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                                                                  EXHIBIT 10.04

                            MASTER LEASE AGREEMENT

     MASTER LEASE AGREEMENT (the "Master Lease") dated March 4, 1999 by and
between COMDISCO, INC. ("Lessor") and dsl.net, inc. ("Lessee").

     IN CONSIDERATION of the mutual agreements described  below, the parties
agree as follows (all capitalized terms are defined in Section 14.18):

1.     Property Leased.

Lessor leases to Lessee all of the Equipment described on each Summary Equipment
Schedule.  In the event of a conflict, the terms of the applicable Schedule
prevail over this Master Lease.

2.     Term.

On the Commencement Date, Lessee will be deemed to accept the Equipment, will be
bound to its rental obligations for each item of Equipment and the term of a
Summary Equipment Schedule will begin and continue through the Initial Term and
thereafter until terminated by either party upon prior written notice received
during the Notice Period.  No termination may be effective prior to the
expiration of the Initial Term.

3.     Rent and Payment.

Rent is due and payable in advance on the first day of each Rent Interval at the
address specified in Lessor's invoice.  Interim Rent is due and payable when
invoiced.  If any payment is not made when due, Lessee will pay a Late Charge on
the overdue amount.  Upon Lessee's execution of each Schedule, Lessee will pay
Lessor the Advance specified on the Schedule.  The Advance will be credited
towards the final Rent payment if Lessee is not then in default.  No interest
will be paid on the Advance.

4.     Selection; Warranty and Disclaimer of Warranties.

4.1    Selection.  Lessee acknowledges that it has selected the Equipment and
disclaims any reliance upon statements made by the Lessor, other than as set
forth in the Schedule.

4.2    Warranty and Disclaimer of Warranties. Lessor warrants to Lessee that, so
long as Lessee is not in default, Lessor will not disturb Lessee's quiet and
peaceful possession, and unrestricted use of the Equipment. To the extent
permitted by the manufacturer, Lessor assigns to Lessee during the term of the
Summary Equipment Schedule any manufacturer's warranties for the Equipment.
LESSOR MAKES NO OTHER WARRANTY, EXPRESS OR IMPLIED AS TO ANY MATTER WHATSOEVER,
INCLUDING, WITHOUT LIMITATION, THE MERCHANTABILITY OF THE EQUIPMENT OR ITS
FITNESS FOR A PARTICULAR PURPOSE. Lessor is not responsible for any liability,
claim, loss, damage or expense of any kind (including strict liability in tort)
caused by the Equipment except for any loss or damage caused by the willful
misconduct or negligent acts of Lessor. In no event is Lessor responsible for
special, incidental or consequential damages.
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5.     Title; Relocation or Sublease; and Assignment.

5.1    Title. Lessee holds the Equipment subject and subordinate to the rights
of the Owner, Lessor, any Assignee and ant Secured Party. Lessee authorizes
Lessor, as Lessee's agent, and at Lessor's expense, to prepare, execute and file
in Lessee's name precautionary Uniform Commercial Code financing statements
showing the interest of the Owner, Lessor, and any Assignee or Secured Party in
the Equipment and to insert serial numbers in Summary Equipment Schedules as
appropriate. Lessee will, at its expense, keep the Equipment free and clear from
any liens or encumbrances of any kind (except any caused by Lessor) and will
indemnify and hold the Owner, Lessor, any Assignee and Secured Party harmless
from and against any loss caused by Lessee's failure to do so, except where such
is caused by Lessor.

5.2    Relocation or Sublease.  Upon prior written notice, Lessee may relocate
Equipment to any location within the continental United States provided (i) the
Equipment will not be used by an entity exempt from federal income tax, and (ii)
all additional costs (including any administrative fees, additional taxes and
insurance coverage) are reconciled and promptly paid by Lessee.

Lessee may sublease the Equipment upon the reasonable consent of the Lessor and
the Secured Party.  Such consent to sublease will be granted if: (i) Lessee
meets the relocation requirements set out above, (ii) the sublease is expressly
subject and subordinate to the terms of the Schedule, (iii) Lessee assigns its
rights in the sublease to Lessor and the Secured Party as additional collateral
and security, (iv) Lessee's obligation to maintain and insure the Equipment is
not altered, (v) all financing statements required to continue the Secured
Party's prior perfected security interest are filed, and (vi) Lessee executes
sublease documents acceptable to Lessor.

No relocation or sublease will relieve Lessee from any of its obligations under
this Master Lease and the relevant Schedule.

5.3    Assignment by Lessor.  The terms and conditions of each Schedule have
been fixed by Lessor in order to permit Lessor to sell and/or assign or transfer
its interest or grant a security in each Schedule and/or the Equipment to a
Secured Party or Assignee. In that event, the term Lessor will mean the Assignee
and any Secured Party. However, any assignment, sale, or other transfer by
Lessor will not relieve Lessor of its obligations to Lessee and will not
materially change Lessee's duties or materially increase the burdens or risks
imposed on Lessee. The Lessee consents to and will acknowledge such assignments
in a written notice given to Lessee. Lessee also agrees that:

       (a)  The Secured Party will be entitled to exercise all of Lessor's
       rights, but will not be obligated to perform any of the obligations of
       Lessor. The Secured Party will not disturb Lessee's quiet and peaceful
       possession and unrestricted use of the Equipment so long as Lessee is not
       in default and the Secured Party continues to receive all Rent payable
       under the Schedule; and

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       (b)  Lessee will pay all Rent and all other amounts payable to the
       Secured Party, despite any defense or claim which it has against Lessor.
       Lessee reserves its right to have recourse directly against Lessor for
       any defense or claim;

       (c)  Subject to and without impairment of Lessee's leasehold rights in
       the Equipment, Lessee holds the Equipment for the Secured Party to the
       extent of the Secured Party's rights in that Equipment.

6.     Net Lease, Taxes and Fees.

6.1    Net Lease.  Each Summary Equipment Schedule constitutes a net lease.
Lessee's obligation to pay Rent and all other amounts due hereunder is absolute
and unconditional and is not subject to any abatement, reduction, set-off,
defense, counterclaim, interruption, deferment or recoupment for any reason
whatsoever.

6.2    Taxes and Fees.  Lessee will pay when due or reimburse Lessor for all
taxes, fees or any other charges (together with any related interest or
penalties not arising from the negligence of Lessor) accrued for or arising
during the term of each Summary Equipment Schedule against Lessor, Lessee or the
Equipment by any governmental authority (except only Federal, state, local and
franchise taxes on the capital or the net income of Lessor). Lessor will file
all personal property tax returns for the Equipment and pay all such property
taxes due. Lessee will reimburse Lessor for property taxes within thirty (30)
days of receipt of an invoice.

7.     Care, Use and Maintenance; Inspection by Lessor.

7.1    Care, Use and Maintenance.  Lessee will maintain the Equipment in good
operating order and appearance, protect the Equipment from deterioration, other
than normal wear and tear, and will not use the Equipment for any purpose other
than that for which it was designed.  If commercially available and considered
common business practice for each item of Equipment, Lessee will maintain in
force a standard maintenance contract with the manufacturer of the Equipment, or
another party acceptable to Lessor, and will provide Lessor with a complete copy
of that contract.  If Lessee has the Equipment maintained by a  party other than
the manufacturer or self maintains, Lessee agrees to pay any costs necessary for
the manufacturer to bring the Equipment to then current release, revision and
engineering change levels, and to re-certify the Equipment as eligible for
manufacturer's maintenance at the expiration of the lease term, provided re-
certification is available and is required by Lessor.  The lease term will
continue upon the same terms and conditions until recertification has been
obtained.

7.2    Inspection by Lessor.  Upon reasonable advance notice, Lessee, during
reasonable business hours and subject to Lessee's security requirements, will
make the Equipment and its related log and maintenance records available to
Lessor for inspection.

8.     Representations and Warranties of Lessee. Lessee hereby represents,
warrants and covenants that with respect to the Master Lease and each Schedule
executed hereunder:

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       (a)  The Lessee is a corporation duly organized and validly existing in
       good standing under the laws of the jurisdiction of its incorporation, is
       duly qualified to do business in each jurisdiction (including the
       jurisdiction where the Equipment is, or is to be, located ) where its
       ownership or lease of property or the conduct of its business requires
       such qualification, except for where such lack of qualification would not
       have a material adverse effect on the Company's business; and has full
       corporate power and authority to hold property under the Master Lease and
       each Schedule and to enter into and perform its obligations under the
       Master Lease and each Schedule.

       (b)  The execution and delivery by the Lessee of the Master Lease and
       each Schedule and its performance thereunder have been duly authorized by
       all necessary corporate action on the part of the Lessee, and the Master
       Lease and each Schedule are not inconsistent with the Lessee's Articles
       of Incorporation or Bylaws, do not contravene any law or governmental
       rule, regulation or order applicable to it, do not and will not
       contravene any provision of, or constitute a default under, any
       indenture, mortgage, contract or other instrument to which it is a party
       or by which it is bound, and the Master Lease and each Schedule
       constitute legal, valid and binding agreements of the Lessee, enforceable
       in accordance with their terms, subject to the effect of applicable
       bankruptcy and other similar laws affecting the rights of creditors
       generally and rules of law concerning equitable remedies.

       (c)  There are no actions, suits, proceedings or patent claims pending
       or, to the knowledge of the Lessee, threatened against or affecting the
       Lessee in any court or before any governmental commission, board or
       authority which, if adversely determined, will have a material adverse
       effect on the ability of the Lessee to perform its obligations under the
       Master Lease and each Schedule.

       (d)  The Equipment is personal property and when subjected to use by the
       Lessee will not be or become fixtures under applicable law.

       (e)  The Lessee has no material liabilities or obligations, absolute or
       contingent (individually or in the aggregate), except the liabilities and
       obligations of the Lessee as set forth in the Financial Statements and
       liabilities and obligations which have occurred in the ordinary course of
       business, and which have not been, in any case or in the aggregate,
       materially adverse to Lessee's ongoing business.

       (f)  To the best of the Lessee's knowledge, the Lessee owns, possesses,
       has access to, or can become licensed on reasonable terms under all
       patents, patent applications, trademarks, trade names, inventions,
       franchises, licenses, permits, computer software and copyrights necessary
       for the operations of its business as now conducted, with no known
       infringement of, or conflict with , the rights of others.

       (g)  All material contracts, agreements and instruments to which the
       Lessee is a party are in full force and effect in all material respects,
       and are

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       valid, binding and enforceable by the Lessee in accordance with their
       respective terms, subject to the effect of applicable bankruptcy and
       other similar laws affecting the rights of creditors generally, and rules
       of law concerning equitable remedies.

9.     Delivery and Return of Equipment.

Lessee hereby assumes the full expense of transportation and in-transit
insurance to Lessee's premises and installation thereat of the Equipment.  Upon
termination (by expiration or otherwise) of each Summary Equipment Schedule,
Lessee shall, pursuant to Lessor's instructions and at Lessee's full expense
(including, without limitation, expenses of transportation and in-transit
insurance), return the Equipment to Lessor in the same operating order, repair,
condition and appearance as when received, less normal depreciation and wear and
tear.  Lessee shall return the Equipment to Lessor at 6111 North River Road,
Rosemont, Illinois 60018 or at such other address within the continental United
States as directed by Lessor, provided, however, that Lessee's expense shall be
limited to the cost of returning the Equipment to Lessor's address as set forth
herein.  During the period subsequent to receipt of a notice under Section 2,
Lessor may demonstrate the Equipment's operation in place and Lessee will supply
any of its personnel as may reasonably be required to assist in the
demonstrations.

10.    Labeling.

Upon request, Lessee will mark the Equipment indicating Lessor's interest with
labels provided by Lessor.  Lessor will keep all Equipment free from any other
marking or labeling which might be interpreted as a claim of ownership.

11.    Indemnity.

With regard to bodily injury and property damage liability only, Lessee will
indemnify and hold Lessor, any Assignee and any Secured Party harmless from and
against any and all claims, costs, expenses, damages and liabilities, including
reasonable attorneys' fees, arising out of the ownership (for strict liability
in tort only), selection, possession, leasing, operation, control, use,
maintenance, delivery, return or other disposition of the Equipment during the
term of the Master Lease or until Lessee's obligations under the Master Lease
terminate.  However, Lessee is not responsible to a party indemnified hereunder
for any claims, costs, expenses, damages and liabilities occasioned by the
negligent acts of such indemnified party.  Lessee agrees to carry bodily injury
and property damage liability insurance during the term of the Master Lease in
amounts and against risks customarily insured against by the Lessee on equipment
owned by it.  Any amounts received by Lessor under that insurance will be
credited against Lessee's obligations under this Section.

12.    Risk of Loss.

Effective upon delivery and until the Equipment is returned, Lessee relieves
Lessor of responsibility for all risks of physical damage to or loss or
destruction of the Equipment.  Lessee will carry casualty insurance for each
item of Equipment in an amount not less than the Casualty Value.  All policies
for such insurance will name the Lessor and any

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Secured Party as additional insured and as loss payee, and will provide for at
least thirty (30) days prior written notice to the Lessor of cancellation or
expiration, and will insure Lessor's interests regardless of any breach or
violation by Lessee of any representation, warranty or condition contained in
such policies and will be primary without right of contribution from any
insurance effected by Lessor. Upon the execution of any Schedule, the Lessee
will furnish appropriate evidence of such insurance acceptable to Lessor.

Lessee will promptly repair any damaged item of Equipment unless such Equipment
has suffered a Casualty Loss.  Within fifteen (15) days of a Casualty Loss,
Lessee will provide written notice of that loss to Lessor and Lessee will, at
Lessee's option, either (a) replace the item of Equipment with Like Equipment
and marketable title to the Like Equipment will automatically vest in Lessor or
(b) pay the Casualty Value and after that payment and the payment of all other
amounts due and owing with respect to that item of Equipment, Lessee's
obligation to pay further Rent for the item of Equipment will cease.

13.    Default, Remedies and Mitigation.

13.1   Default.  The occurrence of any one or more of the following Events of
Default constitutes a default under a Summary Equipment Schedule:

       (a)  Lessee's failure to pay Rent or other amounts payable by Lessee when
       due if that failure continues for five (5) business days after written
       notice; or

       (b)  Lessee's failure to perform any other term or condition of the
       Schedule or the material inaccuracy of any representation or warranty
       made by the Lessee in the Schedule or in any document or certificate
       furnished to the Lessor hereunder if that failure or inaccuracy continues
       for ten (10) business days after written notice; or

       (c)  An assignment by Lessee for the benefit of its creditors, the
       failure by Lessee to pay its debts when due, the insolvency of Lessee,
       the filing by Lessee or the filing against Lessee of any petition under
       any bankruptcy or insolvency law or for the appointment of a trustee or
       other officer with similar powers, the adjudication of Lessee as
       insolvent, the liquidation of Lessee, or the taking of any action for the
       purpose of the foregoing; or

       (d)  The occurrence of an Event of Default under any Schedule, Summary
       Equipment Schedule or other agreement between Lessee and Lessor or its
       Assignee or Secured Party.

13.2   Remedies.  Upon the occurrence of any of the above Events of Default,
Lessor at its option, may:

       (a)  enforce Lessee's performance of the provisions of the applicable
       Schedule by appropriate court action in law or in equity;

       (b)  recover from Lessee any damages and or expenses, including Default
       Costs;

       (c)  with notice and demand, recover all sums due and accelerate and
       recover the present value of the remaining payment stream of all Rent due
       under the defaulted Schedule (discounted at the same rate of interest at
       which such

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       defaulted Schedule was discounted with a Secured Party plus any
       prepayment fees charged to Lessor by the Secured Party or, if there is no
       Secured Party, then discounted at 6%) together with all Rent and other
       amounts currently due as liquidated damages and not as a penalty;

       (d)  with notice and process of law and in compliance with Lessee's
       security requirements, Lessor may enter on Lessee's premises to remove
       and repossess the Equipment without being liable to Lessee for damages
       due to the repossession, except those resulting from Lessor's, its
       assignees', agents' or representatives' negligence; and

       (e)  pursue any other remedy permitted by law or equity.

The above remedies, in Lessor's discretion and to the extent permitted by law,
are cumulative and may be exercised successively or concurrently.

13.3   Mitigation. Upon return of the Equipment pursuant to the terms of Section
13.2, Lessor will use its best efforts in accordance with its normal business
procedures (and with out obligation to give any priority to such Equipment) to
mitigate Lessor's damages as described below. EXCEPT AS SET FORTH IN THIS
SECTION, LESSEE HEREBY WAIVES ANY RIGHTS NOW OR HEREAFTER CONFERRED BY STATUTE
OR OTHERWISE WHICH MAY REQUIRE LESSOR TO MITIGATE ITS DAMAGES OR MODIFY ANY OF
LESSOR'S RIGHTS OR REMEDIES STATED HEREIN. Lessor may sell, lease or otherwise
dispose of all or any part of the Equipment at a public or private sale for case
or credit with the privilege of purchasing the Equipment. The proceeds from any
sale, lease or other disposition of the Equipment are defined as either:

       (a)  if sold or otherwise disposed of, the cash proceeds less the Fair
       Market Value of the Equipment at the expiration of the Initial Term less
       the Default Costs; or

       (b)  if leased, the present value (discounted at three percent (3%) over
       the U.S. Treasury Notes of comparable maturity to the term of there
       lease) of the rentals for a term not to exceed the Initial Term, less the
       Default Costs.

Any proceeds will be applied against liquidated damages and any other sums due
to Lessor from Lessee. However, Lessee is liable to Lessor for, and Lessor may
recover, the amount by which the proceeds are less than the liquidated damages
and other sums due to Lessor from Lessee.

14.    Additional Provisions

14.1   Board Attendance. Upon invitation of Lessee, one representative of Lessor
will have the right to attend Lessee's corporate Board of Directors meetings and
Lessee will give Lessor reasonable notice in advance of any special Board of
Directors meeting, which notice will provide an agenda of the subject matter to
be discussed at such board meeting. Lessee will provide Lessor with a certified
copy of the minutes of each Board of Director's meeting within thirty (30) days
following the date of such meeting held during the term of this Master Lease.

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14.2   Financial Statements. As soon as practicable at the end of each month
(and in any event within thirty (30) days), Lessee will provide to Lessor the
same information which Lessee provides to its Board of Directors, but which will
include not less than a monthly income statement, balance sheet and statement of
cash flows prepared in accordance with generally accepted accounting principles,
consistently applied (the "Financial Statements"). As soon as practicable at the
end of each fiscal year, Lessee will provide to Lessor audited Financial
Statements setting forth in comparative form the corresponding figures for the
fiscal year (and in any event within ninety (90) days), and accompanied by an
audit report and opinion of the independent certified public accountants
selected by Lessee. Lessee will promptly furnish to Lessor any additional
information (including, but not limited to, tax returns, income statements,
balance sheets and names of principal creditors) as Lessor reasonably believes
necessary to evaluate Lessee's continuing ability to meet financial obligations.
After the effective date of the initial registration statement covering a public
offering of Lessee's securities, the term "Financial Statements" will be deemed
to refer to only those statements required by the Securities and Exchange
Commission.

14.3   Obligation to Lease Additional Equipment.  Upon notice to Lessee, Lessor
will not be obligated to lease any Equipment which would have a Commencement
Date after said notice if: (I) Lessee is in default under this Master Lease or
any Schedule; (ii) Lessee is in default under any loan agreement, the result of
which would allow the lender or any secured party to demand immediate payment of
any material indebtedness; (iii) there is a material adverse change in Lessee's
credit standing; or (iv) Lessor determines (in reasonable good faith) that
Lessee will be unable to perform its obligations under this Master Lease or any
Schedule.

14.4   Merger and Sale Provisions.  Lessee will notify Lessor of any proposed
Merger at least sixty (60) days prior to the closing date. Lessor may, in its
discretion, either (i) consent to the assignment of the Master Lease and all
relevant Schedules to the successor entity, or (ii) terminate the Master Lease
and all relevant Schedules. If Lessor elects to consent to the assignment,
Lessee and its successor will sign the assignment documentation provided by
Lessor. If Lessor elects to terminate the Master Lease and all relevant
Schedules, the Lessee will pay Lessor all amounts then due and owing and a
termination fee equal to the present value (discounted at 6%) of the remaining
Rent for the balance of the initial Term(s) of all Schedules, and will return
the Equipment in accordance with Section 9. Lessor hereby consents to any Merger
in which the acquiring entity has a Moody's Bond Rating of BA3 or better or a
commercially acceptable equivalent measure of creditworthiness as reasonably
determined by Lessor.

14.5   Entire Agreement. This Master Lease and associated Schedules and Summary
Equipment Schedules supersede all other oral or written agreements or
understandings between the parties concerning the Equipment including, for
example, purchase orders. ANY AMENDMENT OF THIS MASTER LEASE OR A SCHEDULE,

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MAY ONLY BE ACCOMPLISHED BY A WRITING SIGNED BY THE PARTY AGAINST WHOM THE
AMENDMENT IS SOUGHT TO BE ENFORCED.

14.6   No Waiver.  No action taken by Lessor or Lessee will be deemed to
constitute a waiver of compliance with any representation, warranty or covenant
contained in this Master Lease or a Schedule. The waiver by Lessor or Lessee of
a breach of any provision of this Master Lease or a Schedule will not operate or
be construed as a waiver of any subsequent breach.

14.7   Binding Nature. Each Schedule is binding upon, and inures to the benefit
of Lessor and its assigns. LESSEE MAY NOT ASSIGN ITS RIGHTS OR OBLIGATIONS.

14.8   Survival of Obligations. All agreements, obligations including, but not
limited to those arising under Section 6.2, representations and warranties
contained in this Master Lease, any Schedule, Summary Equipment Schedule or in
any document delivered in connection with those agreements and for the benefit
of Lessor and any Assignee or Secured Party and survive the execution, delivery,
expiration or termination of this Master Lease.

14.9   Notices. Any notice, request or other communication to either party by
the other will be given in writing and deemed received upon the earlier of (1)
actual receipt or (3) three day after mailing if mailed postage prepaid by
regular or airmail to Lessor (to the attention of "the Comdisco Venture Group")
or Lessee, at the address set out in the Schedule, (3) one day after it is sent
by courier or (4) on the same day that is sent via facsimile transmission,
provided that the original is sent by personal delivery or mail by the sending
party.

14.10  Applicable Law.  THIS MASTER LEASE HAS BEEN, AND EACH SCHEDULE WILL HAVE
BEEN MADE, EXECUTED AND DELIVERED IN THE STATE OF ILLINOIS AND WILL BE GOVERNED
AND CONSTRUED FOR ALL PURPOSES IN ACCORDANCE WITH THE LAWS OF THE STATE OF
ILLINOIS WITHOUT GIVING EFFECT TO CONFLICT OF LAW PROVISIONS. NO RIGHTS OR
REMEDIES REFERRED TO  IN ARTICLE 2A OF THE UNIFORM COMMERCIAL CODE WILL BE
CONFERRED ON LESSEE UNLESS EXPRESSLY GRANTED IN THIS MASTER LEASE OR A SCHEDULE.

14.11  Severability.  If any one or more of the provisions of this Master Lease
or any Schedule is for any reason held invalid, illegal or unenforceable, the
remaining provisions of this Master Lease and any such Schedule will be
unimpaired, and the invalid, illegal or unenforceable provision replaced by a
mutually acceptable valid, legal and enforceable provision that is closest to
the original intention of the parties.

14.12  Counterparts  This Master Lease and any Schedule may be executed in any
number of counterparts, each of which will be deemed an original, but all such
counterparts together constitute one and the same instrument. If Lessor grants a
security interest in all or any part of a Schedule, the Equipment or sums
payable thereunder, only that

                                      -9-
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counterpart Schedule marked "Secured Party's Original" can transfer Lessor's
rights and all other counterparts will be marked "Duplicate".

14.13  Licensed Products. Lessee will obtain no title to Licensed Products which
will at all times remain the property of the owner of the Licensed Products. A
license from the owner may be required and it is Lessee's responsibility to
obtain any required license before the use of the Licensed Products. Lessee
agrees to treat the Licensed Products as confidential information of the owner,
to observe all copyright restrictions, and not to reproduce or sell the Licensed
Products.

14.14  Secretary's Certificate.  Lessee will, upon execution of this Master
Lease, provide Lessor with a secretary's certificate on incumbency and
authority. Upon the execution of each Schedule with a purchase price in excess
of $1,000,000, Lessee will provide Lessor with an opinion from Lessee's counsel
in a form acceptable to Lessor regarding the representations and warranties in
Section 8.

14.15  Electronic Communications.  Each of the parties may communicate with the
other by electronic means under mutually agreeable terms.

14.16  Landlord/Mortgagee Waiver.  Lessee agrees to provide Lessor with a
Landlord/Mortgagee Waiver with respect to the Equipment. Such waiver shall be in
a form satisfactory to Lessor.

14.17  Equipment Procurement Charges/Progress Payments.  Lessee hereby agrees
that Lessor shall not, by virtue of its entering into this Master Lease, be
required to remit any payments to any manufacturer or other third party until
Lessee accepts the Equipment subject to this Master Lease.

14.18  Definitions.

Advance--means the amount due to Lessor by Lessee upon Lessee's execution of
-------
each Schedule.

Assignee--means an entity to whom Lessor has sold or assigned its rights as
--------
owner and Lessor of Equipment.

Casualty Loss--means the irreparable loss or destruction of Equipment.
-------------

Casualty Value--means the greater of the aggregate Rent remaining to be paid for
--------------
the balance of the lease term or the Fair Market Value of the Equipment
immediately prior to the Casualty Loss. However, if a Casualty Value Table is
attached to the relevant Schedule its terms will control.

Commencement Date--is defined in each Schedule.
-----------------

Default Costs--means reasonable attorney's fees and remarketing costs resulting
-------------
from a Lessee default or Lessor's enforcement of its remedies.

Delivery Date--means date of delivery of Inventory Equipment to Lessee's
-------------
address.

Equipment--means the property described on a Summary Equipment Schedule and any
---------
replacement for that property required or permitted by this Master Lease or a
Schedule.

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Event of Default--means the events described in Subsection 13.1.
----------------

Fair Market Value--means the aggregate amount which would be obtainable in an
-----------------
arm's length transaction between an informed and willing buyer/user and an
informed and willing seller under no compulsion to sell.

Initial Term--means the period of time beginning on the first day of the first
------------
full Rent Interval following the Commencement Date for all items of Equipment
and continuing for the number of Rent Intervals indicated on a Schedule.

Interim Rent--means the pro-rata portion of Rent due for the period from the
------------
Commencement Date through but not including the first day of the first full rent
Interval included in the Initial Term.

Late Charge--means the lesser of five percent (5%) of the payment due or the
-----------
maximum amount permitted by the law of the state where the Equipment is located.

Licensed Products--means any software or other licensed products attached to the
-----------------
Equipment.

Like Equipment--means replacement Equipment which is lien free and of the same
--------------
model, type, configuration and manufacture as Equipment.

Merger--means any consolidation or merger of the Lessee with or into any other
------
corporation or entity, any sale or conveyance of all or substantially all of the
assets or stock of the Lessee by or to any other person or entity in which
Lessee is not the surviving entity.

Notice Period--means not less than ninety (90) days nor more than twelve (12)
-------------
months prior to the expiration of the lease term.

Owner--means the owner of Equipment.
-----

Rent--means the rent Lessee will pay for each item of Equipment expressed in a
----
Summary Equipment Schedule either as a specific amount or an amount equal to the
amount which lessor pays for an item of equipment multiplied by a lease rate
factor plus all other amounts due to Lessor under this Master Lease or a
Schedule.

Rent Interval--means a full calendar month or quarter as indicated on a
-------------
Schedule.

Schedule--means either an Equipment Schedule or a Licensed Products Schedule
--------
which incorporates all of the terms and conditions of this Master Lease.

Secured Party--means an entity whom Lessor has granted a security interest for
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the purpose of securing a loan.

Summary Equipment Schedule--means a certificate provided by Lessor summarizing
--------------------------
all of the Equipment for which Lessor has received Lessee approved vendor
invoices, purchase documents and/or evidence of delivery during a calendar
quarter which will incorporate all of the terms and conditions of the related
Schedule and this Master Lease and will constitute a separate lease for the
equipment leased thereunder.

                                      -11-
<PAGE>

IN WITNESS WHEREOF, the parties hereto have executed this Master Lease on or as
of the day and year first above written.


DSL.NET, INC.,                     COMDISCO, INC.,
as Lessee                          as Lessor



By: /s/ David F. Struwas           By: /s/ James P. Labe
   ---------------------              ------------------

Title:  President & CEO          Title:  President
      -----------------                -----------

                                      -12-
<PAGE>

                                                                  EXHIBIT 10.04

                                ADDENDUM TO THE
               MASTER LEASE AGREEMENT DATED AS OF March 4, 1999
                       BETWEEN DSL.NET, INC., AS LESSEE
                         AND COMDISCO, INC., AS LESSOR


     The undersigned hereby agree that the terms and conditions of the above-
referenced Master Lease are hereby modified and amended as follows:

1)   Section 3., "Rent and Payment"
                  ----------------

     Line 2, after the words "when invoiced" insert, "or within five (5) days
     thereafter'

     In the third sentence, line 3, delete the word "when" and replace it with
     "within 5 days after it is".

2)   Section 4.2., "Warranty and Disclaimer of Warranties"
                     -------------------------------------

     In the first sentence, line 2, after the word "Lessor" insert the following
     "(and all assignees and secured parties)".

     After the end of the second sentence, insert the following "To the extent
     that such assignment is not permitted by the manufacturer, upon the request
     of Lessee, Lessor will use its best efforts to enforce such warrantees for
     the benefit of Lessee.

3)   Section 5.1., "Title"
                    -----

     In the third sentence, line 8, after the words "caused by Lessor" insert
     the words "or other Owner".

     At the end of the paragraph, insert "or other Owner".

4)   Section 5.3., "Assignment by Lessor"
                    --------------------

     At the beginning of paragraphs (a) and (b), insert the words "After such an
     assignment to a Secured Party," and at the beginning of paragraph (a)
     delete "The" and replace it with "the".

     Paragraph (a), line 2, after the word "Lessor" delete "." and insert "and"
     and delete "The" and replace with "the".

5)   Section 6.2., "Taxes and Fees"
                    --------------

     In the first sentence, line 2, after the word "charges", insert the
     following "relating to the Equipment".
<PAGE>

6)   Section 7.1., "Care, Use and Maintenance"
                    -------------------------

     Line 10 and Line 11 after the word "Equipment" insert, "(except for
     Licensed Products)"

7)   Section 11., "Indemnity"
                   ---------

     Line 6, delete the words "this Master Lease" and replace with "the
     applicable Summary Equipment Schedule" and after the word "under" insert
     "such Summary Equipment Schedule or".

8)   Section 12., "Risk of Loss"
                   ------------

     Paragraph 2, line 5, insert the following "(less any amounts paid to Lessor
     under an insurance policy obtained pursuant to this Section 12)" after the
     words "Casualty Value"

9)   Section 13.1., "Default"
                     -------

     Paragraph (c), line 2, after the word "debts", insert the following "(other
     than debts which are not, in the aggregate, material to Lessee and debts
     which Lessee is contesting in good faith)".

10)  Section 14.1., "Board Attendance"
                     ----------------

     Delete this section in its entirety.

11)  Section 14.2 "Financial Statements"
                   --------------------

     In the first sentence, change the words "month" and "monthly" to "quarter"
     and "quarterly".

     Line 8, after the words "fiscal year" delete "(and in any event within
     ninety (90 days)," and insert this language to Line 6 after the words
     "fiscal year", except leave out the ",".

12)  Section 14.5., "Entire Agreement"
                     ----------------

     Line 1, insert "addendum," after the word "associated".

13)  Section 14.7., "Binding Nature"
                     --------------

     At the end of the second sentence, insert ",except as provided herein".

14)  Section 14.9. "Notices"
                    -------

                                      -2-
<PAGE>

     In line 6, insert "overnight or same day" after the words "sent by".

15)  Section 14.10., "Applicable Law"
                      --------------

     In line 3 and 4, delete "Illinois" and replace with "Connecticut".

16)  Section 14.18., "Definitions
                      -----------

     In the definition of "Interim Rent", delete "the pro-rata portion" and
                          --------------
     replace with "interest only portion of".

     In the definition of "Summary Equipment Schedule", in line 4, delete
                          ----------------------------
     "quarter" and replace with "period as stated on the Summary Equipment
     Schedule".



DSL.NET, INC.                      COMDISCO, INC.
as LESSEE                          as LESSOR

By: /s/ David F. Struwas           By: /s/ James P. Labe
   ----------------------              ------------------

Title:  President and CEO          Title:  President
      -------------------                -----------

Date:                               Date:
     --------------------                ----------------

                                      -3-