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                                                                   Exhibit 10.15








                         ARROWPOINT COMMUNICATIONS, INC.




                   SERIES C PREFERRED STOCK PURCHASE AGREEMENT




                               September 30, 1998








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                                TABLE OF CONTENTS

PAGE

Disclosure Schedule

Exhibit A                  Certificate of Amendment

Exhibit B                  Opinion of Hale and Dorr LLP

Exhibit C                  Investor Rights Agreement

Exhibit D                  Right of First Refusal and Co-Sale Agreement



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                   SERIES C PREFERRED STOCK PURCHASE AGREEMENT

This Agreement dated as of September 30, 1998 is entered into by and among
ArrowPoint Communications, Inc., a Delaware corporation (the "Company"), and the
persons and entities listed on SCHEDULE I attached hereto (individually, a
"Purchaser" and, collectively, the "Purchasers")

In consideration of the mutual promises and covenants contained in this
Agreement, the parties hereto agree as follows:

         1.       AUTHORIZATION AND SALE OF SHARES.

                  1.1      AUTHORIZATION. The Company has duly authorized the
sale and issuance, pursuant to the terms of this Agreement, of 278,464 shares of
its Series C Convertible Preferred Stock, $0.01 par value per share (the "Series
C Preferred Stock"), having the rights, restrictions, privileges and preferences
set forth in the Certificate of Amendment attached hereto as EXHIBIT A (the
"Certificate of Amendment"). The Company has adopted and filed the Certificate
of Amendment with the Secretary of State of the State of Delaware.

                  1.2      SALE OF SHARES. Subject to the terms and conditions
of this Agreement, at the Closing (as defined below) the Company will issue and
sell to each Purchaser, and each Purchaser will purchase, for a purchase price
of $7.86 per share, such number of shares of Series C Preferred Stock as is set
forth opposite such Purchaser's name on SCHEDULE I attached hereto. The shares
of Series C Preferred Stock being sold under this Agreement are referred to as
the "Shares."

                  1.3      USE OF PROCEEDS. The Company will use the proceeds
from the sale of the Shares for working capital purposes.

         2.       THE CLOSING. The closing ("Closing") of the sale and purchase
of the Shares under this Agreement shall take place at the offices of Hale and
Dorr LLP, 60 State Street, Boston, Massachusetts at 9:00 a.m. on the date of
this Agreement, or at such other time, date and place as are mutually agreeable
to the Company and the Purchasers. The date of the Closing is hereinafter
referred to as the "Closing Date." At the Closing:


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                  (a)      the Company shall deliver to the Purchasers a
certificate, as of the most recent practicable date, as to the corporate good
standing of the Company issued by the Secretary of State of the State of
Delaware;

                  (b)      the Company shall deliver to the Purchasers the
Certificate of Incorporation of the Company, as amended and in effect as of the
Closing Date (including the Certificate of Amendment), certified by the
Secretary of State of the State of Delaware;

                  (c)      the Company shall deliver to the Purchasers a
Certificate of the Secretary of the Company attesting as to (i) the By-laws of
the Company, and (ii) resolutions of the Board of Directors and stockholders of
the Company authorizing and approving all matters in connection with this
Agreement and the transactions contemplated hereby.

                  (d)      Hale and Dorr LLP, counsel for the Company, shall
deliver to the Purchasers an opinion, dated the Closing Date, in the form
attached hereto as EXHIBIT B;

                  (e)      the Company, Chin-Cheng Wu (the "Founder") and the
Purchasers shall execute and deliver the Investor Rights Agreement in the form
attached hereto as EXHIBIT C (the "Investor Agreement");

                  (f)      the Company, the Founding Stockholders (as defined
therein) and the Purchasers shall execute and deliver the Right of First Refusal
and Co-Sale Agreement in the form attached hereto as EXHIBIT D (the "Right of
First Refusal Agreement");

                  (g)      the Company shall deliver to each Purchaser a
certificate for the number of Shares being purchased by such Purchaser,
registered in the name of such Purchaser;

                  (h)      each Purchaser shall pay to the Company the purchase
price for the Shares being purchased by such Purchaser, by wire transfer or
certified check; and

                  (i)      the Company and the Purchasers shall execute and
deliver a Cross-Receipt.

         3.       REPRESENTATIONS OF THE COMPANY. Subject to and except as
disclosed by the Company in the Disclosure Schedule attached hereto (the
"Disclosure Schedule"), the Company hereby represents and warrants to the
Purchasers as follows:


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                  3.1      ORGANIZATION AND STANDING. The Company is a
corporation duly organized, validly existing and in good standing under the laws
of the State of Delaware and has full corporate power and authority to conduct
its business as presently conducted and as proposed to be conducted by it and to
enter into and perform this Agreement and to carry out the transactions
contemplated by this Agreement. The Company is duly qualified to do business as
a foreign corporation and is in good standing in the Commonwealth of
Massachusetts and in any other jurisdiction in which the failure to so qualify
would have a material adverse effect on the operations or financial condition of
the Company. The Company has furnished to special counsel to the Purchasers true
and complete copies of its Certificate of Incorporation and By-laws, each as
amended to date and presently in effect.

                  3.2      CAPITALIZATION. The authorized capital stock of the
Company (immediately prior to the Closing) consists of (a) 20,000,000 shares of
common stock, $0.001 par value per share (the "Common Stock"), of which
3,496,850 shares are issued and outstanding, 993,150 shares have been reserved
for issuance pursuant to the Company's 1997 Stock Incentive Plan, 5,750,000
shares have been reserved for issuance upon the conversion of the outstanding
shares of Series A Convertible Preferred Stock ("Series A Preferred Stock"),
2,213,828 shares have been reserved for issuance upon conversion of the
outstanding shares of Series B Convertible Preferred Stock ("Series B Preferred
Stock"), and 278,464 shares have been reserved for issuance upon conversion of
the Shares and (b) 10,000,000 shares of preferred stock, $0.01 par value per
share, of which (i) 5,750,000 shares have been designated as Series A Preferred
Stock, all of which are issued and outstanding, (ii) 2,213,828 shares have been
designated as Series B Preferred Stock, all of which are issued and outstanding,
and (iii) 278,464 shares have been designated as Series C Preferred Stock, none
of which are issued or outstanding. At the Closing, the Common Stock, the Series
A Preferred Stock, the Series B Preferred Stock and the Series C Preferred Stock
will have the voting powers, designations, preferences, rights and
qualifications, and limitations or restrictions set forth in the Certificate of
Incorporation, as amended by the Certificate of Amendment. All of the issued and
outstanding shares of Common Stock, Series A Preferred Stock and Series B
Preferred Stock have been duly authorized and validly issued and are fully paid
and nonassessable. Except as contemplated by this Agreement or set forth in the
Disclosure Schedule, (i) no subscription, warrant, option, convertible security
or other right (contingent or otherwise) to purchase or acquire any shares of
capital stock of the Company is authorized or outstanding, (ii) the Company has
no obligation (contingent or otherwise) to issue any subscription, warrant,
option, convertible security or other such right or to issue or distribute to
holders of any shares of its capital stock any evidences of indebtedness or
assets of the Company, and (iii) the Company has no obligation (contingent or
otherwise) to purchase, redeem


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or otherwise acquire any shares of its capital stock or any interest therein or
to pay any dividend or make any other distribution in respect thereof. All of
the issued and outstanding shares of capital stock of the Company have been
offered, issued and sold by the Company in compliance with applicable Federal
and state securities laws.

                  3.3      SUBSIDIARIES, ETC. The Company has no subsidiaries
and does not own or control, directly or indirectly, any shares of capital stock
of any other corporation or any interest in any partnership, joint venture or
other non-corporate business enterprise.

                  3.4      STOCKHOLDER LIST AND AGREEMENTS. Section 3.4 of the
Disclosure Schedule sets forth a true and complete list of the stockholders of
the Company, showing the number of shares and class or series of capital stock
or other securities of the Company held by each stockholder immediately prior to
the execution of this Agreement and the consideration paid to the Company
therefor. Except as listed in Section 3.4 of the Disclosure Schedule or as
contemplated by this Agreement, there are no agreements, written or oral,
between the Company and any holder of its capital stock, or, to the best of the
Company's knowledge, among any holders of its capital stock, relating to the
future acquisition (including without limitation rights of first refusal or
pre-emptive rights), disposition, registration under the Securities Act of 1933,
as amended (the "Securities Act"), or voting of the capital stock of the
Company.

                  3.5      ISSUANCE OF SHARES. The issuance, sale and delivery
of the Shares in accordance with this Agreement, and the issuance and delivery
of the shares of Common Stock issuable upon conversion of the Shares, have been
duly authorized by all necessary corporate action on the part of the Company,
and all such shares have been duly reserved for issuance. The Shares when so
issued, sold and delivered against payment therefor in accordance with the
provisions of this Agreement, and the shares of Common Stock issuable upon
conversion of the Shares, when issued upon such conversion, will be duly and
validly issued, fully paid and non-assessable.

                  3.6      AUTHORITY FOR AGREEMENT. The execution, delivery and
performance by the Company of this Agreement and all other agreements required
to be executed by the Company at the Closing pursuant to Section 2 (the
"Ancillary Agreements"), and the consummation by the Company of the transactions
contemplated hereby and thereby, have been duly authorized by all necessary
corporate action. This Agreement and the Ancillary Agreements have been duly
executed and delivered by the Company and constitute valid and binding
obligations of the Company enforceable in accordance with their respective
terms. The execution of and performance of the transactions contemplated by this
Agreement and the Ancillary Agreements


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and compliance with their provisions by the Company will not violate any
provision of law and will not conflict with or result in any breach of any of
the terms, conditions or provisions of, or constitute a default under, or
require a consent or waiver under, its Certificate of Incorporation or By-laws
(each as amended to date) or any indenture, lease, agreement or other instrument
to which the Company is a party or by which it or any of its properties is
bound, or any decree, judgment, order, statute, rule or regulation applicable to
the Company.

                  3.7      GOVERNMENTAL CONSENTS. No consent, approval, order or
authorization of, or registration, qualification, designation, declaration or
filing with, any governmental authority is required on the part of the Company
in connection with the execution and delivery of this Agreement, the offer,
issuance, sale and delivery of the Shares, or the other transactions to be
consummated at the Closing, as contemplated by this Agreement, except such
filings as shall have been made prior to and shall be effective on and as of the
Closing. Based on the representations made by the Purchasers in Section 5 of
this Agreement, the offer and sale of the Shares to the Purchasers will be
exempt from the registration requirements of applicable Federal and state
securities laws.

                  3.8      LITIGATION. There is no action, suit or proceeding,
or governmental inquiry or investigation, pending, or, to the best of the
Company's knowledge, any basis therefor or threat thereof, against the Company
or the Founder, which questions the validity of this Agreement or the right of
the Company or the Founder to enter into it, or which might result, either
individually or in the aggregate, in any material adverse change in the
business, prospects, assets or condition, financial or otherwise, of the
Company, nor is there any litigation pending, or, to the best of the Company's
knowledge, any basis therefor or threat thereof, against the Company or the
Founder by reason of the past employment relationships of the Founder, the
proposed activities of the Company, or negotiations by the Company and/or the
Founder with possible investors in the Company.

                  3.9      FINANCIAL STATEMENTS. The Company has furnished to
each of the Purchasers a complete and correct copy of the audited balance sheet
(the "Balance Sheet") of the Company as at December 31, 1997 and the related
audited statement of operations and cash flow for the year then ended and the
unaudited balance sheet (the "Unaudited Balance Sheet") of the Company as of
June 30, 1998 (the "Balance Sheet Date") and the related unaudited statement of
income for the six months then ended (collectively, the "Financial Statements").
The Financial Statements are complete and correct in all material respects, are
in accordance with the books and records of the Company and present fairly the
financial condition and results of operations of


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the Company, as at the dates and for the periods indicated, and have been
prepared in accordance with generally accepted accounting principles
consistently applied, except that the Financial Statements have been prepared
for the internal use of management and may not be in accordance with generally
accepted accounting principles because of the absence of footnotes normally
contained therein and are subject to normal year-end audit adjustments which in
the aggregate will not be material.

                  3.10     ABSENCE OF LIABILITIES. Except as set forth in
Section 3.10 of the Disclosure Schedule, the Company did not have, at the
Balance Sheet Date, any liabilities of any type which in the aggregate exceeded
$25,000, whether absolute or contingent, which were not fully reflected on the
Balance Sheet, and, since the Balance Sheet Date, the Company has not incurred
or otherwise become subject to any such liabilities or obligations except in the
ordinary course of business.

                  3.11     TAXES. The amount shown on the Balance Sheet as
provision for taxes is sufficient in all material respects for payment of all
accrued and unpaid Federal, state, county, local and foreign taxes for the
period then ended and all prior periods. The Company has filed or has obtained
presently effective extensions with respect to all Federal, state, county, local
and foreign tax returns which are required to be filed by it, such returns are
true and correct in all material respects and all taxes shown thereon to be due
have been timely paid with exceptions not material to the Company. Neither the
Company nor any of its stockholders has ever filed (a) an election pursuant to
Section 1362 of the Internal Revenue Code of 1986, as amended (the "Code"), that
the Company be taxed as an S Corporation, or (b) consent pursuant to Section
341(f) of the Code relating to collapsible corporations.

                  3.12     PROPERTY AND ASSETS. The Company has good title to
all of its material properties and assets, including all properties and assets
reflected in the Balance Sheet, except those disposed of since the date thereof
in the ordinary course of business, and none of such properties or assets is
subject to any mortgage, pledge, lien, security interest, lease, charge or
encumbrance other than those the material terms of which are described in
Section 3.12 of the Disclosure Schedule.

                  3.13     INTELLECTUAL PROPERTY.

                           (a)      To the best of the Company's knowledge, no
third party has claimed or has reason to claim that any person employed by or
affiliated with the Company, in connection with his or her employment by or
affiliation with the Company, (i) has violated or is


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violating any of the terms or conditions of his employment, non-competition or
non-disclosure agreement with such third party, (ii) has disclosed or is
disclosing or has utilized or is utilizing any trade secret or proprietary
information or documentation of such third party or (iii) has interfered or is
interfering in the employment relationship between such third party and any of
its present or former employees. No third party has requested information from
the Company which suggests that such a claim might be contemplated. To the best
of the Company's knowledge, no person employed by or affiliated with the Company
has employed or proposes to employ any trade secret or any information or
documentation proprietary to any former employer, and to the best of the
Company's knowledge, no person employed by or affiliated with the Company has
violated any confidential relationship which such person may have had with any
third party, in connection with the development, manufacture or sale or any
product or proposed product or the development or sale of any service or
proposed service of the Company, and the Company has no reason to believe there
will be any such employment or violation. To the best of the Company's
knowledge, none of the execution or delivery of this Agreement, or the carrying
on of business of the Company as officers, employees or agents by any officer,
director or key employee of the Company, or the conduct or proposed conduct of
the business of the Company, will conflict with or result in a breach of the
terms, conditions or provisions of or constitute a default under any contract,
covenant or instrument under which any such person is obligated.

                           (b)      Set forth in Section 3.13 of the Disclosure
Schedule is a list of all domestic and foreign patents, patent rights, patent
applications, trademarks, trademark applications, service marks, service mark
applications, trade names and copyrights, and all applications for such which
are in the process of being prepared, owned by or registered in the name of the
Company, or of which the Company is a licensor or licensee or in which the
Company has any right, and in each case a brief description of the nature of
such right. The Company owns or possesses adequate licenses or other rights to
use all patents, patent applications, trademarks, trademark applications,
service marks, service mark applications, trade names, copyrights, manufacturing
processes, formulae, trade secrets, customer lists and know-how (collectively,
"Intellectual Property") necessary for the conduct of its business as conducted
and as proposed to be conducted, and no claim is pending or, to the best of the
Company's knowledge, threatened to the effect that the operations of the Company
infringe upon or conflict with the asserted rights of any other person under any
Intellectual Property, and, to the best of the Company's knowledge, there is no
basis for any such claim (whether or not pending or threatened). No claim is
pending or threatened to the effect that any such Intellectual Property owned or
licensed by the Company, or which the Company otherwise has the right to use, is


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invalid or unenforceable by the Company, and, to the best of the Company's
knowledge, there is no basis for any such claim (whether or not pending or
threatened). To the best of the Company's knowledge, all technical information
developed by and belonging to the Company which has not been patented has been
kept confidential. The Company has not granted or assigned to any other person
or entity any right to manufacture, have manufactured, assemble or sell the
products or proposed products or to provide the services or proposed services of
the Company.

                  3.14     MATERIAL CONTRACTS AND OBLIGATIONS. Except as
contemplated by this Agreement or as listed in the Disclosure Schedule, the
Company is not a party to any material agreement or commitment of any nature,
including without limitation (a) any agreement which requires future
expenditures by the Company in excess of $250,000, (b) any employment or
consulting agreement, employee benefit, bonus, pension, profit-sharing, stock
option, stock purchase or similar plan or arrangement, or distributor or sales
representative agreement, (c) any agreement with any stockholder, officer or
director of the Company, or any "affiliate" or "associate" of such persons (as
such terms are defined in the rules and regulations promulgated under the
Securities Act), including without limitation any agreement or other arrangement
providing for the furnishing of services by, rental of real or personal property
from, or otherwise requiring payments to, any such person or entity or (d) any
agreement relating to the intellectual property rights of the Company.

                  3.15     COMPLIANCE. The Company has, in all material
respects, complied with all laws, regulations and orders applicable to its
present and proposed business and has all material permits and licenses required
thereby. There is no term or provision of any mortgage, indenture, contract,
agreement or instrument to which the Company is a party or by which it is bound,
or, to the best of the Company's knowledge, of any provision of any state or
Federal judgment, decree, order, statute, rule or regulation applicable to or
binding upon the Company, which materially adversely affects or, so far as the
Company may now foresee, in the future is reasonably likely to materially
adversely affect, the business, prospects, assets or condition, financial or
otherwise, of the Company. To the best of the Company's knowledge, neither the
Founder nor any other employee of the Company is in violation of any term of any
contract or covenant (either with the Company or with another entity) relating
to employment, patents, proprietary information disclosure, non-competition or
non-solicitation.



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                  3.16     EMPLOYEES AND FOUNDER.

                           (a)      The Founder and the other holders of Common
Stock have executed and delivered to the Company a Stock Restriction Agreement,
copies of which have been made available to the Purchasers, and all of such
agreements are in full force and effect.

                           (b)      Each employee of the Company (including the
Founder) who is at or above the director level or who holds at least 100,000
shares of Common Stock (or options exercisable therefor) (as adjusted for stock
splits, stock dividends, recapitalizations and similar events) has executed and
delivered to the Company a Noncompetition and Confidentiality Agreement covering
a period of one year following the termination of such employee's employment
with the Company, copies of which have been made available to the Purchasers.
Each employee of the Company not covered by the foregoing sentence has executed
and delivered to the Company a Confidentiality Agreement, copies of which have
been made available to the Purchasers. All of such agreements are in full force
and effect.

                           (c)      None of the employees of the Company is
represented by any labor union, and there is no labor strike or other labor
trouble pending with respect to the Company (including, without limitation, any
organizational drive) or, to the best of the Company's knowledge, threatened.

                  3.17     ERISA. Except as described in the Disclosure
Schedule, the Company does not have or otherwise contribute to or participate in
any employee benefit plan subject to the Employee Retirement Income Security Act
of 1974.

                  3.18     BOOKS AND RECORDS. The minute books of the Company
contain complete and accurate records of all meetings and other corporate
actions of its stockholders and its Board of Directors and committees thereof.
The stock ledger of the Company is complete and reflects all issuances,
transfers, repurchases and cancellations of shares of capital stock of the
Company.

                  3.19     BOARD OF DIRECTORS.  The Board of Directors is
comprised of four members, and consists of Chin-Cheng Wu, Edward T. Anderson,
Paul J. Ferri and Bruce I. Sachs.

                  3.20     U.S. REAL PROPERTY HOLDING CORPORATION. The Company
is not now and has never been a "United States Real Property Holding
Corporation" as defined in Section 897(c)(2) of the Code and Section 1.897-2(b)
of the Regulations promulgated by the Internal Revenue Service.


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                  3.21     DISCLOSURES. Neither this Agreement nor any Schedule
or Exhibit hereto, nor any certificate or instrument furnished to the Purchasers
at the Closing or as required by the terms of this Agreement, when read
together, contains or will contain any untrue statement of a material fact or
omits or will omit to state a material fact necessary in order to make the
statements contained herein or therein, in light of the circumstances under
which they were made, not misleading.

         4.       [Intentionally omitted]

         5.       REPRESENTATIONS OF THE PURCHASERS. Each Purchaser represents
and warrants to the Company as follows:

                  5.1      INVESTMENT. Such Purchaser is acquiring the Shares,
and the shares of Common Stock into which the Shares may be converted, for its
or his own account for investment and not with a view to, or for sale in
connection with, any distribution thereof, nor with any present intention of
distributing or selling the same; and such Purchaser has no present or
contemplated agreement, undertaking, arrangement, obligation, indebtedness or
commitment providing for the disposition thereof. Such Purchaser acknowledges
that the Shares are restricted securities as defined under the Securities Act
and shall bear the legends set forth in Section 7.3 hereof.

                  5.2      AUTHORITY. Such Purchaser has full power and
authority to enter into and to perform this Agreement in accordance with its
terms. Such Purchaser represents that it has not been organized, reorganized or
recapitalized specifically for the purpose of investing in the Company. This
Agreement and the Ancillary Agreement to be executed by such Purchaser have been
duly executed and delivered by such Purchaser and constitute valid and binding
obligations of such Purchaser enforceable in accordance with their respective
terms. The execution of and performance of the transactions contemplated by this
Agreement and the Ancillary Agreements to be executed by such Purchaser and
compliance with their provisions by such Purchaser will not violate any
provision of law and will not conflict with or result in any breach of any of
the terms, conditions or provisions of, or constitute a default under, or
require a consent or waiver under, its organizational documents (each as amended
to date) or any indenture, lease, agreement or other instrument to which the
Purchaser is a party or by which it or any of its properties is bound, or any
decree, judgment, order, statute, rule or regulation applicable to such
Purchaser.

                  5.3      EXPERIENCE. Such Purchaser has carefully reviewed the
representations concerning the Company contained in this Agreement and has made
detailed inquiry concerning


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<PAGE>   13

the Company, its business and its personnel; the officers of the Company have
made available to such Purchaser any and all written information which it has
requested and have answered to such Purchaser's satisfaction all inquiries made
by such Purchaser; and such Purchaser has sufficient knowledge and experience in
investing in companies similar to the Company so as to be able to evaluate the
risks and merits of its investment in the Company and is able financially to
bear the risks thereof, including a complete loss of its investment. Such
Purchaser understands that an investment in the Company involves a high degree
of risk in view of the fact that the Company is a start-up enterprise with no
operating history, and there may never be an established market for the
Company's capital stock.

                  5.4      STATUS. Such Purchaser is an "accredited Investor"
as that term is defined in Rule 501 of Regulation D promulgated under the
Securities Act.

         6.       COVENANTS OF THE COMPANY.

                  6.1      INSPECTION. The Company shall permit each Purchaser,
or any authorized representative thereof, to visit and inspect the properties of
the Company, including its corporate and financial records, and to discuss its
business and finances with officers of the Company, during normal business hours
following reasonable notice and as often as may be reasonably requested, without
interruption of the business of the Company and subject to the confidentiality
obligations of Section 8.2 hereof.

                  6.2      FINANCIAL STATEMENTS AND OTHER INFORMATION.

                           (a)      So long as a Purchaser (or any of its
affiliates) holds shares of Series A Preferred Stock, Series B Preferred Stock
or Series C Preferred Stock, the Company shall deliver to such Purchaser:

                                    (i)     within 120 days after the end of
each fiscal year of the Company, an audited balance sheet of the Company as at
the end of such year, and audited statements of income and of cash flows of the
Company for such year, certified by certified public accountants of established
national reputation selected by the Company, and prepared in accordance with
generally accepted accounting principles; and

                                    (ii)    within 45 days after the end of each
fiscal quarter of the Company,
an unaudited balance sheet of the Company as at the end of such quarter, and


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<PAGE>   14

unaudited statements of income and of cash flows of the Company for such fiscal
quarter and for the current fiscal year to the end of such fiscal quarter.

                           (b)      So long as a Purchaser (or any of its
affiliates) holds shares of Series A Preferred Stock, Series B Preferred Stock
or Series C Preferred Stock convertible into at least 300,000 shares of Common
Stock (as adjusted for stock splits, stock dividends, recapitalizations and
similar events), the Company shall deliver to such Purchaser:

                                    (i)     as soon as available, but in any
event within 30 days after commencement of each new fiscal year, a budget,
consisting of a business plan and projected financial statements for such fiscal
year; and

                                    (ii)    with reasonable promptness, such
other notices, information and data with respect to the Company as the Company
delivers to the holders of its Common Stock, and such other information and data
as such Purchaser may from time to time reasonably request.

                           (c)      The foregoing financial statements shall be
prepared on a consolidated basis if the Company then has any subsidiaries.

                  6.3      MATERIAL CHANGES AND LITIGATION. The Company shall
promptly notify the Purchasers of any material adverse change in the business,
prospects, assets or condition, financial or otherwise, of the Company and of
any litigation or governmental proceeding or investigation brought or, to the
best of the Company's knowledge, threatened against the Company, or against the
Founder or an officer, director, key employee or principal stockholder of the
Company materially adversely affecting or which, if adversely determined, would
materially adversely affect its business, prospects, assets or condition,
financial or otherwise.

                  6.4      INSURANCE.

                           (a) The Company shall maintain, for a period of five
years from April 17, 1997, term
life insurance upon the life of the Founder, in the amount of $1,000,000, with
the proceeds payable to the Company.

                           (b) The Company shall maintain in effect policies of
workers' compensation insurance
and of insurance with respect to its properties and business of the kinds and in
the amounts not less than is customarily obtained by corporations engaged in the
same or


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<PAGE>   15

similar business and similarly situated, including, without limitation,
insurance against loss, damage, fire, theft, public liability and other risks.

                  6.5      EMPLOYEE AGREEMENTS. The Company shall require all
employees hereafter employed or engaged by the Company who are at or above the
director level or who holds at least 100,000 shares of Common Stock (or options
exercisable therefor) (as adjusted for stock splits, stock dividends,
recapitalizations and similar events) to enter into a Noncompetition and
Confidentiality Agreement covering a period of one year following the
termination of such employee's employment with the Company, in the form approved
by the Board of Directors. The Company shall require all employees not covered
by the foregoing sentence to enter into a Confidentiality Agreement in the form
approved by the Board of Directors.

                  6.6      RELATED PARTY TRANSACTIONS. The Company shall not
enter into any agreement with any stockholder, officer or director of the
Company, or any "affiliate" or "associate" of such persons (as such terms are
defined in the rules and regulations promulgated under the Securities Act),
including without limitation any agreement or other arrangement providing for
the furnishing of services by, rental of real or personal property from, or
otherwise requiring payments to, any such person or entity, without the consent
of at least a majority of the members of the Company's Board of Directors having
no interest in such agreement or arrangement.

                  6.7      DIRECTORS. The Company shall promptly reimburse in
full each director of the Company who is not an employee of the Company and who
was elected as a director solely by the holders of the Series A Preferred Stock
for all of his reasonable out-of-pocket expenses incurred in attending each
meeting of the Board of Directors of the Company or any committee thereof.

                  6.8      OPTION SHARES AND RESTRICTED STOCK. The Company has
reserved an aggregate of 993,150 shares of Common Stock for future issuance to
employees and consultants of the Company pursuant to the 1997 Stock Incentive
Plan of the Company. Unless otherwise agreed by the Board of Directors, all
options or restricted stock awards granted under such Plan shall vest at the
rate of 20% on the first anniversary of grant and 1.667% per month thereafter
over the subsequent four years so long as the optionee or stockholder continues
to be an employee or consultant of the Company, subject to acceleration of 50%
of the unvested portion of such options in the event of an Acquisition Event (as
defined in the standard form of agreements for use under such Plan).


                                      -16-
<PAGE>   16

                  6.9      RESERVATION OF COMMON STOCK. The Company shall
reserve and maintain a sufficient number of shares of Common Stock for issuance
upon conversion of all of the outstanding shares of Series A Preferred Stock,
Series B Preferred Stock and all of the outstanding Shares.

                  6.10     TERMINATION OF COVENANTS. The covenants of the
Company contained in Sections 6.1 through 6.9 shall terminate, and be of no
further force or effect, upon the effective date of a registration statement
filed by the Company under the Securities Act covering the Company's first
offering of Common Stock, resulting in net proceeds to the Company of at least
$10,000,000, and at a price per share of at least $16.00 (as adjusted for stock
splits, stock dividends, recapitalizations and similar events) or at such time
as the aggregate number of shares of Common Stock into which all shares of
Series A Preferred Stock, Series B Preferred Stock and Series C Preferred Stock
owned by the Purchasers (together with any affiliated entities to whom Shares
have been transferred) is less than 2,060,573 (as adjusted for stock splits,
stock dividends, recapitalizations and similar events).

                  6.11     TERMINATION OF PRIOR COVENANTS.

                           (a)      The Series B Preferred Stock Purchase
Agreement among the Company, the Founder, certain of the Purchasers and certain
other parties dated February 5, 1998 (the "Series B Agreement") is hereby
amended by deleting Section 6 thereof in its entirety.

                           (b)      Each of Yeh-Tsong Wen, James A. Dolce, Jr.,
Rubin Gruber, Harry Daniel Lowe and Bruce I. Sachs, North Bridge Venture
Partners II, L.P., Matrix Partners IV, L.P., Matrix IV Entrepreneurs Fund, L.P.,
Chin-Cheng Wu, John Prendergast, Brian Walck, Cynthia Deysher (as an individual
and as Custodian), Gary Bowen and Stephen Van Beaver, who are parties to the
Series B Agreement, shall be deemed a Purchaser for purposes of Sections 6, 8.1,
8.2 and 8.8 of this Agreement and shall have all rights and obligations of a
Purchaser under such Sections.

                  6.12     QUALIFIED SMALL BUSINESS STOCK. The Company shall
submit to its stockholders (including the Purchasers) and to the Internal
Revenue Service any reports that may be required under Section 1202(d)(1)(C) of
the Code and the Regulations promulgated thereunder. In addition, within ten
days after a Purchaser's written request therefor, the Company shall deliver to
such Purchaser a written statement indicating whether such Purchaser's interest
in the Company constitutes "qualified small business stock" as defined in
Section 1202(c) of the Code.


                                      -17-
<PAGE>   17

         7.       TRANSFER OF SHARES.

                  7.1      RESTRICTED SHARES. "Restricted Shares" means (i) the
Shares, (ii) the shares of Common Stock issued or issuable upon conversion of
the Shares, (iii) any shares of capital stock of the Company acquired by a
Purchaser pursuant to the Investor Agreement or the Right of First Refusal
Agreement, and (iv) any other shares of capital stock of the Company issued in
respect of such shares (as a result of stock splits, stock dividends,
reclassifications, recapitalizations, or similar events); PROVIDED, HOWEVER,
that shares of Common Stock which are Restricted Shares shall cease to be
Restricted Shares (i) upon any sale pursuant to a registration statement under
the Securities Act, Section 4(1) of the Securities Act or Rule 144 under the
Securities Act, or (ii) at such time as they become eligible for sale under Rule
144(k) under the Securities Act.

                  7.2      REQUIREMENTS FOR TRANSFER.

                           (a)      Restricted Shares shall not be sold or
transferred unless (1) either (i) they first shall have been registered under
the Securities Act, or (ii) the Company first shall have been furnished with an
opinion of legal counsel, reasonably satisfactory to the Company, to the effect
that such sale or transfer is exempt from the registration requirements of the
Securities Act and (2) such actions are in compliance with applicable state
securities laws.

                           (b)      Notwithstanding the foregoing, no
registration or opinion of counsel shall be required for (i) a transfer by a
Purchaser which is a partnership to a partner of such partnership or a retired
partner of such partnership who retires after the date hereof, or to the estate
of any such partner or retired partner, if the transferee agrees in writing to
be subject to the terms of this Section 7 to the same extent as if he were an
original Purchaser hereunder, or (ii) a transfer made in accordance with Rule
144 under the Securities Act.

                  7.3      LEGEND. Each certificate representing Restricted
Shares shall bear a legend substantially in the following form:

         "The shares represented by this certificate have not been registered
         under the Securities Act of 1933, as amended, and may not be offered,
         sold or otherwise transferred, pledged or hypothecated unless and until
         such shares are registered under such Act or an opinion of counsel
         satisfactory to the Company is obtained to the effect that such
         registration is not required."


                                      -18-
<PAGE>   18

The foregoing legend shall be removed from the certificates representing any
Restricted Shares, at the request of the holder thereof, at such time as they
become eligible for resale pursuant to Rule 144(k) under the Securities Act.

                  7.4      RULE 144A INFORMATION. The Company shall, at all
times during which it is neither subject to the reporting requirements of
Section 13 or 15(d) of the Securities Exchange Act of 1934, as amended (the
"Exchange Act"), nor exempt from reporting pursuant to Rule 12g3-2(b) under the
Exchange Act, upon the written request of a Purchaser, provide in writing to
such Purchaser, and to any prospective transferee of any Restricted Shares of
such Purchaser, the information concerning the Company described in Rule
144A(d)(4) under the Securities Act ("Rule 144A Information"). The Company also
shall, upon the written request of a Purchaser, cooperate with and assist such
Purchaser or any member of the National Association of Securities Dealers, Inc.
PORTAL system in applying to designate and thereafter maintain the eligibility
of the Restricted Shares for trading through PORTAL. The Company's obligations
under this Section 7.4 shall at all times be contingent upon receipt from the
prospective transferee of Restricted Shares of a written agreement to take all
reasonable precautions to safeguard the Rule 144A Information from disclosure to
anyone other than persons who will assist such transferee in evaluating the
purchase of any Restricted Shares and to use such Rule 144A Information only for
such evaluation purposes.

         8.       MISCELLANEOUS.

                  8.1      SUCCESSORS AND ASSIGNS. This Agreement, and the
rights and obligations of a Purchaser hereunder, may be assigned by such
Purchaser to any person or entity to which at least 100,000 Shares (or 100% of
the Shares originally purchased hereunder by such Purchaser, if less than
100,000 Shares) or (with respect to the assignment of rights under Section 6
hereof by a party other than a Purchaser of the Shares) 300,000 shares of Series
A Preferred Stock or 100,000 shares of Series B Preferred Stock (or 100% of the
shares of Series A Preferred Stock or Series B Preferred Stock originally
purchased under the Series A Agreement or Series B Agreement by such Purchaser,
if less than 300,000 or 100,000 shares, respectively), in each case as adjusted
for stock splits, stock dividends, recapitalizations and similar events, are
transferred by such Purchaser, and such transferee shall be deemed a "Purchaser"
for purposes of this Agreement; provided that the transferee provides written
notice of such assignment to the Company and agrees to be bound by the terms and
conditions set forth herein and the transferee is not a company that the Company
reasonably considers to be a competitor.


                                      -19-
<PAGE>   19

                  8.2      CONFIDENTIALITY. The Purchasers agree that they will
keep confidential and will not disclose or divulge any confidential, proprietary
or secret information which they may obtain from the Company pursuant to
financial statements, reports and other materials submitted by the Company to
the Purchasers pursuant to this Agreement, or pursuant to visitation or
inspection rights granted hereunder, unless such information is known, or until
such information becomes known, to the public; PROVIDED, HOWEVER, that a
Purchaser may disclose such information (i) to its attorneys, accountants,
consultants, and other professionals to the extent necessary to obtain their
services in connection with its investment in the Company, (ii) to any
prospective purchaser of any Shares from such Purchaser as long as such
prospective purchaser agrees in writing to be bound by the provisions of this
Section, or (iii) to any affiliate of such Purchaser or to a partner,
shareholder or subsidiary of such Purchaser; subject to the agreement of such
party to keep such information confidential as set forth herein.

                  8.3      SURVIVAL OF REPRESENTATIONS AND WARRANTIES. All
agreements, representations and warranties contained herein shall survive the
execution and delivery of this Agreement and the closing of the transactions
contemplated hereby.

                  8.4      [Intentionally omitted]

                  8.5      NOTICES. All notices, requests, consents, and other
communications under this Agreement shall be in writing and shall be delivered
by hand, sent via a reputable nationwide overnight courier service or mailed by
first class certified or registered mail, return receipt requested, postage
prepaid:

If to the Company, at ArrowPoint Communications, Inc., 235 Littleton Road,
Westford, MA 01886, Attn: President, or at such other address or addresses as
may have been furnished in writing by the Company to the Purchasers, with a copy
to Hale and Dorr LLP, Boston, MA 02109, Attn: Patrick J. Rondeau, Esq.;

If to a Purchaser, at its address as set forth on SCHEDULE I attached hereto, or
at such other address or addresses as may have been furnished to the Company in
writing by such Purchaser.

Notices provided in accordance with this Section 8.5 shall be deemed delivered
upon personal delivery, one business day after being sent via a reputable
nationwide overnight courier service, or two business days after deposit in the
mail.


                                      -20-
<PAGE>   20

                  8.6      BROKERS. The Company, the Founder and the Purchasers
each (i) represents and warrants to the other parties hereto that he, she or it
has retained no finder or broker in connection with the transactions
contemplated by this Agreement, and (ii) will indemnify and save the other
parties harmless from and against any and all claims, liabilities or obligations
with respect to brokerage or finders' fees or commissions in connection with the
transactions contemplated by this Agreement asserted by any person on the basis
of any agreement, statement or representation alleged to have been made by such
indemnifying party.

                  8.7      ENTIRE AGREEMENT. This Agreement and the Ancillary
Agreements embody the entire agreement and understanding between the parties
hereto with respect to the subject matter hereof and supersedes all prior
agreements and understandings relating to such subject matter.

                  8.8      AMENDMENTS AND WAIVERS. Except as otherwise expressly
set forth in this Agreement, any term of this Agreement may be amended and the
observance of any term of this Agreement may be waived (either generally or in a
particular instance and either retroactively or prospectively), with the written
consent of the Company and the holders of at least 66 2/3% of the shares of
Common Stock issued or issuable upon conversion of the Shares; provided that an
amendment or waiver with respect to Section 6 hereof shall instead require the
written consent of the holders of at least 66 2/3% of the shares of Common Stock
issued or issuable upon conversion of the Shares, the shares of Series B
Preferred Stock and the shares of Series A Preferred Stock, taken together. Any
amendment or waiver effected in accordance with this Section 8.8 shall be
binding upon each holder of any Shares, shares of Series B Preferred Stock or
shares of Series A Preferred Stock (including shares of Common Stock into which
such Shares, shares of Series B Preferred Stock or shares of Series A Preferred
Stock have been converted), each future holder of all such securities and the
Company. No waivers of or exceptions to any term, condition or provision of this
Agreement, in any one or more instances, shall be deemed to be, or construed as,
a further or continuing waiver of any such term, condition or provision. No
amendment shall increase any obligation of the Founder hereunder without the
express written consent of the Founder. No waivers of or exceptions to any term,
condition or provision of this Agreement, in any one or more instances, shall be
deemed to be, or construed as, a further or continuing waiver of any such term,
condition or provision.

                  8.9      COUNTERPARTS. This Agreement may be executed in one
or more counterparts, each of which shall be deemed to be an original, but all
of which shall be one and the same document.


                                      -21-
<PAGE>   21

                  8.10     SECTION HEADINGS. The section headings are for the
convenience of the parties and in no way alter, modify, amend, limit, or
restrict the contractual obligations of the parties.

                  8.11     SEVERABILITY. The invalidity or unenforceability of
any provision of this Agreement shall not affect the validity or enforceability
of any other provision of this Agreement.

                  8.12     GOVERNING LAW.  This Agreement shall be governed by
and construed in accordance with the laws of the State of Delaware.


                                      -22-
<PAGE>   22


                      [Preferred Stock Purchase Agreement}

         Executed as of the date first written above.

         ARROWPOINT COMMUNICATIONS, INC.

         By:
                  -------------------------------
                  Chin-Cheng Wu
                  President


         PURCHASERS:

         Accel V L.P.
         By:      Accel V Associates L.L.C.
                  its General Partner

                  By:
                     ----------------------------
                           Managing Member

         Accel Internet/Strategic Technology
         Fund L.P.

         By:      Accel Internet/Strategic
                  Technology Fund Associates L.L.C.
                  its General Partner

                  By:
                     ----------------------------
                           Managing Member

         Accel Keiretsu V L.P.

         By:      Accel Keiretsu V Associates L.L.C.
                  its General Partner
                  By:
                     ----------------------------
                           Managing Member


                                      -23-
<PAGE>   23
         Accel Investors `97 L.P.

         By:
            ----------------------------
                  General Partner


         Ellmore C. Patterson Partners


         By:
            ----------------------------
                  General Partner


         Net One Systems Co., Ltd.

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

         Westcon Group, Inc.

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

         Solely as to Sections 6, 8.1, 8.2 and 8.8


         -------------------------------------
         Yeh-Tsong Wen


         -------------------------------------
         James A. Dolce, Jr.


         -------------------------------------
         Rubin Gruber


         -------------------------------------
         Harry Daniel Lowe


                                     -24-
<PAGE>   24

         -------------------------------------
         Bruce I. Sachs


         North Bridge Venture Partners II, L.P.

         By:      North Bridge Venture Management II, L.P.,
                  its General Partner

                  By:
                           ------------------------
                           Edward T. Anderson
                           General Partner


         Matrix Partners IV, L.P.

         By:      Matrix IV Management Co., L.P.,
                  its General Partner

                  By:
                           ------------------------
                           Paul J. Ferri
                           General Partner


         Matrix IV Entrepreneurs Fund, L.P.

         By:      Matrix IV Management Co., L.P.,
                  its General Partner

                  By:
                           ------------------------
                           Paul J. Ferri
                           General Partner


         ------------------------------------
         Chin-Cheng Wu


                                      -25-
<PAGE>   25

         ------------------------------------
         John Prendergast


         --------------------------------------
         Brian Walck


         --------------------------------------
         Cynthia Deysher


         --------------------------------------
         Cynthia Deysher, as Custodian for Lauren
         Deysher under the Massachusetts
         Uniform Transfers to Minors Act


         --------------------------------------
         Cynthia Deysher, as Custodian for Jacqueline
         Deysher under the Massachusetts
         Uniform Transfers to Minors Act


         --------------------------------------
         Gary Bowen


         --------------------------------------
         Stephen Van Beaver


                                      -26-
<PAGE>   26


                                   SCHEDULE I
                                   ----------

Name and Address                           No. of Shares of            Aggregate
of Purchaser                             Series C Preferred       Purchase Price
----------------                         ------------------       --------------
Accel V L.P.                                         18,919          $148,703.34
One Palmer Square
Princeton, NJ  08542
Attn:  G. Carter Sednaoui
Accel Internet/Strategic Technology                   2,506            19,697.16
Fund L.P.
One Palmer Square
Princeton, NJ  08542
Attn:  G. Carter Sednaoui
Accel Keiretsu V L.P.                                   988             7,765.68
One Palmer Square
Princeton, NJ  08542
Attn:  G. Carter Sednaoui
Accel Investors `97 L.P.                              1,157             9,094.02
One Palmer Square
Princeton, NJ  08542
Attn:  G. Carter Sednaoui
Ellmore C. Patterson Partners                           530             4,165.80
One Palmer Square
Princeton, NJ  08542
Attn:  G. Carter Sednaoui
Net One Systems Co., Ltd.                           127,182           999,650.52
2-2-8 Higashi-Shinagawa
Shinagawa, Tokyo 140
Japan

Westcon Group, Inc.                                 127,182           999,650.52
150 Main Street
Eastchester, NY  10707


                                                    278,464        $2,188,727.04






                                      -27-