Equinix, Inc. 3,662,556 Shares Common Stock ($0.001 per share par value) Underwriting Agreement

Exhibit 1.1

Equinix, Inc.

3,662,556 Shares

Common Stock ($0.001 per share par value)

Underwriting Agreement

New York, New York

September 20, 2007

To the Representatives

  named in Schedule I

  hereto of the several

  Underwriters named in

  Schedule II hereto

Ladies and Gentlemen:

Equinix, Inc., a corporation organized under the laws of Delaware (the “Company”), proposes to sell to the several underwriters named in Schedule II hereto (the “Underwriters”), for whom you (the “Representatives”) are acting as representatives, the number of shares of common stock, $0.001 par value (“Common Stock”), of the Company set forth in Schedule I hereto (the “Underwritten Securities”). The Company also proposes to grant to the Underwriters an option to purchase up to the number of additional shares of Common Stock set forth in Schedule II hereto to cover over-allotments (the “Option Securities”; the Option Securities, together with the Underwritten Securities, hereinafter called the “Securities”). To the extent there are no additional Underwriters listed on Schedule I other than you, the term Representatives as used herein shall mean you, as Underwriters, and the terms Representatives and Underwriters shall mean either the singular or plural as the context requires. Any reference herein to the Registration Statement, the Base Prospectus, any Preliminary Prospectus or the Final Prospectus shall be deemed to refer to and include the documents incorporated by reference therein pursuant to Item 12 of Form S-3 which were filed under the Exchange Act on or before the Effective Date of the Registration Statement or the issue date of the Base Prospectus, any Preliminary Prospectus or the Final Prospectus, as the case may be; and any reference herein to the terms “amend,” “amendment” or “supplement” with respect to the Registration Statement, the Base Prospectus, any Preliminary Prospectus or the Final Prospectus shall be deemed to refer to and include the filing of any document under the Exchange Act after the Effective Date of the Registration Statement or the issue date of the Base Prospectus, any Preliminary Prospectus or the Final Prospectus, as the case may be, deemed to be incorporated therein by reference. Certain terms used herein are defined in Section 20 hereof.

Concurrent with the offering and sale of the Securities by the Company pursuant to the terms of this Agreement, the Company is offering to sell $350,000,000 in aggregate principal amount (or up to $395,986,000 in aggregate principal amount if the underwriters exercise the over-allotment option in full) of 3.0% Convertible Subordinated Notes due 2014 pursuant to the terms of an underwriting agreement, dated of even date herewith between the

Company and certain of the Underwriters (the “Concurrent Debt Offering”). The offering, issuance and sale of the Securities by the Company pursuant to the terms of this Agreement is contingent on the completion of the Concurrent Debt Offering.

1. Representations and Warranties. The Company represents and warrants to, and agrees with, each Underwriter as set forth below in this Section 1.

(a) The Company meets the requirements for use of Form S-3 under the Act and has prepared and filed with the Commission an automatic shelf registration statement, as defined in Rule 405. Such Registration Statement, including any amendments thereto filed prior to the Execution Time, became effective upon filing. The Company may have filed with the Commission, as part of an amendment to the Registration Statement or pursuant to Rule 424(b), one or more preliminary prospectus supplements relating to the Securities, each of which has previously been furnished to you. The Company will file with the Commission a final prospectus supplement relating to the Securities in accordance with Rule 424(b). As filed, such final prospectus supplement shall contain all information required by the Act and the rules thereunder, and, except to the extent the Representatives shall agree in writing to a modification, shall be in all substantive respects in the form furnished to you prior to the Execution Time or, to the extent not completed at the Execution Time, shall contain only such specific additional information and other changes (beyond that contained in the Base Prospectus and any Preliminary Prospectus) as the Company has advised you, prior to the Execution Time, will be included or made therein. The Registration Statement, at the Execution Time, meets the requirements set forth in Rule 415(a)(1)(x).

(b) On each Effective Date, the Registration Statement did, and when the Final Prospectus is first filed in accordance with Rule 424(b) and on the Closing Date (as defined herein) and on any date on which Option Securities are purchased, if such date is not the Closing Date (a “settlement date”), the Final Prospectus (and any supplement thereto) will, comply in all material respects with the applicable requirements of the Act, the Exchange Act and the rules thereunder; on each Effective Date and at the Execution Time, the Registration Statement did not and will not contain any untrue statement of a material fact or omit to state any material fact required to be stated therein or necessary in order to make the statements therein not misleading and on the date of any filing pursuant to Rule 424(b) and on the Closing Date and any settlement date, the Final Prospectus (together with any supplement thereto) will not, include any untrue statement of a material fact or omit to state a material fact necessary in order to make the statements therein, in the light of the circumstances under which they were made, not misleading; provided, however, that the Company makes no representations or warranties as to the information contained in or omitted from the Registration Statement or the Final Prospectus (or any supplement thereto) in reliance upon and in conformity with information furnished in writing to the Company by or on behalf of any Underwriter through the Representatives specifically for inclusion in the Registration Statement or the Final Prospectus (or any supplement thereto), it being understood and agreed that the only such information furnished by or on behalf of any Underwriter consists of the information described as such in Section 8 hereof.

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(c) (i) The Disclosure Package and (ii) each electronic road show when taken together as a whole with the Disclosure Package, does not contain any untrue statement of a material fact or omit to state any material fact necessary in order to make the statements therein, in the light of the circumstances under which they were made, not misleading. The preceding sentence does not apply to statements in or omissions from the Disclosure Package based upon and in conformity with written information furnished to the Company by any Underwriter through the Representatives specifically for use therein, it being understood and agreed that the only such information furnished by or on behalf of any Underwriter consists of the information described as such in Section 8 hereof.

(d) (i) At the time of filing the Registration Statement, (ii) at the time of the most recent amendment thereto for the purposes of complying with Section 10(a)(3) of the Act (whether such amendment was by post-effective amendment, incorporated report filed pursuant to Sections 13 or 15(d) of the Exchange Act or form of prospectus), (iii) at the time the Company or any person acting on its behalf (within the meaning, for this clause only, of Rule 163(c)) made any offer relating to the Securities in reliance on the exemption in Rule 163, and (iv) at the Execution Time (with such date being used as the determination date for purposes of this clause (iv)), the Company was or is (as the case may be) a “well-known seasoned issuer” as defined in Rule 405. The Company agrees to pay the fees required by the Commission relating to the Securities within the time required by Rule 456(b)(1) without regard to the proviso therein and otherwise in accordance with Rules 456(b) and 457(r).

(e) (i) At the earliest time after the filing of the Registration Statement that the Company or another offering participant made a bona fide offer (within the meaning of Rule 164(h)(2)) of the Securities and (ii) as of the Execution Time (with such date being used as the determination date for purposes of this clause (ii)), the Company was not and is not an Ineligible Issuer (as defined in Rule 405), without taking account of any determination by the Commission pursuant to Rule 405 that it is not necessary that the Company be considered an Ineligible Issuer.

(f) Each Issuer Free Writing Prospectus and the final term sheet prepared and filed pursuant to Section 5(b) hereto does not include any information that conflicts with the information contained in the Registration Statement, including any document incorporated by reference therein and any prospectus supplement deemed to be a part thereof that has not been superseded or modified. The foregoing sentence does not apply to statements in or omissions from any Issuer Free Writing Prospectus based upon and in conformity with written information furnished to the Company by any Underwriter through the Representatives specifically for use therein, it being understood and agreed that the only such information furnished by or on behalf of any Underwriter consists of the information described as such in Section 8 hereof.

(g) The Company has been duly incorporated and is an existing corporation in good standing under the laws of State of Delaware, with power and authority (corporate and other) to own its properties and conduct its business as described in the Disclosure Package and the Final Prospectus; and the Company is duly qualified to do business as a

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foreign corporation in good standing in all other jurisdictions in which its ownership or lease of property or the conduct of its business requires such qualification, except to the extent that the failure to be so qualified or in good standing would not have a material adverse effect on the condition (financial or other), prospects, business, properties or results of operations of the Company and the Subsidiaries (as defined below) taken as a whole (each, a “Company Material Adverse Effect”).

(h) Equinix Operating Co., Inc., Equinix Pacific, Inc., Equinix RP II LLC, Equinix RP, Inc., Equinix Japan KK, Equinix Hong Kong Ltd., Equinix Singapore Holdings Pte Ltd, Equinix Singapore Pte Ltd, IXEurope plc, Equinix UK Ltd Interconnect Exchange Europe Ltd, Interconnect Exchange Europe SAS, IX Services Ltd and IXEurope (Switzerland) AG (each a “Subsidiary” and, together, the “Subsidiaries”) are the direct and indirect subsidiaries of the Company that are material to the business of the Company and its subsidiaries taken as a whole. Each of the Subsidiaries has been duly incorporated and is an existing corporation in good standing under the laws of the jurisdiction of its incorporation, with power and authority (corporate and other) to own its properties and conduct its business as described in the Disclosure Package and the Prospectus; and each Subsidiary is duly qualified to do business as a foreign corporation in good standing in all other jurisdictions in which its ownership or lease of property or the conduct of its business requires such qualification except to the extent that the failure to be so qualified or in good standing would not have a Company Material Adverse Effect; all of the issued and outstanding capital stock of each subsidiary of the Company has been duly authorized and validly issued and is fully paid and nonassessable. The Company owns all of the shares of capital stock of each subsidiary of the Company, directly or through subsidiaries, free from liens, encumbrances and defects. In addition, each of Equinix Europe, Inc., Equinix Cayman Islands Holdings, Equinix Dutch Holdings N.V., Equinix Netherlands B.V., Equinix Pacific Pte Ltd, Equinix Asia Pacific Pte Ltd, CHI 3 LLC, Intelisite RV, Interconnect Exchange Europe GmbH, IXEurope Real Estate GmbH and IXEurope GmbH (the “Other Subsidiaries”), individually do not constitute a “significant subsidiary,” as defined by Rule 1-02 of Regulation S-X; however, when taken together, do constitute a “significant subsidiary” as defined by Rule 1-02 of Regulation S-X. The Subsidiaries are the only significant subsidiaries of the Company as defined by Rule 1-02 of Regulation S-X, and all subsidiaries (excluding the Subsidiaries and the Other Subsidiaries), when taken together, do not constitute a “significant subsidiary” as defined by Rule 1-02 of Regulation S-X.

(i) The authorized capital stock of the Company conforms as to legal matters to the description thereof contained in, as applicable, the Disclosure Package and the Final Prospectus. All outstanding shares of capital stock of the Company have been duly authorized and validly issued, fully paid and nonassessable and conform as to legal matters to the description thereof contained in or incorporated by reference into, as applicable, the Preliminary Prospectus and the Final Prospectus; and the stockholders of the Company have no preemptive rights with respect to the Securities. Except as set forth in the Disclosure Package and the Final Prospectus, neither the Company nor any of the Subsidiaries has outstanding any options to purchase, or any preemptive rights or other rights to subscribe for or to purchase, any securities or obligations convertible into, or any contracts or commitments to issue or sell, shares of its capital stock or any such options,

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rights, convertible securities or obligations. All outstanding shares of capital stock and options and other rights to acquire capital stock have been issued in compliance with the registration and qualification provisions of all applicable securities laws and were not issued in violation of any preemptive rights, rights of first refusal or other similar rights.

(j) Except as disclosed in the Disclosure Package and the Final Prospectus, there are no contracts, agreements or understandings between the Company and any person that would give rise to a valid claim against the Company or any Underwriter for a brokerage commission, finder’s fee or other like payment as a result of the transactions contemplated by this Agreement.

(k) Except as disclosed in the Disclosure Package and the Final Prospectus or as have been validly waived, there are no contracts, agreements or understandings involving the Company granting to any person the right to require the Company to file a registration statement under the Act with respect to any securities of the Company owned or to be owned by such person or to require the Company to include such securities in the securities registered pursuant to the Registration Statement or in any securities being registered pursuant to any other registration statement filed by the Company under the Act.

(l) The Securities have been duly authorized and, when issued and delivered to and paid for by the Underwriters pursuant to this Agreement, will be duly and validly issued and will be fully paid and non-assessable and will conform to descriptions thereof in the Disclosure Package and the Final Prospectus; and the issuance of the Securities is not subject to any statutory, preemptive or other similar contractual rights to subscribe for the Securities.

(m) No consent, approval, authorization, or order of, or filing with, any governmental agency or body or any court is required to be obtained or made by the Company for the consummation of the transactions contemplated by this Agreement, except such as have been obtained and made under the Act, the Exchange Act or state securities or blue sky laws in connection with the offer and sale of the Securities.

(n) The execution and delivery by the Company of, and performance by the Company of its obligations under, this Agreement and the consummation of the transactions contemplated herein will not result in a material breach or material violation of any of the terms and provisions of, or constitute a material default under, any statute, any rule, regulation or order of any governmental agency or body or any court, domestic or foreign, having jurisdiction over the Company or any of the Subsidiaries or any of their properties, or any agreement or instrument to which the Company or any such Subsidiary is a party or by which the Company or any such Subsidiary is bound or to which any of the properties of the Company or any such Subsidiary is subject (except a breach or violation that would not have a Material Adverse Effect on the execution and delivery by the Company of, and performance by the Company of its obligations under, this Agreement, and the consummation of the transactions contemplated herein), or the charter or by-laws of the Company or any such Subsidiary.

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(o) This Agreement has been duly authorized, executed and delivered by the Company.

(p) Except as disclosed in the Disclosure Package and the Final Prospectus, the Company and the Subsidiaries have good and marketable title to all real properties and all other properties and assets owned by them, in each case free from liens, encumbrances and defects that would materially affect the value thereof or materially interfere with the use made or to be made thereof by them; and the Company and its Subsidiaries hold any leased real or personal property under valid and enforceable leases with no exceptions that would materially interfere with the use made or to be made thereof by them.

(q) The Company and the Subsidiaries possess adequate certificates, authorities or permits issued by appropriate governmental agencies or bodies necessary to conduct the business now operated by them and have not received any notice of proceedings relating to the revocation or modification of any such certificate, authority or permit that, if determined adversely to the Company or any of its subsidiaries, would individually or in the aggregate have a Company Material Adverse Effect.

(r) No labor dispute with the employees of the Company or any of the Subsidiaries exists or, to the knowledge of the Company, is imminent that might have a Company Material Adverse Effect.

(s) The Company and the Subsidiaries own, possess or can acquire on reasonable terms, adequate trademarks, trade names and other rights to inventions, know-how, patents, copyrights, confidential information and other intellectual property (collectively, the “Intellectual Property Rights”) necessary to conduct the business now operated by them, or presently employed by them, and have not received any notice of infringement of or conflict with asserted rights of others with respect to any Intellectual Property Rights that, if determined adversely to the Company or any of the Subsidiaries, would individually or in the aggregate have a Company Material Adverse Effect.

(t) Except as disclosed in the Disclosure Package and the Final Prospectus, neither the Company nor any of the Subsidiaries (A) is in violation of any statute, any rule, regulation, decision or order of any governmental agency or body or any court, domestic or foreign, relating to the use, disposal or release of hazardous or toxic substances or relating to the protection or restoration of the environment or human exposure to hazardous or toxic substances (collectively, the “Environmental Laws”), (B) owns leases or operates any real property contaminated with any substance that is subject to any Environmental Laws, (C) is liable for any off-site disposal or contamination pursuant to any Environmental Laws, or (D) is subject to any claim relating to any Environmental Laws, in each case which violation, contamination, liability or claim would individually or in the aggregate have a Company Material Adverse Effect; and the Company is not aware of any pending or threatened investigation which is reasonably expected to lead to such a claim. Except as disclosed in the Disclosure Package and the Final Prospectus, there are no costs or liabilities associated with Environmental Laws (including, without limitation, any capital or operating expenditures required for clean-up,

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closure of properties or compliance with Environmental Laws or any permit, license or approval, any related constraints on operating activities and any potential liabilities to third parties) that might have a Company Material Adverse Effect.

(u) Except as disclosed in the Disclosure Package and the Final Prospectus, there are no pending actions, suits or proceedings against or affecting the Company, any of the Subsidiaries or any of their respective properties that, if determined adversely to the Company or any of its Subsidiaries, would individually or in the aggregate have a Company Material Adverse Effect, or would materially and adversely affect the ability of the Company to perform its obligations under this Agreement, or which are otherwise material in the context of the transactions contemplated by this Agreement; and no such actions, suits or proceedings are threatened or, to the Company’s knowledge, contemplated.

(v) The financial statements of the Company included in the Preliminary Prospectus, the Final Prospectus and the Registration Statement present fairly the financial position of the Company and its consolidated subsidiaries as of the dates shown and their consolidated statements of operations and cash flows for the periods shown, and such financial statements have been prepared in conformity with the generally accepted accounting principles in the United States applied on a consistent basis and the schedules included in the Registration Statement present fairly the information required to be stated therein.

(w) The financial statements of IXEurope plc (“IXEurope”) included in the Preliminary Prospectus, the Final Prospectus and the Registration Statement present fairly the financial position of IXEurope and its consolidated subsidiaries as of the dates shown and their consolidated income statement, consolidated statement of recognized income and expense and consolidated statement of cash flows for the periods shown, and such financial statements have been prepared in conformity with International Financial Reporting Standards (“IFRS”) applied on a consistent basis.

(x) The pro forma financial statements included in the Preliminary Prospectus, the Prospectus, the Final Prospectus and the Registration Statement have been prepared in accordance with the applicable requirements of the Act and the Exchange Act, as applicable. The assumptions used in preparing such pro forma financial statements provide a reasonable basis for presenting the significant effects directly attributable to the transactions or events described therein; the related pro forma adjustments give appropriate effect to those assumptions; and the pro forma columns therein reflect the proper application of those adjustments to the corresponding historical financial statement amounts.

(y) Except as disclosed in the Disclosure Package and the Final Prospectus, since the date of the latest audited financial statements included in the Disclosure Package and the Final Prospectus (i) there has not occurred any Company Material Adverse Effect, or any development or event that would reasonably be expected to involve a prospective Company Material Adverse Effect, and (ii) there has been no dividend or distribution of any kind declared, paid or made by the Company on any class of its capital stock.

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(z) Neither the Company nor any of the Subsidiaries is currently in breach of, or in default under, any other written agreement or instrument to which it or its property is bound or affected except to the extent that such breach or default would not have a Company Material Adverse Effect.

(aa) The documents incorporated by reference into the Disclosure Package and the Final Prospectus, when they were filed (or, if any amendment with respect to any such document was filed, when such amendment was filed), conformed in all material respects with the requirements of the Exchange Act; and any further such documents incorporated by reference will, when they are filed, conform in all material respects with the requirements of the Exchange Act.

(bb) The Company and each of the Subsidiaries is insured by insurers of recognized financial responsibility against such losses and risks and in such amounts as are prudent and customary in the businesses in which they are engaged; neither the Company nor any such Subsidiary has been refused any insurance coverage sought or applied for; and neither the Company nor any such Subsidiary has any reason to believe, absent a significant change in overall insurance market conditions, that it will not be able to renew its existing insurance coverage as and when such coverage expires or to obtain similar coverage from similar insurers as may be necessary to continue its business at a cost that would not have a Company Material Adverse Effect.

(cc) The accountants who certified the financial statements and supporting schedules included in the Registration Statement are independent registered public accountants as required by the Act.

(dd) The Company and each of the Subsidiaries maintain a system of internal accounting controls sufficient to provide reasonable assurance that: (A) transactions are executed in accordance with management’s general or specific authorizations; (B) transactions are recorded as necessary to permit preparation of financial statements in conformity with generally accepted accounting principles and to maintain asset accountability; (C) access to assets is permitted only in accordance with management’s general or specific authorization; and (D) the recorded accountability for assets is compared with the existing assets at reasonable intervals and appropriate action is taken with respect to any differences; the Company and its subsidiaries’ internal controls over financial reporting are effective and the Company and its subsidiaries are not aware of any material weakness in their internal controls over financial reporting.

(ee) Neither the Company nor any of its subsidiaries nor, to the knowledge of the Company, any director, officer, agent, employee or affiliate of the Company or any of its subsidiaries is aware of or has taken any action, directly or indirectly, that would result in a violation by such persons of the Foreign Corrupt Practices Act of 1977, as amended, and the rules and regulations thereunder (the “FCPA”), including, without limitation, making use of the mails or any means or instrumentality of interstate commerce corruptly

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in furtherance of an offer, payment, promise to pay or authorization of the payment of any money, or other property, gift, promise to give, or authorization of the giving of anything of value to any “foreign official” (as such term is defined in the FCPA) or any foreign political party or official thereof or any candidate for foreign political office, in contravention of the FCPA; and the Company, its subsidiaries and, to the knowledge of the Company, its affiliates have conducted their businesses in compliance with the FCPA and have instituted and maintain policies and procedures designed to ensure, and which are reasonably expected to continue to ensure, continued compliance therewith.

(ff) The operations of the Company and its subsidiaries are and have been conducted at all times in compliance with applicable financial recordkeeping and reporting requirements and the money laundering statutes and the rules and regulations thereunder and any related or similar rules, regulations or guidelines, issued, administered or enforced by any governmental agency (collectively, the “Money Laundering Laws”) and no action, suit or proceeding by or before any court or governmental agency, authority or body or any arbitrator involving the Company or any of its subsidiaries with respect to the Money Laundering Laws is pending or, to the best knowledge of the Company, threatened.

(gg) Neither the Company nor any of its subsidiaries nor, to the knowledge of the Company, any director, officer, agent, employee or affiliate of the Company or any of its subsidiaries is currently subject to any sanctions administered by the Office of Foreign Assets Control of the U.S. Treasury Department (“OFAC”); and the Company will not directly or indirectly use the proceeds of the offering, or lend, contribute or otherwise make available such proceeds to any subsidiary, joint venture partner or other person or entity, for the purpose of financing the activities of any person currently subject to any U.S. sanctions administered by OFAC.

(hh) None of the Company nor any of the Subsidiaries has taken, directly or indirectly, any action designed to, or that might reasonably be expected to, cause or result in stabilization or manipulation of the price of any security of the Company to facilitate the sale or resale of the Securities. Except as permitted by the Act and the Investment Company Act, the Company has not distributed any registration statement, preliminary prospectus, prospectus or other offering material in connection with the offering and sale of the Securities.

(ii) The Company is subject to the reporting requirements of either Section 13 or Section 15(d) of the Exchange Act and files reports with the Commission on the Electronic Data Gathering, Analysis and Retrieval (“EDGAR”) system.

(jj) The Company is not and, after giving effect to the offering and sale of the Securities and the application of the proceeds thereof as described in the Disclosure Package and the Final Prospectus, will not be, an “investment company” as defined in the Investment Company Act.

Any certificate signed by any officer of the Company and delivered to the Representatives or counsel for the Underwriters in connection with the offering of the Securities shall be deemed a representation and warranty by the Company, as to matters covered thereby, to each Underwriter.

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2. Purchase and Sale. (a) Subject to the terms and conditions and in reliance upon the representations and warranties herein set forth, the Company agrees to sell to each Underwriter, and each Underwriter agrees, severally and not jointly, to purchase from the Company, at the purchase price set forth in Schedule I hereto the number of Underwritten Securities set forth opposite such Underwriter’s name in Schedule II hereto.

(b) Subject to the terms and conditions and in reliance upon the representations and warranties herein set forth, the Company hereby grants an option to the several Underwriters to purchase, severally and not jointly, up to the number of Option Securities set forth in Schedule I hereto at the same purchase price per share as the Underwriters will pay for the Underwritten Securities. Said option may be exercised only to cover over-allotments in the sale of the Underwritten Securities by the Underwriters. Said option may be exercised in whole or in part at any time on or before the 30th day after the date of the Final Prospectus upon written or telegraphic notice by the Representatives to the Company setting forth the number of Option Securities as to which the several Underwriters are exercising the option and the settlement date. The number of Option Securities to be purchased by each Underwriter shall be the same percentage of the total number of Option Securities to be purchased by the several Underwriters as such Underwriter is purchasing of the Underwritten Securities, subject to such adjustments as you in your absolute discretion shall make to eliminate any fractional shares.

3. Delivery and Payment. Delivery of and payment for the Underwritten Securities and the Option Securities (if the option provided for in Section 2(b) hereof shall have been exercised on or before the third Business Day immediately preceding the Closing Date) shall be made on the date and at the time specified in Schedule I hereto or at such time on such later date not more than three Business Days after the foregoing date as the Representatives shall designate, which date and time may be postponed by agreement between the Representatives and the Company or as provided in Section 9 hereof (such date and time of delivery and payment for the Securities being herein called the “Closing Date”). Delivery of the Securities shall be made to the Representatives for the respective accounts of the several Underwriters against payment by the several Underwriters through the Representatives of the purchase price thereof to or upon the order of the Company by wire transfer payable in same-day funds to an account specified by the Company. Delivery of the Underwritten Securities and the Option Securities shall be made through the facilities of The Depository Trust Company unless the Representatives shall otherwise instruct.

If the option provided for in Section 2(b) hereof is exercised after the third Business Day immediately preceding the Closing Date, the Company will deliver the Option Securities (at the expense of the Company) to the Representatives, at 388 Greenwich Street, New York, New York, on the date specified by the Representatives (which shall be within three Business Days after exercise of said option) for the respective accounts of the several Underwriters, against payment by the several Underwriters through the Representatives of the purchase price thereof to or upon the order of the Company by wire transfer payable in same-day funds to an account specified by the Company. If settlement for the Option Securities occurs

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after the Closing Date, the Company will deliver to the Representatives on the settlement date for the Option Securities, and the obligation of the Underwriters to purchase the Option Securities shall be conditioned upon receipt of, supplemental opinions, certificates and letters confirming as of such date the opinions, certificates and letters delivered on the Closing Date pursuant to Section 6 hereof.

4. Offering by Underwriters. It is understood that the several Underwriters propose to offer the Securities for sale to the public as set forth in the Final Prospectus.

5. Agreements. The Company agrees with the several Underwriters that:

(a) Prior to the termination of the offering of the Securities, the Company will not file any amendment of the Registration Statement or supplement to the Base Prospectus (including the Final Prospectus or any Preliminary Prospectus). The Company will cause the Final Prospectus, properly completed, and any supplement thereto to be filed in a form approved by the Representatives with the Commission pursuant to the applicable paragraph of Rule 424(b) within the time period prescribed and will provide evidence satisfactory to the Representatives of such timely filing. The Company will promptly advise the Representatives (i) when the Final Prospectus, and any supplement thereto, shall have been filed (if required) with the Commission pursuant to Rule 424(b), (ii) when, prior to termination of the offering of the Securities, any amendment to the Registration Statement shall have been filed or become effective, (iii) of any request by the Commission or its staff for any amendment of the Registration Statement, or for any supplement to the Final Prospectus or for any additional information, (iv) of the issuance by the Commission of any stop order suspending the effectiveness of the Registration Statement or of any notice objecting to its use or the institution or threatening of any proceeding for that purpose and (v) of the receipt by the Company of any notification with respect to the suspension of the qualification of the Securities for sale in any jurisdiction or the institution or threatening of any proceeding for such purpose. The Company will use its reasonable best efforts to prevent the issuance of any such stop order or the occurrence of any such suspension or objection to the use of the Registration Statement and, upon such issuance, occurrence or notice of objection, to obtain as soon as possible the withdrawal of such stop order or relief from such occurrence or objection, including, if necessary, by filing an amendment to the Registration Statement or a new registration statement and using its reasonable best efforts to have such amendment or new registration statement declared effective as soon as practicable.

(b) The Company will prepare a final term sheet, containing solely a description of the offering of the Securities thereof and the terms of the Securities and the Concurrent Debt Offering, in the form approved by you and attached as Schedule IV hereto and file such term sheet pursuant to Rule 433(d) within the time required by such Rule.

(c) If, at any time prior to the filing of the Final Prospectus pursuant to Rule 424(b), any event occurs as a result of which the Disclosure Package would include any untrue statement of a material fact or omit to state any material fact necessary to make the

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statements therein in the light of the circumstances under which they were made or the circumstances then prevailing not misleading, the Company will (i) notify promptly the Representatives so that any use of the Disclosure Package may cease until it is amended or supplemented; (ii) amend or supplement the Disclosure Package to correct such statement or omission; and (iii) supply any amendment or supplement to you in such quantities as you may reasonably request.

(d) If, at any time when a prospectus relating to the Securities is required to be delivered under the Act (including in circumstances where such requirement may be satisfied pursuant to Rule 172), any event occurs as a result of which the Final Prospectus as then supplemented would include any untrue statement of a material fact or omit to state any material fact necessary to make the statements therein in the light of the circumstances under which they were made at such time not misleading, or if it shall be necessary to amend the Registration Statement, file a new registration statement or supplement the Final Prospectus to comply with the Act or the Exchange Act or the respective rules thereunder, including in connection with use or delivery of the Final Prospectus, the Company promptly will (i) notify the Representatives of any such event, (ii) prepare and file with the Commission, subject to the second sentence of paragraph (a) of this Section 5, an amendment or supplement or new registration statement which will correct such statement or omission or effect such compliance, (iii) use its reasonable best efforts to have any amendment to the Registration Statement or new registration statement declared effective as soon as practicable in order to avoid any disruption in use of the Final Prospectus and (iv) supply any supplemented Final Prospectus to you in such quantities as you may reasonably request.

(e) As soon as practicable, the Company will make generally available to its security holders and to the Representatives an earnings statement or statements of the Company and its subsidiaries which will satisfy the provisions of Section 11(a) of the Act and Rule 158.

(f) The Company will furnish to the Representatives, without charge, signed copies of the Registration Statement (including exhibits thereto) and to each other Underwriter a copy of the Registration Statement (without exhibits thereto) and, so long as delivery of a prospectus by an Underwriter or dealer may be required by the Act (including in circumstances where such requirement may be satisfied pursuant to Rule 172), as many copies of each Preliminary Prospectus, the Final Prospectus and each Issuer Free Writing Prospectus and any supplement thereto as the Representatives may reasonably request.

(g) The Company will arrange, if necessary, for the qualification of the Securities for sale under the laws of such jurisdictions as the Representatives may designate and will maintain such qualifications in effect so long as required for the distribution of the Securities; provided that in no event shall the Company be obligated to qualify to do business in any jurisdiction where it is not now so qualified or to take any action that would subject it to service of process in suits, other than those arising out of the offering or sale of the Securities, in any jurisdiction where it is not now so subject.

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(h) The Company agrees that, unless it has or shall have obtained the prior written consent of the Representatives, and each Underwriter, severally and not jointly, agrees with the Company that, unless it has or shall have obtained, as the case may be, the prior written consent of the Company, it has not made and will not make any offer relating to the Securities that would constitute an Issuer Free Writing Prospectus or that would otherwise constitute a “free writing prospectus” (as defined in Rule 405) required to be filed by the Company with the Commission or retained by the Company under Rule 433, other than the free writing prospectus containing the information contained in the final term sheet prepared and filed pursuant to Section 5(b) hereto; provided that the prior written consent of the parties hereto shall be deemed to have been given in respect of the Free Writing Prospectuses included in Schedule III hereto and any electronic road show. Any such free writing prospectus consented to by the Representatives or the Company is hereinafter referred to as a “Permitted Free Writing Prospectus.” The Company agrees that (x) it has treated and will treat, as the case may be, each Permitted Free Writing Prospectus as an Issuer Free Writing Prospectus and (y) it has complied and will comply, as the case may be, with the requirements of Rules 164 and 433 applicable to any Permitted Free Writing Prospectus, including in respect of timely filing with the Commission, legending and record keeping.

(i) The Company will not, without the prior written consent of Citigroup Global Markets Inc., offer, sell, contract to sell, pledge, or otherwise dispose of (or enter into any transaction which is designed to, or might reasonably be expected to, result in the disposition (whether by actual disposition or effective economic disposition due to cash settlement or otherwise) by the Company or any affiliate of the Company), directly or indirectly, including the filing (or participation in the filing) of a registration statement with the Commission in respect of, or establish or increase a put equivalent position or liquidate or decrease a call equivalent position within the meaning of Section 16 of the Exchange Act, any other shares of Common Stock or any securities convertible into, or exercisable, or exchangeable for, shares of Common Stock; or publicly announce an intention to effect any such transaction, until the 90^th day after the date of this Agreement, provided, however, that the Company may (A) issue and sell Common Stock pursuant to any employee stock option plan, stock ownership plan or dividend reinvestment plan of the Company in effect at the Execution Time, (B) issue Common Stock issuable upon the conversion of securities or the exercise of warrants outstanding at the Execution Time, (C) issue and sell 3.0% Convertible Subordinated Notes due 2014 in connection with the Concurrent Debt Offering and issue Common Stock upon conversion thereof and (D) issue and sell up to 500,000 shares of Common Stock in connection with future acquisitions.

(j) The Company will not take, directly or indirectly, any action designed to or that would constitute or that might reasonably be expected to cause or result in, under the Exchange Act or otherwise, stabilization or manipulation of the price of any security of the Company to facilitate the sale or resale of the Securities.

(k) The Company agrees to pay the costs and expenses relating to the following matters: (i) the preparation, printing, authentication, issuance and delivery of certificates for the Securities, including any stamp or transfer taxes in connection with the

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original issuance and sale of the Securities; (ii) the printing (or reproduction) and delivery of this Agreement, any blue sky memorandum and all other agreements or documents printed (or reproduced) and delivered in connection with the offering of the Securities; (iii) the registration of the Securities under the Exchange Act and the listing of the Securities on the NASDAQ Global Select Market; (iv) any registration or qualification of the Securities for offer and sale under the securities or blue sky laws of the several states (including filing fees and the reasonable fees and expenses of counsel for the Underwriters relating to such registration and qualification); (v) any filings required to be made with the NASD, Inc. (including filing fees and the reasonable fees and expenses of counsel for the Underwriters relating to such filings); (vi) the transportation and other expenses incurred by or on behalf of Company representatives (but not the Underwriters) in connection with presentations to prospective purchasers of the Securities; (vii) the fees and expenses of the Company’s accountants and the fees and expenses of counsel (including local and special counsel) for the Company; and (viii) all other costs and expenses incident to the performance by the Company of its obligations hereunder.

6. Conditions to the Obligations of the Underwriters. The obligations of the Underwriters to purchase the Underwritten Securities and the Option Securities, as the case may be, shall be subject to the accuracy of the representations and warranties on the part of the Company contained herein as of the Execution Time, the Closing Date and any settlement date pursuant to Section 3 hereof, to the accuracy of the statements of the Company made in any certificates pursuant to the provisions hereof, to the performance by the Company of its obligations hereunder and to the following additional conditions:

(a) The Final Prospectus, and any supplement thereto, have been filed in the manner and within the time period required by Rule 424(b); the final term sheet contemplated by Section 5(b) hereto and any other material required to be filed by the Company pursuant to Rule 433(d) under the Act shall have been filed with the Commission within the applicable time periods prescribed for such filings by Rule 433; and no stop order suspending the effectiveness of the Registration Statement or any notice objecting to its use shall have been issued and no proceedings for that purpose shall have been instituted or threatened.

(b) The Representatives shall have received from Gunderson Dettmer Stough Villeneuve Franklin & Hachigian, LLP, counsel for the Company, such opinion, dated the Closing Date and addressed to the Representatives, to the effect set forth on Exhibit B hereto and of Brandi Galvin Morandi to the effect set forth on Exhibit C hereto.

(c) The Representatives shall have received from Davis Polk & Wardwell, counsel for the Underwriters, such opinion or opinions, dated the Closing Date and addressed to the Representatives, with respect to such matters as the Representatives may reasonably require, and the Company shall have furnished to such counsel such documents as they reasonably request for the purpose of enabling them to pass upon such matters.

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(d) The Company shall have furnished to the Representatives a certificate of the Company, signed by the Chairman of the Board or the President and the principal financial or accounting officer of the Company, dated the Closing Date, to the effect that:

(i) the representations and warranties of the Company in this Agreement are true and correct on and as of the Closing Date with the same effect as if made on the Closing Date and the Company has complied with all the agreements and satisfied all the conditions on its part to be performed or satisfied at or prior to the Closing Date;

(ii) no stop order suspending the effectiveness of the Registration Statement or any notice objecting to its use has been issued and no proceedings for that purpose have been instituted or, to the Company’s knowledge, threatened; and

(iii) since the date of the most recent financial statements included in the Disclosure Package and the Final Prospectus (exclusive of any supplement thereto), there has been no material adverse effect on the condition (financial or other), business, properties or results of operation of the Company and the Subsidiaries, taken as a whole, whether or not arising from transactions in the ordinary course of business, except as set forth in or contemplated in the Disclosure Package and the Final Prospectus (exclusive of any supplement thereto).

(e) The Representatives shall have received (i) from PricewaterhouseCoopers LLP, at the Execution Time and at the Closing Date, “comfort” letters (which may refer to letters previously delivered to one or more of the Representatives), dated respectively as of the Execution Time and as of the Closing Date, in form and substance satisfactory to the Representatives, confirming that they are an independent registered accounting firm with respect to the Company within the meaning of the Act and the applicable rules and regulations adopted by the Commission and the Public Company Accounting Oversight Board (United States) (PCAOB) substantially in the form of Exhibit D hereto and (ii) from BDO Stoy Hayward LLP, at the Execution Time and at the Closing Date, “comfort” letters (which may refer to letters previously delivered to one or more of the Representatives), dated respectively as of the Execution Time and as of the Closing Date, in form and substance satisfactory to the Representatives, confirming that they are an independent registered accounting firm with respect to IXEurope within the meaning of the Act and the applicable rules and regulations adopted by the Commission and the PCAOB substantially in the form of Exhibit E hereto.

(f) Subsequent to the Execution Time or, if earlier, the dates as of which information is given in the Registration Statement (exclusive of any amendment thereof) and the Final Prospectus (exclusive of any amendment or supplement thereto), there shall not have been (i) any change or decrease specified in the letters referred to in paragraph (e) of this Section 6 or (ii) any change, or any development involving a prospective change, in or affecting the condition (financial or otherwise), earnings, business or properties of the Company and its subsidiaries taken as a whole, whether or

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not arising from transactions in the ordinary course of business, except as set forth in or contemplated in the Disclosure Package and the Final Prospectus (exclusive of any amendment or supplement thereto) the effect of which, in any case referred to in clause (i) or (ii) above, is, in the sole judgment of the Representatives, so material and adverse as to make it impractical or inadvisable to proceed with the offering or delivery of the Securities as contemplated by the Registration Statement (exclusive of any amendment thereof), the Disclosure Package and the Final Prospectus (exclusive of any amendment or supplement thereto).

(g) Subsequent to the Execution Time, there shall not have been any decrease in the rating of any of the Company’s debt securities by any “nationally recognized statistical rating organization” (as defined for purposes of Rule 436(g) under the Act) or any notice given of any intended or potential decrease in any such rating or of a possible change in any such rating that does not indicate the direction of the possible change.

(h) Prior to the Closing Date, the Company shall have furnished to the Representatives such further information, certificates and documents as the Representatives may reasonably request.

(i) At or prior to the Execution Time, the Company shall have furnished to the Representatives a letter substantially in the form of Exhibit A hereto from each Section 16 officer and director of the Company addressed to the Representatives.

(i) Subsequent to the execution and delivery of this Agreement and concurrently with or prior to the Closing Date, the Concurrent Debt Offering shall have been completed.

If any of the conditions specified in this Section 6 shall not have been fulfilled when and as provided in this Agreement, or if any of the opinions and certificates mentioned above or elsewhere in this Agreement shall not be reasonably satisfactory in form and substance to the Representatives and counsel for the Underwriters, this Agreement and all obligations of the Underwriters hereunder may be canceled at, or at any time prior to, the Closing Date by the Representatives. Notice of such cancellation shall be given to the Company in writing or by telephone or facsimile confirmed in writing.

The documents required to be delivered by this Section 6 shall be delivered at the office of Davis Polk & Wardwell, counsel for the Underwriters, at 1600 El Camino Real, Menlo Park, CA 94025, on the Closing Date.

7. Reimbursement of Underwriters’ Expenses. If the sale of the Securities provided for herein is not consummated because any condition to the obligations of the Underwriters set forth in Section 6 hereof is not satisfied, because of any termination pursuant to Section 10 hereof or because of any refusal, inability or failure on the part of the Company to perform any agreement herein or comply with any provision hereof other than by reason of a default by any of the Underwriters, the Company will reimburse the Underwriters severally through Citigroup Global Markets Inc. on demand for all expenses (including fees and disbursements of counsel) that shall have been reasonably incurred by them in connection with the proposed purchase and sale of the Securities.

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8. Indemnification and Contribution. (a) The Company agrees to indemnify and hold harmless each Underwriter, the directors, officers, employees and agents of each Underwriter and each person who controls any Underwriter within the meaning of either the Act or the Exchange Act against any and all losses, claims, damages or liabilities, joint or several, to which they or any of them may become subject under the Act, the Exchange Act or other Federal or state statutory law or regulation, at common law or otherwise, insofar as such losses, claims, damages or liabilities (or actions in respect thereof) arise out of or are based upon any untrue statement or alleged untrue statement of a material fact contained in the registration statement for the registration of the Securities as originally filed or in any amendment thereof, or in the Base Prospectus, any Preliminary Prospectus or any other preliminary prospectus supplement relating to the Securities, the Final Prospectus, any Issuer Free Writing Prospectus or the information contained in the final term sheet required to be prepared and filed pursuant to Section 5(b) hereto, or in any amendment thereof or supplement thereto, or arise out of or are based upon the omission or alleged omission to state therein a material fact required to be stated therein or necessary to make the statements therein not misleading, and agrees to reimburse each such indemnified party, as incurred, for any legal or other expenses reasonably incurred by them in connection with investigating or defending any such loss, claim, damage, liability or action; provided, however, that the Company will not be liable in any such case to the extent that any such loss, claim, damage or liability arises out of or is based upon any such untrue statement or alleged untrue statement or omission or alleged omission made therein in reliance upon and in conformity with written information furnished to the Company by or on behalf of any Underwriter through the Representatives specifically for inclusion therein. This indemnity agreement will be in addition to any liability which the Company may otherwise have.

(b) Each Underwriter severally and not jointly agrees to indemnify and hold harmless the Company, each of its directors, each of its officers who signs the Registration Statement, and each person who controls the Company within the meaning of either the Act or the Exchange Act, to the same extent as the foregoing indemnity from the Company to each Underwriter, but only with reference to written information relating to such Underwriter furnished to the Company by or on behalf of such Underwriter through the Representatives specifically for inclusion in the documents referred to in the foregoing indemnity. This indemnity agreement will be in addition to any liability which any Underwriter may otherwise have. The Company acknowledges that the statements set forth (i) in the last paragraph of the cover page regarding delivery of the Securities and, under the heading “Underwriting” or “Plan of Distribution”, (ii) the list of Underwriters and their respective participation in the sale of the Securities, (iii) the sentences related to concessions and reallowances and (iv) the paragraph related to stabilization, syndicate covering transactions and penalty bids in any Preliminary Prospectus and the Final Prospectus constitute the only information furnished in writing by or on behalf of the several Underwriters for inclusion in any Preliminary Prospectus, the Final Prospectus or any Issuer Free Writing Prospectus.

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(c) Promptly after receipt by an indemnified party under this Section 8 of notice of the commencement of any action, such indemnified party will, if a claim in respect thereof is to be made against the indemnifying party under this Section 8, notify the indemnifying party in writing of the commencement thereof; but the failure so to notify the indemnifying party (i) will not relieve it from liability under paragraph (a) or (b) above unless and to the extent it did not otherwise learn of such action and such failure results in the forfeiture by the indemnifying party of substantial rights and defenses and (ii) will not, in any event, relieve the indemnifying party from any obligations to any indemnified party other than the indemnification obligation provided in paragraph (a) or (b) above. The indemnifying party shall be entitled to appoint counsel of the indemnifying party’s choice at the indemnifying party’s expense to represent the indemnified party in any action for which indemnification is sought (in which case the indemnifying party shall not thereafter be responsible for the fees and expenses of any separate counsel retained by the indemnified party or parties except as set forth below); provided, however, that such counsel shall be satisfactory to the indemnified party. Notwithstanding the indemnifying party’s election to appoint counsel to represent the indemnified party in an action, the indemnified party shall have the right to employ separate counsel (including local counsel), and the indemnifying party shall bear the reasonable fees, costs and expenses of such separate counsel if (i) the use of counsel chosen by the indemnifying party to represent the indemnified party would present such counsel with a conflict of interest, (ii) the actual or potential defendants in, or targets of, any such action include both the indemnified party and the indemnifying party and the indemnified party shall have reasonably concluded that there may be legal defenses available to it and/or other indemnified parties which are different from or additional to those available to the indemnifying party, (iii) the indemnifying party shall not have employed counsel satisfactory to the indemnified party to represent the indemnified party within a reasonable time after notice of the institution of such action or (iv) the indemnifying party shall authorize the indemnified party to employ separate counsel at the expense of the indemnifying party. An indemnifying party will not, without the prior written consent of the indemnified parties, settle or compromise or consent to the entry of any judgment with respect to any pending or threatened claim, action, suit or proceeding in respect of which indemnification or contribution may be sought hereunder (whether or not the indemnified parties are actual or potential parties to such claim or action) unless such settlement, compromise or consent includes an unconditional release of each indemnified party from all liability arising out of such claim, action, suit or proceeding.

(d) In the event that the indemnity provided in paragraph (a), (b) or (c) of this Section 8 is unavailable to or insufficient to hold harmless an indemnified party for any reason, the Company and the Underwriters severally agree to contribute to the aggregate losses, claims, damages and liabilities (including legal or other expenses reasonably incurred in connection with investigating or defending the same) (collectively “Losses”) to which the Company and one or more of the Underwriters may be subject in such proportion as is appropriate to reflect the relative benefits received by the Company on the one hand and by the Underwriters on the other from the offering of the Securities; provided, however, that in no case shall any Underwriter (except as may be provided in any agreement among underwriters relating to the offering of the Securities) be responsible for any amount in excess of the underwriting discount or commission

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applicable to the Securities purchased by such Underwriter hereunder. If the allocation provided by the immediately preceding sentence is unavailable for any reason, the Company and the Underwriters severally shall contribute in such proportion as is appropriate to reflect not only such relative benefits but also the relative fault of the Company on the one hand and of the Underwriters on the other in connection with the statements or omissions which resulted in such Losses as well as any other relevant equitable considerations. Benefits received by the Company shall be deemed to be equal to the total net proceeds from the offering (before deducting expenses) received by it, and benefits received by the Underwriters shall be deemed to be equal to the total underwriting discounts and commissions, in each case as set forth on the cover page of the Final Prospectus. Relative fault shall be determined by reference to, among other things, whether any untrue or any alleged untrue statement of a material fact or the omission or alleged omission to state a material fact relates to information provided by the Company on the one hand or the Underwriters on the other, the intent of the parties and their relative knowledge, access to information and opportunity to correct or prevent such untrue statement or omission. The Company and the Underwriters agree that it would not be just and equitable if contribution were determined by pro rata allocation or any other method of allocation which does not take account of the equitable considerations referred to above. Notwithstanding the provisions of this paragraph (d), no person guilty of fraudulent misrepresentation (within the meaning of Section 11(f) of the Act) shall be entitled to contribution from any person who was not guilty of such fraudulent misrepresentation. For purposes of this Section 8, each person who controls an Underwriter within the meaning of either the Act or the Exchange Act and each director, officer, employee and agent of an Underwriter shall have the same rights to contribution as such Underwriter, and each person who controls the Company within the meaning of either the Act or the Exchange Act, each officer of the Company who shall have signed the Registration Statement and each director of the Company shall have the same rights to contribution as the Company, subject in each case to the applicable terms and conditions of this paragraph (d).

9. Default by an Underwriter. If any one or more Underwriters shall fail to purchase and pay for any of the Securities agreed to be purchased by such Underwriter or Underwriters hereunder and such failure to purchase shall constitute a default in the performance of its or their obligations under this Agreement, the remaining Underwriters shall be obligated severally to take up and pay for (in the respective proportions which the amount of Securities set forth opposite their names in Schedule II hereto bears to the aggregate amount of Securities set forth opposite the names of all the remaining Underwriters) the Securities which the defaulting Underwriter or Underwriters agreed but failed to purchase; provided, however, that in the event that the aggregate amount of Securities which the defaulting Underwriter or Underwriters agreed but failed to purchase shall exceed 10% of the aggregate amount of Securities set forth in Schedule II hereto, the remaining Underwriters shall have the right to purchase all, but shall not be under any obligation to purchase any, of the Securities, and if such nondefaulting Underwriters do not purchase all the Securities, this Agreement will terminate without liability to any nondefaulting Underwriter or the Company. In the event of a default by any Underwriter as set forth in this Section 9, the Closing Date shall be postponed for such period, not exceeding five Business Days, as the Representatives shall determine in order that the required changes in the Registration Statement and the Final Prospectus or in any other documents or arrangements

19

may be effected. Nothing contained in this Agreement shall relieve any defaulting Underwriter of its liability, if any, to the Company and any nondefaulting Underwriter for damages occasioned by its default hereunder.

10. Termination. This Agreement shall be subject to termination in the absolute discretion of the Representatives, by notice given to the Company prior to delivery of and payment for the Securities, if at any time prior to such delivery and payment (i) trading in the Company’s Common Stock shall have been suspended by the Commission or the NASDAQ Global Select Market or trading in securities generally on the New York Stock Exchange or the NASDAQ Global Market shall have been suspended or limited or minimum prices shall have been established on either of such exchanges, (ii) a banking moratorium shall have been declared either by Federal or New York State authorities or (iii) there shall have occurred any outbreak or escalation of hostilities, declaration by the United States of a national emergency or war, or other calamity or crisis the effect of which on financial markets is such as to make it, in the sole judgment of the Representatives, impractical or inadvisable to proceed with the offering or delivery of the Securities as contemplated by any Preliminary Prospectus or the Final Prospectus (exclusive of any supplement thereto).

11. Representations and Indemnities to Survive. The respective agreements, representations, warranties, indemnities and other statements of the Company or its officers and of the Underwriters set forth in or made pursuant to this Agreement will remain in full force and effect, regardless of any investigation made by or on behalf of any Underwriter or the Company or any of the officers, directors, employees, agents or controlling persons referred to in Section 8 hereof, and will survive delivery of and payment for the Securities. The provisions of Sections 7 and 8 hereof shall survive the termination or cancellation of this Agreement.

12. Notices. All communications hereunder will be in writing and effective only on receipt, and, if sent to the Representatives, will be mailed, delivered or telefaxed to the Citigroup Global Markets Inc. General Counsel (fax no.: (212)  ###-###-####) and confirmed to the General Counsel, Citigroup Global Markets Inc., at 388 Greenwich Street, New York, New York, 10013, Attention: General Counsel; or, if sent to the Company, will be mailed, delivered or telefaxed to the Company General Counsel (650)  ###-###-#### and confirmed to it at 301 Velocity Way, Fifth Floor, Foster City, California 94404, Attention: the Legal Department.

13. Successors. This Agreement will inure to the benefit of and be binding upon the parties hereto and their respective successors and the officers, directors, employees, agents and controlling persons referred to in Section 8 hereof, and no other person will have any right or obligation hereunder.

14. No fiduciary duty. The Company hereby acknowledges that (a) the purchase and sale of the Securities pursuant to this Agreement is an arm’s-length commercial transaction between the Company, on the one hand, and the Underwriters and any affiliate through which it may be acting, on the other, (b) the Underwriters are acting as principal and not as an agent or fiduciary of the Company and (c) the Company’s engagement of the Underwriters in connection with the offering and the process leading up to the offering is as independent contractors and not in any other capacity. Furthermore, the Company agrees that it is solely responsible for making its own judgments in connection with the offering (irrespective of

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whether any of the Underwriters has advised or is currently advising the Company on related or other matters). The Company agrees that it will not claim that the Underwriters have rendered advisory services of any nature or respect, or owe an agency, fiduciary or similar duty to the Company, in connection with such transaction or the process leading thereto.

15. Integration. This Agreement supersedes all prior agreements and understandings (whether written or oral) between the Company and the Underwriters, or any of them, with respect to the subject matter hereof.

16. Applicable Law. This Agreement will be governed by and construed in accordance with the laws of the State of New York applicable to contracts made and to be performed within the State of New York.

17. Waiver of Jury Trial. The Company hereby irrevocably waives, to the fullest extent permitted by applicable law, any and all right to trial by jury in any legal proceeding arising out of or relating to this Agreement or the transactions contemplated hereby.

18. Counterparts. This Agreement may be signed in one or more counterparts, each of which shall constitute an original and all of which together shall constitute one and the same agreement.

19. Headings. The section headings used herein are for convenience only and shall not affect the construction hereof.

20. Definitions. The terms that follow, when used in this Agreement, shall have the meanings indicated.

“Act” shall mean the Securities Act of 1933, as amended, and the rules and regulations of the Commission promulgated thereunder.

“Base Prospectus” shall mean the base prospectus referred to in paragraph 1(a) above contained in the Registration Statement at the Execution Time and all documents incorporated by reference therein.

“Business Day” shall mean any day other than a Saturday, a Sunday or a legal holiday or a day on which banking institutions or trust companies are authorized or obligated by law to close in New York City.

“Commission” shall mean the Securities and Exchange Commission.

“Disclosure Package” shall mean (i) the Base Prospectus, (ii) the Preliminary Prospectus used most recently prior to the Execution Time, (iii) the Issuer Free Writing Prospectuses, if any, identified in Schedule III hereto, (iv) the final term sheet prepared and filed pursuant to Section 5(b) hereto, if any, and (v) any other Free Writing Prospectus that the parties hereto shall hereafter expressly agree in writing to treat as part of the Disclosure Package.

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“Effective Date” shall mean each date and time that the Registration Statement and any post-effective amendment or amendments thereto became or becomes effective.

“Exchange Act” shall mean the Securities Exchange Act of 1934, as amended, and the rules and regulations of the Commission promulgated thereunder.

“Execution Time” shall mean the date and time that this Agreement is executed and delivered by the parties hereto.

“Final Prospectus” shall mean the prospectus supplement relating to the Securities that was first filed pursuant to Rule 424(b) after the Execution Time and all documents incorporated by reference therein, together with the Base Prospectus.

“Free Writing Prospectus” shall mean a free writing prospectus, as defined in Rule 405.

“Investment Company Act” shall mean the Investment Company Act of 1940, as amended.

“Issuer Free Writing Prospectus” shall mean an issuer free writing prospectus, as defined in Rule 433.

“Preliminary Prospectus” shall mean any preliminary prospectus supplement to the Base Prospectus referred to in paragraph 1(a) above which is used prior to the filing of the Final Prospectus and all documents incorporated by reference therein, together with the Base Prospectus .

“Registration Statement” shall mean the registration statement referred to in paragraph 1(a) above, including exhibits, financial statements, any prospectus supplement relating to the Securities that is filed with the Commission pursuant to Rule 424(b) and deemed part of such registration statement pursuant to Rule 430B, as amended on each Effective Date and, in the event any post-effective amendment thereto becomes effective prior to the Closing Date, shall also mean such registration statement as so amended and, in each case, all documents incorporated by reference therein.

“Rule 158”, “Rule 163”, “Rule 164”, “Rule 172”, “Rule 405”, “Rule 415”, “Rule 424”, “Rule 430B” and “Rule 433” refer to such rules under the Act.

“Well-Known Seasoned Issuer” shall mean a well-known seasoned issuer, as defined in Rule 405.

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If the foregoing is in accordance with your understanding of our agreement, please sign and return to us the enclosed duplicate hereof, whereupon this letter and your acceptance shall represent a binding agreement among the Company and the several Underwriters.

The foregoing Agreement is

hereby confirmed and accepted

as of the date specified in

Schedule I hereto.

For themselves and the other

several Underwriters, if any,

named in Schedule II to the

foregoing Agreement.

SCHEDULE I

Underwriting Agreement dated September 20, 2007

Registration Statement No. 333-146065

Representative(s): Citigroup Global Markets Inc.

Title, Purchase Price and Description of Securities:

Title: Common Stock, $0.001 par value per share

Number of Underwritten Securities: 3,662,556

Purchase price: $295,909,253

Description: See Schedule IV

Closing Date, Time and Location: September 26, 2007 at 07:00 a.m. (Pacific Time) at the offices of Davis Polk & Wardwell, 1600 El Camino Real, Menlo Park, CA 94025

Type of Offering: Non-Delayed

Date referred to in Section 5(i) after which the Company may offer or sell securities issued by the Company without the consent of the Representative(s): 90

Modification of items to be covered by the letter from PricewaterhouseCoopers LLP delivered pursuant to Section 6(e)(i) at the Execution Time:

Modification of items to be covered by the letter from BDO Stoy Hayward LLP delivered pursuant to Section 6(e)(i) at the Execution Time:

SCHEDULE II

SCHEDULE III

Schedule of Free Writing Prospectuses included in the Disclosure Package

SCHEDULE IV

Final Term Sheet

EXHIBIT A

[Form of Lock-Up Agreement]

EXHIBIT B

[Gunderson Dettmer Opinion]

EXHIBIT C

[General Counsel Opinion]

(i) to her knowledge, the Company is not in default in the performance or observance of any material obligation, agreement, covenant or condition contained in any agreement filed as an exhibit to the Registration Statement or appearing on the list of exhibits to the Company’s quarterly report on Form 10-Q for the quarter ended June 30, 2007 or any current report on Form 8-K filed by the Company with the Commission after June 30, 2007 and before the date of such opinion (each a “Company Material Agreement”); and

(ii) the compliance by the Company with all of the provisions of this Agreement and the consummation of the transactions contemplated herein, will not conflict with or result in a breach or violation of any terms or provisions of, or constitute a default under any Company Material Agreement (other than those agreements listed on a schedule to the related opinion required by Section 6(b) of the Underwriting Agreement).

In rendering such opinion, such counsel may rely (A) as to matters involving the application of laws of any jurisdiction other than the States of California or Delaware or the Federal laws of the United States, to the extent they deem proper and specified in such opinion, upon the opinion of other counsel of good standing whom they believe to be reliable and who are satisfactory to counsel for the Underwriters and (B) as to matters of fact, to the extent they deem proper, on certificates of responsible officers of the Company and public officials.

References to the Final Prospectus in this opinion shall also include any supplements thereto at the Closing Date.

EXHIBIT D

[Comfort Letter from PricewaterhouseCoopers LLP]

EXHIBIT E

[Comfort Letter from BDO Stoy Hayward LLP]

B-2