Document:

<PAGE>

CONFIDENTIAL TREATMENT HAS BEEN REQUESTED FOR CERTAIN PORTIONS OF THIS DOCUMENT
PURSUANT TO AN APPLICATION FOR CONFIDENTIAL TREATMENT SENT TO THE SECURITIES AND
EXCHANGE COMMISSION. SUCH PORTIONS ARE OMITTED FROM THIS FILING AND ARE FILED
SEPARATELY WITH THE SECURITIES AND EXCHANGE COMMISSION.

                                                                   EXHIBIT 10.37

                          AMENDMENT TO LOAN AGREEMENT

          THIS AMENDMENT TO LOAN AGREEMENT dated as of May 4, 2001 (this
"Amendment") between LEHMAN BROTHERS BANK FSB, having an address at 921 North
Orange Street, Wilmington, Delaware 19801  ("Lender") and EXODUS COMMUNICATIONS
REAL PROPERTY I, LLC, a Delaware limited liability company, having its address
at 2831 Mission College Boulevard, Suite C, Santa Clara, California  95054-1838,
and EXODUS COMMUNICATIONS REAL PROPERTY I, LP, a Texas limited partnership,
having its address at 2831 Mission College Boulevard, Suite A, Santa Clara,
California  95054-1838 (collectively, "Borrower").

                              W I T N E S S E T H:
                              - - - - - - - - - -

          WHEREAS, Lender and Borrower are parties to a loan agreement dated as
of March 30, 2001 (the "Loan Agreement") wherein Lender agreed to make a loan to
Borrower in the maximum principal amount of $105,000,000;

          WHEREAS, Lender and Borrower have agreed to increase the amount of the
loan by an additional $11,000,000;

          WHEREAS, Lender and Borrower are desirous of amending the Loan
Agreement in the manner hereinafter provided.

          NOW, THEREFORE, for good and valuable consideration, the parties
hereto hereby agree that the Loan Agreement is hereby amended as follows:

          1.  All capitalized terms not otherwise defined herein shall have the
meanings provided in the Loan Agreement.

          2.  The amount of the Subsequent Advance shall be * Dollars ($*),
which Subsequent Advance has been made in full concurrently herewith.

          3.  The Applicable Interest Rate with respect to the Subsequent
Advance for the Interest Period commencing as of the date hereof and ending May
9, 2001 shall be (i) *% with respect to Component A, (ii) *% with respect to
Component B, (iii) *% with respect to Component C and (iv) *% with respect to
Component D.

          4.  Borrower and Lender hereby acknowledge and agree that with
respect to the Payment Date occurring on May 10, 2001, Borrower shall pay (a)
interest at the Applicable Interest Rate (i) with respect to the Subsequent
Advance for the Interest Period commencing as of the date hereof and ending May
9, 2001 and (ii) with respect to the Initial Advance for the Interest Period
commencing as of April 10, 2001 and ending May 9, 2001 and (b) a principal
amount determined in accordance with clause (ii) of the definition of Monthly
Debt Service Payment Amount.

*  Confidential treatment has been requested for certain portions of this
   document pursuant to an application for confidential treatment sent to the
   Securities and Exchange Commission. Such portions are omitted from this
   filing and are filed separately with the Securities and Exchange Commission.

<PAGE>

          5.  Any and all references to 4650 Ironsides Drive, Santa Clara,
California and 4700 Ironsides Drive, Santa Clara, California shall be amended to
refer to, respectively, 4650 Old Ironsides Drive, Santa Clara, California and
4700 Old Ironsides Drive, Santa Clara, California.

          6.  The term "Assignment of Leases" is hereby amended to delete the
                        --------------------
words "as of the date hereof" from the definition thereof.

          7.  The term "Component A" is hereby amended in its entirety to
                        -----------
mean that certain portion of the Loan in the initial principal amount of
* Dollars ($*).

          8.  The term "Component B" is hereby amended in its entirety to mean
                        -----------
that certain portion of the Loan in the initial principal amount of * Dollars
($*).

          9.  The term "Component C" is hereby amended in its entirety to mean
                        -----------
that certain portion of the Loan in the initial principal amount of * Dollars
($*).

         10.  The term "Component D" is hereby amended in its entirety to
                        -----------
mean that certain portion of the Loan in the initial principal amount of *
Dollars ($*).

         11.  The term "Interest Rate Cap Event" is hereby amended in its
                        -----------------------
entirety to mean (i) LIBOR is equal to or greater than *% or (ii) notice from
Lender that a Securitization is expected to occur within the next twenty (20)
days.

         12.  The term "Note" is hereby amended in its entirety to mean that
                        ----
certain Amended and Restated Promissory Note of even date herewith in the
principal amount of One Hundred Sixteen Million and No/100 Dollars
($116,000,000), made by Borrower in favor of Lender, as the same may be amended,
restated, replaced, supplemented or otherwise modified from time to time.

         13.  The term "Release Amount" is hereby amended in its entirety to
                        --------------
mean for an Individual Property the amount set forth on Schedule I hereto.
                                                        ----------

         14.  The term "Spread" is hereby amended in its entirety to mean (a)
                        ------
*% with respect to Component A, (b) *% with respect to Component B, (c)
*% with respect to Component C, and (d) *% with respect to Component D.

         15.  The term "Strike Price" is hereby amended to mean *%.
                        ------------

         16.  Section 7.3 is hereby deleted in its entirety and all references
in the Loan Agreement or in any of the other Loan Documents to the terms
Replacement Reserve Monthly Deposit, Replacements, Replacement Reserve Fund or
Replacement Reserve Account shall be of no further force or effect.

                                       2

*  Confidential treatment has been requested for certain portions of this
   document pursuant to an application for confidential treatment sent to the
   Securities and Exchange Commission. Such portions are omitted from this
   filing and are filed separately with the Securities and Exchange Commission.

<PAGE>

         17.  The following shall be added as Section 5.1.11(h):
                                              -----------------

               "Within thirty (30) days of January 1 and July 1 of each calendar
          year, an update of * delivered in connection with the closing of the
          Loan shall be performed, which update shall be in form and substance
          reasonably satisfactory to Lender. Borrower shall provide * in
          connection with each such update. Borrower shall be responsible for
          the cost of such updates delivered during the extension periods
          described in Section 2.2.5(c) of this agreement.

         18.  Schedule I of the Loan Agreement is hereby amended in its
entirety and replaced with Schedule I attached hereto.

         19.  Borrower hereby affirms each of the representations and
warranties made as of the date of the Initial Advance and each of such
representations and warranties are incorporated herein and made a part hereof.
In addition, California Borrower hereby represents and warrants that it has
good, marketable and insurable fee simple title to the real property comprising
part of the Individual Property located at 4650 and 4700 Ironsides Drive, Santa
Clara, California and good title to the balance of such Individual Property,
free and clear of all Liens whatsoever except the Permitted Encumbrances, such
other Liens as are permitted pursuant to the Loan Documents and the Liens
created by the Loan Documents.

         20.  As herein amended, the Loan Agreement is hereby ratified and
remains in full force and effect.

                    [THERE IS NO FURTHER TEXT ON THIS PAGE]

                                       3

*  Confidential treatment has been requested for certain portions of this
   document pursuant to an application for confidential treatment sent to the
   Securities and Exchange Commission. Such portions are omitted from this
   filing and are filed separately with the Securities and Exchange Commission.

<PAGE>

     IN WITNESS WHEREOF, the parties hereto have caused this Amendment to be
duly executed by their duly authorized representatives, all as of the day and
year first above written.

                                 EXODUS COMMUNICATIONS REAL PROPERTY I, LLC, a
                                    Delaware limited liability company

                                    By: Exodus Communications Real Property
                                        Managers I, LLC, a Delaware limited
                                        liability company, its managing member

                                    By: Exodus Communications, Inc., a
                                        Delaware corporation, its sole member

                                        By: /s/ Adam Wegner
                                           ------------------------------------
                                            Name:  Adam Wegner
                                            Title: EVP, Corporate and Legal
                                                   Affairs, General Counsel and
                                                   Secretary

                                 EXODUS COMMUNICATIONS REAL PROPERTY I, LP, a
                                    Texas limited partnership

                                    By: Exodus Communications Real Property
                                        Managers I, LLC, a Delaware limited
                                        liability company, its general partner

                                    By: Exodus Communications, Inc., a
                                        Delaware corporation, its sole member

                                        By: /s/ Adam Wegner
                                           ------------------------------------
                                            Name:  Adam Wegner
                                            Title: EVP, Corporate and Legal
                                                   Affairs, General Counsel and
                                                   Secretary

                                 LEHMAN BROTHERS BANK FSB

                                        By: /s/ Larry Kravetz
                                           ------------------------------------
                                            Name: Larry Kravetz
                                            Title: Senior Vice President

                                       4
<PAGE>

                                  Schedule I
                                  ----------

                    Properties - Allocated Release Amounts
                    --------------------------------------

<TABLE>
<CAPTION>

-------------------------------------------------------------------------------------------------------
Borrower                                        Property                Allocated          Release
                                                                          Loan              Amount
                                                                         Amount
-------------------------------------------------------------------------------------------------------
-------------------------------------------------------------------------------------------------------

<S>                                   <C>                              <C>               <C>
Exodus Communications Real              1.  2401 and 2403 Walsh          $*                $*
 Property I, LLC                            Avenue, Santa Clara,
                                            California
                                        2.  4650 Old Ironsides           $*                $*
                                            Drive, Santa Clara,
                                            California
                                        3.  4700 Old Ironsides           $*                $*
                                            Drive, Santa Clara,
                                            California

-------------------------------------------------------------------------------------------------------
-------------------------------------------------------------------------------------------------------

Exodus Communications Real              1.  1418 Park Center Drive,      $*                $*
  Property I, LP                            Austin, Texas
-------------------------------------------------------------------------------------------------------
</TABLE>

                                       5

*  Confidential treatment has been requested for certain portions of this
   document pursuant to an application for confidential treatment sent to the
   Securities and Exchange Commission. Such portions are omitted from this
   filing and are filed separately with the Securities and Exchange Commission.<PAGE>

                                                                    Exhibit 10.1

                               SYMMETRICOM, INC.
                               SENIOR EXECUTIVE
                                   LOAN PLAN

     This memorandum memorializes the executive loan plan as adopted by the
Board of Directors (the "Board") of Symmetricom, Inc. (the "Company") on January
19, 2001.

     1.   Purpose

     The Company has determined that in order to attract and retain qualified
senior executive management, and to encourage their retention of Company stock,
it is appropriate to adopt an executive loan plan to provide loans from lawfully
available Company funds to assist certain key senior executives with the
exercise of their Company stock options and the payment of taxes arising from
such exercise.  While the Company's 1990 Employee Stock Plan and 1999 Employee
Stock Plan (each as amended and approved by the Company's stockholders)
authorize the Company's accepting a promissory note as one method for an
optionee's payment of the option exercise price, some of the option agreements
entered into with certain senior executives under the 1990 Employee Stock Plan
do not incorporate a promissory note as a permitted payment method for the
option's exercise.  This has, in some instances, hindered certain optionees'
ability to realize the full intended benefit from their options.

     2.   Authority

     This executive loan plan is adopted pursuant to California Corporations
Code sections 408 and 315(f), and is in furtherance of the Company's 1990
Employee Stock Plan and 1999 Employee Stock Plan, each as amended and approved
by the Company's stockholders.  It is further intended to comply with Regulation
U as codified at 12 Code of Federal Regulations Part 221.

     3.   Program Duration

     The executive loan plan is subject to annual review by the Board which
shall determine whether such plan continues to benefit the Company.

     4.   Eligible Participants

     Persons potentially eligible to participate in the loan plan include such
officers and key employees as may be determined from time to time by the
Company's Board.  The Board has determined initially to restrict participation
to the Company's CEO and his direct reports.

     5.   Secured Recourse Promissory Note

     A borrower under the Plan shall execute and deliver to the Company a full
recourse promissory note for the purchase of his shares.  To provide security
for payment of the note, the certificate for shares so purchased shall be held
by the Company, and the borrower shall deliver the certificate to the Company
together with an executed security agreement and blank stock assignment
transferring all or some of the shares to the Company if, as, and when required
by the

                                      -1-

<PAGE>
security agreement. The security agreement shall substantially conform to that
attached hereto as Exhibit 1.
                   ---------

     6.   Term of Note

     The principal balance, together with interest accrued and unpaid, shall be
due no later than five (5) years from the date of the promissory note's making,
and shall otherwise become due in full upon the occurrence of an Event of
Acceleration.  Principal and interest may be prepaid at any time without
penalty.

     7.   Rate and Payment of Interest

     The interest rate on borrowed funds shall be at the borrower's market rate
for a similarly secured loan from a commercial lender.  Accrued interest shall
be due and payable on the anniversary of the loan's making for each year during
the note's term.

     8.  Events of Acceleration

     (a) The entire unpaid principal sum and unpaid interest under amounts
borrowed shall become immediately due and payable upon the earliest to occur of
the following (each of which constitutes an "Event of Acceleration"):

          (i)    The date when the borrower ceases to provide services to the
     Company as an employee;

          (ii)   The insolvency of the borrower, the commission of an act of
     bankruptcy by the borrower, the execution by the borrower of a general
     assignment for the benefit of creditors, or the filing by or against the
     borrower of a petition in bankruptcy or a petition for relief under the
     provisions of the federal bankruptcy act or another state or federal law
     for the relief of debtors and the continuation of such petition without
     dismissal for a period of 90 days or more; or

          (iii)  The failure of the borrower to perform a material obligation
     imposed upon the borrower under his secured promissory note or security
     agreement.

     (b) Notwithstanding the absence of a triggering event under section 8(a)
above, such portion of the unpaid principal balance and unpaid interest under
amounts borrowed shall become immediately due and payable on a pro rata basis
concurrently with the borrower's sale of shares acquired through the exercise of
options.  For example, if one-third of the shares initially acquired by the
borrower [after adjustment for any stock splits and stock dividends] were sold,
one-third of the unpaid principal balance plus one-third of the accrued interest
not previously discharged shall be paid to the Company concurrently with
borrower's receipt, or right to receive, any sale proceeds from the sale of
shares.

                                      -2-

<PAGE>

     9.  Additional Terms

     The Company shall adopt such additional executive loan plan terms as may be
recommended by the Company's Chief Financial Officer as necessary to effectuate
the plan upon concurrence by Company counsel that such terms comply with
applicable law.

                  [remainder of page intentionally left blank]

                                      -3-
<PAGE>

                                   EXHIBIT 1

                              SECURITY AGREEMENT

     THIS SECURITY AGREEMENT is made as of _____________, 200__ between
Symmetricom, Inc., a California corporation ("Pledgee"), and ________________
("Pledgor"), with reference to the following facts:

     Pursuant to a Stock Option Agreement entered into under the [Symmetricom,
Inc. Amended and Restated 1999 Employee Stock Plan / Amended 1990 Employee Stock
Plan] (the "Plan") Pledgor has purchased ________ shares of Pledgee's Common
Stock (the "Shares") at a price of $________ per share, for a total purchase
price of $_____________.  Pledgor has delivered to Pledgee a Full Recourse
Promissory Note (the "Note") for the purchase price of the Shares.  Pledgee
desires to obtain security for payment of the Note in the form of a pledge of
the Shares, as set forth herein.

     NOW, THEREFORE, it is agreed as follows:

     1.   Creation and Description of Security Interest. To provide security for
payment of the Note, Pledgor, pursuant to the California Commercial Code, hereby
pledges all of the Shares (herein sometimes referred to as the "Collateral")
represented by Certificate No. _____, duly endorsed in blank or with executed
stock powers, and herewith delivers the certificate to the Secretary of Pledgee
("Pledgeholder"), who shall hold the certificate subject to the terms and
conditions of this Security Agreement. The Shares (together with an executed
blank stock assignment for use in transferring all or a portion of the Shares to
Pledgee if, as and when required pursuant to this Security Agreement) shall be
held by the Pledgeholder as security for the repayment of the Note, and any
extensions or renewals thereof, and the Pledgeholder shall not encumber or
dispose of such Shares except in accordance with the provisions of this Security
Agreement.

     2.   Pledgee's Covenants. At all times while Pledgee is holding the Shares
as security under this Security Agreement, Pledgee shall:

     (a)  Collect any dividends that may be declared on the Shares and credit
such dividends against any accrued interest or unpaid principal under the Note,
as part payment; and

     (b)  Collect and hold any shares that may be issued upon conversion of the
Shares; and

     (c)  Collect and hold any other securities or other property that may be
distributed with respect to the Shares; and

     (d)  Any such shares and other securities or property shall be subject to
the security interest granted in Section 1 of this Security Agreement and shall
be held by Pledgee under this Security Agreement.

                                  EXHIBIT 1-1
<PAGE>

     3.   Pledgor's Representations and Covenants. To induce Pledgee to enter
into this Security Agreement, Pledgor represents and covenants to Pledgee, its
successors and assigns, as follows:

     (a)  Pledgor will pay the principal sum of the Note secured hereby,
together with interest thereon, at the time and in the manner provided in the
Note.

     (b)  The Shares are free of all other encumbrances, defenses and liens, and
Pledgor will not further encumber the Shares without the prior written consent
of Pledgee.

     (c)  In the event that Pledgee's Common Stock is now or later becomes
margin-listed by the Federal Reserve Board and Pledgee is classified as a
"lender" within the meaning of the regulations under Part 221 of Title 12 of the
Code of Federal Regulations ("Regulation U"), Pledgor agrees to cooperate with
Pledgee in making any amendments to the Note or providing any additional
collateral as may be necessary to comply with such regulations.

     4.   Voting Rights. During the term of this Security Agreement and so long
as all payments of principal and interest are made as they become due under the
terms of the Note, Pledgor shall have the right to vote all of the Shares
pledged hereunder.

     5.   Stock Adjustments. In the event that during the term of the pledge any
stock dividend, reclassification, readjustment or other change is declared or
made in the capital structure of Pledgee, all new, substituted and additional
shares or other securities issued by reason of any such change shall be
delivered to and held by Pledgee under the terms of this Security Agreement in
the same manner as the Shares originally pledged hereunder. In the event of
substitution of such securities, Pledgor, Pledgee and Pledgeholder shall
cooperate and execute such documents as are reasonable so as to provide for the
substitution of such Collateral and, upon such substitution, references to
"Shares" in this Security Agreement shall include the substituted shares of
capital stock of Pledgor as a result thereof.

     6.   Options and Rights. In the event that, during the term of this
Security Agreement, subscription options or other rights or options shall be
issued in connection with the pledged Shares, such options and other rights and
options shall be the property of Pledgor and, if exercised by Pledgor, all new
stock or other securities so acquired by Pledgor as it relates to the pledged
Shares then held by Pledgeholder shall be immediately delivered to Pledgeholder,
to be held under the terms of this Security Agreement in the same manner as the
Shares pledged.

     7.   Default. Pledgor shall be deemed to be in default of the Note and of
this Security Agreement in the event either of the following occurs:

     (a)  Payment of principal or interest on the Note shall be delinquent for
a period of 10 days or more; or

     (b)  Pledgor fails to perform any of the covenants set forth in the Stock
Option Agreement entered into under the Plan pursuant to which the Shares were
acquired or contained in this Security Agreement for a period of 10 days after
written notice thereof from Pledgee.

                                  EXHIBIT 1-2

<PAGE>

     7.1     In the event of a default, Pledgee shall have all of the rights and
remedies of a creditor and secured party at law and in equity, including
(without limitation) the rights and remedies provided under the California
Commercial Code. Without limiting the foregoing, Pledgee may, after giving 10
days' prior written notice to the Pledgor by certified mail at his residence or
business address, sell any or all of the Shares in such manner and for such
price as Pledgee may determine, including (without limitation) through a public
or private sale or at any broker's board or on any securities exchange, for
cash, upon credit or for future delivery. Pledgee is authorized at any such
sale, if it deems it advisable to do so, to restrict the prospective bidders or
purchasers of any of the Shares to persons who will represent and agree that
they are purchasing for their own account for investment, and not with a view to
the distribution or sale of any of the Shares, to restrict the prospective
bidders or purchasers and the use any purchaser may make of the Shares and
impose any other restriction or condition that Pledgee deems necessary or
advisable under the federal and state securities laws.

     7.2     Upon any sale described in Section 7.1, Pledgee shall have the
right to deliver, assign and transfer to the purchaser thereof the Shares so
sold. Each purchaser at any such sale shall hold the Shares so sold absolute,
free from any claim or right of any kind. In case of any sale of any or all of
the Shares on credit or for future delivery, the Shares so sold may be retained
by Pledgee until the selling price is paid by the purchaser thereof, but Pledgee
shall not incur any liability in case of the failure of such purchaser to take
up and pay for the Shares so sold and, in case of any such failure, such Shares
may again be sold under the terms of Section 7.1.

     7.3     Pledgor hereby agrees that any disposition of any or all of the
Shares by way of a private placement or other method, which in the opinion of
Pledgee is required or advisable under federal and state securities laws, is
commercially reasonable. At any public sale, Pledgee may (if it is the highest
bidder) purchase all or any part of the Shares at such price as Pledgee deems
proper. Out of the proceeds of any sale, Pledgee may retain an amount sufficient
to pay all amounts then due under the Note, together with the expenses of the
sale and reasonable attorneys' fees. Pledgee shall pay the balance of such
proceeds, if any, to Pledgor. Pledgor shall be liable for any deficiency that
remains after Pledgee has exercised its rights under this Security Agreement.

       8. Release of Collateral. Upon payment in full of the outstanding
principal balance of the Note and all interest and other charges due under the
Note, Pledgee shall release from pledge and deliver to Pledgor the Collateral
pledged hereunder.

       9. Withdrawal or Substitution of Collateral. Pledgor shall not sell,
withdraw, pledge, substitute or otherwise dispose of all or any part of the
Collateral without the prior written consent of Pledgee.

       10. Term. This Security Agreement and the pledge of Shares effected
hereunder, shall continue until the payment of all indebtedness secured hereby,
at which time the remaining pledged Shares shall be promptly delivered to
Pledgor.

       11. Insolvency. Pledgor agrees that if a bankruptcy or insolvency
proceeding is instituted by or against it, or if a receiver is appointed for the
property of Pledgor, or if Pledgor makes an assignment for the benefit of
creditors, the entire amount unpaid on the Note shall

                                  Exhibit 1-3
<PAGE>

become immediately due and payable, and Pledgee may proceed as provided in the
case of default.

       12. Pledgeholder Liability. In the absence of willful or gross
negligence, Pledgeholder shall not be liable to any party for any of his acts,
or omissions to act, as Pledgeholder.

       13. Invalidity of Particular Provisions. Pledgor and Pledgee agree that
the enforceability or invalidity of any provision or provisions of this Security
Agreement shall not render any other provision or provisions herein contained
unenforceable or invalid.

       14. Successors or Assigns. Pledgor and Pledgee agree that all of the
terms of this Security Agreement shall be binding on their respective successors
and assigns, and that the term "Pledgor" and the term "Pledgee" as used herein
shall be deemed to include, for all purposes, the respective designees;
successors, assigns, heirs, executors and administrators.

       15. Governing Law. This Security Agreement shall be interpreted and
governed under the laws of the State of California.

                           [Signature Page Follows]

                                  Exhibit 1-4

<PAGE>

     IN WITNESS WHEREOF, the parties hereto have executed this Security
Agreement as of the day and year first above written.

                                    PLEDGOR
                                    -------

                                    ----------------------------------
                                    Print Name

                                    Address:
                                             -------------------------

                                    ----------------------------------

                                    ----------------------------------

                                    PLEDGEE
                                    -------

                                    SYMMETRICOM, INC.
                                    a California corporation

                                    By
                                       --------------------------------

                                    Title
                                          -----------------------------

                                    PLEDGEHOLDER
                                    ------------

                                    ----------------------------------
                                    Secretary of
                                    SYMMETRICOM, INC.

                                  Exhibit 1-5

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