Document:

EXHIBIT 10.26
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                                    GUARANTY
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         GUARANTY, dated as of December 27, 2002, by COLUMBIA CAPITAL EQUITY
PARTNERS II (QP), L.P., a Delaware limited partnership ("Columbia II (QP)"),
COLUMBIA CAPITAL EQUITY PARTNERS II (CAYMAN), L.P., a Delaware limited
partnership ("Columbia II Cayman"), COLUMBIA CAPITAL EQUITY PARTNERS II, L.P., a
Delaware limited partnership ("Columbia Equity II"), COLUMBIA CAPITAL EQUITY
PARTNERS III (QP), L.P., a Delaware limited partnership ("Columbia III (QP)"),
COLUMBIA CAPITAL EQUITY PARTNERS III (CAYMAN), L.P., a Delaware limited
partnership ("Columbia III Cayman"), and COLUMBIA CAPITAL EQUITY PARTNERS III
(AI), L.P., a Delaware limited partnership ("Columbia Equity III and,
collectively with Columbia II (QP), Columbia II Cayman, Columbia Equity II,
Columbia III (QP), and Columbia III Cayman, the "Guarantors" and each
individually, a "Guarantor"), in favor of FLEET NATIONAL BANK, a national
banking association (the "Lender").

         WHEREAS, DSL.NET, Inc. a Delaware corporation (the "Company") has
entered into a Revolving Credit and Term Loan Agreement dated as of December 13,
2002 (as amended and in effect from time to time, the "Credit Agreement") with
the Lender, pursuant to which the Lender, subject to the terms and conditions
contained therein, is to make loans or otherwise extend credit to the Company;

         WHEREAS, the Guarantors collectively own certain of the capital stock
of the Company;

         WHEREAS, each of the Guarantor expects to receive substantial direct
and indirect benefits from the extensions of credit to the Company by the Lender
pursuant to the Credit Agreement (which benefits are hereby acknowledged);

         WHEREAS, it is a condition precedent to the Lender's making any loans
or otherwise extending credit to the Company under the Credit Agreement that the
Guarantors execute and deliver to the Lender a guaranty substantially in the
form hereof; and

         WHEREAS, each of the Guarantors jointly and severally wishes to
guaranty the Company's obligations to the Lender under or in respect of the
Credit Agreement as provided herein;

         NOW, THEREFORE, each Guarantor hereby agrees with the Lender as
follows:

         1. DEFINITIONS. Unless otherwise defined herein, all capitalized terms
used herein without definition shall have the respective meanings provided
therefor in the Credit Agreement.
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                                       -2-

         The term "Capital Call Obligation" means, as to any Guarantor, the
obligation of each Partner to pay his, her or its Unpaid Capital Commitment in
accordance with the terms and obligations of the Partnership Agreement of such
Guarantor.

         The term "Capital Commitment" means, as to any Guarantor, the total
amount agreed to be paid to such Guarantor by each Partner of such Guarantor,
all as set forth in the Partnership Agreement of such Guarantor.

         The term "Capital Contribution" means, as to any Guarantor, with
respect to any Partner of such Guarantor, that portion of such Partner's Capital
Commitment which has already been paid, funded or otherwise satisfied by such
Partner as of any date of determination.

         The term "Credit Agreement Guarantor" means a "Guarantor" as defined in
the Credit Agreement which has executed and delivered a Credit Agreement
Guaranty, provided, for purposes hereof, to the extent any such Guarantor is
jointly and severally liable under any Credit Agreement Guaranty, the term
Credit Agreement Guarantor shall include all Guarantors which are so jointly and
severally liable to the Lender.

         The term "Credit Agreement Guaranty" means each "Guaranty" as defined
in the Credit Agreement, and which guaranty remains in full force and effect.

         The term "Defaulted Capital Call Obligations" means, as to any
Guarantor, any and all Capital Call Obligations of all Defaulting Partners, to
the extent that the Capital Commitments of such Defaulting Partners have not
otherwise been purchased by or allocated to other Partners of such Guarantor
which are not Defaulting Partners pursuant to the terms of the Partnership
Agreement of such Guarantor within thirty (30) days after any such Partner
becomes a Defaulting Partner.

         The term "Defaulting Partner" means, as to any Guarantor, any Partner
who or which (a) is considered a "Defaulting Partner" or "Defaulting Member", as
the case may be, under the terms of the applicable Partnership Agreement or (b)
fails to pay any Capital Call Obligation on or before the fifteenth (15th)
Business Day following the date on which the applicable General Partner requires
such payment pursuant to a written notice of a Capital Call to such Partners,
unless and until such failure to pay any such Capital Call Obligation is
subsequently cured or waived with the consent of, and to the satisfaction of,
such General Partner and the Lender.

         The term "Eligible Capital Call Commitments" means, as to any
Guarantor, the aggregate Capital Call Obligations of such Guarantor's Partners
(a) that are not subject to any lien, security interest or other encumbrance
other than the lien or other security interest expressly permitted hereunder and
described on Schedule 9.2 hereof (the "BofA Lien") to secure the BofA Facility;
(b) that have not been paid (and are not the subject of any capital call which
has been made by such Guarantor's general partner but not yet funded by the
Partner and are not otherwise committed by such general partner) or otherwise
funded by the Partner or Partners; and (c) that do not include amounts with
respect to Defaulted Capital Call Obligations or (without duplication) amounts
with respect to any other Capital Call Obligations payable by a Defaulting
Partner.
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                                       -3-

         The term "Indebtedness" shall mean, as to any individual, corporation,
partnership, trust, unincorporated association, business or other legal entity
and any government or any governmental agency or political subdivision thereof
(collectively, a "Person") and whether recourse is secured by or is otherwise
available against all or only a portion of the assets of such Person and whether
or not contingent, but without duplication: (i) every obligation of such Person
for money borrowed, (ii) every obligation of such Person evidenced by bonds,
debentures, notes or other similar instruments, including obligations incurred
in connection with the acquisition of property, assets or businesses, (iii)
every reimbursement obligation of such Person with respect to letters of credit,
bankers' acceptances or similar facilities issued for the account of such
Person, (iv) every obligation of such Person issued or assumed as the deferred
purchase price of property or services (including securities repurchase
agreements but excluding trade accounts payable or accrued liabilities arising
in the ordinary course of business which are not overdue or which are being
contested in good faith), (v) every obligation of such Person under any
capitalized lease, (vi) every obligation of such Person under any lease (a
"synthetic lease") treated as an operating lease under generally accepted
accounting principles and as a loan or financing for U.S. income tax purposes,
(vii) all sales by such Person of (A) accounts or general intangibles for money
due or to become due, (B) chattel paper, instruments or documents creating or
evidencing a right to payment of money or (C) other receivables (collectively
"receivables"), whether pursuant to a purchase facility or otherwise, other than
in connection with the disposition of the business operations of such Person
relating thereto or a disposition of defaulted receivables for collection and
not as a financing arrangement, and together with any obligation of such Person
to pay any discount, interest, fees, indemnities, penalties, recourse, expenses
or other amounts in connection therewith, (viii) every obligation of such Person
(an "equity related purchase obligation") to purchase, redeem, retire or
otherwise acquire for value any shares of capital stock of any class issued by
such Person, any warrants, options or other rights to acquire any such shares,
or any rights measured by the value of such shares, warrants, options or other
rights, (ix) every obligation of such Person under any forward contract, futures
contract, swap, option or other financing agreement or arrangement (including,
without limitation, caps, floors, collars and similar agreements), the value of
which is dependent upon interest rates, currency exchange rates, commodities or
other indices (a "derivative contract"), (x) every obligation in respect of
Indebtedness of any other entity (including any partnership in which such Person
is a general partner) to the extent that such Person is liable therefor as a
result of such Person's ownership interest in or other relationship with such
entity, except to the extent that the terms of such Indebtedness provide that
such Person is not liable therefor and such terms are enforceable under
applicable law, (xi) every obligation, contingent or otherwise, of such Person
guaranteeing, or having the economic effect of guarantying or otherwise acting
as surety for, any obligation of a type described in any of clauses (i) through
(x) (the "primary obligation") of another Person (the "primary obligor"), in any
manner, whether directly or indirectly, and including, without limitation, any
obligation of such Person (A) to purchase or pay (or advance or supply funds for
<PAGE>
                                       -4-

the purchase of) any security for the payment of such primary obligation, (B) to
purchase property, securities or services for the purpose of assuring the
payment of such primary obligation, or (C) to maintain working capital, equity
capital or other financial statement condition or liquidity of the primary
obligor so as to enable the primary obligor to pay such primary obligation.

         The term "Partner" means, as to any Guarantor, any Person who or which
holds a limited partnership interest or membership interest, as the case may be,
in such Guarantor pursuant to the Partnership Agreement of such Guarantor.

         The term "Partnership Agreements" shall mean collectively, (a) as to
Columbia II (QP), that certain Second Amended and Restated Agreement of Limited
Partnership dated as of May 27, 1999 by and among Columbia Capital Equity
Partners, L.L.C., a Delaware limited liability company (in its capacity as
general partner of Columbia II (QP)), Columbia Capital, L.L.C., a Delaware
limited liability company, as initial limited partners and the persons and/or
entities listed on Schedule I thereto, as limited partners; (b) as to Columbia
II Cayman, that certain Second Amended and Restated Agreement of Limited
Partnership dated as of March 30, 2000 by and among Columbia Capital Equity
Partners, L.L.C., a Delaware limited liability company (in its capacity as
general partner of Columbia II Cayman), CCEP II Cayman-SLP, Inc., a Delaware
corporation as Special Limited Partner and the persons and/or entities listed on
Schedule I thereto, as limited partners; (c) as to Columbia Equity II, that
certain Second Amended and Restated Agreement of Limited Partnership dated as of
May 27, 1999 by and among Columbia Capital Equity Partners, L.L.C., a Delaware
limited liability company (in its capacity as general partner of Columbia Equity
II), Columbia Capital, L.L.C., a Delaware limited liability company, as initial
limited partners and the persons and/or entities listed on Schedule I thereto,
as limited partners; (d) as to as to Columbia III (QP), that certain Amended and
Restated Agreement of Limited Partnership dated as of June 6, 2000 by and among
Columbia Capital Equity Partners III, L.P., a Delaware limited partnership (in
its capacity as general partner of Columbia III (QP)), Columbia Capital III,
L.L.C., a Delaware limited liability company, as initial limited partners and
the persons and/or entities listed on Schedule I thereto, as limited partners;
(e) as to Columbia III Cayman, that certain Amended and Restated Agreement of
Limited Partnership dated as of June 6, 2000 by and among Columbia Capital
Equity Partners (Cayman) III, Ltd. (in its capacity as general partner of
Columbia III Cayman), Columbia Capital III, LLC, as initial limited partners and
the persons and/or entities listed on Schedule I thereto, as limited partners;
and (f) as to Columbia Equity III, that certain Amended and Restated Agreement
of Limited Partnership dated as of August 17, 2000 by and among Columbia Capital
Equity Partners III, L.P., a Delaware limited partnership (in its capacity as
general partner of Columbia II (QP)), Columbia Capital III, L.L.C., a Delaware
limited liability company, as initial limited partners and the persons and/or
entities listed on Schedule I thereto, as limited partners.

         The term "Pro Rata Share" shall mean, as to each Credit Agreement
Guarantor, that portion of the principal amount of the Obligations which are
guaranteed by such Credit Agreement Guarantor pursuant to a Credit Agreement
Guaranty as compared to the principal amount of the Obligations which are
guaranteed by all Credit Agreement Guarantors pursuant to all Credit Agreement
Guarantees.
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                                       -5-

         The term "Related Guarantees" shall mean each Credit Agreement Guaranty
issued to the Lender from any Credit Agreement Guarantor other than the
Guarantors.

         The term "Total Guarantor Obligations" means, as to any Guarantor, the
sum of (a) the Obligations which are guaranteed by the Guarantors pursuant to
this Guaranty, plus (b) the aggregate amount of all Indebtedness of the
Guarantors (which, for purposes of this Guaranty, shall include the entire
committed amount of the BofA Facilities, whether or not there exists any
outstanding amounts owing thereunder).

         The term "Unpaid Capital Commitment" means, as to any Guarantor, with
respect to any Partner of such Guarantor, such Partner's Capital Commitment less
such Partner's Capital Contribution.

         2. GUARANTY OF PAYMENT AND PERFORMANCE. Each of the Guarantors hereby
jointly and severally guarantees to the Lender the full and punctual payment
when due (whether at stated maturity, by required pre-payment, by acceleration
or otherwise), as well as the performance, of all of the Obligations including
all such which would become due but for the operation of the automatic stay
pursuant to ss.362(a) of the Federal Bankruptcy Code and the operation of
ss.ss.502(b) and 506(b) of the Federal Bankruptcy Code. In addition, each of the
Guarantors agrees that payments by the Guarantor hereunder shall be made without
recoupment, setoff or counterclaim and free and clear of and without deduction
for any taxes, levies, imposts, duties, charges, fees, deductions, withholdings,
compulsory loans, restrictions or conditions of any nature now or hereafter
imposed or levied by any jurisdiction or any political subdivision thereof or
taxing or other authority therein unless the Guarantor is compelled by law to
make such deduction or withholding. If any such obligation is imposed upon any
Guarantor with respect to any amount payable by it hereunder or under any of the
other Loan Documents, such Guarantor will pay to the Lender, on the date on
which such amount is due and payable under any Loan Document, such additional
amount in United States dollars as shall be necessary to enable the Lender to
receive the same net amount which the Lender would have received on such due
date had no such obligation been imposed upon such Guarantor. This Guaranty is
an absolute, unconditional and continuing guaranty of the full and punctual
payment and performance of all of the Obligations and not of their
collectibility only and is in no way conditioned upon any requirement that the
Lender first attempt to collect any of the Obligations from the Company or
resort to any collateral security or other means of obtaining payment. Should
the Company default in the payment or performance of any of the Obligations, the
joint and several obligations of the Guarantors hereunder with respect to such
Obligations in default shall, upon demand by the Lender, become immediately due
and payable to the Lender, without demand or notice of any nature, all of which
are expressly waived by each Guarantor. Payments by the Guarantors hereunder may
be required by the Lender on any number of occasions.
<PAGE>
                                       -6-

         3. GUARANTOR'S AGREEMENT TO PAY ENFORCEMENT COSTS, ETC. Each Guarantor
further agrees, as the principal obligor and not as a guarantor only, to pay to
the Lender, on demand, all reasonable costs and expenses (including court costs
and legal expenses) incurred or expended by the Lender in connection with the
Obligations, this Guaranty and the enforcement thereof, together with interest
on amounts recoverable under this ss.3 from the time when such amounts become
due until payment, whether before or after judgment, at the rate of interest for
overdue principal set forth in the Credit Agreement, provided that if such
interest exceeds the maximum amount permitted to be paid under applicable law,
then such interest shall be reduced to such maximum permitted amount.

         4. LIMITED GUARANTY. Notwithstanding any other term or provision of
this Guaranty to the contrary, the Guarantors' liability hereunder shall be
limited to an amount equal to (a) $1,100,000 in principal amount, plus, without
limitation as to the amounts thereof, (b) the Guarantors' Pro Rata Share of all
interest, banking charges, commissions, costs and reasonable expenses chargeable
to the Company in respect of the Obligations (other than costs and expenses,
including attorneys fees, incurred in connection with the enforcement against
the Company of the Credit Agreement or other Loan Documents, unless the Lender
is required to incur just costs and/or expenses prior to being able to demand
payment hereunder), plus (c) the Guarantors' Pro Rata Share of all interest and
other costs and reasonable expenses payable by the Guarantors pursuant to ss.3
hereof (other than costs and expenses, including attorneys fees, incurred in
connection with the enforcement against the Company of the Credit Agreement or
other Loan Documents, unless the Lender is required to incur just costs and/or
expenses prior to being able to demand payment hereunder), provided, the
Guarantors shall pay all of the costs and expenses incurred or expended by the
Lender in connection with this Guaranty and the enforcement thereof. Each
payment made by any Guarantor hereunder which is applied against the Obligations
referred to in clause (a) above shall reduce such Guarantor's liability by such
amount. The Lender's dealings with the Company need not be limited to any
particular sum notwithstanding any limitation herein upon the liability of each
Guarantor. The Lender hereby agrees that to the extent it shall require any
payments be made hereunder, the Lender will, to the extent permissable,
simultaneously make a claim for payment on all Credit Agreement Guarantees such
that any payment being required to be made hereunder will not exceed the
Guarantors' Pro Rata share of the aggregate amount being claimed by the Lender
under all Credit Agreement Guarantees (and, to the extent the Lender is not
permitted or otherwise able to make a claim under any Credit Agreement Guaranty,
the Lender shall be deemed to have made such a claim under such Credit Agreement
Guaranty for purposes of this sentence).

         5. WAIVERS BY GUARANTOR; LENDER'S FREEDOM TO ACT. Each Guarantor agrees
that the Obligations will be paid and performed strictly in accordance with
their respective terms, regardless of any law, regulation or order now or
hereafter in effect in any jurisdiction affecting any of such terms or the
rights of the Lender with respect thereto. Each Guarantor waives promptness,
diligences, presentment, demand, protest, notice of acceptance, notice of any
Obligations incurred and all other notices of any kind, all defenses which may
be available by virtue of any valuation, stay, moratorium law or other similar
<PAGE>
                                       -7-

law now or hereafter in effect, any right to require the marshalling of assets
of the Company or any other entity or other person primarily or secondarily
liable with respect to any of the Obligations, and all suretyship defenses
generally. Without limiting the generality of the foregoing, each Guarantor
agrees to the provisions of any instrument evidencing, securing or otherwise
executed in connection with any Obligation and agrees that the obligations of
such Guarantor hereunder shall not be released or discharged, in whole or in
part, or otherwise affected by (a) the failure of the Lender to assert any claim
or demand or to enforce any right or remedy against the Company or any other
entity or other person primarily or secondarily liable with respect to any of
the Obligations; (b) any extensions, compromise, refinancing, consolidation or
renewals of any Obligation; (c) any change in the time, place or manner of
payment of any of the Obligations or any rescissions, waivers, compromise,
refinancing, consolidation, amendments or modifications of any of the terms or
provisions of the Credit Agreement, the other Loan Documents or any other
agreement evidencing, securing or otherwise executed in connection with any of
the Obligations; (d) the addition, substitution or release of any entity or
other person primarily or secondarily liable for any Obligation, (e) the
adequacy of any rights which the Lender may have against any collateral security
or other means of obtaining repayment of any of the Obligations; (f) the
impairment of any collateral securing any of the Obligations, including without
limitation the failure to perfect or preserve any rights which the Lender might
have in such collateral security or the substitution, exchange, surrender,
release, loss or destruction of any such collateral security; or (g) any other
act or omission which might in any manner or to any extent vary the risk of the
Guarantor or otherwise operate as a release or discharge of such Guarantor, all
of which may be done without notice to such Guarantor. To the fullest extent
permitted by law, each Guarantor hereby expressly waives any and all rights or
defenses arising by reason of (i) any "one action" or "anti-deficiency" law
which would otherwise prevent the Lender from bringing any action, including any
claim for a deficiency, or exercising any other right or remedy (including any
right of set-off), against such Guarantor before or after the Lender's
commencement or completion of any foreclosure action, whether judicially, by
exercise of power of sale or otherwise, or (ii) any other law which in any other
way would otherwise require any election of remedies by the Lender.

         6. UNENFORCEABILITY OF OBLIGATIONS AGAINST COMPANY. If for any reason
the Company has no legal existence or is under no legal obligation to discharge
any of the Obligations, or if any of the Obligations have become irrecoverable
from the Company by reason of the Company's insolvency, bankruptcy or
reorganization or by other operation of law or for any other reason, this
Guaranty shall nevertheless be binding on each Guarantor to the same extent as
if each Guarantor at all times had been the principal obligor on all such
Obligations. In the event that acceleration of the time for payment of any of
the Obligations is stayed upon the insolvency, bankruptcy or reorganization of
the Company, or for any other reason, all such amounts otherwise subject to
acceleration under the terms of the Credit Agreement, the other Loan Documents
or any other agreement evidencing, securing or otherwise executed in connection
with any Obligation shall be immediately due and payable by each Guarantor.
<PAGE>
                                       -8-

         7.  SUBROGATION; SUBORDINATION.

                  7.1. WAIVER OF RIGHTS AGAINST COMPANY. Until the final payment
         and performance in full of all of the Obligations, neither Guarantor
         shall exercise any rights against the Company arising as a result of
         payment by any Guarantor hereunder, by way of subrogation,
         reimbursement, restitution, contribution or otherwise, and will not
         prove any claim in competition with the Lender in respect of any
         payment hereunder in any bankruptcy, insolvency or reorganization case
         or proceedings of any nature; neither Guarantor will claim any setoff,
         recoupment or counterclaim against the Company in respect of any
         liability of such Guarantor to the Company; and each Guarantor waives
         any benefit of and any right to participate in any collateral security
         which may be held by the Lender.

                  7.2. SUBORDINATION. The payment of any amounts due with
         respect to any indebtedness of the Company now or hereafter owed to
         each Guarantor is hereby subordinated to the prior payment in full of
         all of the Obligations, to the extent and in the manner set forth in
         the next sentence. Each Guarantor agrees that, after the occurrence and
         during the continuance of any default in the payment or performance of
         any of the Obligations, such Guarantor will not demand, sue for or
         otherwise attempt to collect any such indebtedness of the Company to
         such Guarantor until all of the Obligations shall have been paid in
         full. If, notwithstanding the foregoing sentence, a Guarantor shall
         collect, enforce or receive any amounts in respect of such
         indebtedness, such amounts shall be collected, enforced and received by
         such Guarantor as trustee for the Lender and be paid over to the Lender
         on account of the Obligations without affecting in any manner the
         liability of such Guarantor under the other provisions of this
         Guaranty.

                  7.3. PROVISIONS SUPPLEMENTAL. The provisions of this ss.7
         shall be supplemental to and not in derogation of any rights and
         remedies of the Lender under any separate subordination agreement which
         the Lender may at any time and from time to time enter into with the
         Guarantors.

         8. SECURITY; SETOFF. Each Guarantor grants to the Lender, as security
for the full and punctual payment and performance of all of such Guarantor's
obligations hereunder, a continuing lien on and security interest in all
securities or other property belonging to such Guarantor now or hereafter held
by the Lender and in all deposits (general or special, time or demand,
provisional or final) and other sums credited by or due from the Lender to such
Guarantor or subject to withdrawal by such Guarantor. Regardless of the adequacy
of any collateral security or other means of obtaining payment of any of the
Obligations, the Lender is hereby authorized at any time and from time to time,
without notice to such Guarantor (any such notice being expressly waived by such
Guarantor) and to the fullest extent permitted by law, to set off and apply such
deposits and other sums against the obligations of such Guarantor under this
Guaranty, whether or not the Lender shall have made any demand under this
Guaranty and although such obligations may be contingent or unmatured.
<PAGE>
                                       -9-

         9.  REPRESENTATIONS; COVENANTS AND FURTHER ASSURANCES.

                  9.1. REPRESENTATIONS. Each Guarantor and each of Columbia
         Capital Equity Partners, L.L.C., Columbia Capital Equity Partners III,
         L.P., and Columbia Capital Equity Partners (Cayman) III, Ltd., in its
         capacity as sole general partner or managing member, as the case may
         be, of each Guarantor (the "General Partner") hereby represents and
         warrants to the Lender that (a) each of the Guarantors and General
         Partner is duly organized, validly existing, and in good standing under
         the laws of its jurisdiction of formation, and the execution, delivery
         and performance by such Guarantor and the General Partner of this
         Guaranty and the other Loan Documents to which it is a party (i) are
         within its partnership or membership authority, (ii) have been duly
         authorized by all appropriate action, (iii) do not conflict with or
         contravene its Partnership Agreement, or any law, rule, order or
         regulation; (b) upon the execution and delivery thereof, the Guaranty
         and each other Loan Document shall constitute the legal, valid and
         binding obligation of each such Guarantor party thereto, enforceable in
         accordance with its terms; (c) the financial statements provided to the
         Lender as at September 30, 2002 are complete and correct and fairly
         present the position of each Guarantor as at such date and for such
         period in accordance with generally accepted accounting principles
         consistently applied; and (d) the execution, delivery, performance of
         its obligations, and exercise of its rights under the Guaranty and the
         other Loan Documents by each Guarantor (i) do not require any consents
         or approvals; and (ii) are not and will not be in conflict with or
         prohibited or prevented by (A) any law, rule, order or regulation, or
         (B) its Partnership Agreement or any partnership or limited liability
         company action.

                  9.2. COVENANTS. Each Guarantor agrees that at all times the
         ratio of (a) Eligible Capital Call Commitments of such Guarantor to (b)
         Total Guarantor Obligations of such Guarantor shall not be less than
         1.50:1.00. Not later than forty-five (45) days after the end of each
         fiscal quarter, each Guarantor shall provide to the Lender evidence
         demonstrating compliance with this covenant contained in ss.9.2 To the
         extent the ratio of (a) Eligible Capital Call Commitments of a
         Guarantor to (b) Total Guarantor Obligations for such Guarantor is less
         than 1.50:1.00, upon demand by the Lender, such Guarantor shall deposit
         with the Lender cash collateral in an amount sufficient so that when
         added to the Eligible Capital Call Commitment portion of such ratio,
         such Guarantor complies with the covenant set forth in this ss.9.2. In
         addition, each Guarantor agrees that so long as any Obligation is
         outstanding, such Guarantor will not (1) create, incur, assume,
         guarantee or be or remain liable, contingently or otherwise, with
         respect to any Indebtedness other than the Indebtedness listed on
         Schedule 9.2 hereto; (2) create or incur or suffer to be created or
         incurred or permit to exist any lien, encumbrance, mortgage, pledge,
         charge, restriction or other security interest of any kind upon any
         Capital Call Obligation or such Guarantor's rights to receive such
         payments, except for those liens existing on the date hereof and set
         forth on Schedule 9.2 hereto; or (3) or enter into any agreement
         prohibiting the creation or assumption of any lien upon its properties,
         revenues or assets, whether now owned or hereafter acquired.
<PAGE>
                                      -10-

                  9.3. FURTHER ASSURANCES. Each Guarantor agrees that it will
         from time to time, at the request of the Lender, provide to the Lender
         such Guarantor's most recent audited and unaudited balance sheets and
         related statements of income and changes in financial condition and
         such other information relating to the business and affairs of such
         Guarantor as the Lender may reasonably request. Each Guarantor also
         agrees to do all such things and execute all such documents as the
         Lender may consider reasonably necessary or desirable to give full
         effect to this Guaranty and to perfect and preserve the rights and
         powers of the Lender hereunder. Each Guarantor acknowledges and
         confirms that such Guarantor itself has established its own adequate
         means of obtaining from the Company on a continuing basis all
         information desired by such Guarantor concerning the financial
         condition of the Company and that such Guarantor will look to the
         Company and not to the Lender in order for such Guarantor to keep
         adequately informed of changes in the Company's financial condition.

         10. TERMINATION; REINSTATEMENT. This Guaranty shall remain in full
force and effect until the Lender is given written notice of any Guarantor's
intention to discontinue this Guaranty, notwithstanding any intermediate or
temporary payment or settlement of the whole or any part of the Obligations. No
such notice shall be effective unless received and acknowledged by an officer of
the Lender at the address of the Lender for notices set forth in the Credit
Agreement. No such notice shall affect any rights of the Lender hereunder,
including without limitation the rights set forth in ss.ss.5 and 7, with respect
to any Obligations incurred or accrued prior to the receipt of such notice or
any Obligations incurred or accrued pursuant to any contract or commitment in
existence prior to such receipt, and all checks, drafts, notes, instruments
(negotiable or otherwise) and writings made by or for the account of the Company
and drawn on the Lender or any of its agents purporting to be dated on or before
the date of receipt of such notice, although presented to and paid or accepted
by the Lender after that date, shall form part of the Obligations. This Guaranty
shall continue to be effective or be reinstated, notwithstanding any such
notice, if at any time any payment made or value received with respect to any
Obligation is rescinded or must otherwise be returned by the Lender upon the
insolvency, bankruptcy or reorganization of the Company, or otherwise, all as
though such payment had not been made or value received. In addition, promptly
after the Obligations have been indefeasibly repaid in full in cash and all
Commitments have been terminated, the Lender will return to the Guarantors the
Guaranty marked "terminated" and/or "cancelled".

         11. SUCCESSORS AND ASSIGNS. This Guaranty shall be binding upon each
Guarantor, its successors and assigns, and shall inure to the benefit of and be
enforceable by the Lender and its successors, transferees and assigns. Without
limiting the generality of the foregoing sentence, the Lender may assign or
otherwise transfer the Credit Agreement, the other Loan Documents or any other
agreement or note held by it evidencing, securing or otherwise executed in
<PAGE>
                                      -11-

connection with the Obligations, or sell participations in any interest therein,
to any other entity or other person, and such other entity or other person shall
thereupon become vested, to the extent set forth in the agreement evidencing
such assignment, transfer or participation, with all the rights in respect
thereof granted to the Lender herein. No Guarantor may assign any of its
obligations hereunder.

         12. AMENDMENTS AND WAIVERS. No amendment or waiver of any provision of
this Guaranty nor consent to any departure by any Guarantor therefrom shall be
effective unless the same shall be in writing and signed by the Guarantor and
the Lender. No failure on the part of the Lender to exercise, and no delay in
exercising, any right hereunder shall operate as a waiver thereof; nor shall any
single or partial exercise of any right hereunder preclude any other or further
exercise thereof or the exercise of any other right.

         13. NOTICES. All notices and other communications called for hereunder
shall be made in writing and, unless otherwise specifically provided herein,
shall be deemed to have been duly made or given when delivered by hand or mailed
first class, postage prepaid, or, in the case of telegraphic or telexed notice,
when transmitted, answer back received, addressed as follows: if to a Guarantor,
at the address set forth beneath its signature hereto, and if to the Lender, at
the address for notices to the Lender set forth in the Credit Agreement, or at
such address as either party may designate in writing to the other.

         14. GOVERNING LAW; CONSENT TO JURISDICTION. THIS GUARANTY IS INTENDED
TO TAKE EFFECT AS A SEALED INSTRUMENT AND SHALL BE GOVERNED BY, AND CONSTRUED IN
ACCORDANCE WITH, THE LAWS OF THE COMMONWEALTH OF MASSACHUSETTS. Each Guarantor
agrees that any suit for the enforcement of this Guaranty may be brought in the
courts of the Commonwealth of Massachusetts or any federal court sitting therein
and consents to the nonexclusive jurisdiction of such court and to service of
process in any such suit being made upon such Guarantor by mail at the address
specified by reference in ss.13 Each Guarantor hereby waives any objection that
it may now or hereafter have to the venue of any such suit or any such court or
that such suit was brought in an inconvenient court.

         15. WAIVER OF JURY TRIAL. EACH GUARANTOR HEREBY WAIVES ITS RIGHT TO A
JURY TRIAL WITH RESPECT TO ANY ACTION OR CLAIM ARISING OUT OF ANY DISPUTE IN
CONNECTION WITH THIS GUARANTY, ANY RIGHTS OR OBLIGATIONS HEREUNDER OR THE
PERFORMANCE OF ANY OF SUCH RIGHTS OR OBLIGATIONS. Except as prohibited by law,
each Guarantor hereby waives any right which it may have to claim or recover in
any litigation referred to in the preceding sentence any special, exemplary,
punitive or consequential damages or any damages other than, or in addition to,
actual damages. Each Guarantor (a) certifies that neither the Lender nor any
representative, agent or attorney of the Lender has represented, expressly or
otherwise, that the Lender would not, in the event of litigation, seek to
enforce the foregoing waivers and (b) acknowledges that, in entering into the
Credit Agreement and the other Loan Documents to which the Lender is a party,
the Lender is relying upon, among other things, the waivers and certifications
contained in this ss.15.
<PAGE>
                                      -12-

         16. MISCELLANEOUS. This Guaranty constitutes the entire agreement of
the Guarantors and the Lender with respect to the matters set forth herein. The
rights and remedies herein provided are cumulative and not exclusive of any
remedies provided by law or any other agreement, and this Guaranty shall be in
addition to any other guaranty of or collateral security for any of the
Obligations. The invalidity or unenforceability of any one or more sections of
this Guaranty shall not affect the validity or enforceability of its remaining
provisions. Captions are for the ease of reference only and shall not affect the
meaning of the relevant provisions. The meanings of all defined terms used in
this Guaranty shall be equally applicable to the singular and plural forms of
the terms defined.

         17. CONTRIBUTION. To the extent any Guarantor makes a payment hereunder
in excess of the aggregate amount of the benefit received by such Guarantor in
respect of the extensions of credit under the Loan documents (the "Benefit
Amount"), then such Guarantor, after the payment in full, in cash, of all of the
Obligations, shall be entitled to recover from each other Guarantor such excess
payment, pro rata, in accordance with the ratio of the Benefit Amount received
by each such other Guarantor to the total Benefit Amount received by all
Guarantors, and the right to such recovery shall be deemed to be an asset and
property of such Guarantor so funding; provided, that all such rights to
recovery shall be subordinated and junior in right of payment to the final and
undefeasible payment in full in cash of all of the Obligations.
<PAGE>
                                      -13-

         IN WITNESS WHEREOF, each Guarantor has caused this Guaranty to be
executed and delivered as of the date first above written.

                               COLUMBIA CAPITAL EQUITY
                               PARTNERS II (QP), LP
                               By: Columbia Capital Equity Partners, L.P.,
                               its General Partner

                               By: /s/ Donald A. Doering
                                   ---------------------------------------
                                   Name:  Donald A. Doering
                                   Title:  Chief Financial Officer
                                   Address:

                               COLUMBIA CAPITAL EQUITY
                               PARTNERS II (CAYMAN), LP
                               By: Columbia Capital Equity Partners, L.P.,
                               its General Partner

                               By: /s/ Donald A. Doering
                                   ---------------------------------------
                                   Name:  Donald A. Doering
                                   Title:  Chief Financial Officer
                                   Address:

                               COLUMBIA CAPITAL EQUITY PARTNERS II, LP
                               By: Columbia Capital Equity Partners, L.P.,
                               its General Partner

                               By: /s/ Donald A. Doering
                                   ---------------------------------------
                                   Name:  Donald A. Doering
                                   Title:  Chief Financial Officer
                                   Address:
<PAGE>
                                      -14-

                               COLUMBIA CAPITAL EQUITY PARTNERS III (QP), LP
                               By: Columbia Capital Equity Partners III, L.P.,
                               its General Partner

                               By: /s/ Donald A. Doering
                                   ---------------------------------------
                                   Name: Donald A Doering
                                   Title: Chief Financial Officer
                                   Address:

                               COLUMBIA CAPITAL EQUITY PARTNERS III (CAYMAN), LP
                               By: Columbia Capital Equity Partners III, L.P.,
                               its General Partner

                               By: /s/ Donald A. Doering
                                   ---------------------------------------
                                   Name:  Donald A. Doering
                                   Title:  Chief Financial Officer
                                   Address:

                               COLUMBIA CAPITAL EQUITY PARTNERS III (AI), LP
                               By: Columbia Capital Equity Partners III, L.P.,
                               its General Partner

                               By: /s/ Donald A. Doering
                                   ---------------------------------------
                                   Name: Donald A. Doering
                                   Title:  Chief Financial Officer
                                   Address:
<PAGE>
                                  SCHEDULE 9.2

                             PERMITTED INDEBTEDNESS

1. Indebtedness arising under the Credit Agreement dated June 2, 1999 between
Columbia Capital Equity Partners II (QP), L.P., Columbia Capital Equity Partners
II (Cayman), L.P., Columbia Capital Equity Partners II, L.P., Columbia Capital
Employee Investors, L.L.C. and Columbia Capital Investors, L.L.C. and Bank of
America - a $10,000,000 facility (the "BofAII Facility").

2. Indebtedness arising under the Credit Agreement dated June 30, 2000 between
Columbia Capital Equity Partners III (QP), L.P., Columbia Capital Equity
Partners III (Cayman), L.P., Columbia Capital Equity Partners III (AI), L.P.,
Columbia Capital Employee Investors III, LLC and Columbia Capital Investors III,
LLC and Bank of America, N.A. - a $30,000,000 facility (the "BofAIII Facility"
and, collectively with the BofAII Facility, the "BofA Facilities" and each
individually, a "BofA Facility").

3. Additional Indebtedness up to an aggregate of no more than $5,000,000 that
the Guarantors incur in the ordinary course of business.

                                 PERMITTED LIENS

1. First priority security interest of Bank of America, granted under the two
lines of credit list in Schedule 9.2 (1) and (2) above, in the Guarantors'
Assigned Funds. The "Assigned Funds" are defined as all monies due and to become
due to the Guarantors pursuant to Section 3.1(a) of the Guarantors' respective
Partnership Agreements, which monies are the capital contribution requirements
to be made to the Partnerships during the commitment period.EXHIBIT 10.27
                                                                   -------------

                             AMENDMENT NO. 1 TO THE
                     STOCKHOLDERS AGREEMENT OF DSL.NET, INC.

         This Amendment No. 1, dated as of December 24, 2002 (this "Amendment"),
amends that certain Stockholders Agreement, dated as of December 24, 2001, by
and among DSL.net, Inc. (the "Company") and the Investors thereto (the
"Agreement"). Capitalized terms not defined herein shall have the meaning set
forth in the Agreement.

         WHEREAS, simultaneously herewith the Company has entered into an
agreement with Fleet National Bank ("Fleet") pursuant to which Fleet shall
provide a revolving line of credit (the "Fleet Line of Credit") for up to an
aggregate of $15 million to the Company to finance acquisitions, working capital
and other general corporate requirements;

         WHEREAS, borrowings by the Company under the Fleet Line of Credit will
be guaranteed (together the "Guaranties") by VantagePoint Venture Partners III
(Q), L.P., VantagePoint Venture Partners III, L.P., VantagePoint Communications
Partners, L.P., and VantagePoint Venture Partners 1996, L.P. (collectively, the
"VantagePoint Entities"), Columbia Capital Equity Partners II (QP), LP, Columbia
Capital Equity Partners II (Cayman), LP, Columbia Capital Equity Partners II,
LP, Columbia Capital Investors, LLC, Columbia Capital Equity Partners III (QP),
LP, Columbia Capital Equity Partners III (Cayman), LP, Columbia Capital Equity
Partners III (AI), LP, and Columbia Capital Investors III, LLC (collectively the
"Columbia Entities"), Charles River Partnership X, A Limited Partnership,
Charles River Partnership X-A, A Limited Partnership, Charles River Friends X-B,
LLC, and Charles River Friends X-C, LLC (collectively the "Charles River
Entities"), or The Lafayette Investment Fund, L.P. ("Lafayette"), or any other
person approved by Fleet in its sole and absolute discretion (together with the
VantagePoint Entities, Columbia Entities, Charles River Entities, and Lafayette,
the "Guarantors");

         WHEREAS, in order to induce the Guarantors to provide the Guaranties,
the Company has agreed to issue, from time to time, one or more warrants to
purchase an aggregate of 12,950,000 shares of the Company's Common Stock, and to
provide holders of such warrants with registration rights with respect to the
Common Stock issuable upon exercise or conversion of such warrants; and

         WHEREAS, the undersigned believe it is in the best interests of the
Company to amend the Agreement to provide for such registration rights and
matters related thereto.

         NOW THEREFORE in consideration of the premises and the agreements
herein contained, the receipt and sufficiency of which are hereby acknowledged,
the undersigned, intending to be bound hereby, agree as follows:

         1. The following term in the Agreement shall be amended and restated in
its entirety as set forth below:
<PAGE>
                  "Investor" shall mean the Series X Investors, the Series Y
                  Investors and the holders of any Warrants.

         2. Section 3.1(a) of the Agreement shall be amended by deleting the
first sentence of Section 3.1(a) and replacing it with the following:

                  "(a) At any time on or after July 1, 2002, one or more holders
                  (the "Initiating Holders") of at least 50% of the shares (the
                  "Conversion Shares") of the Company's common stock, par value
                  $0.0005 per share (the "Common Stock"), to be issued or
                  issuable (i) upon conversion of either the Series X Preferred
                  Stock or the Series Y Preferred Stock then outstanding and
                  (ii) upon exercise or conversion of the outstanding Warrants
                  issued in connection with the guaranty of Company's
                  obligations under the Guarantee Agreement with the Guarantors
                  thereto, dated as of October 8, 2002, as amended, (the
                  "Warrants"), to purchase up to 12,950,000 shares of the
                  Company's Common Stock (the "Warrant Shares"), and in the case
                  of both subsections (i) and (ii) of this sentence which have
                  not been (A) registered under the Act pursuant to an effective
                  registration statement filed thereunder and disposed of in
                  accordance with the registration statement covering them or
                  (B) publicly sold pursuant to Rule 144 under the Act
                  (collectively, the "Registrable Shares") may notify (the
                  "Initiating Holder Notice") the Company in writing that it or
                  they intend to offer or cause to be offered for public sale
                  Registrable Shares held by them and, if applicable, that they
                  intend to distribute the Registrable Shares by means of an
                  underwriting.

         3. Section 4.3 of the Agreement is deleted in its entirety and replaced
with the following paragraph:

         "4.3 Entire Agreement; Amendment. This Agreement, as amended by this
         Amendment, constitutes the entire agreement of the parties with respect
         to the subject matter hereof and neither this Agreement nor any
         provision hereof may be waived, modified, amended or terminated except
         by a written agreement signed by the party against whom the waiver is
         to be effective; provided, however, that the Series X Investors holding
         at least a majority of the outstanding shares of Series X Preferred
         Stock, voting as a separate class, the Series Y Investors holding at
         least a majority of the outstanding shares of Series Y Preferred Stock,
         voting as a separate class, and the holders of any Warrants then
         outstanding representing at least a majority of the Warrant Shares,
         voting as a separate class, may effect any such waiver, modification,
         amendment or termination on behalf of all of the Series X Investors,
         Series Y Investors and the holders of the Warrants, respectively;
         provided, further, however, that (i) any such waiver, amendment or
         modification made with the consent of less than all of the Series X
         Investors may only be made in a manner which applies to all Series X
         Investors in the same fashion, (ii) any such waiver, amendment or
         modification made with the consent of less than all of the Series Y
         Investors may only be made in a manner which applies to all Series Y
         Investors in the same fashion, (iii) any such waiver, amendment or
<PAGE>
         modification made with the consent of less than all holders of the
         Warrants may only be made in a manner which applies to all such holders
         of the Warrants in the same fashion; and (iv) if this Agreement is
         amended, modified or terminated, or a waiver with respect to all
         parties hereto is given, without the unanimous consent of the Series X
         Investors, the Series Y Investors, or the holders of the Warrants, all
         such Series X Investors, Series Y Investors or holders of the Warrants
         that are not a party to such agreement shall be given prompt notice of
         such amendment, modification, termination or waiver. No waiver
         hereunder shall be deemed a waiver of any subsequent breach or default
         of the same or similar nature."

         4. Section 4.5 of the Agreement is deleted in its entirety and replaced
with the following paragraph:

         "4.5 Additional Parties. The Company shall take all necessary action to
         ensure that each person who shall on or after the date hereof acquire
         shares of Series X Preferred Stock, Series Y Preferred Stock or
         Warrants shall become a party to this Agreement by executing and
         delivering to the Company an Instrument of Adherence, and such
         additional party shall thereafter be added to Annex I hereto and be
         deemed a Series X Investor, Series Y Preferred Investor or a holder of
         Warrants, as the case may be, for all purposes of this Agreement
         without the requirement of consent of the other parties hereto."

         5. By their signature below, each of VantagePoint Venture Partners III
(Q), L.P., VantagePoint Venture Partners III, L.P., VantagePoint Communications
Partners, L.P. and VantagePoint Venture Partners 1996, L.P., as holders of
"Registrable Securities" under that certain Amended and Restated Investors
Rights Agreement, dated as of July 16, 1999 (the "Rights Agreement"), by and
among the Company and the investors party thereto, as amended to the date
hereof, hereby consents pursuant to Section 1.11 of the Rights Agreement to the
registration rights set forth in this Amendment.

                  [REMAINDER OF PAGE INTENTIONALLY LEFT BLANK]
<PAGE>

IN WITNESS WHEREOF, the parties hereto have executed this Amendment or have
caused it to be executed by their respective officers thereunto duly authorized,
as of the date first above written.

                                          DSL.NET, INC.

                                          By:         /s/ David F. Struwas
                                              --------------------------------
                                              Name:   David F. Struwas
                                                   ---------------------------
                                              Title:  Chief Executive Officer
                                                    --------------------------

                  [REMAINDER OF PAGE INTENTIONALLY LEFT BLANK]
<PAGE>

                             SERIES Y INVESTORS:

                             COLUMBIA CAPITAL EQUITY PARTNERS II (QP), L.P.

                             By:  Columbia Capital Equity Partners, L.P.
                                  Its: General Partner

                                  By:       /s/ Donald A. Doering
                                     ---------------------------------------
                                  Name:     Donald A. Doering
                                       -------------------------------------
                                  Title:    Chief Financial Officer
                                        ------------------------------------

                             COLUMBIA CAPITAL EQUITY PARTNERS II (CAYMAN), L.P.

                             By:  Columbia Capital Equity Partners, LP.
                                  Its: General Partner

                                  By:       /s/ Donald A. Doering
                                     ---------------------------------------
                                  Name:     Donald A. Doering
                                       -------------------------------------
                                  Title:    Chief Financial Officer
                                        ------------------------------------

                             COLUMBIA CAPITAL EQUITY PARTNERS II, L.P.

                             By:  Columbia Capital Equity Partners, L.P.
                                  Its: General Partner

                                  By:       /s/ Donald A. Doering
                                     ---------------------------------------
                                  Name:     Donald A. Doering
                                       -------------------------------------
                                  Title:    Chief Financial Officer
                                        ------------------------------------
<PAGE>
                             COLUMBIA CAPITAL INVESTORS, LLC

                             By:  Columbia Capital, LLC
                                  Its: Manager

                                  By:       /s/ Donald A. Doering
                                     ---------------------------------------
                                  Name:     Donald A. Doering
                                       -------------------------------------
                                  Title:    Chief Financial Officer
                                        ------------------------------------

                             COLUMBIA CAPITAL EQUITY PARTNERS III (QP), L.P.

                             By:  Columbia Capital Equity Partners III, L.P.
                                  Its: General Partner

                                  By:       /s/ Donald A. Doering
                                     ---------------------------------------
                                  Name:     Donald A. Doering
                                       -------------------------------------
                                  Title:    Chief Financial Officer
                                        ------------------------------------

                             COLUMBIA CAPITAL EQUITY PARTNERS III (CAYMAN), L.P.

                             By:  Columbia Capital Equity Partners III, L.P.
                                  Its: General Partner

                                  By:       /s/ Donald A. Doering
                                     ---------------------------------------
                                  Name:     Donald A. Doering
                                       -------------------------------------
                                  Title:    Chief Financial Officer
                                        ------------------------------------

                             COLUMBIA CAPITAL EQUITY PARTNERS III (AI), L.P.

                             By:  Columbia Capital Equity Partners III, L.P.
                                  Its: General Partner

                                  By:       /s/ Donald A. Doering
                                     ---------------------------------------
                                  Name:     Donald A. Doering
                                       -------------------------------------
                                  Title:    Chief Financial Officer
                                        ------------------------------------

                             COLUMBIA CAPITAL INVESTORS III, LLC

                             By:  Columbia Capital III, LLC,
                                  Its: Manager

                                  By:       /s/ Donald A. Doering
                                     ---------------------------------------
                                  Name:     Donald A. Doering
                                       -------------------------------------
                                  Title:    Chief Financial Officer
                                        ------------------------------------
<PAGE>

                             THE LAFAYETTE INVESTMENT FUND, L.P.

                             By:  Lafayette Investment Partners, L.P.

                             Its: Sole general partner

                             By:  Lafayette Private Equities, Inc.

                             Its: Sole general partner

                             By:       /s/ Robert Sussman
                                  ----------------------------------------
                             Name:     Robert Sussman
                                  ----------------------------------------
                             Title:    Vice President
                                    --------------------------------------

<PAGE>
                             CHARLES RIVER PARTNERSHIP X, A LIMITED PARTNERSHIP

                             By:  Charles River X GP, LLC
                             Its: General Partner

                             By:     /s/ Richard M. Burnes
                                  ------------------------------------------
                             Name:   Richard M. Burnes
                                    ----------------------------------------
                             Title:  Managing Member
                                     ---------------------------------------

                             CHARLES RIVER PARTNERSHIP X-A, A LIMITED
                             PARTNERSHIP

                             By:  Charles River X GP, LLC
                             Its: General Partner

                             By:     /s/ Richard M. Burnes
                                  ------------------------------------------
                             Name:   Richard M. Burnes
                                  ------------------------------------------
                             Title:  Managing Member
                                  ------------------------------------------

                             CHARLES RIVER FRIENDS X-B, LLC

                             By:     Charles River Friends, Inc.
                             Its:    Manager

                             By:     /s/ Richard M. Burnes
                                  ------------------------------------------
                             Name:   Richard M. Burnes
                                  ------------------------------------------
                             Title:  Authorized Officer
                                     ---------------------------------------

                             CHARLES RIVER FRIENDS X-C, LLC

                             By:     Charles River Friends, Inc.
                             Its:    Manager

                             By:     /s/ Richard M. Burnes
                                  ------------------------------------------
                             Name:   Richard M. Burnes
                                  ------------------------------------------
                             Title:  Authorized Officer
                                     ---------------------------------------

<PAGE>
                               SERIES X INVESTORS:

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

                             By:  VantagePoint Venture Associates III, L.L.C.,
                                  its general partner

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

                             Name:  James D. Marver
                                    -------------------------------------
                             Managing Member

                             VANTAGEPOINT VENTURE PARTNERS III, L.P.

                             By:  VantagePoint Venture Associates III, L.L.C.,
                                  its general
                                  partner

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

                             Name:  James D. Marver
                                    -------------------------------------
                             Managing Member

                             VANTAGEPOINT COMMUNICATIONS PARTNERS, L.P.

                             By:  VantagePoint Communications Associates,
                                  L.L.C., its general partner

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

                             Name:  James D. Marver
                                    -------------------------------------
                             Managing Member

                             VANTAGEPOINT VENTURE PARTNERS 1996, L.P.

                             By:  VantagePoint Associates, L.L.C.,
                                  its general partner

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

                             Name:  James D. Marver
                                    -------------------------------------
                             Managing Member

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