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EXHIBIT 10.21

JUNIPER NETWORKS, INC.

2006 EQUITY INCENTIVE PLAN

PERFORMANCE SHARE AGREEMENT

     1. Grant. The Company hereby grants to the Employee an award of Performance Shares (“Performance Shares”), as set forth in the Notice of Grant of Performance Shares and subject to the terms and conditions in this Agreement and the Company’s 2006 Equity Incentive Plan (the “Plan”). Unless otherwise defined herein, the terms defined in the Plan shall have the same defined meanings in this Performance Share Agreement.

     2. Company’s Obligation. Each Performance Share represents the right to receive a Share on the vesting date. Unless and until the Performance Shares vest, the Employee will have no right to receive Shares under such Performance Shares. Prior to actual distribution of Shares pursuant to any vested Performance Shares, such Performance Shares will represent an unsecured obligation of the Company, payable (if at all) only from the general assets of the Company.

     3. Vesting Schedule. Subject to paragraph 4, to Plan Section 16 and to any other relevant Plan provisions, the Performance Shares awarded by this Agreement will vest in the Employee according to the vesting schedule specified on the Notice of Grant attached hereto as Exhibit A.

     4. Forfeiture upon Termination as Service Provider. Notwithstanding any contrary provision of this Agreement or the Notice of Grant, if the Employee terminates service as a Service Provider for any or no reason prior to vesting, the unvested Performance Shares awarded by this Agreement will thereupon be forfeited at no cost to the Company.

     5. Payment after Vesting. Any Performance Shares that vest in accordance with paragraph 3 will be paid to the Employee (or in the event of the Employee’s death, to his or her estate) in Shares, provided that to the extent determined appropriate by the Company, any national, state and local withholding of taxes and/or social security contributions with respect to such Performance Shares, if applicable, will be paid by the Employee pursuant to Section 18 below.

     6. Payments after Death. Any distribution or delivery to be made to the Employee under this Agreement will, if the Employee is then deceased, be made to the administrator or executor of the Employee’s estate. Any such administrator or executor must furnish the Company with (a) written notice of his or her status as transferee, and (b) evidence satisfactory to the Company to establish the validity of the transfer and compliance with any laws or regulations pertaining to said transfer.

     7. Rights as Stockholder. Neither the Employee nor any person claiming under or through the Employee will have any of the rights or privileges of a stockholder of the Company in respect of any Shares deliverable hereunder unless and until certificates representing such Shares will have been issued, recorded on the records of the Company or its transfer agents or registrars, and delivered to the Employee or Employee’s broker.

     8. No Effect on Employment. The Employee’s employment with the Company and its Subsidiaries is on an at-will basis only. Accordingly, the terms of the Employee’s employment with the Company and its Subsidiaries will be determined from time to time by the Company or the Subsidiary employing the Employee (as the case may be), and the Company or the Subsidiary will have the right, which is hereby expressly reserved, to terminate or change the terms of the employment of the Employee at any time for any reason whatsoever, with or without good cause or notice.

     9. Address for Notices. Any notice to be given to the Company under the terms of this Agreement will be addressed to the Company at 1194 North Mathilda Avenue Sunnyvale, California, 94089 Attn: Stock Administration, or at such other address as the Company may hereafter designate in writing or electronically.

     10. Grant is Not Transferable. Except to the limited extent provided in paragraph 6, this grant and the rights and privileges conferred hereby will not be transferred, assigned, pledged or hypothecated in any way (whether by operation of law or otherwise) and will not be subject to sale under execution, attachment or similar process. Upon any attempt to transfer, assign, pledge, hypothecate or otherwise dispose of this grant, or any right or privilege conferred hereby, or upon any attempted sale under any execution, attachment or similar process, this grant and the rights and privileges conferred hereby immediately will become null and void.

     11. Binding Agreement. Subject to the limitation on the transferability of this grant contained herein, this Agreement will be binding upon and inure to the benefit of the heirs, legatees, legal representatives, successors and assigns of the parties hereto.

     12. Additional Conditions to Issuance of Stock. If at any time the Company will determine, in its discretion, that the listing, registration or qualification of the Shares upon any securities exchange or under any state or federal law, or the consent or approval of any governmental regulatory authority is necessary or desirable as a condition to the issuance of Shares to the Employee (or his or her estate), such issuance will not occur unless and until such listing, registration, qualification, consent or approval will have been effected or obtained free of any conditions not acceptable to the Company. The Company will make all reasonable efforts to meet the requirements of any such state or federal law or securities exchange and to obtain any such consent or approval of any such governmental authority.

     13. Plan Governs. This Agreement and the Notice of Grant are subject to all terms and provisions of the Plan. In the event of a conflict between one or more provisions of this Agreement or the Notice of Grant and one or more provisions of the Plan, the provisions of the Plan will govern.

     14. Administrator Authority. The Administrator will have the power to interpret the Plan and this Agreement and to adopt such rules for the administration, interpretation and application of the Plan as are consistent therewith and to interpret or revoke any such rules (including, but not limited to, the determination of whether or not any Performance Shares have vested). All actions taken and all interpretations and determinations made by the Administrator in good faith will be final and binding upon Employee, the Company and all other interested persons. No member of the Administrator will be personally liable for any action, determination or interpretation made in good faith with respect to the Plan or this Agreement.

     15. Agreement Severable. In the event that any provision in this Agreement will be held invalid or unenforceable, such provision will be severable from, and such invalidity or unenforceability will not be construed to have any effect on, the remaining provisions of this Agreement.

     16. Amendment, Suspension or Termination of the Plan. By accepting this award, the Employee expressly warrants that he or she has received a right to receive stock under the Plan, and has received, read and understood a description of the Plan. The Employee understands that the Plan is discretionary in nature and may be modified, suspended or terminated by the Company at any time.

     17. Notice of Governing Law. This grant of Performance Shares shall be governed by, and construed in accordance with, the laws of the State of California without regard to principles of conflict of laws.

     18. Withholding. Regardless of any action the Company or its affiliates takes with respect to any or all income tax, social insurance, payroll tax or other tax-related withholding (“Tax-Related Items”), the Employee acknowledges that the ultimate liability for all Tax-Related Items legally due by the Employee is, and remains, the Employee’s responsibility and that the Company and/or its affiliates (1) make no representations or undertakings regarding the treatment of any Tax-Related Items in connection with any aspect of the Performance Shares, including the grant of the Performance Shares, the vesting and delivery of the Performance Shares, the subsequent sale of Shares acquired pursuant to the Performance Shares and the receipt of any dividends, if any; and (2) do not commit to structure the terms of the Performance Shares or any aspect of the Performance Shares to reduce or eliminate the Employee’s liability for Tax-Related Items.

     Prior to the vesting of Performance Shares, the Employee agrees to pay or make adequate arrangements satisfactory to the Company and/or its affiliates to satisfy all withholding obligations of the Company and/or its affiliates. In this regard, the Employee authorizes the Company and/or its affiliates to withhold all applicable Tax-Related Items legally payable by the Employee from his or her wages, within legal limits, or other cash compensation paid by the Company and/or its affiliates or from proceeds of the sale of the Shares. The payment of such Tax-Related Items shall generally be made through the Employee’s brokerage account designated by the Company; provided, however, that at the Company’s discretion, it may permit the Employee to satisfy such obligations in whole or in part by having the Company withhold

otherwise deliverable Shares with a value equal to the minimum amount statutorily required to be withheld (“Net Withholding”). With respect to payments from the Employee’s brokerage account, the Employee may choose to cover the payment of Tax-Related Items through (i) cash on deposit at the broker, or (ii) by electing to have the broker sell vested shares to cover taxes, social security contributions and related fees. However, should the Employee’s account have insufficient funds, and if Net Withholding is not permitted by the Company, the Employee will be deemed to have elected to have the broker sell vested shares to cover taxes, social security contributions and related fees. The Employee acknowledges and agrees that if the amount of withholding taxes, social security contributions and related fees satisfied by selling vested shares or by Net Withholding exceeds the amount remitted by the Company, the Company will refund the excess amount to him or her within a reasonable period without any interest. Finally, the Employee shall pay to the Company and/or its affiliates any amount of Tax-Related Items that may be required to withhold as a result of participation in the Plan that cannot be satisfied by the means previously described. The Company may refuse to deliver the Shares if Employee fails to comply with his or her obligations in connection with the Tax-Related Items as described in this section.

     19. Nature of the Grant. In accepting the grant, Employee acknowledges that:

          a. the Plan is established voluntarily by the Company, it is discretionary in nature and it may be modified, amended, suspended or terminated by the Company at any time, unless otherwise provided in the Plan and this letter;

          b. the grant of the Performance Shares is voluntary and occasional and does not create any contractual or other right to receive future Performance Share grants, or benefits in lieu of Performance Shares, even if Performance Shares have been granted repeatedly in the past;

          c. all decisions with respect to future Performance Shares, if any, will be at the sole discretion of the Company;

          d. participation in the Plan shall not create a right to further employment with the Employee’s employer and shall not interfere with the ability of the Employee’s employer to terminate the Employee’s employment relationship at any time with or without cause;

          e. the Employee is voluntarily participating in the Plan;

          f. the Performance Shares are an extraordinary item that does not constitute compensation of any kind for services of any kind rendered to the Company or to the Employee’s employer, and which is outside the scope of the Employee’s employment contract, if any;

          g. the Performance Shares are not part of normal or expected compensation or salary for any purpose, including, but not limited to, calculating any severance, resignation, termination, redundancy, end of service payments, bonuses, long-service Performance Shares, pension or retirement benefits or similar payments;

          h. in the event that the Employee is not an employee of the Company, the Performance Shares will not be interpreted to form an employment contract or relationship with

the Company; and furthermore, the Performance Shares will not be interpreted to form an employment contract with any subsidiary or affiliate of the Company;

          i. the future value of the underlying Shares is unknown and cannot be predicted with certainty;

          j. in consideration of the grant of the Performance Shares, no claim or entitlement to compensation or damages shall arise from termination of the Performance Shares or diminution in value of the Performance Shares or the Shares acquired through the Performance Shares which results from termination of employment by the Company or its affiliates (for any reason whatsoever and whether or not in breach of local labor laws) and the Employee irrevocably releases the Company or its affiliates from any such claim that may arise; if, notwithstanding the foregoing, any such claim is found by a court of competent jurisdiction to have arisen, then, by accepting the Performance Shares, the Employee shall be deemed irrevocably to have waived his or her entitlement to pursue such claim; and

          k. notwithstanding any terms or conditions of the Plan to the contrary, in the event of involuntary termination of the Employee’s employment (whether or not in breach of local labor laws), the Employee’s right to receive Performance Shares and vest in Performance Shares under the Plan, if any, will terminate effective as of the date that the Employee is no longer actively employed; furthermore, in the event of involuntary termination of employment (whether or not in breach of local labor laws), the Employee’s right to receive Shares pursuant to the Performance Shares, if any, will be measured by the date of termination of the Employee’s active employment.

     20. Data Privacy.

          By accepting the Performance Shares the Employee hereby explicitly and unambiguously consents to the collection, use and transfer, in electronic or other form, of the Employee’s personal data as described in this document by and among, as applicable, the Employee’s employer and the Company and its subsidiaries and affiliates for the exclusive purpose of implementing, administering and managing participation in the Plan.

          The Employee understands that the Company and the Employee’s employer hold certain personal information about the Employee, including, but not limited to, his or her name, home address and telephone number, date of birth, social insurance number or other identification number, salary, nationality, job title, any Shares of stock or directorships held in the Company, details of all Options or any other entitlement to Shares of stock Awarded, canceled, exercised, vested, unvested or outstanding in the Employee’s favor, for the purpose of implementing, administering and managing the Plan (“Data”). The Employee understands that Data may be transferred to any third parties assisting in the implementation, administration and management of the Plan, that these recipients may be located in the Employee’s country or elsewhere, and that the recipient’s country may have different data privacy laws and protections than the Employee’s country. The Employee understands that he or she may request a list with the names and addresses of any potential recipients of the Data by contacting the local human resources

representative. The Employee authorizes the recipients to receive, possess, use, retain and transfer the Data, in electronic or other form, for the purposes of implementing, administering and managing participation in the Plan, including any requisite transfer of such Data as may be required to a broker or other third party with whom the Employee may elect to deposit any Shares of stock acquired through the Performance Shares. The Employee understands that Data will be held only as long as is necessary to implement, administer and manage participation in the Plan. The Employee understands that he or she may, at any time, view Data, request additional information about the storage and processing of Data, require any necessary amendments to Data or refuse or withdraw the consents herein, without cost, by contacting in writing the local human resources representative. The Employee understands, however, that refusing or withdrawing consent may affect his or her ability to participate in the Plan. For more information on the consequences of refusal to consent or withdrawal of consent, the Employee understands that the Employee may contact the local human resources representative.

By your signature and the signature of the Company’s representative below, you and the Company agree that this Grant is approved under and governed by the terms and conditions of the Plan and this Agreement. Employee has reviewed the Plan and this Agreement in their entirety, has had an opportunity to obtain the advice of counsel prior to executing this Agreement and fully understands all provisions of the Plan and this Agreement. Employee hereby agrees to accept as binding, conclusive and final all decisions or interpretations of the Administrator upon any questions relating to the Plan and Agreement. Employee further agrees to notify the Company upon any change in the residence address indicated below.

IN WITNESS WHEREOF, the undersigned have executed this Performance Share Agreement

ATTACHMENT A

PERFORMANCE SHARE NOTICE OF GRANT

Employee Name:                                              

Date of Grant:                                              

Maximum number of Performance Shares ([     ] % of total Target number):                                         

Total target number:                                              

Annual target amount:                                              

Vesting: