Document:

<PAGE>

                                                                   EXHIBIT 10.29

*CONFIDENTIAL TREATMENT REQUESTED.  CONFIDENTIAL PORTION HAS BEEN FILED
SEPARATELY WITH THE SECURITIES AND EXCHANGE COMMISSION.

                           SECOND AMENDMENT TO LEASE
                           -------------------------

          THIS SECOND AMENDMENT TO LEASE ("Second Amendment") is made this 1st
day of May, 2000, by and between TRIZECHAHN BEAUMEADE TECHNOLOGY CENTER LLC, a
Delaware limited liability company ("Landlord"), as successor in interest to
Laing Beaumeade, Inc., a Georgia corporation ("Original Landlord"), and EQUINIX,
INC., a Delaware corporation ("Tenant").

                             W I T N E S S E T H:

          WHEREAS, by that certain Lease dated as of November 18, 1998 (the
"Original Lease"), Original Landlord leased to Tenant, and Tenant leased from
Original Landlord, approximately [*] square feet of rentable area (the "Original
Leased Premises"), known as Suite C, located on the first (1st) floor of the
building located at [*], Ashburn, Virginia (the "Building"), upon the terms and
conditions set forth in the Original Lease;

          WHEREAS, as of March 31, 2000 all of the right, title and interest of
Original Landlord in the Building was transferred to TrizecHahn Centers, Inc.
d/b/a TrizecHahn Beaumeade Corporate Management, a California corporation
("Centers"), and all of the right, title and interest of Original Landlord in
the Original Lease was assigned to Centers;

          WHEREAS, by that certain First Amendment to Lease dated September 9,
1999 (the "First Amendment"), Centers leased to Tenant, and Tenant leased from
Centers, approximately [*] rentable square feet of space located on the first
(1st) floor of the Building (the "Expansion Space"), upon the terms and
conditions more specifically set forth therein;

          WHEREAS, the Original Lease and the First Amendment are hereinafter
collectively referred to as the "Lease";

          WHEREAS, all of the right, title and interest of Centers in the
Building was transferred to Landlord, and all of the right, title and interest
of Centers in the Lease was assigned to Landlord;

          WHEREAS, the Original Premises and the Expansion Space are hereinafter
collectively referred to as the "Leased Premises";

_____________
*CONFIDENTIAL TREATMENT REQUESTED.  CONFIDENTIAL PORTION HAS BEEN FILED
SEPARATELY WITH THE SECURITIES AND EXCHANGE COMMISSION.
<PAGE>

          WHEREAS, Tenant desires to lease from Landlord, and Landlord desires
to lease to Tenant, an additional [*] rentable square feet of space located on
the first (1st) floor of the Building (hereinafter referred to as the "Second
Expansion Space"), upon the terms and conditions hereinafter set forth; and

          WHEREAS, Landlord and Tenant desire to amend the Lease to reflect
their understanding and agreement with regard to the lease of such additional
space, and to otherwise amend the Lease, as more particularly set forth herein.

          NOW, THEREFORE, for and in consideration of the mutual promises herein
contained, and other good and valuable consideration, the receipt and
sufficiency of which are hereby acknowledged, the parties hereto mutually agree
as follows:

          1.   Any capitalized terms used in this Second Amendment and not
otherwise defined herein shall have the meanings ascribed to them in the Lease.

          2.   The Lease is hereby amended by adding thereto a new Section 30,
to read as follows:

          "30. SECOND EXPANSION SPACE

               A.   Term.  Landlord hereby leases unto Tenant, and Tenant
                    ----
hereby leases from Landlord, approximately [*] square feet of rentable floor
area (the "Second Expansion Space") located on the first (1st) floor of the
Building, which Second Expansion Space is hereby agreed to be that certain space
which is shown on Exhibit I attached hereto and made a part hereof, for a term
(the "Second Expansion Space Term") commencing on May 1, 2000 (the "Second
Expansion Space Commencement Date"), and continuing through and including the
last day of the Term of this Lease, unless earlier terminated pursuant to the
provisions of this Lease.

               B.   "As-is" Condition.  Tenant accepts the Second Expansion
                    -----------------
Space in its "as-is" condition. Notwithstanding anything contained in this Lease
to the contrary, Landlord shall have no obligation to make any improvements or
alterations to the Second Expansion Space or to the remainder of the Leased
Premises.

               C.   Second Expansion Space Base Rent.  In addition to the Base
                    --------------------------------
Rent for the Leased Premises as set forth in Exhibit C hereof and Section 29
hereof, commencing on the Second Expansion Space Commencement Date and
continuing thereafter throughout the Second Expansion Space Term, Tenant
covenants and agrees to pay to Landlord Base Rent for the Second Expansion Space
in the following amounts (the "Second Expansion Space Annual Base Rent"):

_______________
*CONFIDENTIAL TREATMENT REQUESTED.  CONFIDENTIAL PORTION HAS BEEN FILED
SEPARATELY WITH THE SECURITIES AND EXCHANGE COMMISSION.
<PAGE>

<TABLE>
<CAPTION>
                           Second Expansion
                          Space Annual Base       Second Expansion    Second Expansion
                         Rent Per Square Foot       Space Annual      Space Annual Base
   Time Period                Per Annum               Base Rent        Rent Per Month
   -----------                ---------               ---------        --------------
<S>                      <C>                      <C>                 <C>
5/1/00 - 1/31/01                $[*]                     $[*]               $[*]

2/1/01 - 1/31/02                $[*]                     $[*]               $[*]

2/1/02 - 1/31/02                $[*]                     $[*]               $[*]

2/1/03 - 1/31/04                $[*]                     $[*]               $[*]

2/1/04 - 1/31/05                $[*]                     $[*]               $[*]

2/1/05 - 1/31/06                $[*]                     $[*]               $[*]

2/1/06 - 1/31/07                $[*]                     $[*]               $[*]

2/1/07 - 1/31/08                $[*]                     $[*]               $[*]

2/1/08 - 1/31/09                $[*]                     $[*]               $[*]

</TABLE>

               D.   Except as otherwise herein expressly provided, the Second
Expansion Space shall be deemed a part of the Premises for all purposes of this
Lease, such that both Landlord and Tenant shall have such respective rights and
obligations with respect to the Second Expansion Space as apply to the remainder
of the Leased Premises."

          3.   Section 4.(a) of the Lease (captioned "Operating Expenses") is
hereby amended as of the Second Expansion Space Commencement Date by deleting
from the end thereof the language "[*]% ([*])" and inserting the following
language in lieu thereof: "[*]% ([*])."

          4.   Section 13 of the Lease (captioned "Improvements and Alterations
by Tenant") is hereby amended as of the Second Expansion Space Commencement Date
by deleting all of the language contained therein and inserting the following
language in lieu thereof:

               "(a) Alterations:  Any improvements, alterations, fixed
                    -----------
decorations or modifications, structural or otherwise, to the Leased Premises,
the Building or the Land, including, but not limited to, the installation or
modification of carpeting, partitions, counters, doors, air conditioning ducts,
plumbing, piping, lighting fixtures, wiring, hardware, locks, ceilings and
window and wall coverings.

               (b)  Making of Alterations; Landlord's Consent; [*]
                    ----------------------------------------------
Association's Consent: Tenant shall not make or permit to be made any
---------------------
Alterations without the prior written consent of Landlord both as to whether the
Alterations may be made and as to how and when they will be made, which consent
shall not be unreasonably withheld or delayed with respect to

______________
*CONFIDENTIAL TREATMENT REQUESTED.  CONFIDENTIAL PORTION HAS BEEN FILED
SEPARATELY WITH THE SECURITIES AND EXCHANGE COMMISSION.
<PAGE>

any proposed Alteration which would not be visible from outside of the Leased
Premises nor affect any of the structural components of the Building; provided,
however, that the consent of Landlord shall not be required for (i) painting or
carpeting of the Leased Premises or (ii) Alterations costing less than Fifty
Thousand Dollars ($50,000.00) in the aggregate which are not visible from
outside of the Leased Premises and which do not affect any of the structural
components of the Building; further provided, that Tenant shall give Landlord at
least ten (10) days' prior written notice of any such Alterations not requiring
Landlord's consent and Tenant shall observe all reasonable rules and regulations
promulgated by Landlord with respect to the performance of Alterations. Any
Alterations shall be made at Tenant's expense, by its contractors and
subcontractors and in accordance with complete plans and specifications approved
in advance in writing by Landlord, and only after Tenant: (i) has obtained all
necessary permits from governmental authorities having jurisdiction and has
furnished copies thereof to Landlord, (ii) has submitted to Landlord an
architect's certificate that the Alterations will conform to all applicable laws
and regulations, and (iii) has complied with all other requirements reasonably
imposed by Landlord, including without limitation any requirements due to the
underwriting guidelines of Landlord's insurance carriers. Landlord's consent to
any Alterations and approval of any plans and specifications constitutes
approval of no more than the concept of these Alterations and not a
representation of warranty with respect to the quality or functioning of such
Alterations, plans and specifications. Tenant shall be and is solely responsible
for the Alterations and for the proper integration thereof with the Building,
the Building's systems and existing conditions. Landlord shall have the right,
but not the obligation, to supervise the making of any Alterations. If any
Alterations are made without the prior written consent of Landlord or the [*]
Owners Association, Inc. (the "[*] Association"), if applicable, or which do not
if applicable, or to other conditions imposed by Landlord or the [*]
Association, if applicable, and such nonconformity is not fully corrected by
Tenant within fifteen (15) days after notice from Landlord to Tenant or such
shorter notice period as Landlord, in good faith, reasonably believes to be
necessary in order to comply with the requirements of any applicable law,
governmental regulation or insurance company requirement, then Landlord may, in
its sole discretion, correct or remove such Alterations at Tenant's expense.
Following completion of any Alterations, at Landlord's request, Tenant either
shall deliver to Landlord a complete set of "as built" plans showing the
Alterations or shall reimburse Landlord for any expense incurred by Landlord in
causing the Building plans to be modified to reflect the Alterations. In
addition to the foregoing, any Alterations which are visible from outside of the
Leased Premises are subject to the prior review and approval of the
[*] Association, which approval may be granted or denied in the sole and
absolute discretion of the [*] Association, and which approval Tenant is solely
responsible for obtaining.

               (c)  No Liens:  Tenant shall take all necessary steps to ensure
                    --------
that no mechanic's or materialmen's liens are filed against the Leased Premises,
the Building or the Land as a result of any Alterations made by the Tenant. If
any mechanic's lien is filed, Tenant shall discharge the lien within ten (10)
days thereafter, at Tenant's expense, by paying off or bonding the lien.

______________
*CONFIDENTIAL TREATMENT REQUESTED.  CONFIDENTIAL PORTION HAS BEEN FILED
SEPARATELY WITH THE SECURITIES AND EXCHANGE COMMISSION.
<PAGE>

               (d)  Permitted Equipment: With the exception of the items of
                    -------------------
equipment or machinery which are reflected on Tenant's plans for Tenant's
initial buildout of the Leased Premises, Tenant shall not install or operate in
the Leased Premises any equipment or other machinery without: (i) obtaining the
prior written consent of Landlord, who may condition its consent upon the
payment by Tenant of Additional Rent for additional wiring or other expenses
resulting therefrom, which consent shall not be unreasonably withheld,
conditioned or delayed, unless Landlord determines, in its sole and absolute
discretion, that such equipment or machinery causes noise or vibration which
would disturb any other tenant of [*] (the "Park"), (ii) securing all necessary
permits from governmental authorities and utility companies and furnishing
copies thereof to Landlord, and (iii) complying with all other requirements
reasonably imposed by Landlord. Tenant shall not install any equipment or
machinery which may necessitate any changes, replacements or additions to or
material changes in the use of the water system of the Building without
obtaining the prior written consent of Landlord, who may withhold its consent in
its absolute discretion.

               (e)  Noise; Vibration; Floor Load:  Business machines and
                    ----------------------------
equipment belonging to Tenant, which cause noise or vibration that may be
transmitted to any part of the Building to such a degree as to be objectionable
to Landlord or to any tenant of the Park shall be installed and maintained by
Tenant at Tenant's expense on devices that eliminate the noise and vibration.
Tenant shall not place any load upon the floor of the Premises which exceeds the
per square foot load the floor was designed to carry (it being understood and
agreed that the floor is a six inch (6") slab with a capacity of two hundred
fifty (250) pounds)."

          5.   Section 18 of the Lease (captioned "Parking") is hereby amended
as of the Second Expansion Space Commencement Date by inserting the following
language at the end thereof:

          "In addition to the foregoing, Landlord hereby agrees to
          designate twenty-four (24) parking spaces in the immediate
          vicinity of the Leased Premises for the exclusive use of
          Tenant, its employees and invitees, it being understood,
          acknowledged and agreed, however, that Landlord shall have
          no obligation whatsoever to monitor or police the use of
          such parking spaces and shall have no liability of any
          nature whatsoever if all or any of such spaces are used by
          any other parties, including, but not limited to, other
          tenants in the Building."

          6.   The Lease is hereby further amended by adding thereto a new
Section 31, to read as follows:

          "31. OPTION TO EXTEND

          Provided that Equinix, Inc., a Delaware corporation, or an Affiliate
(as hereinafter defined) (said Equinix, Inc. or an Affiliate being hereinafter
collectively referred to as "Equinix") (i) is not then in default in the payment
of any Rent due under this Lease and is not then in

_____________
*CONFIDENTIAL TREATMENT REQUESTED.  CONFIDENTIAL PORTION HAS BEEN FILED
SEPARATELY WITH THE SECURITIES AND EXCHANGE COMMISSION.
<PAGE>

default in the performance of any of its other obligations under this Lease, and
(ii) has not been in default beyond any applicable notice and cure periods more
than once during the immediately preceding two (2) years of the term, in each
case both at the time of exercise of the Renewal Option, as hereinafter defined,
and at the commencement of the Renewal Period, as hereinafter defined, and is
then in occupancy of the Leased Premises at the time of exercise of the Renewal
Option, as hereinafter defined, and at the time of the commencement of the
Renewal Period, as hereinafter defined, Equinix shall have an option (the
"Renewal Option") to extend the term of this Lease for an additional five (5)
year period (the "Renewal Period") after the expiration of the initial term. The
Renewal Option shall be exercisable only by written notice given by Equinix to
Landlord not later than twelve (12) months, nor earlier than fifteen (15)
months, prior to the expiration of the initial term. In the event that Equinix
does not timely exercise the Renewal Option, the Renewal Option shall be null
and void and of no further force or effect, time being of the essence in the
exercise of the Renewal Option and it being acknowledged and agreed by Equinix
that Landlord shall be entitled to rely on any failure by Equinix to give
written notice of its exercise of the Renewal Option by the date set forth
herein for such exercise thereof.

          All terms and conditions of this Lease shall be applicable during the
Renewal Period except that the amount of Base Rent charged for the Renewal
Period shall be the then "Prevailing Market Rent", which shall be the rent for
comparable space in comparable buildings in Loudoun County, Virginia; provided,
however, that in no event shall the Prevailing Market Rent determined as
aforesaid be deemed to be less than the Base Rent for the entire Leased Premises
payable under this Lease immediately preceding commencement of the Renewal
Period.  If within thirty (30) days following delivery of Equinix's notice,
Landlord and Equinix have not mutually agreed on the Prevailing Market Rent for
the Renewal Period, then within ten (10) days after the expiration of such
thirty-day period, each party shall give written notice to the other setting
forth the name and address of a Broker (as hereinafter defined) selected by such
party who has agreed to act in such capacity, to determine the Prevailing Market
Rent.  If either party shall fail to select a Broker as aforesaid, the
Prevailing Market Rent shall be determined by the Broker selected by the other
party.  Each Broker shall thereupon independently make his determination of the
Prevailing Market Rent within twenty (20) days after the appointment of the
second Broker.  If the two Brokers' determinations are not the same, but the
higher of such two values is not more than one hundred five percent (105%) of
the lower of them, then the Prevailing Market Rent shall be deemed to be the
average of the two values.  If the higher of such two values is more than one
hundred five percent (105%) of the lower of them, then the two Brokers shall
jointly appoint a third Broker within ten (10) days after the second of the two
determinations described above has been rendered.  The third Broker shall
independently make his determination of the Prevailing Market Rent within twenty
(20) days after his appointment.  The highest and the lowest determinations of
value among the three Brokers shall be disregarded and the remaining
determination shall be deemed to be the Prevailing Market Rent.  Within thirty
(30) days after the Prevailing Market Rent is determined as aforesaid, the
parties shall execute an amendment to this Lease setting forth the new Rent to
be paid for the Renewal Period.

          For the purposes of this Section 31, "Broker" shall mean a real estate
broker licensed in the Commonwealth of Virginia, who has been regularly engaged
in such capacity in the business of commercial leasing in Loudoun County,
Virginia for at least ten (10) years immediately preceding such person's
appointment hereunder.  Each party shall pay for the cost of its Broker and one-
half of the cost of the third Broker.  For the purposes of this Section 31, an
<PAGE>

"Affiliate" shall mean (1) any parent corporation of Tenant, (2) any subsidiary
corporation of Tenant or of Tenant's parent corporation, (3) any entity in which
Tenant, any parent corporation of Tenant or any subsidiary corporation of Tenant
or of Tenant's parent corporation holds a majority of the outstanding shares or
ownership interests, or (4) any corporation resulting from the merger,
consolidation or reorganization of Tenant or Tenant's parent corporation with
another corporation."

          7.   Landlord and Tenant acknowledge that they are the landlord and
tenant, respectively, under (i) that certain Deed of Lease dated December 15,
1999 (the "Building F Lease") for space in the building located at [*], Ashburn,
Virginia, and (ii) that pending Deed of Lease between Landlord, as landlord, and
Tenant, as tenant, regarding space in the building located at [*], Ashburn,
Virginia (the "Building E Lease") (the Building F Lease and the Building E Lease
are hereinafter collectively referred to as the "Other Leases"). In the event
that any default occurs under either of the Other Leases, such default shall
constitute a default under this Lease, without the necessity of providing any
separate notice hereunder or thereunder, and if one, the other or both, of the
Other Leases shall be terminated as a result of such a default by Tenant
thereunder, this Lease shall be terminated upon written notice by Landlord to
Tenant, whereupon this Lease shall end and all rights of Tenant (but not the
liability of Tenant) hereunder shall expire and terminate.

          8.   If requested by Landlord at any time during the Second Expansion
Space Term, Tenant promptly will execute a declaration in the form attached
hereto as Exhibit J.

          9.   Section 28.(s) of the Lease (captioned "Brokers") and Exhibit D
to the Lease (captioned "Work Agreement") shall not be applicable to the Second
Expansion Space.

          10.  Landlord and Tenant represent and warrant to each other that the
person signing this Second Amendment on its behalf has the requisite authority
and power to execute this Second Amendment and to thereby bind the party on
whose behalf it is being signed.

          11.  Landlord and Tenant represent and warrant to each other that,
except as hereinafter provided, neither of them has employed any broker in
procuring or carrying on any negotiations relating to this Second Amendment.
Landlord and Tenant shall indemnify and hold each other harmless from any loss,
claim or damage relating to the breach of the foregoing representation and
warranty by the indemnifying party. Landlord recognizes only Trammell Crow
Company ("Tenant's Broker"), as agent of Tenant, with respect to this Second
Amendment and agrees to be responsible for the payment of a commission to
Tenant's Broker, pursuant to a separate agreement with Tenant's Broker.

          12.  Except as expressly amended and modified herein, all terms,
conditions and provisions of the Lease shall remain unmodified and in full force
and effect. In the event of any conflict between the terms and conditions of the
Lease and the terms and conditions of this Second Amendment, the terms and
conditions of this Second Amendment shall govern and control.

________________
*CONFIDENTIAL TREATMENT REQUESTED.  CONFIDENTIAL PORTION HAS BEEN FILED
SEPARATELY WITH THE SECURITIES AND EXCHANGE COMMISSION.
<PAGE>

          IN WITNESS WHEREOF, Landlord and Tenant have executed this Second
Amendment to Lease as of the day and year first hereinabove written.

                                        LANDLORD
                                        --------

WITNESS:                                TRIZECHAHN BEAUMEADE
                                        TECHNOLOGY CENTER LLC,
                                        a Delaware limited liability company

    /s/ signature illegible             By:      /s/ Paul L. Schulman
-------------------------------            ----------------------------------
                                        Name:  Paul L. Schulman
                                        Its:   Assistant Secretary

                   [SIGNATURES CONTINUED ON FOLLOWING PAGE]
<PAGE>

                   [SIGNATURES CONTINUED FROM PREVIOUS PAGE]

                                        TENANT
                                        ------

ATTEST:                                 EQUINIX, INC., a Delaware corporation

[Corporate Seal]

By:    /s/ Albert M. Avery IV           By:    /s/ Philip J. Koen
   -----------------------------           ---------------------------------
Name:  Albert M. Avery IV               Name:  Philip J. Koen
Its:   CEO                              Its:   CFO
<PAGE>

                                   EXHIBIT I

                        PLAN OF SECOND EXPANSION SPACE
<PAGE>

                                   EXHIBIT J
                                   ---------

                      DECLARATION BY LANDLORD AND TENANT
                   AS TO DATE OF DELIVERY AND ACCEPTANCE OF
          POSSESSION, SECOND EXPANSION SPACE COMMENCEMENT DATE, ETC.

          THIS DECLARATION, dated this 1st day of May, 2000, is hereby attached
to and made a part of the Second Amendment to Lease dated the 1st day of May,
2000 (the "Amendment"), entered into by and between TRIZECHAHN BEAUMEADE
TECHNOLOGY CENTER LLC ("Landlord"), as landlord, and EQUINIX, INC. ("Tenant"),
as tenant, which modifies that certain Lease dated as of November 19, 1998, as
amended (the "Original Lease").  All terms used in this Declaration have the
same meaning as they have in the Original Lease as modified by the Amendment
(collectively, the "Lease").

          (i)   Landlord and Tenant do hereby declare that possession of the
Second Expansion Space was accepted by Tenant on the _____ day of ___________,
2000;

          (ii)  As of the date hereof, the Lease is in full force and effect,
and Landlord has fulfilled all of its obligations under the Lease required to be
fulfilled by Landlord on or prior to said date; and

          (iii) The date on which the Term of the Lease is scheduled to expire
is hereby established to be January 14, 2009, unless the Lease is sooner
terminated pursuant to any provision of the Lease.

                                   LANDLORD
                                   --------

WITNESS:                           TRIZECHAHN BEAUMEADE
                                   TECHNOLOGY CENTER LLC,
                                   a Delaware limited liability company

______________________________     By:_________________________________
                                   Name:_______________________________
                                   Its:________________________________

                   [SIGNATURES CONTINUED ON FOLLOWING PAGE]
<PAGE>

                   [SIGNATURES CONTINUED FROM PREVIOUS PAGE]

                                   TENANT
                                   ------

ATTEST:                            EQUINIX, INC., a Delaware corporation

[Corporate Seal]

By:_______________________         By:___________________________
Name:_____________________         Name:  Philip J. Koen
Its:______________________         Its:   CFO<PAGE>

                                                                   EXHIBIT 10.30

*CONFIDENTIAL TREATMENT REQUESTED. CONFIDENTIAL PORTION HAS BEEN FILED
SEPARATELY WITH THE SECURITIES AND EXCHANGE COMMISSION.

August 24, 2000

VIA FACSIMILE
-------------

600 Seventh Street Associates, Inc.
600 West Seventh Street
Suite 600
Los Angeles, California  90014

          Re:  Telecommunications Office Lease by and between 600 Seventh
               ----------------------------------------------------------
               Street Associates, Inc., and Equinix, Inc., dated August 8, 1999
               ----------------------------------------------------------------

Ladies and Gentleman:

     This letter agreement (this "Letter Agreement") is made in connection with
that certain Telecommunications Office Lease (the "Lease"), dated as of August
8, 1999, entered into by and between 600 Seventh Street Associates, Inc., a
California corporation ("Landlord") and Equinix, Inc., a Delaware corporation
("Tenant").  Landlord and Tenant have agreed, and do hereby agree, to modify the
Lease as follows:

     1.   Commencement Date.  Notwithstanding anything in the Lease to the
          -----------------
          contrary, the Lease Commencement Date shall be October 1, 2000;
          provided, however, the Lease Commencement Date shall be delayed one
          (1) day for each day of delay in satisfaction of the following two (2)
          conditions: (a) on or before August 28, 2000, Landlord obtains a
          temporary certificate of occupancy for the Building from the City of
          Los Angeles, (b) on or before August 28, 2000, Landlord obtains
          authorization from the City of Los Angeles to grant Tenant access to
          Tenant's portion of the Generator Fuel Tank so as to allow Tenant to
          connect such Generator Fuel Tank to Tenant's Generators.

     2.   Tenant Improvement Allowance.  Notwithstanding anything to the
          ----------------------------
          contrary contained in the Lease: (i) Tenant shall be entitled to a
          Tenant Improvement Allowance in the amount of $3,458,229.00; (ii)
          Tenant
<PAGE>

          acknowledges receipt of certain invoices sent by Jacqueline C. Wolfe
          of Landlord to Michele Keefhaver of Tenant under cover of letter dated
          July 20, 2000 (the "Invoices"), which Invoices indicate that Landlord
          has performed certain improvement work on behalf of Tenant; (iii)
          Tenant and Landlord agree that the amount to be reimbursed by Tenant
          to Landlord for such work relating to the Invoices is $1,172,282.00
          and such amount shall be offset against the Tenant Improvement
          Allowance; (iv) Tenant shall have no further payment obligation to
          Landlord with respect to such work relating to the Invoices and such
          payment shall constitute full satisfaction of all amounts owed to
          Landlord as reimbursement of the costs of such work relating to such
          Invoices; and (v) the foregoing shall not be deemed a waiver of
          Tenant's right to receive the remainder of the Tenant Improvement
          Allowance in the amount of $2,285,947.00. Landlord shall wire the
          remaining Tenant Improvement Allowance set forth in (v) above to
          Tenant upon the closing of the sale of the Building by Landlord to
          360networks inc. Landlord shall not have the right to perform any
          future work for or on behalf of Tenant except as provided for in the
          Lease. Notwithstanding the foregoing, Tenant expressly reserves all
          rights and remedies with respect to Landlord's performance of any
          Compliance Work or punch list items relating to Landlord's performance
          of the work relating to the Invoices.

     3.   Standard Tenant Services.  The number of bus ducts through which
          ------------------------
          Tenant obtains its electrical supply for the Premises pursuant to
          Section 6.1.2 of the Lease is hereby increased from two (2) to three
          (3).  Landlord shall use its best efforts to assist Tenant in
          energizing the third bus duct and coordinating such energization with
          the Depart of Water and Power of the City of Los Angeles.

     4.   Fuel Tank Capacity.  Section 22.1.4 of the Lease is hereby amended by
          ------------------
          replacing the number "10,000" with the number "20,000" in the first
          sentence of Section 22.1.4.

     5.   Conduits.  Section 22.1.7(ii) of the Lease is hereby deleted in its
          --------
          entirety and replaced with the following:

          "(ii) eight (8) four inch (4.0") aluminum conduits in the interconnect
          riser of the Building (the "Interconnect Riser") running from the
          fifth (5/th/) floor to the seventh (7/th/) floor of the Building, and
          (iii) eight (8) four inch (4.0") aluminum conduits in shafts 510
          through 710 of the Building running from the fifth (5/th/) floor to
          the seventh (7/th/) floor of the Building (collectively, "Tenant's
          Conduit")."

                                       2
<PAGE>

     6.   Exhibit H.  The first paragraph of Section 1 of Exhibit H to the Lease
          ---------
          is hereby deleted in its entirety and replaced with the following:

          "Tenant wishes to install on the top roof of the Building (a) customer
          antennas as more particularly described below in this section
          (collectively, "Antennas"); and (b) four (4) four inch (4.0") conduits
          and three (3) one inch (1.0") conduits connecting customer Antennas to
          the Premises (collectively, the "Antenna Conduits").  The Antennas to
          be installed by Tenant under this Rider shall be installed on a one
          thousand square foot platform on the roof of the Building in the area
          bounded by Carrier Center drawings column lines 5 to 7, and M to N
          ("Antenna Space")."

     7.   Exhibit B.  Exhibit B, Schedule 2, 1/st/ Floor, Item 1 of the Lease is
          ---------
          hereby amended to provide that Tenant shall have shaft access from the
          basement of the Building to the Premises for generator conduits, due
          to relocation of the generators from the roof to the basement and
          Exhibit B, Schedule 2, 7th Floor, Item 1, of the Lease is hereby
          deleted in its entirety.

     8.   Address of Tenant (Section 29.18):  The address of Tenant for
          ---------------------------------
          notices under the Lease is hereby amended as follows:

          Equinix, Inc.
          2450 Bayshore Parkway
          Mountain View, CA 94043-1107
          Attention:  Real Estate Counsel

          With a copy to:

          Equinix, Inc.
          [*]
          ===
          [*]
          ===
          Los Angeles, CA [*]
                          ===

     Except as expressly modified in this Letter Agreement, all terms and
conditions of the Lease shall remain unmodified and in full force and effect.
Defined terms used herein and not otherwise defined shall have the meanings
assigned to such terms in the Lease.

     The Lease as modified by this Letter Agreement sets forth the full and
complete understanding between Landlord and Tenant. This Letter Agreement may be
executed in counterparts. The telecopy transmission of a signed copy of this
Letter Agreement shall constitute a binding and effective execution by the
signing party.

     By executing below the parties acknowledge and agree to the terms and
conditions set forth in this Letter Agreement. Notwithstanding anything in this
Letter

________________
  *CONFIDENTIAL TREATMENT REQUESTED. CONFIDENTIAL PORTION HAS BEEN FILED
SEPARATELY WITH THE SECURITIES AND EXCHANGE COMMISSION.

                                       3
<PAGE>

Agreement to the contrary, this Letter Agreement shall be effective if and when
(and only if and when): (i) this Letter Agreement is executed by each party and
delivered to the other party; and (ii) an original fully executed tenant
estoppel in the form required pursuant to the Lease (as may be modified by the
terms of this Letter Agreement), has been delivered to Landlord by August 25,
2000. Failure of Tenant to deliver the estoppel by August 25, 2000 shall render
this Letter Agreement null and void and of no further force and effect.

EQUINIX, INC.,
a Delaware corporation

By:   /s/ Renee F. Lanam
     _________________________________

      General Counsel
     _________________________________
     [Printed Name and Title]

The foregoing is agreed and consented to this ____ day of August, 2000.

600 SEVENTH STREET ASSOCIATES, INC.,
a California corporation

By:   /s/ Jack Matthews
     _________________________________

      Vice President
     _________________________________
     [Printed Name and Title]

                                       4

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