Amendment No. 4 to the United States Reseller Agreement between Sycamore Networks, Inc.

EXHIBIT 10.23

Amendment No. 4

to the United States Reseller Agreement between

Sycamore Networks, Inc.

and

Sprint Communications Company, L.P. Government Systems Division

This Amendment No. 4 (the “Amendment”), effective as of June 1, 2005 (the “Effective Date”), to the United States Reseller Agreement by and between Sycamore Networks, Inc. (“Sycamore”) and Sprint Communications Company, L.P. (“Sprint”) which agreement is dated January 6, 2004, as amended (the “Reseller Agreement”). Sycamore and Sprint are collectively referred to herein as the “Parties.”

WHEREAS, Attachment I-2 to the Reseller Agreement contains a list of the Labor Categories that Sycamore offers for sale/license to Sprint under the Reseller Agreement;

WHEREAS, the Parties wish to replace the existing Attachment I-2 with a new attachment containing updated Labor Categories and prices, and;

WHEREAS, there are no other changes to the Agreement by this Amendment.

NOW, THEREFORE, for good and valuable consideration the receipt and sufficiency of which is hereby acknowledged, the Parties hereby agree to modify the Reseller Agreement as follows:

1. Capitalized terms used herein and not otherwise defined herein shall have such meaning as set forth in the Reseller Agreement.

2. Attachment I-2 to the Reseller Agreement is hereby replaced with the document attached hereto and incorporated herein labeled “Attachment I-2, Rev. 2.”

3. In the event of a conflict between the terms and conditions of this Amendment and the Reseller Agreement, this Amendment shall prevail. Except as expressly modified in this Amendment, all other terms and conditions of the Reseller Agreement shall remain in full force and effect.

IN WITNESS WHEREOF, the parties have caused this Amendment No. 4 to be executed in duplicate by their respective, duly authorized representatives:

Attachment I-2, Rev 2