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                                                                   EXHIBIT 10.13
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                            OPNET TECHNOLOGIES, INC.

                        2000 Director Stock Option Plan

1.   Purpose.
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     The purpose of this 2000 Director Stock Option Plan (the "Plan") of OPNET
Technologies, Inc., a Delaware corporation (the "Company"), is to encourage
ownership in the Company by non-employee directors of the Company whose
continued services are considered essential to the Company's future progress, to
provide them with a further incentive to remain as directors of the Company and
to align the interests of such persons with those of the Company's stockholders.

2.   Administration.
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     The Board of Directors (the "Board") shall supervise and administer the
Plan. All questions concerning interpretation of the Plan or any options granted
under it shall be resolved by the Board and such resolution shall be final and
binding upon all persons having an interest in the Plan. The Board may, to the
full extent permitted by or consistent with applicable laws or regulations,
delegate any or all of its powers under the Plan to a committee appointed by the
Board, and if a committee is so appointed, all references to the Board in the
Plan shall mean and relate to such committee.

3.   Participation in the Plan.
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     Directors of the Company who are not employees of the Company or any
subsidiary of the Company ("non-employee directors") shall be eligible to
receive options under the Plan.

4.   Stock Subject to the Plan.
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     (a)  The maximum number of shares of the Company's common stock, $0.001 par
value per share ("Common Stock"), which may be issued under the Plan shall be
150,000 shares, subject to adjustment as provided in Section 7.

     (b)  If any outstanding option under the Plan for any reason expires or is
terminated without having been exercised in full, the shares covered by the
unexercised portion of such option shall again become available for issuance
pursuant to the Plan.

     (c)  All options granted under the Plan shall be non-statutory options not
entitled to special tax treatment under Section 422 of the Internal Revenue Code
of 1986, as amended (the "Code").

     (d)  Shares issued under the Plan may consist in whole or in part of
authorized but unissued shares or treasury shares.
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5.   Terms, Conditions and Form of Options.
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     Each option granted under the Plan shall be evidenced by a written
agreement in such form as the Board shall from time to time approve, which
agreements shall comply with and be subject to the following terms and
conditions:

     (a)  (i)  Automatic Option Grant Dates. Options shall automatically be
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granted to all non-employee directors as follows:

               (x)  each person serving as a non-employee director on the
closing date (the "Closing Date") of the Company's initial public offering of
Common Stock (the "Initial Public Offering") pursuant to an effective
registration statement under the Securities Act of 1933, as amended, shall be
granted an option to purchase 10,000 shares of Common Stock on the Closing Date;

               (y)  each person who first becomes a non-employee director after
the Closing Date, other than pursuant to election at an Annual Meeting of
Stockholders of the Company, shall be granted an option on the date of his or
her election to the Board to purchase a number of shares of Common Stock
calculated by multiplying 833 by the number of full calendar months remaining
from the date of his or her initial election to the Board until the first
anniversary of the prior year's Annual Meeting of Stockholders; and

               (z)  each non-employee director shall be granted an option to
purchase 10,000 shares of Common Stock on the date of each Annual Meeting of
Stockholders of the Company commencing with the 2001 Annual Meeting of
Stockholders, provided that he or she is serving as a director immediately
following such Annual Meeting of Stockholders.

          (ii) Periodic Grants of Options. Subject to execution by the non-
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employee director of an appropriate option agreement, the Board may grant
additional options to purchase a number of shares to be determined by the Board
in recognition of services provided by a non-employee director in his or her
capacity as a director.

     Each date of grant of an option pursuant to this Section 5(a) is
hereinafter referred to as an "Option Grant Date."

     (b)  Option Exercise Price. The option exercise price per share for each
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option granted under the Plan shall equal (i) the closing price on any national
securities exchange on which the Common Stock is listed, (ii) the closing price
of the Common Stock on the Nasdaq National Market or (iii) the average of the
closing bid and asked prices in the over-the-counter market, whichever is
applicable, as published in The Wall Street Journal, on the Option Grant Date;
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provided, that the option exercise price per share for each option granted
pursuant to Section 5(a)(i)(x) shall be equal to the price per share to the
public of the shares of Common Stock sold by the Company in the Initial Public
Offering. If no sales of Common Stock were made on the Option Grant Date, the
price of the Common Stock for purposes of clauses (i) and (ii) above shall be
the reported price for the next preceding day on which sales were made.

     (c)  Transferability of Options. Except as the Board may otherwise
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determine or provide in an option granted under the Plan, any option granted
under the Plan to an optionee

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shall not be transferable by the optionee other than by will or the laws of
descent and distribution or pursuant to a qualified domestic relations order as
defined by the Code or Title I of the Employee Retirement Income Security Act,
or the rules thereunder, and shall be exercisable during the optionee's lifetime
only by the optionee or the optionee's guardian or legal representative.
References to an optionee, to the extent relevant in the context, shall include
references to authorized transferees.

     (d)  Vesting Period.
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          (i)  General.  Each option granted under the Plan pursuant to Section
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5(a)(i) above shall become exercisable (vest) in full on the first anniversary
of the Option Grant Date.  Each option granted under the Plan pursuant to
Section 5(a)(ii) above shall become exercisable on such terms as shall be
determined by the Board and set forth in the option agreement with the
respective optionee.

          (ii) Right to Receive Restricted Stock.  The Board shall have the
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authority to grant options which are immediately exercisable subject to the
Company's right to repurchase any unvested shares of stock acquired by the
optionee on exercise of an option in the event such optionee's service as a
director terminates for any reason.

     (e)  Termination. Each option shall terminate, and may no longer be
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exercised, on the earlier of (i) the date ten years after the Option Grant Date
of such option or (ii) the first anniversary of the date on which the optionee
ceases to serve as a director of the Company.

     (f)  Exercise Procedure. An option may be exercised only by written notice
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to the Company at its principal office accompanied by (i) payment in cash or by
certified or bank check of the full consideration for the shares as to which
they are exercised, (ii) delivery of outstanding shares of Common Stock (which
have been owned by the optionee for at least six months) having a fair market
value on the last business day preceding the date of exercise equal to the
option exercise price or (iii) an irrevocable undertaking by a creditworthy
broker to deliver promptly to the Company sufficient funds to pay the exercise
price or delivery of irrevocable instructions to a creditworthy broker to
deliver promptly to the Company cash or a check sufficient to pay the exercise
price.

     (g)  Exercise by Representative Following Death of Director. An optionee,
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by written notice to the Company, may designate one or more persons (and from
time to time change such designation), including his or her legal
representative, who, by reason of the optionee's death, shall acquire the right
to exercise all or a portion of the option. If the person or persons so
designated wish to exercise any portion of the option, they must do so within
the term of the option as provided herein. Any exercise by a representative
shall be subject to the provisions of the Plan.

6.   Limitation of Rights.
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     (a)  No Right to Continue as a Director. Neither the Plan, nor the granting
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of an option nor any other action taken pursuant to the Plan, shall constitute
or be evidence of any agreement or understanding, express or implied, that the
Company will retain the optionee as a director for any period of time.

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     (b)  No Stockholders' Rights for Options. An optionee shall have no rights
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as a stockholder with respect to the shares covered by his or her option until
the date of the issuance to him or her of a stock certificate therefor, and no
adjustment will be made for dividends or other rights (except as provided in
Section 7) for which the record date is prior to the date such certificate is
issued.

     (c)  Compliance with Securities Laws. Each option shall be subject to the
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requirement that if, at any time, counsel to the Company shall determine that
the listing, registration or qualification of the shares subject to such option
upon any securities exchange or under any state or federal law, or the consent
or approval of any governmental or regulatory body, or the disclosure of non-
public information or the satisfaction of any other condition is necessary as a
condition of, or in connection with, the issuance or purchase of shares
thereunder, such option may not be exercised, in whole or in part, unless such
listing, registration, qualification, consent or approval, or satisfaction of
such condition shall have been effected or obtained on conditions acceptable to
the Board. Nothing herein shall be deemed to require the Company to apply for or
to obtain such listing, registration or qualification, or to satisfy such
condition.

7.   Adjustments for Changes in Common Stock and Certain Other Events.
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     (a)  Changes in Capitalization. In the event of any stock split, reverse
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stock split, stock dividend, recapitalization, combination of shares,
reclassification of shares, spin-off or other similar change in capitalization
or event, or any distribution to holders of Common Stock other than a normal
cash dividend, (i) the number and class of securities available under this Plan
and (ii) the number and class of securities and exercise price per share subject
to each outstanding option, shall be appropriately adjusted by the Company to
the extent the Board shall determine, in good faith, that such an adjustment is
necessary and appropriate. If this Section 7(a) applies and Section 7(c) also
applies to any event, Section 7(c) shall be applicable to such event, and this
Section 7(a) shall not be applicable.

     (b)  Liquidation or Dissolution.  In the event of a proposed liquidation or
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dissolution of the Company, the Board shall upon written notice to the optionees
provide that all then unexercised options will (i) become exercisable in full as
of a specified time at least 10 business days prior to the effective date of
such liquidation or dissolution and (ii) terminate effective upon such
liquidation or dissolution, except to the extent exercised before such effective
date.

     (c)  Reorganization Events.
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          (1)  Definition. A "Reorganization Event" shall mean: (a) any merger
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or consolidation of the Company with or into another entity as a result of which
the Common Stock is converted into or exchanged for the right to receive cash,
securities or other property or (b) any exchange of shares of the Company for
cash, securities or other property pursuant to a share exchange transaction.

          (2)  Consequences of a Reorganization Event on Options. Upon the
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occurrence of a Reorganization Event, or the execution by the Company of any
agreement with respect to a Reorganization Event, the Board shall provide that
all outstanding options shall be

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assumed, or equivalent options shall be substituted, by the acquiring or
succeeding corporation (or an affiliate thereof). For purposes hereof, an option
shall be considered to be assumed if, following consummation of the
Reorganization Event, the option confers the right to purchase, for each share
of Common Stock subject to the option immediately prior to the consummation of
the Reorganization Event, the consideration (whether cash, securities or other
property) received as a result of the Reorganization Event by holders of Common
Stock for each share of Common Stock held immediately prior to the consummation
of the Reorganization Event (and if holders were offered a choice of
consideration, the type of consideration chosen by the holders of a majority of
the outstanding shares of Common Stock); provided, however, that if the
consideration received as a result of the Reorganization Event is not solely
common stock of the acquiring or succeeding corporation (or an affiliate
thereof), the Company may, with the consent of the acquiring or succeeding
corporation, provide for the consideration to be received upon the exercise of
options to consist solely of common stock of the acquiring or succeeding
corporation (or an affiliate thereof) equivalent in fair market value to the per
share consideration received by holders of outstanding shares of Common Stock as
a result of the Reorganization Event.

     Notwithstanding the foregoing, if the acquiring or succeeding corporation
(or an affiliate thereof) does not agree to assume, or substitute for, such
options, then the Board shall, upon written notice to the optionees, provide
that all then unexercised options will become exercisable in full as of a
specified time prior to the Reorganization Event and will terminate immediately
prior to the consummation of such Reorganization Event, except to the extent
exercised by the optionees before the consummation of such Reorganization Event;
provided, however, that in the event of a Reorganization Event under the terms
of which holders of Common Stock will receive upon consummation thereof a cash
payment for each share of Common Stock surrendered pursuant to such
Reorganization Event (the "Acquisition Price"), then the Board may instead
provide that all outstanding options shall terminate upon consummation of such
Reorganization Event and that each optionee shall receive, in exchange therefor,
a cash payment equal to the amount (if any) by which (A) the Acquisition Price
multiplied by the number of shares of Common Stock subject to such outstanding
options (whether or not then exercisable) exceeds (B) the aggregate exercise
price of such options.

8.   Termination and Amendment of the Plan.
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     The Board may suspend or terminate the Plan or amend it in any respect
whatsoever.

9.   Notice.
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     Any written notice to the Company required by any of the provisions of the
Plan shall be addressed to the Treasurer of the Company and shall become
effective when it is received.

10.  Governing Law.
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     The Plan and all determinations made and actions taken pursuant hereto
shall be governed by the internal laws of the State of Delaware (without regard
to any applicable conflicts of laws or principles).

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11.  Effective Date.
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     The Plan shall take effect upon the closing of the Initial Public Offering.

                              Adopted by the Board of Directors on March 13,
                              2000

                              Approved by the Stockholders on June __, 2000

                              On June 27, 2000, the Board of Directors approved
                              a three-for-two split of the Common Stock which
                              increased the number of shares of Common Stock
                              available for issuance under the Plan to 225,000
                              shares.

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