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                                                                   EXHIBIT 10.25

                               ONI SYSTEMS CORP.

                  SERIES H PREFERRED STOCK PURCHASE AGREEMENT


     This Series H Preferred Stock Purchase Agreement (the "Agreement") is made
effective as of May 1, 2000, between ONI Systems Corp., a Delaware corporation
(the "Company"), with its principal office at 166 Baypointe Parkway, San Jose,
California 95134 and the parties listed on the Schedule of Investors attached to
this Agreement as Exhibit A (each hereafter individually referred to as an
"Investor" and collectively referred to as the "Investors").


                                   ARTICLE 1

                     AUTHORIZATION AND SALE OF THE SHARES
                     ------------------------------------

     1.1  Authorization.  The Company will have authorized before the Closing
(as defined below) the sale and issuance of up to 2,667,000 shares of the
Company's Series H Preferred Stock (the "Series H Preferred"), having the
rights, preferences, privileges, and restrictions as set forth in the Company's
Amended and Restated Certificate of Incorporation in the form attached hereto as
Exhibit B (the "Restated Certificate").

     1.2  Sale of the Series H Preferred Shares.  Subject to the terms and
conditions hereof at the Closing, the Company shall sell and issue to each
Investor, and each Investor shall purchase from the Company, at a per share
purchase price of $15.00, the number of shares of Series H Preferred set forth
beside such Investor's name on Exhibit A. The shares of Series H Preferred
purchased and sold pursuant to this Agreement will be hereinafter referred to as
the "Shares," the shares of Common Stock issuable upon conversion of the Shares
will be hereinafter referred to as the "Conversion Shares" and the Shares and/or
the outstanding Conversion Shares will be collectively hereinafter referred to
as the "Securities."

                                   ARTICLE 2

                             CLOSINGS; DELIVERIES
                             --------------------

     2.1  Closing.  Subject to the terms and conditions of this Agreement, the
purchase and sale of the Series H Preferred hereunder shall take place at a
closing (the "Closing") to be held at the offices of Fenwick & West LLP, Two
Palo Alto Square, Palo Alto, California at 10:00 a.m. on May ___, 2000, or at
such other place or time upon which the Company and Investors who have agreed to
purchase a majority of the Shares listed on Exhibit A may mutually agree in
writing.  The date of the Closing is referred to as the "Closing Date."

     2.2  Additional Closing(s).

          (a)  Conditions of Additional Closing(s). At any time and from time
to time, but no later than May 18, 2000 (the "Additional Closing Period"), the
Company may, at one or

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more additional closings (each an "Additional Closing"), without obtaining the
signature, consent or permission of any of the Investors, offer and sell to
other investors ("New Investors"), at a price of $15.00 per share, up to that
number of shares of Series H Stock that is equal to 2,667,000 shares of Series H
Stock less the number of shares of Series H Stock actually issued and sold by
the Company at the Closing. New Investors may include persons or entities who
are already Investors under this Agreement.

          (b)  Amendments.  The Company and the New Investors purchasing Series
H Stock at each Additional Closing will execute counterpart signature pages to
this Agreement and the Rights Agreement (as defined in Article 6.8), and such
New Investors will, upon delivery to the Company of such signature pages, become
parties to, and bound by, this Agreement and the Rights Agreement, each to the
same extent as if they had been Investors at the Closing. Immediately after each
Additional Closing, Exhibit A to this Agreement will be amended to list the New
Investors purchasing shares of Series H Stock hereunder and the number of shares
of Series H Stock purchased by each New Investor under this Agreement at each
such Additional Closing. The Company will promptly furnish to each Investor
copies of the amendments to Exhibit A referred to in the preceding sentence.

          (c)  Status of New Investors.  Upon the completion of each Additional
Closing as provided in this Article 2, each New Investor will be deemed to be an
"Investor" for all purposes of this Agreement and the Rights Agreement.

     2.3  Deliveries.  At the Closing and each Additional Closing, the Company
shall deliver to each Investor a stock certificate or certificates representing
the number of Shares that such Investor has agreed to purchase hereunder as
shown on Exhibit A, against payment of the purchase price therefor, by delivery
to the Company of (i) a check payable to the Company or (ii) a wire transfer to
the bank account of the Company.

                                   ARTICLE 3

                 REPRESENTATIONS AND WARRANTIES OF THE COMPANY
                 ---------------------------------------------

     Except as set forth on the "Schedule of Exceptions" attached hereto as
Exhibit C (specifically identifying the relevant Section(s) hereof), the Company
hereby represents and warrants to the Investors as follows:

     3.1  Capitalization.  The capitalization of the Company will, upon the
filing of the Restated Certificate, consist of the following:

          (a)  Preferred Stock.  A total of 82,139,826 authorized shares of
preferred stock (the "Preferred Stock"), consisting of 25,073,436 shares
designated as Series B Preferred Stock ("Series B Preferred"), of which
24,795,510 shares will be issued and outstanding, 2,733,332 shares designated as
Series C Preferred Stock ("Series C Preferred"), of which 2,733,332 shares will
be issued and outstanding, 4,969,148 shares designated Series D Preferred

                                       2
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Stock ("Series D Preferred"), of which 4,969,148 shares will be issued and
outstanding, 26,284,024 shares designated as Series E Preferred Stock ("Series E
Preferred"), of which 26,284,024 shares will be issued and outstanding,
8,249,468 shares designated Series F Preferred ("Series F Preferred"), 8,249,468
of which will be issued and outstanding, 12,163,418 shares designated Series G
Preferred ("Series G Preferred"), 12,163,418 of which will be issued and
outstanding and 2,667,000 shares designated Series H Preferred, none of which
will be issued and outstanding. Upon the Closing, the rights, preferences and
privileges of the Series B Preferred, the Series C Preferred, the Series D
Preferred, the Series E Preferred, the Series F Preferred, the Series G
Preferred and the Series H Preferred will be as stated in the Restated
Certificate and as provided by law. As of the Closing, each share of issued and
outstanding Series B Preferred, Series C Preferred, Series D Preferred, Series E
Preferred, Series F Preferred and Series G Preferred will be convertible into
one share of Common Stock in all cases pursuant to, and subject to, the terms
set forth in the Restated Certificate. The Series H Preferred will be
convertible into Common Stock as provided in the Restated Certificate.

          (b)  Common Stock.  A total of 185,000,000 authorized shares of Common
Stock, of which 35,254,875 shares will be issued and outstanding.

          (c)  Options, Warrants, Reserved Shares.  Except (i) the options,
stock plans and warrants described in the Registration Statement under the
headings "Management--Employee Benefit Plans," "Capitalization," and
"Description of Capital Stock--Warrants," (ii) the conversion privileges of the
Series B Preferred, the Series C Preferred, the Series D Preferred, the Series E
Preferred, the Series F Preferred, the Series G Preferred and the Series H
Preferred, (iii) the right of first offer provided in Section 3 of the Rights
Agreement between the Company and the Investors in Exhibit A thereto (the
"Rights Agreement") and (iv) the right of first refusal in Section 8.7 of the
Bylaws with respect to transfers of shares of the Company's capital stock, there
are no other options, warrants, conversion privileges, or preemptive or other
rights or agreements presently outstanding to purchase or otherwise acquire any
authorized but unissued shares of the capital stock or other securities of the
Company.

          (d)  The outstanding shares of the capital stock of the Company have
been duly authorized and validly issued, and are fully paid and nonassessable
and have been issued in compliance with all applicable federal and state
securities laws.

          (e)  Other than as contemplated in Article 9 of that certain Series D
Preferred Stock Purchase Agreement of the Company dated April 1, 1998 and
Section 1.4 of the Rights Agreement, the Company is not a party or subject to
any agreement or understanding, and, to the best of the Company's knowledge,
there is no agreement or understanding between any persons and/or entities,
which affects or relates to the voting or giving of written consents with
respect to any security or by a director of the Company.

     3.2  Authorization.  All corporate action on the part of the Company, its
directors, and its stockholders necessary for the authorization, execution,
delivery, and performance of this Agreement and the Rights Agreement by the
Company, the authorization, sale, issuance, and delivery of the Shares (and,
except for issuance and delivery thereof, the Conversion Shares), and the
performance of all of the Company's obligations hereunder (except for the
performance of its covenants to be performed subsequent to each Closing) will
have been taken prior to the Closing.

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This Agreement and the Rights Agreement (as such may be amended under Article
2.2) when executed and delivered by the Company, will constitute valid and
legally binding obligations of the Company, enforceable in accordance with their
respective terms, subject to (i) laws of general application relating to
bankruptcy, insolvency, and the relief of debtors, (ii) rules of law governing
specific performance, injunctive relief, or other equitable remedies and (iii)
the extent that the indemnification provisions of Section 2.9 of the Rights
Agreement may be limited by principles of public policy. The Company has
reserved up to 2,667,000 shares of Series H Preferred for issuance hereunder and
the shares of Common Stock issuable upon conversion of the Shares. The Shares,
when issued in accordance with this Agreement, will be duly authorized, validly
issued, fully paid, and nonassessable, and will have the rights, preferences,
privileges, and restrictions as set forth in the Restated Certificate. The
Conversion Shares have been, and at all times will be, duly and validly reserved
and, when issued in accordance with this Agreement and the Restated Certificate,
will be duly authorized, validly issued, fully paid, and nonassessable. The
Securities, when issued, will be free of any liens or encumbrances created by
the Company; provided, however, that the Securities will be subject to
restrictions on transfer under federal and state securities laws and as set
forth in the Restated Certificate, the Bylaws, the Rights Agreement and herein.
Based in part upon the representations and warranties of the Investors in this
Agreement, the Securities will be issued in compliance with all applicable
federal and state securities laws.

     3.3  SEC Filings; Financial Statements.  (a) A registration statement on
Form S-1 (File No. 333-32104) (the "Registration Statement") in respect of the
Shares has been filed with the Securities and Exchange Commission (the
"Commission"); the Registration Statement has not been declared effective by the
Securities and Exchange Commission under the Securities Act of 1933, as amended
(the "Act"); and no stop order regarding the Registration Statement has been
issued and no proceeding for that purpose has been initiated or threatened by
the Commission (any preliminary prospectus included in the Initial Registration
Statement or filed with the Commission pursuant to Rule 424(a) of the rules and
regulations of the Commission under the Act is hereinafter called a
"Prospectus".

     3.4  No Stop Order.  No order preventing or suspending the use of any
Prospectus has been issued by the Commission, and each Prospectus, at the time
of filing thereof, conformed in all material respects to the requirements of the
Act and the rules and regulations of the Commission thereunder, and did not
contain an untrue statement of a material fact or omit to state a material fact
required to be stated therein or necessary to make the statements therein, in
the light of the circumstances under which they were made, not misleading;
provided, however, that this representation and warranty shall not apply to any
statements or omissions made in reliance upon and in conformity with information
furnished in writing to the Company by an Investor expressly for use therein.

     3.5  Securities Compliance.  The Registration Statement and the Prospectus
conform in all material respects to the requirements of the Act and the rules
and regulations of the Commission thereunder and do not contain an untrue
statement of a material fact or omit to state a material fact required to be
stated therein or necessary to make the statements therein not misleading;
provided, however, that this representation and warranty shall not apply to any
statements or omissions made in reliance upon and in conformity with information
furnished in writing to the Company by an Investor expressly for use therein.

                                       4
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     3.6  No Material Loss.  Neither the Company nor any of its subsidiaries has
sustained since the date of the latest audited financial statements included in
the Prospectus any material loss or interference with its business from fire,
explosion, flood or other calamity, whether or not covered by insurance, or from
any labor dispute or court or governmental action, order or decree, otherwise
than as set forth or contemplated in the Prospectus; and, since the respective
dates as of which information is given in the Registration Statement and the
Prospectus, there has not been any change in the capital stock  or long-term
debt of the Company or any of its subsidiaries or any material adverse change,
or any development that may cause a prospective material adverse change, in or
affecting the general affairs, management, financial position, stockholders'
equity or results of operations of the Company and its subsidiaries, otherwise
than as set forth or contemplated in the Prospectus.

     3.7  No Real Estate.  The Company and its subsidiaries own no real property
and have good and marketable title to all personal property owned by them, in
each case free and clear of all liens, encumbrances and defects except as are
described in the documents filed with the Registration Statement or such as do
not materially affect the value of such property and do not materially interfere
with the use made and proposed to be made of such property by the Company and
its subsidiaries; and any real property and buildings held under lease by the
Company and its subsidiaries are held by them under valid, subsisting and
enforceable leases with such exceptions as are not material and do not interfere
with the use made and proposed to be made of such property and buildings by the
Company and its subsidiaries.

     3.8  Due Incorporation.  The Company has been duly incorporated and is
validly existing as a corporation in good standing under the laws of the State
of Delaware, with corporate power and corporate authority to own its properties
and conduct its business as described in the Prospectus, and has been duly
qualified as a foreign corporation for the transaction of business and is in
good standing under the laws of each other jurisdiction in which it owns or
leases properties or conducts any business so as to require such qualification,
except where failure to be so qualified would not have a Material Adverse
Effect. The Company has all requisite corporate power to execute and deliver
this Agreement and the Rights Agreement, to sell and issue the Shares hereunder,
to issue the Conversion Shares, and to carry out and perform its obligations
under the terms of this Agreement and the Rights Agreement.

     3.9  Subsidiary Shares.  All of the issued shares of capital stock of each
"significant subsidiary" of the Company (as defined in Rule 1-02(w) of
Regulation S-X under the Act) have been duly and validly authorized and issued,
are fully paid and non-assessable and (except for directors' qualifying shares)
are owned directly or indirectly by the Company, free and clear of all liens,
encumbrances, equitable interests or claims.

     3.10  The term "Material Adverse Effect" means, for purposes of this
Agreement, any change, event or effect that is materially adverse to the general
affairs, management, consolidated financial position, business prospects,
stockholders' equity or results of operations of the Company and its
subsidiaries, taken as a whole.

     3.11  No Conflict.  The issue and sale of the Series H Preferred Stock by
the Company and the compliance by the Company with all of the provisions of this
Agreement and the

                                       5
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consummation of the transactions herein contemplated will not conflict with or
result in a breach or violation of any of the terms or provisions of, or
constitute a default under, any indenture, mortgage, deed of trust, loan
agreement or other agreement or instrument to which the Company or any of its
subsidiaries is a party or by which the Company or any of its subsidiaries is
bound or to which any of the property or assets of the Company or any of its
subsidiaries is subject, nor will such action result in any violation of the
provisions of the Certificate of Incorporation or By-laws of the Company or any
statute or any order, rule or regulation of any court or governmental agency or
body having jurisdiction over the Company or any of its subsidiaries or any of
their properties; and no consent, approval, authorization, order, registration
or qualification of or with any such court or governmental agency or body is
required for the issue and sale of the Shares or the consummation by the Company
of the transactions contemplated by this Agreement, except such consents,
approvals, authorizations, registrations or qualifications as may be required
under state securities or Blue Sky laws in connection with the purchase and
distribution of the shares of Series H Preferred Stock by the Investors.

     3.12  No Default.  Neither the Company nor any of its significant
subsidiaries is (i) in violation of its Certificate of Incorporation or By-laws
or (ii) in default in the performance or observance of any material obligation,
agreement, covenant or condition contained in any indenture, mortgage, deed of
trust, loan agreement, lease or other agreement or instrument to which it is a
party or by which it or any of its properties may be bound, except, with respect
to subclause (ii), where such default would not have a Material Adverse Effect.

     3.13  Legal Proceedings.  Other than as set forth in the Prospectus under
the headings "Risk Factors--We are involved in an intellectual property dispute
and in the future we may become involved in similar disputes, which could
subject us to significant liability, divert the time and attention of our
management and prevent us from selling our products" and "Business--Legal
Proceedings," there are no legal or governmental proceedings pending to which
the Company or any of its subsidiaries is a party or of which any property of
the Company or any of its subsidiaries is the subject which, if determined
adversely to the Company or any of its subsidiaries, would individually or in
the aggregate have a Material Adverse Effect; and, to the best of the Company's
knowledge, no such proceedings are threatened or contemplated by governmental
authorities or threatened by others.

     3.14  Investment Company.  The Company is not and, after giving effect to
the offering and sale of the shares of Series H Preferred Stock to the
Investors, will not be an "investment company", as such term is defined in the
Investment Company Act of 1940, as amended (the "Investment Company Act").

     3.15  Public Accountants. KPMG LLP, who have certified certain financial
statements of the Company and its subsidiaries, are independent public
accountants as required by the Act and the rules and regulations of the
Commission thereunder.

     3.16  Intellectual Property.  The Company and its subsidiaries own or
possess valid licenses or other rights to use all patents, trademarks, service
marks, trade names, copyrights, know-how, trade secrets and other intellectual
property necessary to conduct the business of the Company and its significant
subsidiaries in the manner in which it has been and is being conducted, and
except as set forth in the Prospectus under the headings "Risk Factors--We are

                                       6
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involved in an intellectual property dispute and in the future we may become
involved in similar disputes, which could subject us to significant liability,
divert the time and attention of our management and prevent us from selling our
products" and "Business--Legal Proceedings," the Company and its subsidiaries
have not received any notice of infringement or of conflict with (and the
Company knows of no such infringement or conflict with) asserted rights of
others with respect to any patents, trademarks, service marks, trade names,
copyrights, know-how, trade secrets or other intellectual property which, if
determined adversely to the Company or its subsidiaries, would individually or
in the aggregate have a Material Adverse Effect; and the inventions, products or
processes referred to in the Prospectus do not, to the knowledge of the Company,
infringe or conflict with any right or patent, or any invention, product or
process which is the subject of a patent application known to the Company, which
if determined adversely would have a Material Adverse Effect.

     3.17  Insurance.  The Company and its subsidiaries, taken as a whole, are
insured by insurers of recognized financial responsibility against such losses
and risks and in such amounts as are prudent and customary in the business in
which they are engaged; and neither the Company nor any of its subsidiaries has
any reason to believe that it will not be able to renew its existing insurance
coverage as and when such coverage expires or to obtain similar coverage from
similar insurers as may be necessary to continue its business at a cost that
would not have a Material Adverse Effect.

     3.18  Exempt Transaction.  Subject to the accuracy of the Investors'
representations in Article 4 hereof, the offer, sale, and issuance of the
Securities in conformity with the terms of this Agreement, constitute
transactions exempt from the registration requirements of Section 5 of the
Securities Act of 1933, as amended (the "Securities Act").

     3.19  Brokers or Finders.  The Company has not incurred, and will not
incur, directly or indirectly, as a result of any action taken by the Company
any liability for brokerage or finders' fees or agents' commissions or any
similar charges in connection with this Agreement or any transaction
contemplated hereby.

     3.20  Registration Rights.  Except as set forth in the Rights Agreement and
in the Prospectus under the heading "Description of Capital Stock--Registration
Rights," the Company is not under any obligation to register (as defined in
Section 2.1 of the Rights Agreement) any of its presently outstanding securities
or any of its securities which may hereafter be issued.


                                   ARTICLE 4

                REPRESENTATIONS AND WARRANTIES OF THE INVESTORS
                -----------------------------------------------

     Each Investor hereby, severally and not jointly, represents and warrants to
the Company with respect to the purchase of the Shares as follows:

     4.1  Experience.  Such Investor has substantial experience in evaluating
and investing in private placement transactions of securities in companies
similar to the Company so that such Investor is capable of evaluating the merits
and risks of such Investor's investment in the Company and has the capacity to
protect such Investor's own interests.

                                       7
<PAGE>

     4.2  Investor Qualifications.  Such Investor is an "accredited investor"
within the meaning of paragraph (a)(1), (a)(2), (a)(3), (a)(7) or (a)(8) of Rule
501 of Regulation D promulgated pursuant to the Securities Act or a qualified
institutional buyer, within the meaning of Rule 144A of the Securities Act and
has substantial experience in evaluating and investing in private placement
transactions, and, as such is capable of evaluating the merits and risks of its
investment in the Company.  Such Investor, by reason of its business or
financial experience or the business or financial experience of its professional
advisors who are unaffiliated with the Company or any affiliate or selling agent
of the Company, directly or indirectly, has the capacity to protect its own
interests in connection with the purchase of the Shares.

     4.3  Investment.  Such Investor is acquiring the Securities for investment
for such Investor's own account, not as a nominee or agent, and not with the
view to, or for resale in connection with, any distribution thereof.  Such
Investor understands that the Securities have not been, and will not be,
registered under the Securities Act by reason of a specific exemption from the
registration provisions of the Securities Act which depends upon, among other
things, the bona fide nature of the investment intent and the accuracy of such
Investor's representations as expressed herein.

     4.4  Rule 144.  Such Investor acknowledges that the Securities must be held
indefinitely unless subsequently registered under the Securities Act or an
exemption from such registration is available.  Such Investor is aware of the
provisions of Rule 144 promulgated under the Securities Act which permit limited
resale of shares purchased in a private placement subject to the satisfaction of
certain conditions, including, among other things, (i) the existence of a public
market for the shares, (ii) the availability of certain current public
information about the Company, (iii) the resale occurring not less than one year
after a party has purchased and fully paid for the shares to be sold, (iv) the
sale being effected through a "broker's transaction" or in transactions directly
with a "market maker" (as provided by Rule 144(f)) and (v) the number of shares
being sold during any three-month period not exceeding specified limitations.

     4.5  No Public Market.  Such Investor understands that no public market now
exists for any of the securities issued by the Company and that there is no
assurance that a public market will ever exist for the Securities.

     4.6  Access to Data.  Such Investor and its representatives, if any, has
had an opportunity to ask questions of, and receive, answers from,
representatives of the Company concerning the Company and the terms and the
conditions of this transaction, as well as to obtain any information requested
by such Investor or its representatives. Any questions raised by such Investor
or its representatives were answered to the satisfaction of such Investor or its
representatives. Such Investor understands that such discussions, as well as any
written information issued by the Company, were intended to describe certain
aspects of the Company's business and prospects but were not a thorough or
exhaustive description. Such Investor's decision to enter into the transaction
contemplated hereby is based in part on the answers to such questions as such
Investor and its representatives have raised and on such Investor's own
evaluation of the risks and merits of the transaction and the Company's proposed
business activities. The foregoing, however, does not limit or modify the
representations and warranties of the Company in Article 3 of this Agreement or
the right of such Investor to rely thereon.

                                       8
<PAGE>

     4.7  Authorization.  This Agreement and the Rights Agreement, when executed
and delivered by such Investor, will constitute valid and legally binding
obligations of such Investor, enforceable in accordance with their respective
terms, subject to (i) laws of general application relating to bankruptcy,
insolvency, and the relief of debtors, (ii) rules of law governing specific
performance, injunctive relief, or other equitable remedies, and (iii) the
extent that the indemnification provisions of Section 2.9 of the Rights
Agreement may be limited by principles of public policy.

     4.8  Brokers or Finders.  The Investor has not incurred, and will not incur
or cause the Company to incur, directly or indirectly, as a result of any action
taken by such Investor, any liability for brokerage or finders' fees or agents'
commissions or any similar charges in connection with this agreement or any
transaction contemplated hereby.

     4.9  Tax Consequences.  Such Investor has reviewed with its own tax
advisors the federal, state, local and, if necessary, foreign tax consequences
of this investment and the transactions contemplated by this Agreement. Such
Investor is relying solely on such advisors and not on any statements or
representations of the Company or any of its agents and understands that such
Investor (and not the Company) shall be responsible for its own tax liability
that may arise as a result of this investment or the transactions contemplated
by this Agreement.


                                   ARTICLE 5

                           RESTRICTIONS ON TRANSFER
                           ------------------------

     5.1  Restrictions on Transfer.  The Securities shall not be sold, assigned,
transferred, or pledged except upon the conditions specified in this Article,
the Restated Certificate, and the Bylaws, which conditions provide a right of
first offer in favor of the Company and are intended to, among other things,
ensure compliance with the provisions of the Securities Act of 1933, as amended
(the "Securities Act").  Any proposed transferee of the Securities held by such
Investor must agree (prior to transfer) to take and hold such securities subject
to the provisions and upon the conditions specified in this Article.

     5.2  Restrictive Legend.  Each stock certificate representing (i) the
Securities, or (ii) any other securities issued in respect of the Securities
upon any stock split, stock dividend, merger, consolidation, recapitalization,
or similar event (collectively the "Restricted Securities"), shall be stamped or
otherwise imprinted with legends in substantially the following form (in
addition to any legend required under applicable state securities laws):

     THE SECURITIES REPRESENTED BY THIS CERTIFICATE HAVE NOT BEEN REGISTERED
     UNDER THE SECURITIES ACT OF 1933, AS AMENDED (THE "ACT"). THESE SECURITIES
     HAVE BEEN ACQUIRED FOR INVESTMENT AND NOT WITH A VIEW TO, OR IN CONNECTION
     WITH, THE DISTRIBUTION THEREOF. THESE SECURITIES ARE SUBJECT TO A RIGHT OF
     FIRST OFFER IN FAVOR OF THE COMPANY AND MAY NOT BE OFFERED, SOLD, PLEDGED,
     OR TRANSFERRED UNLESS (I) A REGISTRATION STATEMENT UNDER THE ACT IS IN
     EFFECT AS TO THESE

                                       9
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     SECURITIES OR (II) THERE IS AN OPINION OF COUNSEL, SATISFACTORY TO THE
     CORPORATION, THAT AN EXEMPTION THEREFROM IS AVAILABLE.

     COPIES OF THE AGREEMENTS COVERING THE PURCHASE OF THESE SECURITIES AND
     RESTRICTING THEIR TRANSFER, THE AMENDED AND RESTATED CERTIFICATE OF
     INCORPORATION OF THE COMPANY CONTAINING SUCH RESTRICTIONS, AND THE
     COMPANY'S BYLAWS IMPOSING A RIGHT OF FIRST OFFER IN FAVOR OF THE COMPANY,
     MAY BE OBTAINED AT NO COST BY WRITTEN REQUEST MADE BY THE HOLDER OF RECORD
     OF THIS CERTIFICATE TO THE SECRETARY OF THE CORPORATION AT THE PRINCIPAL
     EXECUTIVE OFFICES OF THE CORPORATION.

     Each Investor and holder of any Securities consents to the Company making a
notation on its records and giving instructions to any transfer agent of the
Securities in order to implement the restrictions on transfer described in this
Section.

     5.3  Notice of Proposed Transfers.  Prior to any proposed transfer of any
Restricted Securities, unless there is in effect a registration statement under
the Securities Act covering the proposed transfer, the holder thereof shall give
written notice (the "Notice") to the Company of such holder's intention to make
such transfer. The Notice shall describe the manner and circumstances of the
proposed transfer in sufficient detail. If reasonably requested by the Company
prior to the transfer being effected, the holder shall provide to the Company a
written opinion of legal counsel who shall be reasonably satisfactory to the
Company, addressed to the Company and reasonably satisfactory in form and
substance to the Company's counsel, to the effect that the proposed transfer of
the Restricted Securities may be effected without registration under the
Securities Act. Notwithstanding anything to the contrary contained herein, no
such registration statement or opinion of counsel shall be necessary for a
transfer (i) without consideration by a non-"affiliate" (as defined in the
Securities Act) Investor which is (A) a partnership to its partners or former
partners in accordance with partnership interests, (B) a corporation to its
stockholders in accordance with their interest in the corporation, or (C) a
limited liability company to its members or former members in accordance with
their interest in the limited liability company or (ii) with or without
consideration by a non-"affiliate" (as defined in the Securities Act) Investor
which is an entity to an "affiliate" (as defined in the Securities Act) of such
Investor, provided that such affiliate is an "accredited investor" (as defined
in Regulation D promulgated under the Securities Act); provided that in each
case the transferee will be subject to the terms of this Agreement to the same
extent as if such transferee were an original Investor hereunder. Each stock
certificate evidencing the Restricted Securities so transferred shall bear the
appropriate restrictive legends set forth in Section 5.2.

                                      10
<PAGE>

                                   ARTICLE 6

                    CONDITIONS TO CLOSING OF THE INVESTORS
                    --------------------------------------

     Each Investor's obligation to enter into the transactions contemplated
hereby at the Closing is subject to the fulfillment on or prior to the Closing
Date of the following conditions:

     6.1  Representations and Warranties.  The representations and warranties
made by the Company in Article 3 shall have been true and correct in all
material respects when made, provided that, to the extent that each such
representation or warranty contains its own materiality standard, such standard
shall be the sole measure of "material" for the purposes hereof.

     6.2  Covenants.  All covenants, agreements, and conditions contained in
this Agreement to be performed by the Company on or prior to the Closing shall
have been performed or complied with in all respects.

     6.3  Compliance Certificate.  The Company shall have delivered to the
Investors a Compliance Certificate in substantially the form attached hereto as
Exhibit D, executed by an officer of the Company, dated as of the Closing Date,
and certifying to the fulfillment of the conditions specified in Sections 6.1
and 6.2.

     6.4  Opinion of Company's Counsel.  Fenwick & West LLP, counsel for the
Company, shall have delivered to the Investors an opinion in substantially the
form attached hereto as Exhibit E, dated as of the Closing Date.

     6.5  Securities Exemptions.  The offer and sale of the Shares to the
Investors pursuant to this Agreement shall be exempt from the registration
requirements of the Securities Act, the qualification requirements of the
California Corporate Securities Law of 1968, as amended (the "California
Securities Law") and the registration and/or qualification requirements of all
other applicable state securities laws.

     6.6  Restated Certificate.  The Restated Certificate shall have been filed
with and accepted by the Delaware Secretary of State.

     6.7  Proceedings and Documents.  The following corporate proceedings and
documents (in connection with the transactions contemplated at the Closing)
shall be substantially in the form provided to the Investors and their counsel:

          (a)  Certified Charter Documents.  A copy of the Restated Certificate
and the Bylaws (as amended through the date of the Closing), certified by the
Secretary of the Company as true and correct copies thereof as of the Closing.

          (b)  Corporate Actions.  A copy of the resolutions of the Board of
Directors and, if required, the stockholders of the Company evidencing the
approval of the Restated Certificate, the approval of this Agreement and the
Rights Agreement and the issuance of the Shares and the other matters
contemplated hereby.
<PAGE>

          (c)  Secretary's Certificate.  A certificate of the Secretary or other
officer of the Company certifying as true and correct the documents referred to
in subsections (a) and (b) above and certifying the names of the officers of the
Company authorized to sign this Agreement, the Rights Agreement and the
certificates evidencing the Shares, in the form attached as Exhibit F.

     6.8  Investors' Rights Agreement.  The Company each Investor, and holders
of a majority of the Series B Preferred, Series C Preferred, Series D Preferred,
Series E Preferred, Series F Preferred, Series G Preferred and/or Conversion
Stock representing or convertible into a majority of all Registrable Securities
under the Company's existing Investors' Rights Agreement dated September 2, 1999
by and among the Company and the persons and entities listed on Exhibit A
thereto and Venture Lending and Leasing, Inc. (the "Prior Rights Agreement")
shall have executed and delivered the Restated and Amended Investors' Rights
Agreement in the form attached to this Agreement as Exhibit G (the "Rights
Agreement").

     6.9  Existing Refusal Rights.  The right of first offer provided in the
Prior Rights Agreement as it applies to the issuance and sale of the Shares
shall have been waived and released in writing or shall have been satisfied.


                                   ARTICLE 7

                     CONDITIONS TO CLOSING OF THE COMPANY
                     ------------------------------------

     The Company's obligation to enter into the transactions contemplated hereby
at each closing is subject to the fulfillment on or prior to the Closing Date of
the following conditions:

     7.1  Representations and Warranties.  The representations and warranties
made by each Investor in Article 4 shall have been true and correct in all
material respects when made, and shall be true and correct as of the Closing
Date, provided that, to the extent that each such representation or warranty
contains its own materiality standard, such standard shall be the sole measure
of "material" for the purposes hereof.

     7.2  Securities Exemptions.  The offer and sale of the Shares to the
Investors pursuant to this Agreement shall be exempt from the registration
requirements of the Securities Act, the qualification requirements of the
California Securities Law, and the registration and/or qualification
requirements of all other applicable state securities laws.

     7.3  Restated Certificate.  The Restated Certificate shall have been filed
with and accepted by the Delaware Secretary of State.

     7.4  Proceedings and Documents.  The following corporate proceedings and
documents (in connection with the transactions contemplated at the Closing)
shall be substantially in the form provided to the Investors and their counsel:

          (a)  Certified Charter Documents.  A copy of the Restated Certificate
and the Bylaws (as amended through the date of the Closing), certified by the
Secretary of the Company as true and correct copies thereof as of the Closing.

                                      12
<PAGE>

          (b)  Corporate Actions.  A copy of the resolutions of the Board of
Directors and, if required, the stockholders of the Company evidencing the
approval of the Restated Certificate, the approval of this Agreement and the
Rights Agreement and the issuance of the Shares and the other matters
contemplated hereby.

          (c)  Secretary's Certificate.  A certificate of the Secretary or other
officer of the Company certifying as true and correct the documents referred to
in subsections (a) and (b) above and certifying the names of the officers of the
Company authorized to sign this Agreement, the Rights Agreement and the
certificates evidencing the Shares, in the form attached as Exhibit F.

     7.5  Investors' Rights Agreement.  The Company, each Investor, and holders
of a majority of the Series B Preferred, Series C Preferred, Series D Preferred,
Series E Preferred, Series F Preferred, Series G Preferred and/or Conversion
Stock representing or convertible into a majority of all Registrable Securities
under the Prior Rights Agreement shall have executed and delivered the Rights
Agreement.

     7.6  Existing Refusal Rights.  The right of first offer provided in the
Prior Rights Agreement as it applies to the issuance and sale of the Shares
shall have been waived and released in writing or shall have been satisfied.


                                   ARTICLE 8

                             ADDITIONAL COVENANTS
                             --------------------

     8.1  Employee Proprietary Information Agreements.  The Company hereby
covenants and agrees that it will cause each of the Company's employees,
consultants and independent contractors to execute proprietary information and
invention assignment agreements in the Company's standard form, which has been
provided to the Investors and their counsel or a form substantially similar
thereto.

     8.2  Stock Vesting.  Unless otherwise approved by the Board of Directors,
the Company hereby covenants and agrees that all future equity and option
issuances to officers, directors and employees shall be subject to a four year
vesting requirement, which shall also provide that no vesting shall occur until
a minimum of six months shall have passed from the vesting commencement date.


                                   ARTICLE 9

                              GENERAL PROVISIONS
                              ------------------

     9.1  Governing Law.  This Agreement shall be governed by and construed
exclusively in accordance with the internal laws of the State of California as
applied to agreements among California residents entered into and to be
performed entirely within California, excluding that body of law relating to
conflict of laws and choice of law.

                                      13
<PAGE>

     9.2  Survival.  The representations, warranties, and covenants of the
parties made herein shall survive the Closing and any Additional Closings and
shall in no way be affected by any investigation of the subject matter thereof
made by or on behalf of the parties.

     9.3  Successors and Assigns.  Except as otherwise expressly limited herein,
the provisions hereof shall inure to the benefit of, and be binding upon, the
successors, assigns, heirs, executors, and administrators of the parties hereto,
provided, however, that the rights of an Investor to purchase Shares shall not
be assignable without the written consent of the Company.

     9.4  Entire Agreement; Amendment and Waiver.  This agreement and the other
documents delivered pursuant hereto constitute the full and entire understanding
and agreement between the parties with regard to the subject matters hereof and
thereof. Any term of this agreement may be amended and the observance of any
term hereof may be waived (either prospectively or retroactively and either
generally or in a particular instance) only with the written consent of an
Investor and the Company and the holders of Shares and/or Conversion Shares
representing at least a majority of the aggregate number of shares of Common
Stock into which the Purchased Shares then are convertible and/or have been
converted (excluding any of such shares that have been sold to the public or
pursuant to SEC Rule 144).  Any amendment or waiver effected in accordance with
this Section shall be binding upon each holder of any Purchased Shares and/or
Conversion Shares at the time outstanding, each future holder of such
securities, and the Company; provided, however, that no condition set forth in
Article 6 may be waived with respect to any Investor who does not consent
thereto; and provided further, that New Investors may become parties to this
Agreement in accordance with Article 2.2 without any amendment of this Agreement
or any consent or approval of any Investor.

     9.5  Notices, etc.  All notices and other communications required or
permitted hereunder shall be in writing and shall be mailed by registered or
certified mail, postage prepaid, or otherwise delivered by hand or by messenger,
addressed (i) if to an Investor, at its address set forth on Exhibit A, or at
such other address as such Investor shall have furnished to the Company in
writing, or (ii) if to any other holder of any Securities, at such address as
such holder shall have furnished the Company in writing, or, until any such
holder so furnishes an address to the Company, then to and at the address of the
last holder of such Securities who has so furnished an address to the Company,
or (iii) if to the Company, one copy to its address set forth on the first page
of this agreement and addressed to the attention of the President, or at such
other address as the Company shall have furnished to the Investors, and another
copy to the Company's legal counsel to the attention of Richard L. Dickson, Esq.
of Fenwick & West LLP, Two Palo Alto Square, Palo Alto, California 94306.

     9.6  Delays or Omissions.  No delay or omission to exercise any right,
power, or remedy accruing to any party upon any breach or default under this
Agreement, shall be deemed a waiver of any other breach or default theretofore
or thereafter occurring. Any waiver, permit, consent, or approval of any kind or
character on the part of any party of any breach or default under this
Agreement, or any waiver on the part of any party of any provisions or
conditions of this Agreement, must be in writing and shall be effective only to
the extent specifically set forth in such writing. All remedies, either under
this Agreement or by law or otherwise afforded to any of the parties, shall be
cumulative and not alternative.

                                      14
<PAGE>

     9.7  Severability.  If any provision of this Agreement is held to be
unenforceable under applicable law, then such provision shall be excluded from
this Agreement and the balance of this Agreement shall be interpreted as if such
provision were so excluded and shall be enforceable in accordance with its
terms. The court in its discretion may substitute for the excluded provision an
enforceable provision which in economic substance reasonably approximates the
excluded provision.

     9.8  California Corporate Securities Law.  THE SALE OF THE SECURITIES WHICH
ARE THE SUBJECT OF THIS AGREEMENT HAS NOT BEEN QUALIFIED WITH THE COMMISSIONER
OF CORPORATIONS OF THE STATE OF CALIFORNIA AND THE ISSUANCE OF SUCH SECURITIES
OR THE PAYMENT OR RECEIPT OF ANY PART OF THE CONSIDERATION THEREFOR PRIOR TO
SUCH QUALIFICATION IS UNLAWFUL UNLESS THE SALE OF SECURITIES IS EXEMPT FROM THE
QUALIFICATION BY SECTION 25100, 25102, OR 25105 OF THE CALIFORNIA CORPORATIONS
CODE. THE RIGHTS OF ALL PARTIES TO THIS AGREEMENT ARE EXPRESSLY CONDITIONED UPON
SUCH QUALIFICATION BEING OBTAINED, UNLESS THE SALE IS SO EXEMPT.

     9.9  Headings.  The headings and captions used in this Agreement are used
for convenience only and are not to be considered in construing or interpreting
this Agreement.  All references in this Agreement to articles, sections,
paragraphs, exhibits and schedules shall, unless otherwise provided, refer to
articles, sections and paragraphs hereof and exhibits and schedules attached
hereto, all of which exhibits and schedules are incorporated herein by this
reference.

     9.10  Third Parties.  Nothing in this Agreement, express or implied, is
intended to confer upon any person, other than the parties hereto and their
successors and assigns, any rights or remedies under or by reason of this
Agreement.



             [REMAINDER OF THIS PAGE IS INTENTIONALLY LEFT BLANK]

                                      15
<PAGE>

     9.13  Counterparts.  This agreement may be executed in any number of
counterparts, each of which shall be deemed an original and enforceable against
the parties actually executing such counterpart, and all of which together shall
constitute one instrument.

     Executed effective as of the date first set forth above.


ONI Systems Corp.

By: /s/ Hugh C. Martin
   --------------------------------

Name: Hugh C. Martin
     ------------------------------

Title: President and CEO
      -----------------------------


INVESTOR:

Sun Microsystems, Inc.

By: /s/ Jonathan Schwartz
   --------------------------------

Name: Jonathan Schwartz
     ------------------------------

Title: VP, Investments
      -----------------------------