Amendment concurrent with the close of escrow on the sale of the
         Skyport Property.

D.       Tenant and Landlord mutually desire that the Lease be amended on and
         subject to the following terms and conditions.

         NOW, THEREFORE, in consideration of the mutual covenants and agreements
herein contained and other good and valuable consideration, the receipt and
sufficiency of which are hereby acknowledged, Landlord and Tenant agree that,
from the Effective Date and until the

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earlier of (a) that date that is (5) five years after the Effective Date or (b)
that date, if any, upon which Tenant records a grant deed in favor of Skyport
Landlord (or Skyport Landlord's successor in interest) for the Skyport Property,
pursuant to Skyport Landlord's exercise of that certain Right of First Offer
Agreement entered into by and between Purchaser and Skyport Landlord concurrent
with the date of this Amendment , or (c) the date upon which Tenant pays a
Transfer Fee (as defined below) to Landlord under this Amendment (the "AMENDMENT
TERM"), the Lease shall be amended to provide as follows:

         1.       LIMITATION ON DISCRETIONARY TRANSFERS AFFECTING THE PREMISES
                  LOCATED IN BUILDING VI. Notwithstanding anything to the
                  contrary contained in Section 21 of the Original Lease, the
                  following shall apply:

                  a)       Tenant acknowledges and agrees that Tenant may not,
                           under any circumstance, sublease, license, assign or
                           pledge to a third party (each a "DISCRETIONARY
                           TRANSFER" and, collectively, the "DISCRETIONARY
                           TRANSFERS"), space in Building VI that exceeds a
                           maximum of twenty six thousand two hundred sixty
                           eight (26,268) usable square feet in the aggregate
                           across all of the Building VI over any period of time
                           (the "MAXIMUM TRANSFER SPACE"). Tenant shall provide
                           Landlord with Tenant's determination of the amount of
                           usable square footage in any space subject to a
                           Discretionary Transfer, which determination shall be
                           subject to Landlord's approval, including approval of
                           the architect and methods of measurement, in its
                           reasonable discretion. Any improvements required to
                           be made to the Premises in connection with a
                           Discretionary Transfer shall be Alterations subject
                           to Landlord's prior written approval to the extent
                           required by, and on the terms and conditions of, the
                           Lease and any reasonable requirement imposed by
                           Landlord related to the conversion of a single tenant
                           space to multi tenant use. All the approval and
                           consent provisions of Section 21 of the Lease shall
                           continue to apply with regard to any Discretionary
                           Transfer, subject to the additional limitation of the
                           Maximum Transfer Space and provided that Landlord may
                           withhold its consent to any Discretionary Transfer in
                           its sole and absolute discretion, if such
                           Discretionary Transfer will cause Tenant to exceed,
                           in the aggregate, the Maximum Transfer Space and
                           Tenant has not paid, or agreed to pay upon the
                           effective date of such Discretionary Transfer, the
                           Transfer Fee. Regardless of whether or not Landlord
                           has given its consent to or implicitly or expressly
                           approves a Discretionary Transfer, the square footage
                           of space affected by such a Discretionary Transfer
                           shall count against the Maximum Transfer Space and
                           could result in payment of the Transfer Fee if the
                           total space affected by Discretionary Transfers at
                           any particular point in time during the Amendment
                           Term exceeds the Maximum Transfer Space.

                  b)       Tenant further acknowledges and agrees that, as part
                           of the consent process for any Discretionary
                           Transfer, Landlord may continue to exercise the
                           termination right set forth in Section 21.A.(1)(i) of
                           the Original Lease, and, if Landlord exercises such
                           termination right (a "DISCRETIONARY TERMINATION"),
                           any space so terminated by Landlord shall not
                           constitute a Discretionary Transfer and shall not be
                           counted as

                                        2
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                           part of the Maximum Transfer Space.

                  c)       Landlord shall calculate and maintain a running tally
                           of the square footage of the Premises in Building VI
                           affected by Discretionary Transfers and shall, within
                           five (5) business days after Landlord's receipt of
                           Tenant's written request for same, provide a written
                           statement to Tenant of the total square footage
                           applied, as of the date of the statement, to the
                           Maximum Transfer Space. Landlord and Tenant
                           acknowledge and agree that space shall only be
                           included in the Maximum Transfer Space calculation
                           for the period of time that such space is subject to
                           a Discretionary Transfer.

                  d)       Landlord and Tenant agree that it is their mutual
                           intent that all space subject to Discretionary
                           Transfers, regardless of when such Discretionary
                           Transfer has occurred or occurs prior to the end of
                           the Amendment Term (including, without limitation,
                           Discretionary Transfers occurring prior to the
                           Effective Date or affecting space in Building VI that
                           is or was a part of the Original Premises), shall be
                           included in the calculation of space allocated to the
                           Maximum Transfer Space. Permitted Transfers shall
                           continue to be permitted without Landlord's consent
                           to the extent provided in the Lease, and shall not be
                           included in the calculation of space allocated to the
                           Maximum Transfer Space. Tenant hereby represents and
                           warrants to Landlord that, as of the Effective Date,
                           none of the Premises are or have been a part of a
                           Discretionary Transfer, such that Tenant has the
                           benefit of the full Maximum Transfer Space to use in
                           Discretionary Transfers going forward.

                  e)       Landlord and Tenant acknowledge that Landlord is in
                           the business of leasing office space in the same
                           market area of the Skyport Property and the Skyport
                           Landlord would not enter into the Skyport Sale
                           Agreement if such sale would result in increased
                           vacancy at Building VI or a diminution of the benefit
                           of its bargain under the Lease without receipt by
                           Landlord of the Transfer Fee. As such, Landlord and
                           Tenant agree that if Tenant exceeds the Maximum
                           Transfer Space at any time during the term of the
                           Lease, then Tenant shall pay Landlord, within ten
                           (10) days of Landlord's delivery to Tenant of written
                           notice of the occurrence of such event, a one-time
                           fee equal to One Million Nine Hundred Thousand
                           Dollars ($1,900,000), which shall be payable by wire
                           transfer of cash or a cashier's check as requested by
                           Landlord (the "TRANSFER FEE"). Upon payment (if any)
                           of the Transfer Fee, this Amendment shall terminate
                           and be of no further force and effect. Any failure of
                           Brocade to pay the Transfer Fee as provided herein,
                           without further notice or demand by Landlord, shall
                           constitute a breach of this Agreement and shall be
                           deemed an event of default under the Lease on the
                           part of Tenant.

                  f)       At the earlier of the expiration of the Amendment
                           Term and the payment of the Transfer Fee, this
                           Amendment shall be of no further force or effect and
                           the provisions of Section 21 as set forth in the
                           Lease shall be deemed reinstated without modification
                           or effect by this Amendment for the remaining Term of
                           the Lease.

                                       3
<PAGE>

         2.       MISCELLANEOUS.

                  a)       This Amendment and the following exhibits and
                           attachments attached hereto, which are hereby
                           incorporated into and made a part of this Amendment,
                           set forth the entire agreement between the parties
                           with respect to the matters set forth herein. There
                           have been no additional oral or written
                           representations or agreements. In no event shall this
                           Amendment be construed as giving Tenant any new
                           entitlement to any Rent abatement, improvement
                           allowance, leasehold improvements, or other work to
                           the Premises, or any similar economic incentives that
                           may have been provided Tenant in connection with
                           entering into the Lease, unless specifically set
                           forth in this Amendment.

                  b)       Except as herein modified or amended, the provisions,
                           conditions and terms of the Lease shall remain
                           unchanged and in full force and effect.

                  c)       In the case of any inconsistency between the
                           provisions of the Lease and this Amendment, the
                           provisions of this Amendment shall govern and
                           control.

                  d)       Submission of this Amendment by Landlord is not an
                           offer to enter into this Amendment but rather is a
                           solicitation for such an offer by Tenant. Landlord
                           shall not be bound by this Amendment until Landlord
                           has executed and delivered the same to Tenant.

                  e)       The capitalized terms used in this Amendment shall
                           have the same definitions as set forth in the Lease
                           to the extent that such capitalized terms are defined
                           therein and not redefined in this Amendment.

                  f)       Tenant hereby represents to Landlord that Tenant has
                           dealt with no broker in connection with this
                           Amendment. Tenant agrees to indemnify and hold
                           Landlord, its members, principals, beneficiaries,
                           partners, officers, directors, employees,
                           mortgagee(s) and agents, and the respective
                           principals and members of any such agents
                           (collectively, the "Landlord Related Parties")
                           harmless from all claims of any brokers claiming to
                           have represented Tenant in connection with this
                           Amendment. Landlord hereby represents to Tenant that
                           Landlord has dealt with no broker in connection with
                           this Amendment. Landlord agrees to indemnify and hold
                           Tenant, its members, principals, beneficiaries,
                           partners, officers, directors, employees, and agents,
                           and the respective principals and members of any such
                           agents (collectively, the "Tenant Related Parties")
                           harmless from all claims of any brokers claiming to
                           have represented Landlord in connection with this
                           Amendment.

                  g)       Each signatory of this Amendment represents hereby
                           that he or she has the authority to execute and
                           deliver the same on behalf of the party hereto for
                           which such signatory is acting.

                  h)       This Amendment may be executed in any number of
                           identical

                                       4
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                           counterparts, any or all of which may contain the
                           signatures of less than all of the parties, and all
                           of which shall be construed together as but a single
                           instrument.

         IN WITNESS WHEREOF, Landlord and Tenant have duly executed this
Amendment as of the day and year first above written.

                                    LANDLORD:

                                    CA-THE CONCOURSE LIMITED PARTNERSHIP, A
                                    DELAWARE LIMITED PARTNERSHIP

                                    By:  EOM GP, L.L.C., a Delaware limited
                                         liability company, its general partner

                                         By: Equity Office Management, L.L.C., a
                                             Delaware limited liability company,
                                             its non-member manager

                                             By:    /s/ John W. Petersen
                                                    ---------------------------
                                             Name:  John W. Petersen
                                             Title: Regional Senior Vice
                                                    President

                                    TENANT:

                                    BROCADE COMMUNICATIONS SYSTEMS, INC., A
                                    DELAWARE CORPORATION

                                    By:    /s/ Antonio Canova
                                           -------------------------------------
                                    Name:  Antonio Canova
                                    Title: CFO

                                       5

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