Document:

<PAGE>

                                                                   Exhibit 10.10

                           AMENDMENT NO. 3 TO LEASE

     THIS AMENDMENT NO. 3 TO LEASE (the "Third Amendment") is made and entered
into as of the 20/th/ day of January, 2000 between Landlord and Tenant named
               ------        -------------
below.

LANDLORD:           LONG WHARF DRIVE, LLC
                    310 Orange Street
                    New Haven, CT 06511

TENANT:             dsl.net, incorporated
                    545 Long Wharf Drive
                    New Haven, CT 06511

BUILDING:           545 Long Wharf Drive
                    New Haven, CT 06511

     WHEREAS, Landlord and Tenant executed a lease (the "Initial Lease") dated
as of February 5, 1999 (as amended by the amendments more particularly described
below, collectively the "Lease"), by which Tenant leased 12,078 rentable square
feet on the fifth (5/th/) floor of the Building (the "Initial Premises"); and

     WHEREAS, by Amendment No. 1 to Lease dated as of June 9, 1999 (the "First
Amendment"), Tenant leased an additional 19,422 rentable square feet on the
fifth (5/th/) floor of the Building, thereby increasing the size of the entire
Premises to 31,500 rentable square feet; and

     WHEREAS, by Amendment No. 2 to Lease (the "Second Amendment"), Tenant
leased an additional 15,600 rentable square feet of space on the ninth (9/th/)
floor in the Building (the "Ninth Floor Space"), which, upon the commencement
dates thereof, as more particularly described in said Second Amendment, shall
increase the size of the entire Premises to 47,100 rentable square feet; and

     WHEREAS, for the purposes of this Third Amendment, the term "Premises"
shall be equivalent to 31,500 rentable square feet, and shall not include the
Ninth Floor Space; and,

     WHEREAS, pursuant to Section 5C(b) of the Initial Lease and Section 2(d) of
the First Amendment, Landlord shall provide Tenant an Improvement Allowance and
Additional Space Improvement Allowance (collectively, the "Allowance") in an
amount equal to Twelve and 00/100 Dollars ($12.00) per rentable square foot of
the Premises; and

     WHEREAS, Tenant has substantially completed the Construction Work and the
Improvements, as said terms are defined in the Initial Lease and the First
Amendment respectively; and

     WHEREAS, pursuant to Section 5C(b) of the Initial Lease and Section 2(d) of
the First Amendment, Landlord has delivered to Tenant a final accounting of
Tenant's Costs and Tenant's
<PAGE>

Additional Space Costs (collectively, the "Costs"), which accounting states that
said Costs total the sum of Three Hundred Ninety-Three Thousand Eight Hundred
Sixty-One and 79/100 Dollars ($393,861.79), which sum is equal to Twelve and
50/100 Dollars ($12.50) per rentable square foot of the Premises; and

     WHEREAS, the Excess Tenant's Costs and Additional Space Excess Tenant's
Costs, as said terms are defined in Section 5C(d) of the Initial Lease and
Section 2(d) of the First Amendment respectively (collectively, the "Excess
Costs"), are Sixty-Three Thousand and 00/100 Dollars ($63,000.00), which sum is
equal to Two and 00/100 Dollars ($2.00) per rentable square foot of the
Premises, and which, pursuant to said provisions of the Lease, shall be payable
by Tenant through an increase in annual Base Rent; and

     WHEREAS , the remaining balance of the Costs in excess of the Allowance
("Remaining Balance"), is Fifteen Thousand Seven Hundred Fifty and 00/100
Dollars ($15,750.00), which sum is equal to 50/100 Dollars ($.50) per rentable
square foot of the Premises, and which, pursuant to Section 5C(c) of the Initial
Lease and Section 2(e) the First Amendment, is to be payable by Tenant through a
payment to Landlord of Additional Rent, and which payment has been received by
Landlord; and

     WHEREAS, the parties wish to acknowledge the commencement of the Lease; and

     WHEREAS, Landlord and Tenant wish to execute an amendment of the Lease
stating, among other things, the new Base Rent for the Premises, the new
Additional Rent obligation of Tenant, and confirmation of the Lease
commencement.

     NOW, THEREFORE, the parties to this Third Amendment, in consideration of
the covenants hereinafter contained and the sum of One Dollar ($ 1.00) to each
party paid by the other, the receipt of which is hereby acknowledged, do
covenant and agree as follows:

     1.   Unless otherwise stated herein, this Third Amendment is effective on
the day and year written above. Further, all capitalized terms used in this
Third Amendment, but not defined herein, shall have the same meanings ascribed
thereto in the Lease.

     2.   The Excess Costs shall, pursuant to the Lease, be fully amortized on a
straight-line basis over the remaining initial term of the Lease using an annual
interest factor of ten percent (10%) and payable through an increase in annual
Base Rent. Thus, effective January 1, 2000, the annual Base Rent shall be
increased in an amount equal to 49/100 Dollars ($.49) per rentable square foot
and the paragraph entitled "Base Rent" in Paragraph 3 of the Lease shall be
deleted in its entirety and replaced with the following:

          "Base Rent: The Base Rent payable during the initial Term shall be
     Four Hundred Fifty-Six Thousand Four Hundred Thirty-Five and 00/100 Dollars
     ($456,435.00) per annum (based on a per rentable square foot per annum rate
     of $14.49), which shall be payable in advance, in equal monthly
     installments of Thirty-Eight Thousand Thirty-Six and 25/100 Dollars
     ($38,036.25)."
<PAGE>

     3.   Landlord hereby acknowledges that Tenant has paid in full to Landlord
the Remaining Balance of Fifteen Thousand Seven Hundred Fifty and 00/100 Dollars
($15,750.00) pursuant to Section 5C(c) of the Initial Lease and Section 2(e) of
the First Amendment.

     4.   In compliance with their respective obligations regarding the
execution of a Commencement Date agreement, as set forth in subparagraph 2A of
the Lease, the parties represent the following: (i) the Commencement Date, as
defined in subparagraph 2A of the Lease, occurred on May 14, 1999 as to the
Premises described in the Initial Lease; (ii) the Additional Space Commencement
Date, as defined in subparagraph 2(a) of the First Amendment, occurred on August
9, 1999; (iii) as of the date hereof, the Premises consists of 31,500 rentable
square feet and the Tenant's Proportionate Share is 11.80%; (iv) the Base Rent
shall be as defined in Paragraph 3 hereof; (v) the Term of the Lease shall
expire on May 31, 2005.

     5.   The representations made in Paragraph 4 hereof do not include the
Ninth Floor Space, as the commencement dates, the term, the rent and the
increase in the size of the Premises associated with said space are separately
described in the Second Amendment.

     6.   Each party represents to the other that it has not dealt with any
broker, agent or other intermediary who is or may be entitled to be paid a
broker commission or finder's fee in connection with this Third Amendment, and
each party agrees to indemnify the other and hold it harmless from all
liabilities arising from breach of the representations stated above. The
representations and obligations contained in this Paragraph 6 shall survive the
termination of the Lease.

     7.   Except as modified by this Third Amendment, the terms and provisions
of the Lease are hereby confirmed and ratified, and that instrument shall remain
in full force and effect as modified herein.
<PAGE>

     IN WITNESS WHEREOF,  Landlord and Tenant have signed this Amendment No. 3
to Lease as of the day and year first above written.

Signed, Sealed, and Delivered
in the Presence of:                   LANDLORD:

                                      LONG WHARF DRIVE, LLC

____________________________________  By: _______________________________

____________________________________  Its:

                                      TENANT:

                                      dsl.net, incorporated

____________________________________  By: _______________________________

____________________________________  Its Authorized Signatory
<PAGE>

STATE OF CONNECTICUT)
         ===========
                       ) ss.:  New Haven
COUNTY OF NEW HAVEN)
          ---------

     On this the 22nd day of December 1999, before me Theresa C. Meltese, the
                 ----          -------------          ------------------
undersigned officer, personally appeared Alan A. BoLanc who acknowledged himself
                                         --------------
to be the VP Operations of DSL.net, and that she, as such VP Operations and
          -------------
being authorized to do so, executed the foregoing instrument for the purposes
therein contained.

     IN WITNESS WHEREOF, I hereunto set my hand and official seal.

                                    ____________________________________
                                    Theresa C. Maltse
                                    Notary Public
                                    My Commission Expires: 11/30/2003

STATE OF TEXAS)
                       ) ss.:
COUNTY OF BEXAR)

     On this the 3rd day of January, 2000, before me Diana Vaughan, the
                            -------------            -------------
undersigned officer, personally appeared J. Stephen Suandby who acknowledged
                                         ------------------
himself to be the Vice President of SNET Real Estate, and that he, as such Vice
                  --------------    ----------------                       ----
President and being authorized to do so, executed the foregoing instrument for
---------
the purposes therein contained.

     IN WITNESS WHEREOF, I hereunto set my hand and official seal.

                                    ____________________________________
                                    Diana Vaughn
                                    Notary Public
                                    My Commission Expires: 07/17/2007<PAGE>

                                                                   Exhibit 10.22

                     MCI WORLDCOM ON-NET SERVICE AGREEMENT

This On-Net Service Agreement (the "Agreement") for services described below is
made by and between WorldCom Technologies, Inc. ("WTI"), for itself and on
behalf of its U.S.-based affiliates (collectively, "MCI WorldCom") and

Customer Name:  DSL.NET, INC. (hereinafter "Customer")

Address:  50 Washington Street, 7th Floor, Norwalk, Connecticut  06854

--------------------------------------------------------------------------------

Customer agrees to an On-Net Service term plan and Annual Volume Commitment
("AVC") or Monthly Volume Commitment ("MVC") as set forth in Schedule A,
attached hereto and incorporated herein.  Effective upon the next billing cycle
following WTI's execution of this Agreement ("Effective Date"), Customer shall
pay the rates and receive the discounts for On-Net Service associated with the
selected Term and Monthly Volume Commitment (MVC) or Annual Volume Commitment
(AVC) as set forth in WTI Tariff FCC No. 2 (such discounts referred to herein as
the "Base Discounts") with the exceptions shown on Schedule A.  Except as
expressly provided to the contrary, the discounts and/or rates set forth in
Schedule A are in lieu of, and not in addition to, any discounts, promotions
and/or credits (Tariffed or otherwise).  AVC or MVC is calculated net of
discounts.  All charges for other services, if any, will be as set forth in the
Tariffs applicable to those services at the time they are provided to Customer.

SERVICE PROVISIONING AND RECEIPT:  MCI WorldCom will provide to Customer
interstate and international Services pursuant to WTI Tariff FCC No. 1, and all
other applicable tariffs of MCI WorldCom and its U.S.-based affiliates
(collectively, the "Tariff").  This Agreement incorporates by reference the
terms of the Tariff.  MCI WorldCom may modify the Tariff from time to time in
accordance with law and thereby affect the services furnished to Customer.  In
the event of inconsistency between the terms of the Tariff and this Agreement,
the Tariff will be deemed controlling.  The rates set forth in the Tariff do not
include, and the discounts set forth in this Agreement and the Tariff do not
apply to, the following:  charges for MCI WorldCom service other than those set
forth in this Agreement; non-tariffed products, access or egress (or related)
charges imposed by third parties; taxes or tax-like surcharges; and other
tariffed charges.  Customer agrees to pay all these additional charges, to the
extent applicable, in addition to the charges set forth in this Agreement.  If
MCI WorldCom voluntarily or involuntarily as a result of government or judicial
action cancels the Tariff in whole or in part, then effective on such
cancellation this Agreement shall, as to canceled Tariff provisions previously
applicable to this Agreement, incorporate by reference the substantively similar
provisions of MCI WorldCom's standard Guide to Services and Pricing ("Guide"),
as amended by MCI WorldCom from time to time.  For purposes of such provisions,
all references to the Tariff shall include reference to the Guide.

TARIFF OPTION:  MCI WorldCom shall, if required, file a Tariff option (a "Tariff
Option") consistent with the terms of Schedule A, which is incorporated into
this Agreement by this reference.

<PAGE>

SERVICE CONSIDERATIONS:  This Agreement shall be binding upon acceptance by MCI
WorldCom.  Acceptance of this Agreement by MCI WorldCom is subject to Customer
meeting the terms and conditions set forth in the Tariffs and the MCI WorldCom
Commercial Customer Profile Attachment.  The initial Term of this Agreement
shall begin not later than the first day of the first full monthly billing
period following acceptance of this Agreement by MCI WorldCom ("Agreement Start
Date").  Customer shall not disclose the terms of this Agreement to any third
party.

APPLICABLE SERVICES:  This On-Net Service Agreement includes only those services
set forth in this Agreement and its attachments.

INTERNET SERVICES:  Should Customer choose to order Internet Service under and
MCI WorldCom Internet Services Agreement ("Internet Agreement") that provides
that charges for these internet services will contribute towards the AVC or MVC
of this Agreement, then MCI WorldCom shall allow such contribution subsequent to
Customer's execution of the Internet Agreement.  In addition, Customer shall be
eligible to receive a discount on the charges for Internet Services as set forth
in the Internet Agreement.  Internet Service monthly recurring and usage
charges, after the application of discounts, shall contribute to the AVC or MVC
if permitted in the Internet Agreement.

PAGING:  Should Customer choose to order Voice Paging Service under an MCI
WorldCom Paging Agreement ("Paging Agreement"), that provides that charges for
paging services will contribute towards the AVC or MVC of this Agreement, then
MCI WorldCom shall allow such contribution subsequent to Customer's execution of
the Paging Agreement.  In addition, Customer shall be eligible to receive a
discount on the charges for paging services as set forth in the Paging
Agreement.  Voice Paging Service monthly recurring and usage charges, after the
application of discounts, shall contribute to the AVC or MVC if permitted in the
Paging Agreement.

MCI WORLDCOM LOCAL SERVICE:  Where MCI WorldCom has received applicable
regulatory approval and filed the necessary tariff(s), Customer will be eligible
to receive a discount based upon the AVC or MVC and Term indicated in Schedule A
on its eligible monthly charges for MCI WorldCom facilities-based local exchange
service.  Local exchange service is provided by an MCI WorldCom affiliate and is
subject to the terms and conditions of the On-Net Service Term Plan program set
forth in the applicable state tariffs and price lists.

UNDERUTILIZATION AND EARLY TERMINATION CHARGES:  Underutilization Charges:  For
Customers with an AVC as set forth in Schedule A, if at the end of any Annual
Period (as hereinafter defined), Customer's Qualifying Volume (as defined in the
Tariff) during such Annual Period fails to meet or exceed the AVC, Customer
shall pay, in addition to all other charges under this Agreement, the difference
between the AVC and Customer's Qualifying Volume during such Annual Period.  Any
Underutilization Charges will be waived for the first three full billing months
of this Agreement.  For purposes of this Agreement, "Annual Period" means the
consecutive twelve (12) month period commencing on the Agreement Start Date
hereof and each consecutive twelve (12) month period thereafter during the Term
or any renewal

                                       2

<PAGE>

Term hereof. Early Termination Charges: If Customer terminates On-Net Service
prior to the expiration of the Term, Customer will be required to pay, in
addition to all accrued but unpaid charges through the date of such termination,
the difference between Customer's actual Qualifying Volume and the AVC for the
year of termination. For each subsequent year of the Term, Customer shall be
required to pay 50% of the AVC.

For Customers with an MVC as set forth in Schedule A, if at the end of any
Monthly Period (as hereinafter defined), Customer's Qualifying Volume (as
defined in the Tariff) during such Monthly Period fails to meet or exceed the
MVC, Customer shall pay, in addition to all other charges under this Agreement,
the difference between the MVC and Customer's Qualifying Volume during such
Monthly Period.  Any Underutilization Charges will be waived for the first three
full billing months of this Agreement.  For purposes of this Agreement, "Monthly
Period" means the period reflected on each monthly invoice.  Early Termination
Charges:  If Customer terminates On-Net Service prior to the expiration of the
Term, Customer will be required to pay, in addition to all accrued but unpaid
charges through the date of such termination, the difference between Customer's
actual Qualifying Volume and the MVC for the remaining months of the year of
termination.  For each subsequent year of the Term, Customer shall be required
to pay 50% of the MVC for each remaining month in the Term.

CONVERSION FROM EXISTING MCI WORLDCOM TERM AGREEMENTS:  If Customer meets the
conditions stated under "Termination without Liability" in the Tariff,
enrollment in this Agreement will cause an existing MCI or WTI term plan
agreement to terminate automatically without incurring Early Termination
Charges.  Termination and underutilization liability charges may apply if
Customer is ineligible for conversion from existing MCI or WTI term plans
without liability and/or all services are not converted to On-Net Service.

GOVERNING LAW:  This Agreement, and all causes of action arising out of this
Agreement, will be subject to the Communications Act of 1934, as amended (the
"Act"), or, if any part of this Agreement is not governed by the Act, by the
domestic law of the State of New York without regard to its choice of law
principles.

ASSIGNMENT:  Neither this Agreement, nor any rights or obligations of Customer
in this Agreement, shall be transferable or assignable by Customer without MCI
WorldCom's prior written consent and any attempted transfer or assignment hereof
by Customer not in accordance herewith shall be null and void.

                                       3

<PAGE>

                      MCI WORLDCOM ON-NET SERVICE AGREEMENT

                                   Schedule A

A.  Customer agrees to a On-Net Service term plan with a FIVE (5) year
commitment ("Term") and FORTY THOUSAND dollars ($40,000) Monthly Volume
Commitment ("MVC")

Term/Contract Year.  The "Term" will begin on MCI WorldCom's execution of this
------------------
Agreement ("Contract Date") and end (5) years following the Effective Date.

Each consecutive twelve (12) Monthly Periods of the Term commencing on the
Effective Date and on each anniversary thereof will be a "Contract Year".

ADDITIONAL ATTACHMENTS:  This Agreement incorporates the following
Attachment(s):

Attachment A  Frame Relay Integration Addendum

--------------------------------------------------------------------------------

ACCEPTANCE DEADLINE:  This Agreement shall be of no force and effect and the
offer contained herein shall be deemed withdrawn unless this Agreement is
executed by Customer and delivered to MCI WorldCom on or before MARCH 26, 1999.

--------------------------------------------------------------------------------

                                      DATA
                                      ----

The following discounts shall be applied to the Private Line and/or Frame Relay
Service(s) rates set forth herein or in the applicable Tariff.

A.  DISCOUNTS:  The following discounts will be applied to Customer's charges
for service during the Customer Commitment Period:

--------------------------------------------------------------------------------
                                    BROADBAND
--------------------------------------------------------------------------------
                  SERVICE TYPE                       DISCOUNT*
                  ------------                       ---------
--------------------------------------------------------------------------------
                  Frame Relay                           47%
--------------------------------------------------------------------------------
                      ATM                               47%
--------------------------------------------------------------------------------
*Discounts apply to Port and PVC only.  Access is additional and
 non-discountable.
--------------------------------------------------------------------------------

B. WAIVER OF DOMESTIC FRAME RELAY AND ATM INSTALLATION CHARGES: Commencing with
the Commencement Date and continuing through the Commitment Ending Date,
WorldCom agrees to waive WorldCom domestic installation charges and Local
Exchange Carrier installation charges (collectively, "INSTALLATION WAIVERS") in
an amount not to exceed four (4) times the base Monthly Recurring Network Node
and PVC charges for Domestic Frame Relay and ATM Service ordered following the
Commencement Date (the "NEW SERVICE"). In the event that Customer terminates
this Agreement prior to the

                                       4

<PAGE>

Commitment Ending Date, WorldCom may debit Customer's account in the amount of
such Installation Waivers.

C.  WAIVER OF MONTHLY RECURRING CHARGES:  On Customer's thirteenth (13th),
twenty-fifth (25th) and 37th invoices, MCI WorldCom will apply a credit to
Customer's account which shall be equal to the monthly recurring Port and PVC
charges.  In the event that this Agreement terminates prior to the expiration of
the Term, MCI WorldCom may debit Customer's account in the amount of the total
of such credit(s).

ENTIRE AGREEMENT:  This Agreement, including the Tariff and the Attachments
referenced below, is the complete agreement of the parties and supersedes any
prior agreements or representations, whether oral or written, with respect
thereto.  Except for Tariff modifications initiated by MCI WorldCom, no
amendment to this Agreement will be valid unless each such change is accepted in
writing by an authorized representative of both parties.

Any capitalized terms not expressly defined in an Attachment to this Agreement
shall have the meaning given to such term in this Agreement.

IN WITNESS WHEREOF, the parties have accepted and signed this Agreement and the
individuals signing below warrant and represent that they have the full legal
and regulatory authority to enter into this Agreement for and on behalf of the
respective parties.

MCI WORLDCOM TECHNOLOGIES, INC.  DSL.NET, INC.

By:                                    By: /s/ Alan A. Bolduc
   ------------------------------         -----------------------------
   (Authorized Representative)            (Authorized Representative)

    Frank Grillo, V.P. Marketing
   ------------------------------         -----------------------------
   (Title)                                (Print Name)

   ------------------------------         -----------------------------
   (Date)                                 (Date)

                                       5

<PAGE>

                                  ATTACHMENT A
                        FRAME RELAY INTEGRATION ADDENDUM

By enrolling in MCI WorldCom Domestic Frame Relay under this On-Net Service
Agreement, Customer's local access channel charges for T-1, DPLS, or DSO access,
domestic monthly recurring port charges, and domestic monthly recurring
permanent virtual circuit ("PVC") charges, after the application of discounts,
will contribute toward the AVC or MVC under this On-Net Service Agreement.  In
addition, local access channel and monthly recurring charges for domestic port
and PVC will receive the discount associated with the term and AVC and MVC of
this On-Net Service Agreement as set forth in Schedule A.  Customer will be
subject to the term length and early termination and under-utilization penalties
in this On-Net Service Agreement.

For Frame Relay, Metro Frame Relay and International Frame Relay, Customer will
pay the standard rates and discounts as set forth in the Tariff, including but
not limited to access charges, standard Tariffed non-recurring charges,
including but not limited to, installation charges and reconfiguration charges,
monthly recurring port and permanent virtual circuit ("PVC") charges as may be
modified in Schedule A.  For High Speed Frame, Customer will pay list rates,
which will be set forth in a High Speed Frame Relay Attachment to this Agreement
if Customer selects such service.  Discounts for High Speed Frame Relay shall be
as set forth in Schedule A.

The rates set forth in the Tariff do not include, and the discounts set forth in
the Tariff do not apply to, the following: charges for Frame Relay Service
Services other than those set forth herein; non-tariffed products; access or
egress (or related) charges imposed by third parties; taxes or tax-like
surcharges; and other tariffed charges, including without limitation, Universal
Service Fund charges, and Primary Interexchange Carrier Charges, which are
additional.

Customer may also enroll in Metro Frame Relay and/or International Frame Relay
under this Agreement.  Such service will be subject to the term and volume
commitment agreed to by Customer under this On-Net Service Agreement, but
associated discounts will be those set forth for Metro and International Frame
Relay in the Tariff as may be modified in Schedule A.

CUSTOMER SHOULD NOT ENROLL FOR FRAME RELAY SERVICE UNDER THIS AGREEMENT IF
CUSTOMER HAS ENROLLED UNDER A MCI WORLDCOM STANDALONE FRAME RELAY AGREEMENT.

Any capitalized terms not expressly defined in this Attachment shall have the
meaning given to such term in the On-Net Service Agreement.

                                       6

<PAGE>

                               FIRST AMENDMENT
                            TO THE ON-NET AGREEMENT
                                    BETWEEN
                          WORLDCOM TECHNOLOGIES, INC.
                               AND DSL.NET, INC.

This First Amendment is made by and between DSL.net, Inc. ("Customer") and MCI
WORLDCOM Communications, Inc. (formerly Worldcom Technologies, Inc.) and its
appropriate affiliated companies, assigns, and successors (collectively, "MCI
Worldcom") as of Customer's execution and delivery of this First Amendment to
MCI Worldcom (the "First Amendment Contract Date").  Provided that this First
Amendment is subsequently accepted by MCI Worldcom, the rates, discounts,
charges, credits and/or other terms set forth herein shall be effective one (1)
month following the First Amendment Contract Date (the "First Amendment
Effective Date").  All capitalized terms used in this First Amendment and not
defined herein will have the meaning ascribed to them in the WTI Tariff FCC No.
1 and all other applicable tariffs of MCI Worldcom and its U.S.-based affiliates
(collectively, "Tariff").

WHEREAS, Customer and MCI Worldcom entered into a MCI Worldcom On-Net Service
Agreement signed by Customer on or about February 2, 1999 (the "On-Net
Agreement"); and

WHEREAS, Customer and MCI Worldcom desire to enter into this First Amendment for
the purpose amending the On-Net Agreement.

NOW, THEREFORE, in consideration of the mutual promises contained herein, the
parties, intending to be legally bound hereby, agree that the On-Net Agreement
is amended as follows:

1.   In the paragraph titled "UNDERUTILIZATION AND EARLY TERMINATION CHARGES" to
     the On-Net Agreement, the following is added thereto.

     "As of the Effective Date of the Option 1 MCI Worldcom Asynchronous
     Transfer Mode Service Enrollment Form and Agreement ("ATM Agreement")
     signed by Customer on or about October 28, 1999, the Underutilization and
     Early Termination charges only pursuant to the On-Net Agreement for Frame
     Realty Service shall be waived and superceded by the applicable
     Underutilization or Termination Provisions as set forth in Sections 6 and
     13 of the ATM Agreement.  The foregoing shall not affect any other Customer
     obligations pursuant to the ATM Agreement or the On-Net Agreement.
     Customer shall remain liable for any accrued Underutilization and Early
     Termination charges pursuant to the On-Net Agreement prior to the Effective
     Date of the ATM Agreement.

2.   In Section A to Schedule A to the On-Net Agreement, the subsection titled
     "Term/Contract Year" is deleted and replaced with a new subsection
      ------------------
     "Term/Contract Year" as follows:
      ------------------

                                       7

<PAGE>

     "Term, Contract Year.  The term of the Agreement will begin upon MCI
      --------------------
     Worldcom's execution of this Agreement ("Contract Date") and the end (60)
     months from the First Amendment Effective Date."

3.   All references in the On-Net Agreement to "ATM" or "ATM Service" are hereby
     deleted.

4.   In Section A of Schedule A to the On-Net Agreement, the subsection titled
     "Discounts" shall be deleted and replaced with the following:
      ---------

                                         BROADBAND
     Service Type                              Discount*
     ------------                              ---------
     Domestic Frame Relay                      60%
                                               ---

     *Discounts apply to Port and PVC only. Access is additional and non-
     discountable.

5.   In Attachment A, Frame Relay Integration Addendum, to the On-Net Agreement
                      --------------------------------
     the following is added to the first paragraph, first sentence after "will
     contribute toward the AVC or MVC under this On-Net Service Agreement":

"and will contribute toward the Annual Minimum under the ATM Agreement signed by
Customer on or about October 28, 1999."

6.   Modification.  No charges to this First Amendment shall be effective or
     valid unless in writing and signed by both parties.

7.   Section References. Section titles and references used in this First
     Amendment shall be without substantive meaning or content of any kind
     whatsoever and are not a part of the agreements among the parties hereto
     evidenced hereby.

8.  Entire Agreement. This First Amendment, and the On-Net Agreement constitute
    the complete and entire understanding of the parties relative to their
    subject matter and supersede all previous communications, proposals,
    representations, or agreements, whether written or oral, between MCI
    Worldcom and Customer in this regard. Except as expressly modified above,
    all other terms and conditions of the On-Net Agreement (which are
    incorporated by this reference) shall remain in full force and effect. In
    the event of a conflict between the terms of this First Amendment and the
    Agreement, the terms of this First Amendment shall govern.

9.  Acceptance. This First Amendment shall be of no force and effect and the
    offer contained herein shall be deemed withdrawn unless this First Amendment
    and the ATM Agreement is executed by Customer and delivered to MCI Worldcom
    on or before October 30, 1999.

                                       8

<PAGE>

IN WITNESS WHEREOF, MCI Worldcom and Customer have caused this First Amendment
to be duly executed by their authorized representatives as of the dates set
forth below.

DSL.net, Inc.                             MCI WORLDCOM Communications, Inc.

By:________________________________       By:_________________________________
                                             Frank Grillo
Name:______________________________          Vice President, Marketing

Title:_______________________________     Date:________________________________

Date:_______________________________

                                       9

Source: [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00001-of-00352.parquet"}, [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00001-of-00352.parquet"}]]