EXHIBIT 10.29
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                           FIRST AMENDMENT TO GUARANTY
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         First Amendment dated as of March 5, 2003 to Guaranty (the "First
Amendment"), by and between VANTAGEPOINT VENTURE PARTNERS III (Q), L.P., a
Delaware limited partnership (the "Guarantor") and FLEET NATIONAL BANK (the
"Lender"), amending certain provisions of the Guaranty dated as of December 27,
2002 from the Guarantor to the Lender (as amended and in effect from time to
time, the "Guaranty"). Terms not otherwise defined herein which are defined in
the Credit Agreement (as hereinafter defined) shall have the same respective
meanings herein as therein.

         WHEREAS, DSL.net, Inc. ("DSLN") and the Lender are parties to that
certain Revolving Credit and Term Loan Agreement dated as of December 13, 2002
(as amended and in effect from time to time, the "Credit Agreement") by and
between DSLN and the Lender; and

         WHEREAS, in connection with the Credit Agreement, the Guarantor
executed and delivered to the Lender the Guaranty; and

         WHEREAS, the Guarantor continues to expect to receive substantial
direct and indirect benefits from the continued extensions of credit to DSLN by
the Lender pursuant to the Credit Agreement (which benefits are hereby
acknowledged); and

         WHEREAS, the Guarantor desires to increase its liability under the
Guaranty as more fully set forth herein and the Guarantor and the Lender have
agreed, subject to the terms and conditions contained herein, to modify certain
terms and conditions of the Guaranty as specifically set forth in this First
Amendment;

         NOW, THEREFORE, in consideration of the premises and the mutual
agreements contained herein and for other good and valuable consideration, the
receipt and sufficiency of which are hereby acknowledged, the parties hereto
hereby agree as follows:

         SS.1. AMENDMENT TO SS.4 OF THE GUARANTY. Section 4 of the Guaranty is
hereby amended by deleting the amount "$5,000,000" which appears in the first
sentence of ss.4 and substituting in place thereof the amount "$8,000,000".

         SS.2. CONDITIONS TO EFFECTIVENESS. This First Amendment shall not
become effective until the Lender receives a counterpart of this First
Amendment, executed by the Guarantor and the Lender.

         SS.3. REPRESENTATIONS AND WARRANTIES. The Guarantor hereby repeats, on
and as of the date hereof, each of the representations and warranties made by it
in the Guaranty, and such representations and warranties remain true as of the
date hereof (except to the extent of changes resulting from transactions
contemplated or permitted by the Guaranty and the other documents executed in
connection thereof) and changes occurring in the ordinary course of business
that singly or in the aggregate are not materially adverse, and to the extent
that such representations and warranties relate expressly to an earlier date),
provided, that all references therein to the Guaranty shall refer to the
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Guaranty as amended hereby. In addition, the Guarantor hereby represents and
warrants that the execution and delivery by the Guarantor of this First
Amendment and the performance by the Guarantor of all of its respective
agreements and obligations under the Guaranty as amended hereby are within the
authority of the Guarantor and have been duly authorized by all necessary action
on the part of the Guarantor.

         SS.4. RATIFICATION, ETC. Except as expressly amended hereby, the
Guaranty and all documents, instruments and agreements related thereto are
hereby ratified and confirmed in all respects and shall continue in full force
and effect. The Guaranty and this First Amendment shall be read and construed as
a single agreement. All references in the Guaranty or any related agreement or
instrument to the Guaranty shall hereafter refer to the Guaranty as amended
hereby.

         SS.5. NO WAIVER. Nothing contained herein shall constitute a waiver of,
impair or otherwise affect any Obligations, any other obligation of the
Guarantor or any rights of the Lender consequent thereon.

         SS.6. COUNTERPARTS. This First Amendment may be executed in one or more
counterparts, each of which shall be deemed an original but which together shall
constitute one and the same instrument.

         SS.7. GOVERNING LAW. THIS FIRST AMENDMENT SHALL BE GOVERNED BY, AND
CONSTRUED IN ACCORDANCE WITH, THE LAWS OF THE COMMONWEALTH OF MASSACHUSETTS
(WITHOUT REFERENCE TO CONFLICT OF LAWS).
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         IN WITNESS WHEREOF, the parties hereto have executed this First
Amendment as a document under seal as of the date first above written.


                                       VANTAGEPOINT VENTURE
                                       PARTNERS III(Q), L.P.

                                       By:  VantagePoint Venture Associates III,
                                             LLC, its General Partner



                                       By: /s/ James D. Marver
                                          ---------------------------------
                                       Title:





                                       FLEET NATIONAL BANK


                                       By: /s/ Lee A. Merkle-Raymond
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                                       Title: