AMENDMENT NO. 2 TO FOURTH AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

QuickLinks -- Click here to rapidly navigate through this document

Exhibit 4.3

IKANOS COMMUNICATIONS, INC.

AMENDMENT NO. 2 TO FOURTH AMENDED
AND RESTATED INVESTOR RIGHTS AGREEMENT

        This AMENDMENT NO. 2 TO FOURTH AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT ("Amendment") is entered into as of March 3, 2006, by and among IKANOS COMMUNICATIONS, INC., a Delaware corporation (the "Company") and certain parties set forth on the attached Exhibit 1 (the "Existing Stockholders") to that certain Fourth Amended and Restated Investor Rights Agreement dated as of March 5, 2004, as amended on February 27, 2006 (collectively the "Agreement"). All capitalized terms not otherwise defined herein shall have the meaning set forth in the Agreement.

RECITALS

        WHEREAS, the Company has provided proper and timely notice to the holders of Registrable Securities in accordance with the terms of the Agreement with respect to the Company's intention to file of a registration statement with the Securities and Exchange Commission ("SEC") pursuant to which the Company proposes to engage in a follow-on underwritten public offering of shares of its Common Stock (the "Proposed Offering");

        WHEREAS, pursuant to Amendment No. 1 dated February 27, 2006, solely for the purposes of the Proposed Offering, the Company and certain of the Holders of Registrable Securities amended Section 6(b) of the Agreement to permit Other Shareholders and certain additional holders of Common Stock to sell shares of Company Common Stock in the Proposed Offering;

        WHEREAS, the Company and certain of the Holders of Registrable Securities desire to further amend Section 6(b) of the Agreement to clarify the number of shares that Other Shareholders and certain additional holders of Company Common Stock will be able to sell in the Proposed Offering;

        WHEREAS, Section 27 of the Agreement provides that the Agreement may be amended by the written consent of the Company and the holders of at least two-thirds (²/3) of the Registrable Securities (excluding any shares held by the Founder), provided any such amendment, waiver or modification applies by its terms and to the extent applicable in the same manner to the Founder, the Series A Investors, the Series B Investors, the Series C Investors, the Series D Investors, Series E Investors and each such assignee;

        WHEREAS, the undersigned below constitute at least two-thirds (²/3) of the Registrable Securities (excluding any shares held by the Founder); and

        WHEREAS, the relationship of the parties shall continue to be governed by the terms of the Agreement as amended by this Amendment,

        NOW, THEREFORE, the parties, intending to be legally bound, hereby agree as follows:

        1.    Amendment.    Section 6(b) of the Agreement is hereby amended and restated in its entirety to read as follows:

"6.    Company Registration.

        (b)    Underwriting.    If the registration of which the Company gives notice is for a registered public offering involving an underwriting, the Company shall so advise the Holders as a part of the written notice given pursuant to Section 6(a)(i). In such event the right of any Holder to registration pursuant to Section 6 shall be conditioned upon such Holder's participation in such underwriting and the inclusion of such Holder's Registrable Securities in the underwriting to the extent provided herein. All Holders proposing to distribute their securities through such underwriting shall (together with the Company and the Other Shareholders distributing their

securities through such underwriting) enter into an underwriting agreement in customary form with the Underwriter selected for underwriting by the Company. Notwithstanding any other provision of this Section 6, if the Underwriter in its sole discretion advises the Company in writing that marketing factors require a limitation on the number of shares to be underwritten, then (a) if such registration is the first registered offering of the Company's securities to the public, the Company may (subject to the allocation priority set forth below) exclude from such registration and underwriting some or all of the Registrable Securities which would otherwise be underwritten pursuant hereto; (b) if such registration is the second registered offering of the Company's securities to the public and occurs on or prior to September 30, 2006, Other Shareholders, holders of vested Company options and shareholders who otherwise do not h