Document:

<Page>
                                                                     Exhibit 4.3

                                VOTING AGREEMENT

Cogent Communications Group, Inc.
1015 31st Street, N.W.
Washington, D.C. 20007

Allied Riser Communications Corporation
1700 Pacific Avenue, Suite 400
Dallas, TX 75201

Ladies and Gentlemen:

                  The undersigned, _________________________________, is a
beneficial owner of, or has the right to vote, the number of shares set forth on
Schedule I hereto (the "Shares") of Allied Riser Communications Corporation, a
Delaware corporation (the "Company"), and wishes to facilitate the merger of
August Caesar Merger Sub, Inc., a Delaware corporation ("Merger Sub"), which is
a wholly-owned subsidiary of Cogent Communications Group, Inc., a Delaware
corporation ("Cogent"), with and into the Company, pursuant to that certain
Agreement and Plan of Merger by and among the Company, Cogent and Merger Sub,
dated as of August 28, 2001 and amended as of October ____, 2001 (the
"Agreement" and such merger, the "Merger"). The undersigned recognizes that the
Merger will be of benefit to the undersigned, and that adoption of the Merger
Agreement by stockholders of the Company at a meeting of Company stockholders
(the "Company Stockholders Meeting") is a condition to the consummation of the
Merger and hereby executes and delivers this Voting Agreement pursuant to
Section 5.17 of the Agreement. All capitalized terms used and not defined herein
shall have the meanings assigned to them in the Agreement.

                  In consideration of the foregoing and in order to induce
Cogent to act in connection with the Merger, the undersigned hereby agrees, for
the benefit of the Company and of Cogent, to (i) attend the Company Stockholders
Meeting, in person or by proxy, or by written consent in lieu of a stockholders
meeting, as applicable, and (ii) vote (or cause to be voted) all Shares -- and
any additional voting securities of the Company beneficial ownership of which
may be acquired by the undersigned (whether by purchase or otherwise) after the
date of this Voting Agreement -- in favor of adoption of the Agreement and
approval of the Merger and any other matters necessary to consummate the
transactions contemplated in the Agreement in order to effectuate the Merger.
The above agreement to vote shall apply also to any adjournment or adjournments
of the Company Stockholders Meeting.

                  From and after the date hereof through the earlier of the
Effective Time of the Merger or the termination of the Agreement, the
undersigned hereby agrees not to sell, transfer, pledge, encumber or otherwise
dispose of any Shares or any voting interest in such Shares (collectively,
"Transfer"). Any such Transfer shall be null and void, and such transferee shall
have no rights as a stockholder of the Company. To the extent inconsistent with
the foregoing provisions of this Voting Agreement, the undersigned hereby
revokes any and all proxies granted by him with respect to the Shares, and
further agrees to execute and deliver such additional instruments and other
documents and to take such further actions as may be necessary or appropriate to
effectuate, carry out, and comply with all of its obligations hereunder.

<Page>

Without limiting the generality of the foregoing, the undersigned shall not
enter into any agreement or arrangement (or alter, amend or terminate any
existing agreement or arrangement) if such action would impair its ability to
effectuate, carry out, or comply with all the terms of this Voting Agreement.

                  The undersigned represents and warrants that: (i) the
undersigned has full power and authority to enter into the agreements set forth
herein; (ii) this Voting Agreement has been duly executed and delivered and
constitutes a valid and binding obligation of the undersigned, enforceable
against the undersigned in accordance with its terms; and (iii) the Shares set
forth on Schedule I hereto are the only voting securities, or voting rights in
capital stock of the Company, owned (beneficially or of record) by the
undersigned as of the date hereof.

                  This Voting Agreement shall be binding upon and shall inure to
the benefit of and be enforceable by the undersigned and its respective
successors and assigns. The undersigned agrees that irreparable damage would
occur if any provision of this Voting Agreement were not performed in accordance
with the terms hereof and that Cogent and/or the Company shall be entitled to an
injunction or injunctions to prevent breaches of this Voting Agreement or to
enforce specifically the performance of the terms and provisions hereof in any
federal court located in the State of Delaware or any Delaware state court, in
addition to any other remedy to which it is entitled at law or in equity. In the
event that the Agreement is terminated in accordance with its terms or is
amended in a manner that is material, this Voting Agreement shall automatically
terminate and be of no further force or effect. Upon such termination, except
for any rights Cogent or the Company may have in respect of any breach by the
undersigned of its obligations hereunder, there shall be no further obligation
or liability hereunder.

                                         Very truly yours,

                                         ---------------------------------
                                         dated this 12th  day of October, 2001.

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                                                                      SCHEDULE I

                                 COMPANY SHARES

TYPE:                            NUMBER:
----                             ------

<Page>

                         SCHEDULE PURSUANT TO
                     INSTRUCTION 2 TO ITEM 601 OF
                           REGULATION S-K.

<Table>
<Caption>

Date                         Undersigned
----                         -----------
<S>                        <C>
10/15/2001                   Norwest Venture Partners VII, LP
10/15/2001                   Telecom Partners II, LP
10/15/2001                   Crescendo World Fund, LLC

</Table><Page>

                                                                    Exhibit 10.1

                   FIBER OPTIC NETWORK LEASED FIBER AGREEMENT
                                  PRODUCT ORDER

This Product Order ("Product Order") together with the General Terms and
Conditions constitute the Fiber Optic Private Network Agreement ("Agreement")
which is effective as of February 7, 2000 (the "Effective Date") by and between
METROMEDIA FIBER NETWORK SERVICES, INC. ("MFN"), One North Lexington Ave.,
Fourth Floor, White Plains, New York 10601, and COGENT COMMUNICATIONS, INC.
("Carrier"), 1015 31st Street NW, Suite 330, Washington, DC 20007. Definitions
of terms used in this Agreement appear in this Product Order and in the General
Terms and Conditions.

Carrier hereby orders and MFN hereby agrees to provide Leased Fiber as follows:

     1.   Lease Term: The Lease Term for each Supplement shall commence on the
          respective Service Date and shall terminate two hundred forty months
          after the earlier of (i) sixty (60) months after the Effective Date or
          (ii) the date on which Carrier satisfies its Commitment set forth
          below.

     2.   Number of Leased Fibers and requests for Building Access into Carrier
          Locations: To be specified in each Supplement ("Supplements" and each
          a "Supplement") to this Product Order to be executed by the parties.

     3.   Commitment:

          3.1. Number of Leased Fiber Miles: A minimum aggregate of [*]
               [*] fiber miles [*] to be leased within sixty (60)
               months after the Effective Date.

          3.2. Number of Carrier Locations into which Carrier will order
               Building Access: A minimum aggregate of [*]
               buildings within sixty (60) months after the Effective Date.

     4.   Specifications pertinent to testing the Leased Fiber is attached
          herewith: as Exhibit A.

     5.   Installation Charge and Monthly Lease Payments:

          5.1  One Time Installation Charge: To be specified in each Supplement,
               if any. There shall be no one time installation charge for Leased
               Fiber or Lateral Extensions into any Carrier Location which is
               already part of the MFN Network or any Proposed Carrier Location,
               provided that the Leased Fiber is to be brought to the MFN point
               of demarcation in such Carrier Location.

          5.2  Monthly Lease Payments:

               5.2.1. Monthly Fiber Charge:

<Table>
<Caption>
                                                                INCREMENTAL
                                                                 PRICE PER
                                         FIBER MILE              FIBER MILE
                                                                 PER MONTH
                              ------------------------------------------------
                              <S>                                   <C>
                              [********************************************]
                              ------------------------------------------------
                              [********************************************]
                              ------------------------------------------------
                              [********************************************]
                              ------------------------------------------------
                              [********************************************]
                              ------------------------------------------------
                              [********************************************]
                              ------------------------------------------------

[*] Indicates confidential treatment requested.

</Table>

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                      [*******************************************************]
                      [*******************************************************]
                      [*******************************************************]
                      [*******************************************************]
                      [*******************************************************]

               5.2.2. Notwithstanding the table set forth in Section 5.2.1,
                      above, in the event Carrier orders Leased Fiber in a
                      network route ring configuration, such Leased Fiber shall
                      be provided for a minimum Monthly Fiber Charge of [*]
                      [*] regardless of the
                      number of the fiber miles and fiber strands ordered.
                      Subject to availability, MFN will lease to Carrier a
                      minimum of one (1) fiber strand and a maximum of eight (8)
                      fiber strands in any single MFN network ring. MFN shall
                      promptly notify Carrier when MFN has available eight (8)
                      or fewer fibers on a single ring.

               5.2.3. Monthly Building Access Charge: [*] per Carrier
                      Location except as otherwise provided in Section 8.2.3.2
                      to this Product Order.

              5.2.4.  Applicable Taxes (as defined in the Agreement) on any
                      Installation Charge incurred pursuant to a Supplement and
                      all Monthly Lease Payments are to be paid by Carrier as
                      and when due.

6.   Estimated Installation Completion Dates: To be specified in Supplements

7.   Early Termination Charge:

     In the event of termination of this Agreement or any Supplement to this
     Product Order pursuant to Section 11.2 of the General Terms and Conditions
     of this Agreement, Carrier will pay to MFN an Early Termination Charge
     (plus Applicable Taxes) for the affected Leased Fiber and Building Access
     determined as follows:

     1st year termination - [*]% of all unpaid Monthly Lease Payments for the
     affected Leased Fiber for the first year, plus [*]% of all unpaid Monthly
     Lease Payments for the affected Leased Fiber and Building Access for the
     second year, plus [*]% of all unpaid Monthly Lease Payments for the
     affected Leased Fiber for the third year, plus [*]% of all unpaid Monthly
     Lease Payments for the affected Leased Fiber and Building Access for the
     fourth year, plus [*]% of all unpaid Monthly Lease Payments for the
     affected Leased Fiber and Building Access for the fifth year, plus [*]% of
     all unpaid Monthly Lease Payments for the affected Leased Fiber and
     Building Access for the sixth through the last day of the then scheduled
     Lease Term.

     2nd year termination - [*]% of all unpaid Monthly Lease Payments for the
     affected Leased Fiber and Building Access for the second year, plus [*]% of
     all unpaid Monthly Lease Payments for the affected Leased Fiber and
     Building Access for the third year, plus [*]% of all unpaid Monthly Lease
     Payments for the affected Leased Fiber and Building Access for the fourth
     year, plus [*]% of all unpaid Monthly Lease Payments for the affected
     Leased Fiber and Building Access for the fifth year, plus [*]% of all
     unpaid Monthly Lease Payments for the affected Leased Fiber and Building
     Access for the sixth through the last day of the then scheduled Lease Term.

     3rd year termination - [*]% of all unpaid Monthly Lease Payments for the
     affected Leased Fiber and Building Access for the third year, plus [*]% of
     all unpaid Monthly Lease Payments for the affected Leased Fiber and
     Building Access for the fourth year, plus [*]% of all unpaid Monthly Lease
     Payments for the affected Leased Fiber and Building Access for the fifth
     year, plus [*]% of all unpaid Monthly Lease Payments for the affected
     Leased Fiber and Building Access for the sixth through the last day of the
     then scheduled Lease Term.

[*] Indicates confidential treatment requested.

<Page>

     4th year termination - [*]% of all unpaid Monthly Lease Payments for the
     affected Leased Fiber and Building Access for the fourth year, plus [*]% of
     all unpaid Monthly Lease Payments for the affected Leased Fiber and
     Building Access for the fifth year, plus [*]% of all unpaid Monthly Lease
     Payments for the affected Leased Fiber and Building Access for the sixth
     through the last day of the then scheduled Lease Term.

     5th year termination - [*]% of all unpaid Monthly Lease Payments for the
     affected Leased Fiber and Building Access for the fifth year, plus [*]% of
     all unpaid Monthly Lease Payments for the affected Leased Fiber and
     Building Access for the sixth through the last day of the then scheduled
     Lease Term.

     6th through 20th year termination - [*]% of all unpaid Monthly Lease
     Payments for the affected Leased Fiber and Building Access for the balance
     of the then scheduled Lease Term.

     In the event that this Agreement is terminated, and if Carrier has not yet
     leased [*] fiber miles from MFN hereunder as
     of the date of any termination, then such termination shall be calculated
     as if Carrier has actually leased [*] fiber
     miles as of the date of termination. For purposes of this Section 7 only,
     except in cases of Carrier's gross negligence or willful misconduct,
     Carrier's payment to MFN of (i) the Early Termination Charge, (ii) MFN's
     costs of construction and installation plus fifteen percent (15%) plus
     applicable sales or other taxes, and (iii) the Applicable Taxes (set forth
     in Section 2 of the General Terms and Conditions of this Agreement) shall
     be MFN's sole and exclusive remedy under this Agreement.

8.   Fiber, Locations and Requirements

     8.1  Leased Fiber Commitment. Carrier acknowledges and agrees that within
          [*] days of the effective date of this Agreement,
          Carrier will lease Leased Fiber subject to the terms and conditions of
          this Agreement totaling at least [*] fiber miles in
          metropolitan areas where MFN has or reasonably expects to have within
          such [*] day period an installed Network as set
          forth in Exhibit B. Carrier acknowledges and agrees that within sixty
          (60) months after the Effective Date of this Agreement, Carrier will
          lease Leased Fiber subject to the terms and conditions of this
          Agreement totaling at least [*] fiber
          miles in the United States and/or Canada in metropolitan markets in
          which MFN itself or through one or more of its affiliated companies
          has constructed or plans to construct a Network within the next twelve
          (12) months. Any fiber mile leased in a Canadian metropolitan market
          shall be pursuant to a Supplement entered into by either MFN or one of
          its affiliates directly.

          8.1.1. For the purposes of this Agreement, fiber miles will be
                 calculated by multiplying the physical mileage of Carrier's
                 Leased Fiber route(s) by the quantity of Leased Fiber along the
                 same route(s).

          8.1.2. The Monthly Fiber Charge for the initial [*]
                 [*] Leased Fiber miles that MFN leases to Carrier
                 within sixty (60) months after the Effective Date of this
                 Agreement shall be [*] per
                 fiber mile per month.

          8.1.3. Carrier further acknowledges and agrees that for the period
                 beginning at the end of sixty (60) months after the Effective
                 Date until such time as Carrier has leased [*]
                 [*] fiber miles pursuant to Supplements, Carrier
                 shall be liable to MFN for any difference that may exist
                 between the Monthly Fiber Charge for [*]
                 [*] fiber miles and Carrier's actual total Monthly Lease
                 Payments for Leased Fiber miles pursuant to Supplements (the
                 "Contract Balance"). In the event that MFN has reason to
                 believe that such difference may exist, MFN will provide
                 Carrier written notice of the deficiency fifty-nine (59) months

[*] Indicates confidential treatment requested.

<Page>

                 after the Effective Date of this Agreement and Carrier will
                 then have thirty (30) days to order additional fiber subject
                 to the terms and conditions of this Agreement necessary to
                 achieve Supplements for [*]
                 Leased Fiber miles. If after sixty (60) months after the
                 Effective Date of this Agreement, Carrier does not lease
                 from MFN Leased Fiber totaling [*]
                 [*] fiber miles pursuant to Supplements, then in advance
                 of the sixty-first (61st) month after the Effective Date,
                 MFN will invoice and Carrier will pay the Monthly Fiber
                 Charge each month equal to the aggregate Monthly Fiber
                 Charge pursuant to Supplements plus the Contract Balance (as
                 the Contract Balance may be reduced in accordance with the
                 final sentence of this paragraph) multiplied by [*]
                 dollars [*] per fiber mile per month until such
                 time as Carrier has leased an aggregate of [*]
                 [*] fiber miles pursuant to Supplements. Any
                 such amount will be subject to an Early Termination Charge
                 as set forth in Section 7. As and when Carrier has leased
                 additional Leased Fiber miles pursuant to Supplements, the
                 Contract Balance shall be reduced by the amount of the fiber
                 miles subject to such Supplements. Notwithstanding anything
                 to the contrary contained in this Agreement, Carrier will
                 have no liability under this provision or Section 7 of this
                 Product Order in the event that any failure of Carrier to
                 lease [*] fiber miles is due
                 to MFN's inability to deliver fiber in accordance with any
                 Supplements, including, without limitation, any failure of
                 MFN to timely deliver Leased Fiber, any failure of any
                 Leased Fiber to meet the Specifications, MFN's failure to
                 build to announced build plans, and/or any other failure or
                 inability of MFN to timely deliver Leased Fiber in
                 accordance with the terms of the Agreement.

          8.1.4. In no event shall Carrier be obligated to lease Leased Fiber
                 from MFN in excess of [*] fiber
                 miles.

     8.2  Building Access Commitment. Carrier acknowledges and agrees that
          within sixty (60) months after the Effective Date, Carrier will order
          from MFN Building Access into at least [*] Carrier
          Locations. Such Carrier Locations will consist of buildings and/or
          central offices connected to the Network selected from the target
          building list (the "Target Building List"), annexed herewith as
          Exhibit C and updated from time to time by MFN, but not more
          frequently than once every three (3) months.. Notwithstanding anything
          herein to the contrary, MFN shall not be obligated to provide Building
          Access into [*] Carrier Locations. Within sixty (60)
          months after the Effective Date, in the event that MFN fails to
          provide Building Access into a minimum of [*] buildings
          designated on the Target Building List, exclusive of Proposed Carrier
          Locations (defined in Section 8.2.3, below), then Carrier's Building
          Access Commitment shall be reduced accordingly by such number of
          buildings into which MFN fails to provide Building Access.

          8.2.1. Subject to Section 8.2.3.2, the Monthly Building Access Charge
                 shall be [*] per month.

          8.2.2. Carrier further acknowledges and agrees that for the period
                 beginning at the end of sixty (60) months after the Effective
                 Date until such time as Carrier has requested Building Access
                 into [*] Carrier Locations, selected from the
                 Target Building List, pursuant to Supplements, Carrier shall be
                 liable to MFN for any difference that may exist between the
                 Monthly Building Access Charge for [*] Carrier
                 Locations and Carrier's actual total Monthly Building Access
                 Charge pursuant to Supplements (the "BA Contract Balance"). In
                 the event that MFN has reason to believe that such difference
                 may exist, MFN will provide Carrier written notice of the
                 deficiency fifty-nine (59) months after the Effective Date
                 of this Agreement and Carrier will then have thirty (30) days
                 to order additional Building Access into Carrier Locations
                 subject to the terms and conditions of this Agreement
                 necessary to achieve Supplements for [*] Carrier
                 Locations. If after

[*] Indicates confidential treatment requested.

<Page>

                 sixty (60) months after the Effective Date of this Agreement,
                 Carrier does not order Building Access into Carrier Locations
                 totaling [*] pursuant to Supplements, then in
                 advance of the sixty-first (61st) month after the Effective
                 Date, MFN will invoice and Carrier will pay the Monthly
                 Building Access Charge each month equal to the aggregate
                 Monthly Access Charge pursuant to Supplements plus the BA
                 Contract Balance (as the BA Contract Balance may be reduced in
                 accordance with the final sentence of this paragraph)
                 multiplied by [*] per
                 Carrier Location per month until such time as Carrier has
                 ordered Building Access into an aggregate of [*]
                 Carrier Locations pursuant to Supplements or such lesser number
                 as provided in Section 8.2 of the Product Order Any such amount
                 will be subject to an Early Termination Charge as set forth in
                 Section 7. As and when Carrier has ordered Building Access in
                 Carrier Locations pursuant to Supplements, the BA Contract
                 Balance shall be reduced by the amount of the Carrier Locations
                 subject to such Supplements. Notwithstanding anything to the
                 contrary contained in this provision, Carrier will have no
                 liability under this provision in the event that any failure of
                 Carrier to order Building Access into [*]
                 Carrier Locations is due to (i) MFN's inability to deliver
                 Building Access into [*] Carrier Locations or (ii) MFN's
                 failure to timely deliver Building Access pursuant to any
                 Supplements in accordance with the terms of the Agreement.

          8.2.3. Notwithstanding anything contained in this Section 8.2. to
                 the contrary, Carrier shall have the right to request Building
                 Access into a proposed Carrier Location not designated on the
                 Target Building List. Such requests shall be provided to MFN in
                 a written notice pursuant to Section 9.2, specifying the
                 proposed Carrier Location(s) (the "Proposed Carrier Location")
                 and any necessary documentation (including, without limitation,
                 a copy of the telecommunications license agreement between
                 Carrier and the building owner or manager), in a form
                 acceptable to MFN, certifying that a Proposed Carrier Location
                 meets MFN's commercial building criteria (the "Commercial
                 Building Criteria") set forth in Exhibit D, annexed herewith.
                 MFN will determine, in its sole discretion, whether or not the
                 proposed Carrier Location(s) meets the Commercial Building
                 Criteria, and to provide Building Access and construct a
                 Lateral Extension to and into such Proposed Carrier
                 Location(s). All right, title and interest to the Lateral
                 Extensions constructed by MFN shall vest in MFN.

                 8.2.3.1.  Carrier shall use its best efforts to assist MFN in
                           entering into a Telecommunications License Agreement
                           with the owner or manager of a Proposed Carrier
                           Location in the form attached hereto as Exhibit E.
                           Carrier agrees to promptly forward or deliver to
                           MFN's Real Estate Group any and all communications by
                           the owner or manager of a Proposed Carrier Location
                           regarding the Telecommunications License Agreement.
                           Subject to Section 8.2.3, MFN may enter into a
                           Telecommunications License Agreement with a building
                           owner or manager of proposed Carrier Location,
                           pursuant to this Section 8.2.3.1 wherein the terms of
                           such agreement differ from the terms of the form
                           Telecommunications License Agreement attached hereto
                           as Exhibit E, provide that such terms are not in
                           variance with the Building Access Criteria. All such
                           communications should be sent or forwarded to:

                                     Metromedia Fiber Networks, Inc.
                                     685 Third Avenue, 3rd floor
                                     New York, NY  10017
                                     Attn: Mark Pearlman
                                     Vice President - Real Estate Group
                                     (212) 687-9177 x518
                                     mpearlman@mmfn.com

[*] Indicates confidential treatment requested.

<Page>

                 8.2.3.2.  In the event that MFN provides Carrier with Building
                           Access into a Proposed Carrier Location and in
                           consideration of Carrier assisting MFN to enter into
                           a Telecommunications License Agreement with an owner
                           or manager of a Proposed Carrier Location as set
                           forth in Section 8.2.3.1, such Building Access with
                           respect to the Carrier Location shall be provided to
                           Carrier at no charge during the Lease Term.

                 8.2.3.3.  In no event shall Carrier be obligated to order
                           Building Access into an excess of [*]
                           Carrier Locations.

     8.3. Carrier will, from time to time, request Leased Fiber and Building
          Access pursuant to the terms and provisions hereof, by providing MFN
          with one or more written notices (each a "Carrier Request Notice").
          Each such notice shall indicate the number of fibers, the MFN
          metropolitan market and Carrier's proposed Locations. Within thirty
          (30) days after receipt of such notice, MFN will respond to Carrier
          with a Supplement confirming the availability, the Monthly Lease
          Payment for the Leased Fiber and Building Access subject to the
          Supplement, the one time installation charge, if any, and the
          estimated installation completion date for the requested fiber.
          Carrier may order fiber in any metropolitan market in which MFN has
          constructed a Network, except for the first [*] fiber
          miles which must be requested in the metropolitan markets set forth in
          Exhibit B. Carrier will execute and return to MFN each such Supplement
          within ten (10) days of receipt thereof. Carrier shall do so by
          following the procedure set forth in this Section 8.3. Carrier
          acknowledges and agrees that any Leased Fiber in international
          metropolitan markets may be provided directly by one or more
          affiliates of MFN and that Carrier will enter into an agreement with
          such affiliate for such provision of Leased Fiber.

     8.4. Provided Carrier is not in default of this Agreement, Carrier may
          request additional Carrier Locations be added to any then existing
          Supplement by providing MFN one or more written requests. Such
          requests shall indicate the number of fibers, requested term, and any
          relevant information necessary to identify the requested Locations
          including, but not limited to, the address, floor, suite, and room
          number of the requested Location. Within thirty (30) days after
          receipt of such orders, MFN will respond to Carrier with a revised
          Supplement confirming the availability, the Monthly Lease Payment for
          the additional fiber miles, the one time installation charge, if any,
          and the estimated installation completion date for the requested
          additional Locations. Carrier will execute and return to MFN each such
          Supplement within ten (10) days of receipt thereof, failing which such
          Supplement shall be deemed rejected.

9.   MFN address (and contact person) is as follows:

       Metromedia Fiber Network Services, Inc.
       One North Lexington Ave., Fourth Floor
       White Plains, NY  10601
       Attn.: Vice President - Marketing

       For purposes of declaring a default or termination, a copy of the notice
must be sent to:

       Vice President - Legal Affairs
       Metromedia Fiber Network Services, Inc.
       One North Lexington Ave., Fourth Floor
       White Plains, NY  10601

       Carrier address (and contact person) is as follows:

       Cogent Communications, Inc.

[*] Indicates confidential treatment requested.

<Page>

       1015 31st Street NW
       Suite 330
       Washington, DC  20007
       Attn: David Schaeffer

       For purposes of declaring a default or termination, a copy of the notice
must be sent to:

       Cogent Communications, Inc.
       1015 31st Street NW
       Suite 330
       Washington, DC  20007
       Attn:  David Schaeffer

METROMEDIA FIBER NETWORK SERVICES, INC.     COGENT COMMUNICATIONS, INC.

By: /s/ Nicholas M. Tanzi                   By: /s/ David Schaeffer
    ----------------------                      ---------------------------
         Nicholas M. Tanzi                  Name:  David Schaeffer
         President                                   Title:  President

<Page>

                      FIBER OPTIC PRIVATE NETWORK AGREEMENT

                          GENERAL TERMS AND CONDITIONS

1.   TERM AND LEASE

1.1  MFN hereby leases to Carrier, pursuant to Supplements to be executed by the
     parties, optical fiber ("Leased Fiber") on MFN's fiber optic cable network
     ("Network") and/or constructed and installed specifically for Carrier and
     the equipment and interfaces described in the Supplements to the Product
     Order ("Equipment"), as provided in the Product Order and the Supplements
     thereto. The Leased Fiber, Building Access and Equipment leased by Carrier
     will be referred to as the "Product". The lease term ("Lease Term") and
     other specific terms pertaining to the Product are set forth in the
     Supplements. The term "Party" will refer, individually, to either MFN or
     Carrier and the term "Parties" will refer to both of them. The term
     "Agreement" will mean and include the Product Order, Supplements and all
     Exhibits thereto and these General Terms and Conditions.

1.2  MFN will use commercially reasonable efforts to complete installation of
     and provide Carrier with access to the Product on or about the Estimated
     Installation Completion Date specified in the Supplements at the Carrier
     Locations specified in the Supplement ("Turnover Date"). For a period of
     time not to exceed ten (10) business days after the Turnover Date (the
     "Acceptance Test Period"), Carrier will conduct such testing as it
     reasonably deems necessary to ensure that the Product conforms in all
     material respects to the technical specifications set forth in Exhibit A to
     the Product Order ("Specifications"). Carrier will use commercially
     reasonable efforts to complete such acceptance testing and notify MFN in
     writing within five (5) business days after the Turnover Date, but in any
     event within the Acceptance Test Period, of acceptance or of any
     "Deficiencies" (as defined herein) in the Product. Deficiencies exist if
     the Product does not conform in all respects to the relevant
     Specifications. Upon receipt of such notification from Carrier, MFN will
     promptly undertake correction of such Deficiencies and restore access to
     and use of the Product to Carrier. The "Service Date," whereupon the Lease
     Term commences, will be the earlier of (i) completion of testing and
     acceptance of Product by Carrier, (ii) expiration of the AcceptanceTest
     Period or, (iii) if Carrier has identified Deficiencies, then the first
     date upon which Product conforms in all material respects with the relevant
     Specifications. If the Service Date for any Leased Fiber does not occur
     within one hundred and eighty (180) days of the Estimated Installation
     Completion Date set forth in the applicable Supplement, or such other date
     as may be mutually extended by the Parties, Carrier may terminate the
     Supplement with respect to such Leased fiber.

1.3  Carrier will obtain all necessary approvals for collocation in a building
     and for the use of any required building riser conduit or other required
     building facilities at all Carrier Locations. Unless otherwise provided for
     in the Product Order, if there is no existing and available riser conduit
     or other required facilities within such buildings then MFN will perform
     all construction and installation of such riser conduit and Carrier will
     reimburse MFN for the entire out of pocket cost to construct and install
     such riser conduit plus fifteen percent (15%) plus Applicable Taxes.

1.4. Upon the expiration of the Lease Term, or any earlier termination of this
     Agreement or a Supplement, Carrier will promptly remove from any property
     owned, leased or licensed by MFN all Carrier property, equipment and other
     materials used in connection with the Product within forty five (45) days
     from such expiration or termination. Carrier will complete such removal in
     a manner that does not interfere with or damage the Product or the Network.
     Subject to the preceding sentence, in all events, carrier may remove its
     optronic and electronic equipment. If Carrier fails to remove its property
     within such period, such property will be deemed abandoned, and MFN will
     make such disposition of the property as it deems necessary or advisable at
     Carrier's sole expense.

2.   2. TERMS OF PAYMENT

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2.1  Unless otherwise provided for in the Product Order, Carrier agrees to pay
     the One Time Installation Charge, if any, as provided in each Supplement,
     upon the execution of the Supplement. Carrier will also pay to MFN all
     applicable sales or other similar taxes assessed on the transactions
     contemplated by this Agreement other than taxes on or measured by MFN's
     income or capital, or any franchise or permit fees payable by MFN (except
     those fees directly attributable to Carrier) ("Applicable Taxes"), unless
     Carrier is eligible for an exemption and Carrier provides to MFN an
     exemption certificate or other documentation. Commencing on the earlier of
     (i) the Service Date for the first Location of each Ring or (ii) 180 days
     after the Effective Date of the Supplement (unless all such delays are
     caused by or result from the act or omission of MFN) and continuing each
     month thereafter for the duration of the Lease Term, Carrier will pay the
     Monthly Lease Payment and for such Supplement (and the Monthly Maintenance
     Payment for the Equipment, if applicable) plus Applicable Taxes in advance
     for each month. If service commences after the first day of any month or
     terminates before the last day of a month, then the payment for such
     partial month will be pro rated based on the number of days of the Lease
     Term during that month to the number of days in that month. Carrier will
     include such pro rata payment for the initial partial month in the first
     monthly payment at the commencement of the Lease Term for such Supplement.
     The Prepaid Lease Payment, not to exceed four (4) months if any, will be
     paid as provided in the Supplement.

2.2  If Carrier fails to pay any sum when due pursuant to this Agreement, then,
     in addition to such sum, Carrier will pay interest on such unpaid sum at
     the lower of the highest legal rate of interest permitted in the State of
     New York or one and one-half percent (1.5%) per month.

3.   MAINTENANCE, RESTORATION AND REPAIR OF THE NETWORK AND PRODUCT MONITORING

3.1  MFN will provide remote monitoring of the Network and the Product to the
     extent that the Product is incorporated into the Network. MFN will use
     commercially reasonable efforts to maintain the Product in accordance with
     the Specifications (subject to reasonable wear and tear) and the Network in
     good operating condition at all times during the Lease Term. The foregoing
     maintenance will be at no additional charge to Carrier, except as set forth
     in Section 3.4 hereof.

3.2  An "Outage" will mean the complete interruption of communications on one or
     more of Carrier's Leased Fibers resulting from physical damage to, or
     severance of, or a break in, or other failure of any Product. If an Outage
     or any other material degradation of service on any Leased Fibers occurs
     Carrier will immediately notify MFN by telephone at (888) 636-2778 or
     through such other notification procedure as Parties may establish.
     Provided that MFN personnel or contractors have access to affected Carrier
     facilities immediately upon notification, MFN will respond and commence
     work within two (2) hours after the time of notification by Carrier and
     restore effective use of the Product as expeditiously as practicable, but
     in no event more than four (4) hours after receipt by MFN of Carrier's
     notification, subject to "Force Majeure" as provided in Section 11 hereof.

3.3  Except for any Outage caused by or resulting from (i) Force Majeure as set
     forth in Section 11 hereof; (ii) the act or omission of Carrier, its
     employees, agents or contractors; (iii) any of Carrier's equipment or
     facilities used in connection with the Product; or (iv) planned Outages by
     reason of Services which have been scheduled and approved in advance by
     Carrier ("Excepted Outages") in the event of an Outage, Carrier will
     receive from MFN a credit ("Outage Credit") calculated at 5% of the Monthly
     Lease Payment for the affected Leased Fiber strands for each four (4) hours
     of Outage, up to a maximum of the Monthly Lease Payment for one (1) full
     month. Except in the case of a Prepaid Lease Payment or termination as
     provided in this Section 3.3, the Outage Credit will be applied against
     future payments which may become due and payable by Carrier to MFN. The
     Outage Credit will be determined by dividing the total Monthly Lease
     Payment by the number of Carrier Locations and dividing this result by the
     number of Leased Fiber strands to determine the Monthly Lease Payment per
     Leased Fiber Strand. This result is then multiplied by five percent (5%)
     and by the number of four (4) hour Outage periods. For example, if the
     Monthly Lease Payment for six (6) Carrier Locations is $60,000.00, the
     Monthly Lease Payment for each Location would be $10,000.00, and if there
     were four (4) Leased Fiber strands for each Location, the result would be

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     $2,500.00 per Fiber Strand. If the Outage affected two (2) strands at one
     Location for eight (8) hours, the Outage Credit would be $2,500 x 5% x 2 =
     $250.00. For the purposes of determining the Outage Credit pursuant to this
     Section 3.3, if the Product Order provides for a Prepaid Lease Payment,
     then the Monthly Lease Payment will be determined by dividing the Prepaid
     Lease Payment by the total number of months of the Lease Term. The Outage
     Credit will be in the form of a cash payment to Carrier by MFN if the
     Carrier has paid the Prepaid Lease Payment in full or if this Agreement is
     terminated by either Party as provided in Section 3.4 hereof. Outage
     Credits will not be credited or payable for any period of time during which
     MFN personnel or contractors are denied access to Carrier Locations or
     other facilities to remedy an Outage.

3.4  If an Outage occurs and continues for a period longer than fifteen (15)
     days for any reason other than "Force Majeure" as defined in this
     Agreement, then at any time thereafter, unless and until such Outage is
     corrected, either Party can terminate this Agreement and the Supplement
     with respect to the Product subject to the Outage by written notice of such
     termination delivered to the other Party. Notwithstanding the foregoing, if
     such Outage occurs and continues by reason of a breach by a Party of its
     obligations under this Agreement, such breaching Party will not have any
     right to terminate this Agreement. The Outage Credit and right to terminate
     will be the sole and exclusive remedy of Carrier and liability of MFN for
     any Outage regardless of the cause of such Outage.

3.5  If all or part of the Product requires restoration, replacement or repair
     by reason of an act or omission of Carrier, its employees, agents, or
     contractors or any of Carrier's equipment or facilities used in connection
     with the Product, such repair, replacement and/or restoration will be made
     by MFN, at Carrier's sole expense, in accordance with MFN's then current
     time and materials rates plus Applicable Taxes. In addition, Carrier will
     not receive any Outage Credit by reason of the foregoing.

3.6  MFN may assign or subcontract to any third party any or all of its
     performance obligations (including without limitation maintenance) under
     this Agreement and Product Order at any time, without the consent of
     Carrier, provided that MFN will remain obligated for such performance in
     accordance with the terms of this Agreement.

3.7  MFN will have the right to inspect Carrier's use of the Product at any time
     and from time to time during normal business hours upon at least
     `twenty-four (24) hours" prior notice by MFN provided that such inspection
     does not interfere with or hinder Carrier's use of its Product as permitted
     hereunder.

4.   USE AND OWNERSHIP OF THE PRODUCT

4.1  Carrier will not, by itself or through any agent or contractor, make any
     repair to or replacement of the Product or the Network or any other
     equipment or facilities provided by MFN in connection with the Product or
     otherwise. Carrier will not install any equipment to be used with the
     Product or use the Product in any manner which damages or interferes with
     the Product or the Network.

4.2  Carrier will use the Product in material compliance with all applicable
     federal, state and local laws, rules and regulations and all applicable
     franchises, rights of way, leases, licenses, contracts and other
     obligations to third parties with respect to the Network or Product.
     Carrier will obtain and maintain in effect during the Lease term all
     rights, leases, licenses, permits and governmental or non-governmental
     approvals necessary for use of the Product by Carrier and its customers.

4.3  Carrier acknowledges and agrees that the Product is provided for use (1)
     exclusively by Carrier and/or affiliated entities which control or are
     controlled by or commonly controlled with Carrier ("Affiliates") which are
     named in the Product Order (if so named, then the term "Carrier" as used in
     this Agreement will include any such Affiliates of Carrier), (2) customers
     of Carrier and (3) in either case only in the ordinary course of business
     of Carrier. For purposes of this Agreement, the ordinary course of
     Carrier's business shall not include the sale, leasing or granting of any
     rights of

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     use in "dark fiber", as such term is commonly understood in the
     telecommunications industry. Carrier will not under any circumstances (a)
     permit or provide access to or use of the Product, in whole or part, to any
     third party (other than a customer of Carrier in the ordinary course of
     business of Carrier), pursuant to (by way of example and not in limitation)
     sublease, license, sublicense or resale, or any other right to use, or (b)
     share or otherwise utilize in conjunction with a third party (including
     without limitation in any joint venture or as part of any outsourcing
     activity) any of the Product. Any breach of this Section 4.3 will be deemed
     to be a material breach of this Agreement and in the event of such material
     breach MFN will have the right to immediately terminate this Agreement, any
     applicable Product Orders and Carrier's access to the Network, in addition
     to any and all rights and remedies. ,

4.4  MFN retains all right, title and interest in and to the Product and the
     Network to the points within the Carrier Locations specified in the Product
     Order at which MFN's facilities end and Carrier's facilities begin, subject
     only to the grant of access and use provided to Carrier pursuant to this
     Agreement.

4.5  MFN reserves the right to utilize unused external building access and space
     within the building conduit(s) occupied by the Product at the Carrier
     Locations and otherwise, provided that such use does not interfere with or
     hinder Carrier's use of its Product as permitted hereunder.

5.   AUTHORIZATIONS; RELOCATION; CONDEMNATION

"Authorization(s)" will mean all material and applicable governmental or
non-governmental licenses, easements, rights of way, conduit, pole attachment
and any other facilities or property rights, licenses, contracts, franchises,
approvals, permits, orders, consents, and all other rights required for MFN to
operate and maintain the Network or provide the Product to Carrier pursuant to
this Agreement.

5.1  MFN will use commercially reasonable efforts to have or obtain by the
     Service Date, all Authorizations and to maintain or renew all such
     Authorizations through the Initial Term and to replace such Authorizations
     with reasonably suitable replacement Authorizations if any expire or are
     terminated or discontinued during the Initial Term. If any Authorizations
     are modified, terminated or discontinued and not replaced, and the loss of
     such Authorizations threatens to cause or does cause material financial
     harm to MFN, or prevents or materially interferes with MFN's control,
     possession and/or use of the Network or ability to lease the Product or
     materially and adversely affects the use by Carrier of the Product, then
     MFN will at its option either (i) provide Carrier with comparable Product
     or fiber optic capacity on portions of MFN's then existing Network (and/or
     other MFN Networks, including networks belonging to or controlled by MFN
     Affiliates) or on networks of third parties, or (ii) terminate this
     Agreement with respect to the affected Product and rebate to Carrier the
     pro rata portion of all Prepaid Lease Payments allocable to the terminated
     Product and amortized over the remainder of the Lease Term. The foregoing
     will be MFN's sole and exclusive liability and Carrier's sole and exclusive
     remedy with respect to the foregoing.

5.2  If MFN receives notice of any request, intent or plan by any governmental
     or non-governmental third party, to relocate any material part of the
     Product or any material segment of MFN's Network used in the provision of
     the Product, MFN will notify Carrier of such request, intent, or plan. If
     MFN is required by any such third party to relocate any segment of MFN's
     network used in providing the Product, MFN will give Carrier at least sixty
     (60) days (or such lesser period of notice that MFN may have received)
     prior written notice of any such relocation ("Relocation Notice"). Together
     with the Relocation Notice, MFN will provide an estimate of the cost of
     such relocation. MFN will relocate the Leased Fibers, and, to the extent
     MFN is not reimbursed for the cost of such relocation by a third party,
     governmental entity or otherwise, Carrier will pay its pro rata share
     (based on the ratio of leased fiber to total fiber in the affected
     portion)of the costs associated with the relocation of the Product; except,
     however, to the extent that such relocation is the direct result of any
     negligent or willful act or omission of MFN. MFN will use its commercially
     reasonable efforts to secure an agreement for reimbursement from any third
     party, governmental entity or otherwise, requiring any relocation of the
     Network and the Product.

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5.3  If any portion of the Network or the Product and/or the Authorizations in
     or upon which the Product has been installed, become the subject of a
     condemnation proceeding which is not dismissed within one hundred eighty
     (180) days after the date of filing of such proceeding and which could
     reasonably be expected to result in a taking by any governmental agency or
     other party having the power of eminent domain for public purpose or use,
     both Parties will be entitled, to the extent permitted under applicable
     law, to participate in any condemnation proceedings for compensation by
     either joint or separate awards for the economic value of their respective
     interests in the Leased Fibers that are subject to such condemnation
     proceeding.

6.   WARRANTIES

6.1  MFN warrants to Carrier that upon the Service Date and/or over the Lease
     Term the Product will operate in all material respects in accordance with
     the Specifications related thereto.

          EXCEPT AS OTHERWISE EXPRESSLY PROVIDED IN THIS AGREEMENT, MFN
          DISCLAIMS ALL WARRANTIES WHETHER EXPRESS OR IMPLIED INCLUDING ANY AND
          ALL WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE
          WITH RESPECT TO THE (i) NETWORK OR PRODUCT, (ii) THE LEASE GRANTED
          PURSUANT HERETO, (iii) MAINTENANCE SERVICES (iv) CONSTRUCTION AND
          INSTALLATION SERVICES, IF ANY, AND (v) ANY OTHER SERVICE(S)
          (HEREINAFTER (iii) THROUGH (v) WILL COLLECTIVELY BE REFERRED TO AS
          "SERVICES") PROVIDED BY OR ON BEHALF OF MFN HEREUNDER.

7.   LIABILITY/INDEMNIFICATION

7.1  Except for the gross negligence or willful misconduct of a Party hereto and
     except where a specific remedy is provided in this Agreement, the liability
     of each Party to the other Party for damages will be limited to the total
     Installation Charges and the Monthly Lease Payments paid or payable by
     Carrier for the Lease Term during which the damages were incurred. In no
     event will either Party be liable to the other Party for any incidental,
     indirect, special, consequential, exemplary, or punitive damages arising
     out of or relating to this Agreement, the lease granted hereunder, the
     Network, Product or Services provided hereunder, including damages based on
     loss of revenues, profits or lost business opportunities, regardless of
     whether the respective Party had been advised of or could have foreseen the
     possibility of such damages.

7.2  Each Party agrees to indemnify, defend and hold the other, its officers,
     directors, employees, agents and contractors harmless from and against all
     loss, damage, liability, cost and expense (including reasonable attorney's
     fees and expenses) by reason of any claims or actions by third parties for
     (i) bodily injury, including death, (ii) damage, loss or destruction of any
     real or tangible personal property (including without limitation the
     Network and Product) which third party claims arise out of or relate to (a)
     any Product or Services provided by or on behalf of MFN hereunder, (b) a
     Party's performance of or failure to perform any term, condition or
     obligation under this Agreement, (c) any act or omission of a Party's
     directors, agents, employees, contractors, representatives or invitees, or
     (d) Carrier's or its customer's use of the Product and conduct of their
     respective businesses including without limitation the content of any
     video, voice or data carried by Carrier or its customers on the Product or
     Network.

7.3  Except as otherwise set forth in this Agreement, nothing contained herein
     will operate as a limitation on the right of either Party to bring an
     action for damages against any third party based on any act or omission of
     such third party as such act or omission may affect the construction,
     operation, or use of the Product. Each Party agrees to execute such
     documents and provide such commercially reasonable assistance, at the
     claiming Party's sole expense, as may be reasonably necessary to enable the
     claiming Party to pursue any such action against such third party.

8.   CONFIDENTIALITY

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8.1  The Parties acknowledge and agree that this Agreement and the information
     each Party has provided or will provide in connection with this Agreement
     or that the other Party learns or obtains from a source other than public
     domain or from a source (including a Party) not in violation of any
     obligation of confidentiality, are and will be confidential and proprietary
     to the Party providing such information (the "Providing Party"). The Party
     in receipt of or learning or obtaining the confidential information (the
     "Receiving Party") agrees not to distribute, use or disclose to any third
     party the confidential information of the Providing Party.

8.2  Except as may be required by applicable legal requirements in the course of
     defending or prosecuting a legal, insurance or other claim or as required
     by applicable law, rule or regulation, Receiving Party will restrict
     dissemination of confidential information to only those persons who must
     have access to such confidential information in order to perform their
     respective rights or obligations hereunder (a) or otherwise to know such
     confidential information in connection with such Party's business and (b)
     the Party's legal tax and accounting personnel and advisors and investors.
     The Receiving Party will promptly notify the Disclosing Party of any such
     required disclosure to enable the Disclosing Party to seek protective
     relief therefrom and shall cooperate as the Disclosing Party may request in
     connection therewith.

8.3  Carrier may disclose the identity of MFN as a supplier of Carrier, and MFN
     may disclose the identity of Carrier as customer of MFN, each with the
     prior written consent from the other; which consent will not be
     unreasonably withheld or delayed; provided, that no such disclosure shall
     imply any endorsement of the disclosed Party or contain any misleading
     reference to the nature of the relationship between the Parties. Each Party
     may, in connection with a financing transaction, disclose confidential
     information to an equity investor or a lending financial institution which
     has executed an agreement with such Party to maintain the confidentiality
     of this Agreement in a manner consistent with the terms of this Section 8.
     Furthermore and notwithstanding anything contained herein to the contrary,
     each Party may disclose the general nature of this Agreement to such third
     parties PROVIDED THAT no such disclosure will indicate the pricing or
     pricing terms under this Agreement without the prior written consent of the
     other Party.

8.4  Each Party acknowledges and agrees that the information of the Disclosing
     Party described in this Section 8 constitutes valuable property of the
     Disclosing Party and that Disclosing Party will suffer irreparable injury
     not compensable by money damages for which the Disclosing Party will not
     have an adequate remedy at law in the event of a breach by the Receiving
     Party of the provisions of this Section 8 and therefore the Disclosing
     Party shall be entitled to injunctive relief to prevent or curtail any such
     breach, threatened or actual. The foregoing shall be without prejudice to
     or limitation on any other rights a Party may have under this Agreement, at
     law or in equity.

9.   NOTICES

Unless otherwise provided herein, all notices and communications concerning this
Agreement will be in writing and sent to the address (and contact person)
specified in the Product Order, or at such other address as may be designated in
writing by a Party. Unless otherwise provided herein, notices will be sent by
certified US Postal Service, return receipt requested, or by commercial
overnight delivery service, or by facsimile, and will be deemed delivered, if
sent by US Postal Service, five (5) days after deposit, if sent by facsimile,
upon verification or receipt or, if sent by commercial overnight delivery
service, one (1) business day after deposit therewith.

10.  RENEWAL TERM

Provided that Carrier is not in breach of any of its material obligations under
this Agreement and subject to the conditions of this Agreement, Carrier may
renew the term of this Agreement for the Product for one (1) additional renewal
term upon the terms and conditions of this Agreement, except for the length of
such renewal term and the Installation and Lease Fee payments, which the Parties
will negotiate in good faith

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following Carrier's written request for renewal delivered to MFN no earlier than
one year before the scheduled expiration date of the initial term and no later
that ninety (90) days before such expiration date.

11.  TERMINATION/FORCE MAJEURE

11.1 If any of the following events of default occur, the non-breaching Party
     (if MFN) will have the right to deny access by Carrier to the Product or
     Network and (if either Party) to terminate this Agreement or, if
     applicable, the affected Supplement, by written notice following the
     expiration of any periods of time included in the following, such
     termination to be effective in the on the date set forth in the written
     notice of termination:

     11.1 (a) If Carrier terminates any Supplement at any time before the
          expiration of the Lease Term (whether before or after the Turnover
          Date) or fails to make any payment hereunder within five (5) days or
          receipt of written notice of late payment from MFN, MFN will have the
          right to terminate such Supplement and/or deny access by Carrier to
          the Product or Network immediately without further notice to Carrier.

     11.1 (b) If a Party breaches any material term or condition of this
          Agreement and such breach remains uncured thirty (30) days after
          delivery to the breaching Party of written notice of such breach,
          unless the breach is of a nature or involves circumstances requiring
          more than thirty (30) days to cure, the time period may be extended
          for such time as will be reasonably required, up to a maximum of one
          hundred and twenty (120) days provided the defaulting party proceeds
          diligently to cure the breach.

     11.1 (c) A Party applies for or consents to the appointment of a receiver,
          trustee or similar officer for it or any substantial part of its
          property or assets, or any such appointment is made without such
          application or consent by such Party and remains undischarged for a
          period of sixty (60) days; or

     11.1 (d) A Party consents to the institution of a petition, application,
          answer, consent, default of otherwise of any bankruptcy, insolvency or
          reorganization and any such proceeding as instituted against such
          Party remains undischarged for a period of sixty (60) days.

11.2 In the event of termination of a Supplement by MFN pursuant to Section 11.1
     hereof or by Carrier after execution of the Supplement or before the end of
     the Lease Term (other than by Carrier for cause as provided in this Section
     11), MFN will be entitled to receive, and Carrier will immediately pay, the
     early termination charge ("Early Termination Charge") set forth in the
     Product Order, and to offset any remaining portion of the Prepaid Lease
     Payment against any sums otherwise due and payable by Carrier to MFN
     pursuant to this Agreement.

11.3 If any Authorization is modified, terminated or discontinued and not
     replaced as provided in Section 5.2 of these General Terms and Conditions,
     and MFN has not notified Carrier in writing within sixty (60) days after
     the occurrence of such modification, termination or discontinuance that MFN
     will provide additional or substitute Product or capacity as provided in
     Section 5.2, then and thereafter either party has the right, exercisable in
     its sole discretion, to terminate the applicable Supplement with respect to
     the affected Product upon thirty (30) days prior written notice (or such
     other notice as is practicable under the circumstances) without liability
     whatsoever by either Party to the other Party or any party claiming by,
     through or under such other Party other than the return to Carrier, of the
     unamortized portion of any Prepaid Lease Payment as of the date of such
     termination as provided in Section 5.2.

11.4 Neither Party will be in breach of this Agreement resulting from delay or
     prevention of performance of such Party which is caused by any act
     attributable to an occurrence or an event of "Force Majeure" as defined
     herein. Neither party will, however, be relieved of liability for failure
     of performance due to a claimed Force Majeure hereunder if such failure is
     due to causes arising out

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     of its own negligence or to removable or remedial causes that it fails to
     remove or remedy using commercially reasonable efforts and within a
     reasonable period of time.

11.5 The term "Force Majeure" will mean any cause beyond the control of Carrier
     (or MFN, as applicable) which, by the exercise of due foresight, Carrier
     (or MFN) could not reasonably have been expected to avoid, and which by the
     exercise of reasonable diligence, Carrier (or MFN) will be unable to
     overcome, including but not limited to action by governmental authority
     including without limitation moratorium on any activities related to the
     Agreement, third party labor dispute, flood, earthquake, fire, lightning,
     epidemic war, riot, civil disturbance, sabotage and the like. The party
     affected by an event of Force Majeure (the "Affected Party") will notify
     the other party (the "Other Party") promptly of any occurrence or condition
     which, in the Affected Party's reasonable opinion, warrants an extension of
     time. Such notice will specify in detail the anticipated length of delay,
     the cause of the delay and a timetable by which any remedial measures will
     be implemented.

12.  ASSIGNMENT; SUCCESSION

12.1 Carrier will not assign any right nor delegate any duty under this
     Agreement, in whole or in part, whether by operation of law or otherwise,
     without the prior written consent of MFN, which shall not be unreasonably
     withheld. Notwithstanding the foregoing, this Agreement may be assigned to
     any entity controlling, controlled by or under common control with Carrier,
     or who acquires all or substantially all of the assets or stock of Carrier,
     or any entity surviving merger or consolidation of such party or entity
     without the consent of MFN, provided that MFN is given prompt notice of
     such assignment. Upon any permitted assignment (or delegation) hereunder,
     Carrier will remain jointly and severally responsible for the performance
     under this Agreement, unless released in writing by MFN. Any permitted
     assignee will expressly assume all liabilities hereunder prior to the
     effectiveness of such assignment. Any attempted assignment or delegation
     without such consent will be null and void and may be deemed by MFN, in its
     sole discretion, to constitute a material breach of this Agreement.

12.2 The Agreement and Product Order will be binding upon and inure to the
     benefit of the Parties hereto and their respective successors and permitted
     assigns.

13.  GOVERNING LAW

13.1 THIS AGREEMENT WILL BE INTERPRETED AND CONSTRUED IN ACCORDANCE WITH THE
     INTERNAL LAWS OF THE STATE 0F NEW YORK WITHOUT GIVING EFFECT TO ITS
     PRINCIPLES OF CONFLICTS OF LAWS.

14.  SURVIVAL

The Parties' respective representation, warranties, and covenants, together with
obligations of indemnification, confidentiality and limitations on liability
will survive the expiration, termination or rescission of this Agreement and
continue in full force and effect.

15.  ENTIRE AGREEMENT

This Agreement, Product Order, Supplements, Exhibits and all addenda attached
hereto constitute the entire agreement between the parties hereto with respect
to the subject matter hereof and supersede any and all prior negotiations,
understandings, and agreement with respect hereto, whether oral or written.

16.  REMEDIES CUMULATIVE

Except as otherwise expressly provided, the rights and remedies set forth in
this Agreement will be in addition to, and cumulative of, all other rights and
remedies at law or in equity.

17.  REPRESENTATIONS, WARRANTIES AND COVENANTS

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Each Party represents, warrants and covenants to the other that (a) it is a
corporation, limited liability company, partnership, or other legal entity, duly
organized, validly existing and in good standing under the laws of the state of
its organization, (b) it has all requisite power and authority to enter into and
perform its obligations under this Agreement and Product Order and (c) this
Agreement, when executed, will become the legal, valid and binding obligation of
such Party.

18.  NO AGENCY

Nothing in this Agreement shall be deemed to place the parties in the
relationship of employer-employee, principal-agent, or partners or joint
venturers.

19.  MISCELLANEOUS

19.1 The covenants, undertakings, and agreements set forth in this Agreement
     will be solely for the benefit of and will be enforceable only by the
     Parties hereto or their respective successors or permitted assigns.

19.2 The headings of the Sections in this Agreement are strictly for convenience
     and will not in any way be construed as amplifying or limiting any of the
     terms, provisions or conditions thereof.

19.3 In the event any term of this Agreement will be held valid, illegal or
     unenforceable, in whole or in part, neither the validity of the remaining
     part of such term nor the validity of the remaining terms of this Agreement
     will be in any way affected thereby.

19.4 This Agreement may be amended only by a written instrument executed by the
     Parties.

19.5 No failure to exercise and no delay in exercising, on the part of either
     Party hereunder, any right, power or privilege hereunder will operate as a
     waiver hereof, except as expressly provided herein.

19.6 This Agreement may be executed in multiple counterparts, each of which will
     constitute one and the same instrument.

METROMEDIA FIBER NETWORK SERVICES, INC.     COGENT COMMUNICATIONS, INC.

By: /s/ Nicholas M. Tanzi                   By: /s/ David Schaeffer
    --------------------                        ---------------------------
      Nicholas M. Tanzi                     Name:  David Schaeffer
      President                             Title:  President

<Page>

                                    EXHIBITS

Exhibit A:    Leased Fiber Specifications
Exhibit B:    Initial Metropolitan Markets
Exhibit C:    Target Building List
Exhibit D:    Commercial Building Criteria
Exhibit E:    Telecommunications License Agreement

<Page>

                                    EXHIBIT A
                           LEASED FIBER SPECIFICATIONS
                                       AND
          FIBER OPTIC CABLE SPLICING, TESTING AND ACCEPTANCE STANDARDS

MFN will perform fiber testing as described below on each Leased Fiber and will
provide the documentation (hard copy and/or diskette) of results to the
Customer. Each "span" will be defined in documentation included in the
Customer's package. Acceptance of a span by Customer will be an acknowledgement
by the Customer that all Leased Fiber complies with all performance criteria
contained herein.

1)   POWER TESTING: this end-to-end loss measurement will be conducted for each
     Leased Fiber in the span and from both directions using an
     industry-accepted laser source and power meter. The b-directional average
     will be used to determine the end-to-end loss of the span at each
     appropriate wavelength. This test will be conducted at both 1310 nm and 150
     nm for Standard Single Mode Fiber; Dispersion Shifted Fiber (True Wave
     (TM), LEAF(TM), etc.) will be tested at 1550 nm only. In the event that a
     span consists of both Standard Single Mode and Dispersion Shifted fiber
     types, only 15450 nm testing will be conducted. This power testing will
     ensure fiber continuity and the absence of crossed fibers in the span.
     Power testing will only be conducted where the Leased Fiber is terminated
     by MFN in fiber distribution panels at both ends of the span.

2)   OTDR TESTING: All traces will be provided in hard copy and diskette form
     using GR 196 format. This testing will be conducted at both 1310 nm and
     1550 nm only if the Leased Fiber consists of either Dispersion Shifted
     Fiber (True-Wave(TM), LEAF(TM), etc.) or a combination of Single Mode and
     Dispersion Shifted fiber types.

     OTDR testing will be conducted on a bi-directional basis for each Leased
     Fiber in each span at the appropriate wavelengths for the Leased Fiber
     described above. However, if due to length or attenuation reasons that the
     Leased Fiber span exceeds the dynamic range of an OTDR, a portion or the
     entire span may be tested on a unidirectional basis only. Alternatively,
     the Leased Fiber span may be divided into shorter testing spans, to the
     extent reasonably possible, in order to obtain bi-directional analysis.
     Also, in instances where a Customer intends to accept Leased Fiber that is
     not terminated at one end by MFN in a fiber distribution panel (such as in
     a manhole or handhole) only unidirectional testing will be performed.

     The turnover documentation package delivered to Customer will contain the
     actual traces that detail the testing parameters (including pulse width,
     averaging and range). The average bi-directional splice loss for all
     splices within each span will be 0.15 dB or less while each connector pair
     (such as at a FDP) will have an average bi-directional connector loss for
     all splices within each span of 0.5 dB or less for all connectors within
     each span. (Note that the front and end connector of the span can only be
     measured uni-directionally and will also have a loss equal to or less than
     0.5 dB). In the event that OTDR acceptance testing must be done on a
     unidirectional basis (for reasons described above), an average per span
     splice loss will be 0.30 dB.

     All traces will be provided in hard copy and/or diskette form using GR 196
     format. If the average bi-directional splice loss of each span exceeds 0.15
     dB (or 0.30 dB uni-directionally), MFN will provide upon the Customer's
     request documentation of at least three attempts to reduce this value to
     below 0.15 dB dB (0.30 dB uni-directionally). The only exception to this
     will be in the instance of splice between two different fiber types
     (Standard Single-mode to Dispersion Shifted, Depressed-Clad, fibers with
     different mode-field diameters).

     Customer should also note that the loss and/or reflectance of the front-end
     connector (as measured using a launch cord) is only an indicator of a
     problem such as a defective port, bulkhead, or the like. Since a different
     patch cord will be used by Customer (that connects to their equipment), for
     example) to make to this connector, a different loss and/or the reflectance
     may occur.

<Page>

                                    EXHIBIT B

o    New York City
o    Northern New Jersey
o    Philadelphia
o    Chicago
o    Dallas
o    Washington, DC

<Page>

                                    EXHIBIT C

<Page>

                                     [*]

[*] Indicates confidential treatment requested.

<Page>

                                    EXHIBIT D
                    MFN'S COMMERCIAL BUILDING ACCESS CRITERIA

1.   The building qualifies as a Class A commercial building.

2.   The building is located within [*] mile of the Network.

3.   The building has at least [*] square feet.

4.   The building has a lest [*] tenants.

5.   MFN obtains the following access rights for a minimum term of [*]
     years after either (1) directly from the building owner or manager via a
     Telecommunications License Agreement or (ii) through an existing Carrier's
     arrangement with the building owner or manager (without MFN being subject
     to any additional rent or exclusive dealing provisions):

     a.   May bring up to four hundred thirty two (432) fiber strands through
          two (2) diverse locations and into MFN-installed distribution panels
          or racks,

     b.   cross-connect and provide dark fiber services to MFN carrier clients
          and tenants, with right, subject to availability, to fiber home run to
          MFN private network customers,

     c.   install three-inch (3") conduits from up to two (2) diverse
          points-of-entry to Carrier or MFN's space, and from Carrier or MFN's
          space to riser access points.

     d.   Except for its pre-existing private network clients (for which there
          shall be no by-pass fees), MFN will use Carrier's managed or other
          building central distribution system (including, without limitation,
          all internal conduit, risers, space and other building facilities)
          ("CDS") under "most favored nation" terms and conditions and without a
          requirement for by-pass fees,

     e.   MFN retains all right, title and interest in and to the optical fiber
          strands, equipment and interfaces (including, without limitation,
          riser conduits) which MFN installs,

     f.   MFN's rights set forth above will survive the expiration or
          termination of any agreement between MFN and Carrier or any agreement
          between Carrier and the Building owner or manager, at no cost or
          additional rent to MFN, and

     g.   if the Carrier's arrangement is terminated, then the Building owner or
          manager will provide such rights to MFN for a total term of ten (10)
          years with two (2) five (5) year renewal options for a charge
          determined by the Building owner or manager but in accordance with the
          applicable fair market value and agreed upon by MFN, provided MFN is
          not in default.

6.   MFN reserves the right to revise the foregoing criteria from time to time
     in its sole discretion.

[*] Indicates confidential treatment requested.

<Page>

                                    EXHIBIT E

                     METROMEDIA FIBER NETWORK SERVICES, INC.

                      TELECOMMUNICATIONS LICENSE AGREEMENT

THIS TELECOMMUNICATIONS LICENSE AGREEMENT ("Agreement) is made as of this __ day
of __________ 2000 between("Licensor"), having an address of
____________________ and METROMEDIA FIBER NETWORK SERVICES, INC., its permitted
successors and/or assigns, having an address of One North Lexington Avenue,
White Plains, New York 10601 ("Licensee").
                                     RECITAL

A. Licensor is the owner of certain lands as more particularly described on
Exhibit (the "Land") and a building on the Land (the "Building") commonly known
as
B. Licensor desires to give the Building access to telecommunications services
without restricting Licensor's or its tenants' choice of service providers,
C. Licensee desires to connect the Building to its fiber optic network (the
"Network") and to install certain telecommunications facilities on or in the
land and inside the Building so that the Licensor's tenants may obtain
telecommunications services over Licensee's network.
NOW, THEREFORE, in consideration of the mutual covenants contained herein and
for other good and valuable consideration, the receipt and sufficiency of which
are hereby acknowledged, the parties agree as follows:
     1. Grant of License Licensor hereby grants to Licensee the non-exclusive
right and license to do the following:
          a.   to install, maintain, operate, replace and remove cable and
               optical fibers , junction boxes, hangers, pull boxes, splicing
               boxes, ground wiring, racks, cabinets, vents, ducts, conduits,
               pipes, equipment, supplemental HVAC and other facilities
               (collectively. the "Telecommunications Facilities") as generally
               described on Exhibit B;
          b.   to use any building entrance links, communications wiring and
               other facilities, as presently exist or which may exist during
               the License Term to the extent reasonably necessary in connection
               with the Telecommunications Facilities and to connect Licensee's
               present and future private customers and Service Providers to the
               Network;
          c.   to install or construct additional Telecommunications Facilities
               as may be reasonably necessary to connect Licensee's private
               customers and/or Service Providers in the Building to the
               Network, subject to Section 6 hereof.

<Page>

     2. EQUIPMENT ROOM. Licensee shall have, on an exclusive basis, the right to
occupy the space shown on Exhibit (the "Equipment Room") for any of the
foregoing purposes, and to install In the Equipment Room, in addition to
Telecommunications Facilities, equipment belonging to Licensee's private
customers and/or Service Providers.
     3. TERM. The rights and obligations of Licensee hereunder shall be for a
term of ten (10) years. Provided Licensee is not then in default, Licensee shall
be entitled to an automatic renewal of the term for an additional ten (10) years
commencing on the expiration of the initial ten (10) year period. Thereafter,
provided Licensee is not then in default, Licensee shall be entitled to
successive one (1) year renewals on the same terms as are contained herein.
     4. LICENSE FEE. Commencing on the date Licensee completes its installation,
Licensee shall pay Licensor the sum of Dollars ($) per month ("License Fee").
The License Fee shall be payable to Licensor, in advance, on the first day of
each calendar month. If the term commences on other than the first day of a
month, the License Fee shall be prorated for that first month for the number of
days from the Commencement Date to the end of the month.
     5. INSTALLATION AND CONSTRUCTION. All work permitted pursuant to this
Agreement to be performed on the Land or in the Building shall be performed by
Licensee or its Approved Contractors (defined below), at Licensee's sole cost
and expense and in accordance with plans approved by Licensor in accordance with
this Agreement. The term "Approved Contractors" shall mean any contractor listed
on Exhibit Q annexed hereto or any other contractor approved by Licensor, such
approval not to be unreasonably withheld or delayed. All installations by
Licensee shall be made in compliance with applicable law. Prior to installing
any Telecommunications Facilities, Licensee shall submit detailed plans and
specifications of the planned installation to Licensor, for Licensor's approval,
which approval shall not be unreasonably withheld or delayed. Licensor shall
respond to Licensee's proposed plans within ton (10) business days after receipt
with either approval or the changes required for Licensor's approval. Licensor
shall cooperate with Licensee, at no cost to Licensor, in obtaining third party
permits, easements or agreements necessary for Licensee to exercise its rights
hereunder. During construction, Licensor shall permit Licensee to place a
40-yard rubbish container on the Land near the freight elevator or loading dock.
     6. ACCESS. Licensee shall have 24 hour/day 365 days/year access to its
Telecommunications Facilities and Equipment Room.
     7. UTILITIES. Licensee shall be responsible for procuring such utility
services as are necessary for the operation of the Telecommunications
Facilities, on a sub-metered basis. To the extent that Licensor offers
electrical service to tenants in the Building, Licensee shall purchase its
electricity from Licensor on a sub-metered basis, provided Licensor's charges
are no greater than those that Licensee would experience on the open market.
Licensee shall be responsible for the cost of any utilities consumed by it at
the Building together with any costs incurred to sub-meter the connections to
the Telecommunications Facilities.
     8. ACCESS BY SERVICE PROVIDERS. Licensee shall have the right to enter into
agreements with third party Service Providers granting such providers the right,
on a non-exclusive basis, to provide services to tenants of the Building over
Licensee's Network and Telecommunications Facilities ("Service Providers"), and
where necessary

<Page>

(in connection with the provision of such services) to install and maintain
equipment in Licensee's Equipment Room. The foregoing shall not prevent the
Licensor from requiring Service Providers to enter into separate license
agreements on mutually acceptable terms.
     9. INSURANCE. Licensee shall, at its sole cost and expense, maintain
property insurance covering its Telecommunications Facilities and any other
personal property of Licensee located on the Land or in the Building and hereby
releases Licensor from any liability for damage to such personal property except
to the extent caused by Licensor's negligence or willful misconduct. Licensee
shall also maintain comprehensive general liability insurance in an amount not
less than $2,000,000 combined single limit and shall, upon request, furnish
Licensor with a certificate of insurance naming Licensor as an additional
insured, as its interest may appear. Licensee agrees to carry such other
insurance as it may be required to carry by law, such as worker's compensation
insurance coverage. Licensor and Licensee both hereby waive any property damage
claim which either party may in the future have against the other to the extent
such party's damages are covered by the waiving party's own-insurance. Each
party agrees to obtain, for the benefit of the other, a policy or endorsement
waiving such party's insurance carrier's right of subrogation
     10. LIENS. Licensee shall not suffer or permit any mechanic's, laborer's or
materialman's lien to be filed against the Land or Building or any part thereof
by reason of work, labor, services or materials furnished to Licensee, and if
such lien shall be so filed, Licensee shall, following notice thereof, cause
such lien to be discharged of record or bonded during the continuance of any
dispute. The Telecommunications Facilities shall at all times remain the
property of Licensee and Licensee shall have the right to finance the
Telecommunications Facilities and to grant liens to its lenders against the
Telecommunications Facilities. Licensee shall have the right to record uniform
commercial code notice filings to give public notice of Licensee's ownership of
the Telecommunications Facilities.
     11. CASUALTY AND CONDEMNATION. In the event that the Building, or any part
thereof is damaged by fire or other casualty, Licensor shall, at its expense,
cause the damage to be repaired to a condition as nearly as practicable to that
existing prior to the damage, with reasonable speed and diligence, subject to
delays in adjustment of loss under insurance policies, compliance with
applicable governmental requirements and other delays beyond the control of
Licensor. Notwithstanding the foregoing, in the event that the damage to the
Building is so severe that it results in the termination of leases such that
Licensee or any Service Provider no longer has any customers in the Building,
then Licensee shall have the right to terminate this Agreement. In the event
that the Building or Land is taken by eminent domain or deed in lieu thereof
such that Licensee is denied access to the Building, the Telecommunications
Facilities or the ability to remain connected to the end users in the Building,
then Licensee shall have the right to terminate this Agreement
     12. SUBORDINATION AND NONDISTURBANCE. (a) Subject to compliance with
Section 12 (b), this Agreement Is and shall be subject and subordinate to all
ground or underlying leases of the entire Building and to all mortgages, deeds
of trust and similar security documents which may now or hereafter be secured
upon the Building, and to all renewals, modifications, consolidations,
replacements and extensions thereof.

<Page>

(b) Licensor shall cause: (I) any party holding a mortgage or deed of trust on
any portion of the Building and (ii) the fee owner (if Licensor is a ground
lessee) and any other party having an interest that Is superior to Licensee's
interest in the Premises to execute and deliver to Licensee a non-disturbance,
subordination and attornment agreement on such mortgagee's trustee's or other
party's standard form within thirty (30) days of the date of this License (or
within thirty (30) day's after the execution of a mortgage or dead of trust or
conveyance that is entered Into after the date of this License).
     13. TAXES. Licensee shall be responsible for any personal property taxes
levied or assessed against the Telecommunications Facilities owned by Licensee
and installed on the Land or in the Building. Licensee shall furnish Licensor
with evidence of payment of such taxes promptly following Licensors request
therefor.
     14. REMOVAL OF TELECOMMUNICATIONS FACILITIES. At the termination of this
Agreement Licensee shall have the right to remove the Telecommunications
Facilities, provided Licensee restores any damage caused by such removal.
     15. ATTORNEY'S FEES. The prevailing party shall be entitled to reasonable
attorneys' fees and disbursements incurred in connection with the institution of
any action or proceeding in court to enforce any provision hereof or for damages
by reason of any alleged breach or default of any provision of this Agreement or
for a declaration of either party's rights or obligations hereunder or for any
other judicial remedy, at law or in equity.
     16. BIND AND INURE; ASSIGNMENT. This Agreement shall be binding upon and
inure to the benefit of the parties hereto, their successors and/or assigns.
This Agreement Is irrevocable, except in accordance with Its terms. This
Agreement and the rights of Licensee hereunder may be assigned without the prior
written consent of the Licensor in connection with a sale of all or
substantially all of the assets of Licensee, or to an entity controlling
Licensee, under common control with Licensee or controlled by Licensee. All
other assignments shall be subject to the prior written consent of the Licensor,
which consent shall not be unreasonably withheld, conditioned or delayed.
     17. NO IMPLIED WAIVER. No delay or omission by a party in the exercise of
any right or remedy upon any breach by the other party shall impair such right
or remedy or be construed as a waiver.
     18. NOTICES. Except in the case of emergencies, all notices and other
communications hereunder shall be in writing either personally delivered or
mailed, via certified mail, return receipt requested, or sent by overnight
courier to the parties at the address first set forth above or such other
address as is subsequently given by written notice in accordance with this
Section. Notices will be deemed to have been given upon receipt or rejection.
     19. AUTHORITY; QUIET ENJOYMENT. Licensor represents and warrants to
Licenses that Licensor is the sole owner in fee of the Land and Building and has
full legal capacity, power and authority to grant the license created hereby.
Licensor covenants that Licensee shall and may peaceably and quietly have, hold
and enjoy the license hereby granted without interference by Licensor or anyone
claiming under Licensor.
     20. SEVERABILITY; INTEGRATION. A determination by a court of competent
jurisdiction that any provision of this Agreement or any part thereof is illegal
or unenforceable shall not invalidate the remainder of this Agreement or such
provision, which shall continue to be in effect This Agreement represents the
entire agreement of

<Page>

the parties with respect to the subject matter hereof and supersedes any prior
written or oral understandings. This Agreement cannot be modified except in a
writing signed by the party to be bound.
     21. GOVERNING LAW. This Agreement and the rights and obligations of the
parties shall be governed and construed in accordance with the laws of the State
where the Building is located.
     22. CONFIDENTIALITY. Licensor shall (1) treat as proprietary and
confidential to Licensee any plan, study, report or other data or material which
is designated as confidential or which from all circumstances, in good faith,
ought to be treated as confidential or which is not publicly available other
then through breach of this covenant, and (ii) not disclose or release the same
to any third party except with the prior written consent of Licensee. Licensor
agrees not to disclose any of the business terms of this Agreement to any third
parties without the prior consent of Licensee, except that Licensor shall have
the right without Licensee's consent, to disclose such information to
prospective purchasers, investors or mortgagees of the Building.
     23. MASTER AGREEMENT. The parties intend this Agreement to be one of
several between them concerning the subject matter hereof. In the event that
Licensee identifies other properties owned or managed by Licensor, and to the
extent that (a) there are suitable premises available in such other properties,
and (b) Licensee desires to license such additional premises, then the parties
shall enter into a separate written license agreement substantially in the form
and content of this. Agreement.
     24. NO PRICE DISCRIMINATION. Licensor agrees not to discriminate against
Licenses by offering more favorable licensing terms to third parties than are
offered to Licensee pursuant to this Agreement or offering more favorable
licensing terms to third parties than are offered to Licensee's customers
pursuant Section 9 of this Agreement, without, in each instance, offering the
same terms to Licensee or its customers, as the case may be.
     [remainder of this page left blank]

<Page>

     26. LIMITATION ON LICENSOR'S LIABILITY. Licensor's liability hereunder
shall be limited to Licensor's interest in the Building or any proceeds thereof
     IN WITNESS WHEREOF, the parties have executed this Agreement as of the date
first set forth above.

                                   [LICENSOR]
WITNESS:                                 _____________________________

____________________               By:_______________________________
                                   Name:_____________________________
                                   Title:____________________________
WITNESS:                                  METROMEDIA FIBER
                                          NETWORK SERVICES, INC.

____________________               By:_______________________________
                                       Howard Finkelstein, President

<Page>

            FIRST AMENDMENT TO FIBER OPTIC PRIVATE NETWORK AGREEMENT

This First Amendment to Fiber Optic Private Network Agreement ("AMENDMENT"),
dated July 19, 2001 ("EFFECTIVE Date"), is entered into by and between
Metromedia Fiber Network Services, Inc., 360 Hamilton Avenue, White Plains, New
York 10601 ("MFN"), and Cogent Communications, Inc., 1015 31st Street NW,
Washington, DC 20007 ("CARRIER"), and amends the Fiber Optic Private Network
Agreement ("AGREEMENT"), dated February 7, 2000, entered into by and between MFN
and Carrier. Unless otherwise provided, definitions of terms used in this
Amendment appear in the Agreement.

Notwithstanding any contrary provision contained in the Agreement, the following
shall apply:

1.   CARRIER TARGET BUILDING LIST AND MFN TARGET BUILDING LIST.

     1.1. Within fifteen (15) days following the execution of this Amendment by
          both parties, Carrier shall supply to MFN a draft list of targeted
          buildings (in both paper and electronic format) ("BUILDINGS" and
          "CARRIER TARGET BUILDING LIST") to which Carrier seeks fiber optic
          access. The Carrier Target Building List shall be subject to periodic
          adjustment by Carrier not to exceed more than once per quarter. The
          initial Carrier Target Building List shall be attached as EXHIBIT A to
          this Amendment.

     1.2. Carrier shall still have the obligation pursuant to Section 8.2 of the
          Product Order of the Agreement to take at least [*]
          Carrier Locations as per the Agreement Target Building List, provided,
          however, that the charges for such Building Access will be set forth
          in Sections 3, 4 and 5 of this Amendment. All Buildings connected to
          MFN Network rings pursuant to the Agreement or this Amendment shall
          count toward Carrier's [*] Carrier Locations
          obligation, except for any Buildings contained in a Cancelled Product
          Order which were already counted toward the obligation pursuant
          Section 1.4 below.

     1.3. Within fifteen (15) days following the execution of this Amendment by
          both parties, MFN will supply to Carrier a draft list of targeted
          buildings (in both paper and electronic format) ("MFN BUILDINGS" and
          "MFN TARGET BUILDING LIST") to which MFN seeks fiber optic access. The
          MFN Target Building List shall be subject to periodic adjustment by
          MFN not to exceed more than once per quarter. The initial MFN Target
          Building List shall be attached as EXHIBIT B to this Amendment.

     1.4. The Parties acknowledge and agree that any and all product order
          Supplements previously submitted which were accepted by MFN but
          implementation and/or construction has not begun (collectively
          referred to as "Cancelled Product Orders"), and are listed on EXHIBIT
          C, are hereby considered (i) Carrier Building Access requests rejected
          by MFN but will count toward Carrier's [*] Carrier
          Location obligation, and (ii) null and void by both Parties. MFN shall
          supply Carrier with a list of all such Cancelled Product Orders within
          fifteen (15) days following the execution of this Amendment by both
          parties, which list shall be attached as EXHIBIT C to this Amendment.

2.   TELECOMMUNICATIONS LICENSE AGREEMENTS.

     2.1. Carrier has no obligation to enter into telecommunications license
          agreements ("TELECOMMUNICATIONS LICENSE AGREEMENTS") for any of the
          Buildings on the Carrier Target Building List.

[*] Indicates confidential treatment requested.

<Page>

     2.2. Carrier will endeavor to include, within the Telecommunications
          License Agreements into which it enters for any of the Buildings on
          the Carrier Target Building List, the right for a fiber provider
          ("FIBER PROVIDER") (inclusive of MFN but not necessarily limited to
          MFN) to (a) access the Building, including bringing fiber to a minimum
          point of entry and terminating at a distribution panel/OCEF in
          building; and (b) distribute dark fiber. Such access rights shall be
          at no additional charge from the Building's owner to the Fiber
          Provider.

3.   BUILDINGS WHICH ARE ON-NET.

     3.1. If Carrier submits a new product order Supplement or re-submits a
          product order Supplement previously submitted which was either (i) a
          Cancelled Product Order, or, (ii) not accepted by MFN, as of the date
          of this Amendment, and the Supplement concerns a Building which is
          On-Net, as defined below, Carrier shall obtain its fiber lateral
          access into the Building through a lease commencing upon the
          respective Service Date for the product order Supplement (and
          co-terminating with such product order Supplement) for the same
          Monthly Building Access Charge of [*] per
          Building, as provided in Section 8.2.1 of the Product Order of the
          Agreement. For purposes of this Amendment, a Building is considered
          (i) "On-Net" if MFN has a conduit to the Building containing fibers
          that are connected to a MFN fiber Network ring outside the Building
          ("MFN Lateral Extension"), MFN has general distribution rights within
          the Building, the Building has physical fiber distribution capability
          (E.G., a fiber distribution panel/OCEF) within the Building ("PHYSICAL
          FIBER DISTRIBUTION CAPABILITY"), and fiber is available within the MFN
          Lateral Extension, and (ii) "Off-Net" if it is not an On-Net Building.

     3.2. MFN shall retain all right, title and interest to, and responsibility
          for and cost of maintenance of the MFN Lateral Extensions, subject to
          the grant of access and use provided to Carrier pursuant to the
          Agreement and/or this Amendment.

4.   BUILDINGS WHICH ARE OFF-NET AND ON BOTH THE CARRIER TARGET BUILDING LIST
     AND MFN TARGET BUILDING LIST.

     The following Section 4 will only apply if the Building is Off-Net and is
     listed in both the Carrier Target Building List and the MFN Target Building
     List.

     4.1. MFN LATERAL EXTENSION EXISTS

          4.1.1. If Carrier submits a new product order Supplement or
                 re-submits a product order Supplement previously submitted
                 which was either (i) a Cancelled Product Order, or (ii) not
                 accepted by MFN, as of the date of this Amendment, and the
                 Supplement concerns a Building which is Off-Net, however an MFN
                 Lateral Extension exists but MFN does not have general
                 distribution rights within the Building, then the following
                 shall apply:

                 a) If the Building has Physical Fiber Distribution Capability,
                    fiber is available within the MFN Lateral Extension, and
                    Carrier has obtained landlord consent to utilize such
                    Physical Fiber Distribution Capability, the Monthly Building
                    Access Charge will be [*] per
                    Building;

                 b) If the Building has Physical Fiber Distribution Capability,
                    fiber is available within the MFN Lateral Extension, and
                    Carrier's telecommunications license agreement for the
                    Building provides for the Fiber Provider access rights as
                    outlined in Section 2

[*] Indicates confidential treatment requested.

                                       2
<Page>

                    above, the [*] Monthly Building
                    Access Charge shall be waived;

               c)   If the Building has Physical Fiber Distribution Capability,
                    however, there is no fiber available within the MFN Lateral
                    Extension, the Parties will follow the process set forth in
                    Section 4.1.3 of this Amendment; or

               d)   If the Building does not have Physical Fiber Distribution
                    Capability, the Parties will follow the process set forth in
                    Section 4.1.3 of this Amendment.

          4.1.2. If Carrier submits a new product order Supplement or
                 re-submits a product order Supplement previously submitted
                 which was either (i) a Cancelled Product Order, or (ii) not
                 accepted by MFN, as of the date of this Amendment, and the
                 Supplement concerns a Building which is Off-Net, however an MFN
                 Lateral Extension exists, MFN does have general distribution
                 rights within the Building, but there is no fiber available
                 within the MFN Lateral Extension, the Parties will follow the
                 process set forth in Section 4.1.3 of this Amendment.

          4.1.3. For the Carrier product order Supplements which fall within
                 the scope of Sections 4.1.1.c, 4.1.1.d, and 4.1.2, MFN shall
                 provide to Carrier a fixed One Time Installation Charge not in
                 excess of MFN's cost for constructing, permitting, engineering
                 and installing the facilities necessary to accommodate
                 Carrier's order and a Monthly Building Access Charge calculated
                 as follows: If the One Time Installation Charge is less than or
                 equal to [*] the Monthly Building Access Charge shall be
                 [*] per month (as above). If the One Time Installation Charge
                 is greater than [*] and less than or equal to [*], the
                 Monthly Building Access Charge shall be [*] per month. If the
                 One Time Installation Charge is greater than [*] and less
                 than or equal to [*], the Monthly Building Access Charge
                 shall be [*] per month. If the One Time Installation Charge is
                 greater than [*], the Monthly Building Access Charge shall
                 be [*] per month. If Carrier accepts MFN's offer, Carrier
                 shall pay seventy-five percent (75%) of the One Time
                 Installation Charge within fifteen (15) days of execution of
                 the product order Supplement by MFN and Carrier. The balance of
                 the One Time Installation Charge shall be payable upon
                 completion of the installation (including connection to
                 Carrier's Network rings) and acceptance by Carrier.

     4.2  MFN LATERAL EXTENSION DOES NOT EXIST.

          4.2.1  If Carrier submits a new product order Supplement or
                 re-submits a product order Supplement previously submitted
                 which was either (i) a Cancelled Product Order, or (ii) not
                 accepted by MFN, as of the date of this Amendment, and the
                 Supplement concerns a Building which is Off-Net and to which
                 MFN has not constructed a MFN Lateral Extension, MFN will
                 supply Carrier with a construction estimate of actual
                 construction cost for a fiber lateral extension into each
                 Building covered by the product order Supplement ("CARRIER-MFN
                 LATERAL EXTENSION"). MFN and Carrier will use reasonable
                 efforts to reach an agreed-to estimated construction cost for
                 each Carrier-MFN Lateral Extension.

          4.2.2  MFN and Carrier will have regular planning sessions, the
                 intervals to be mutually agreed upon, concerning the
                 construction of any buildings..

[*] Indicates confidential treatment requested.

                                      3
<Page>

          4.2.3  Once MFN and Carrier have settled on an agreed-to estimated
                 construction cost for a Carrier-MFN Lateral Extension, either
                 Party may elect not to proceed with the Carrier-MFN Lateral
                 Extension. If neither Party makes such an election not to
                 proceed with the build, then the Parties will mutually agree to
                 either (a) use MFN to construct the Carrier-MFN Lateral
                 Extension at the agreed-to estimated construction cost; or (b)
                 use a third party to construct the Carrier-MFN Lateral
                 Extension if the estimated construction cost using such third
                 party (including splice fees) is lower than the Carrier-MFN
                 agreed-to construction estimate for the Carrier-MFN Lateral
                 Extension. Carrier and MFN shall share the construction
                 estimation costs on a fifty (50)/fifty (50) basis. If both
                 Parties elect to have a third party construct the Carrier-MFN
                 Lateral Extension, Carrier and MFN shall share the construction
                 costs on a fifty (50)/fifty (50) basis.

          4.2.4  If MFN elects not to proceed with the Carrier-MFN Lateral
                 Extension, and Carrier still seeks the construction of a
                 lateral extension, Carrier can proceed with the construction of
                 its own lateral extension into the Building ("CARRIER LATERAL
                 EXTENSION") and shall be entitled to MFN's splicing of fiber
                 strands from the Carrier Lateral Extension into the MFN fiber
                 Network ring that will service the Carrier Lateral Extension at
                 a splice fee charge of MFN's actual cost to splice plus [*]
                 [*] ("MFN SPLICE COST"), with MFN to provide
                 reasonable cost assumptions upfront.

                 a) Carrier shall be the owner of the Carrier Lateral
                    Extension and is responsible for the maintenance of the
                    Carrier Lateral Extension at Carrier's sole cost and
                    expense.

                 b) Notwithstanding anything contrary in the General Terms and
                    Conditions, a service interruption experienced by Carrier
                    as a result of damage to Carrier Lateral Extension is not
                    an Outage as that term is defined, and Carrier is not
                    entitled to any Outage Credits or other remedies for such
                    interruptions.

          4.2.5  If MFN elects to proceed with the Carrier-MFN Lateral
                 Extension, and the Carrier-MFN Lateral Extension requires
                 payment of any recurring charge or fee (I.E., utility monthly
                 conduit fee, etc.), Carrier and MFN shall share such recurring
                 charge or fee on a fifty (50)/fifty (50) basis.

          4.2.6  Approvals for cost overruns, exceptions to the plan of work
                 and progress payments to cover the construction of the
                 Carrier-MFN Lateral Extension shall be made pursuant to MFN's
                 standard forms and rules where applicable, and/or MFN's
                 contractors standard forms.

          4.2.7  Carrier will pay to MFN, [*]
                 [*] for each engineering study on each Building prior to
                 the performance of such engineering study, which will not
                 commence until Carrier and MFN mutually agree in writing on
                 undertaking any such study. Upon completion of such engineering
                 study, MFN will invoice Carrier for fifty percent (50%) of the
                 actual cost of the engineering study less the initial payment
                 of [*].

4.3  OWNERSHIP, OPERATION AND SALE OF CARRIER-MFN LATERAL EXTENSIONS.

          4.3.1  MFN shall own title to the Carrier-MFN Lateral Extension, and
                 the fiber contained therein, and will provide Carrier with a
                 lease of a portion of the fiber strands contained therein.

[*] Indicates confidential treatment requested.

                                      4
<Page>

          4.3.2  The Carrier-MFN Lateral Extension shall have single entry
                 penetration into the Building, contain no less than twenty four
                 (24) fiber strands and no more than one hundred forty four
                 (144) fiber strands, unless the Parties mutually agree to a
                 dual penetration and/or a different number of fiber strands.

          4.3.3  Carrier and MFN shall share the responsibility for all taxes
                 and related surcharges or permit fees on the Carrier-MFN
                 Lateral Extension on a fifty (50)/fifty (50) basis.

          4.3.4  Notwithstanding anything contained in the Agreement to the
                 contrary, Carrier may, without the consent of MFN, collaterally
                 assign this Agreement in whole but not in part to any or all
                 parties providing financing to Carrier or any other entity
                 controlled by or under common control with Carrier under a
                 collateral trust for the benefit of the entities providing such
                 financing or similar arrangement for the benefit of such
                 financing entities. Carrier will advise MFN in writing of the
                 assignment at the time of such assignment. If requested by
                 Carrier, MFN will within seven (7) days of such request provide
                 a written consent to any such permitted assignment; provided
                 that such consent will permit reassignment in accordance with
                 the terms of this Agreement if the financing parties exercise
                 their remedies under the documents for such financing upon
                 notice by the financing parties.

          4.3.5  MFN will be responsible for providing all routine and
                 emergency maintenance, and obtaining necessary authorizations
                 and right of way on the Carrier-MFN Lateral Extension. Carrier
                 will not pay any charges for such maintenance. Such maintenance
                 will be provided in accordance with the terms and conditions of
                 the Agreement.

          4.3.6  Carrier can lease from MFN, without additional Leased Fiber
                 charge, the number of dark fibers in the Carrier-MFN Lateral
                 Extension equal to (i) twice the number of Leased Fibers
                 Carrier has leased in the Network rings, provided such
                 Carrier-MFN Lateral Extension is the only Carrier-MFN Lateral
                 Extension existing into the same Building; or (ii) the same
                 number of Leased Fibers Carrier has leased in the Network rings
                 if more than one Carrier-MFN Lateral Extension exists into the
                 same Building.

          4.3.7  Carrier-MFN Lateral Extensions can only be spliced into
                 Network rings. Carrier is permitted to request splicing of a
                 number of fibers from the Carrier-MFN Lateral Extension equal
                 to (i) twice the number of fibers in the Network rings,
                 provided such Carrier-MFN Lateral Extension is the only
                 Carrier-MFN Lateral Extension existing into the same Building,
                 or (ii) the same number of Leased Fibers Carrier has leased in
                 the Network rings if more than one Carrier-MFN Lateral
                 Extension exists into the same Building, in both cases, up to
                 one hundred forty four (144) fibers ("CARRIER FIBERS"). Whether
                 splicing is for Carrier or other party acquiring fiber strands
                 in the Carrier-MFN Lateral Extension, MFN shall be obligated to
                 splice fibers leased in the Carrier-MFN Lateral Extension at
                 MFN's Splice Cost, with MFN to provide reasonable cost
                 assumptions upfront.

          4.3.8  If Carrier wants additional fibers in the Carrier-MFN Lateral
                 Extension, over and above (i) twice the number of fibers
                 Carrier has leased from MFN in the corresponding Network rings,
                 if such Carrier-MFN Lateral Extension is the only Carrier-MFN
                 Lateral Extension existing into the same Building, or (ii) the
                 same number of fibers Carrier has leased from MFN in the
                 corresponding Network rings if more than one Carrier-MFN
                 Lateral Extension exists into the same Building, in both cases,
                 to connect to such Network rings, such fibers are subject to
                 availability and shall be at the terms and conditions
                 (including

                                      5
<Page>

                 splice fees) as is provided below for third party acquisitions
                 of excess fibers in the Carrier-MFN Lateral Extension.

          4.3.9  MFN may not construct additional Lateral Extensions into the
                 Building, or splice additional fiber from the Building into any
                 MFN Network rings until all fibers, over and above the Leased
                 Fiber leased by Carrier, in the Carrier-MFN Lateral Extension
                 ("EXCESS CARRIER-MFN LATERAL FIBERS") are leased either to
                 Carrier or third parties ("DISPOSITION").

          4.3.10 In the event Carrier has located a potential fiber customer
                 who desires to lease Excess Carrier-MFN Lateral Fibers in
                 Carrier-MFN Lateral Extensions, Carrier shall only promptly
                 notify MFN regarding the identity of such potential customer
                 ("FIBER CUSTOMER") and will not, in any matter whatsoever,
                 attempt to negotiate terms of the Disposition with the Fiber
                 Customer. In such event, or in the event MFN has located a
                 potential Fiber Customer, MFN shall negotiate in good faith to
                 enter into the applicable Disposition documents with such
                 potential Fiber Customer. MFN's negotiations of the terms and
                 conditions of the Disposition documents with any potential
                 Fiber Customer shall be subject to the conditions contained in
                 this Amendment, including but not limited to:

                 a) MFN shall use its commercially reasonable efforts to
                    maximize the lease price payable thereunder, which in any
                    event shall be no less than the amount determined in
                    accordance with this Amendment.

                 b) The number of fiber strands which any Fiber Customer shall
                    be entitled to acquire hereunder shall be no greater than
                    (i) twice the number of fiber strands on the Network rings
                    that such Fiber Customer has acquired if such Carrier-MFN
                    Lateral Extension is the only Carrier-MFN Lateral
                    Extension existing into the same Building, or (ii) the
                    same number of fiber strands on the Network rings that
                    such Fiber Customer has acquired if more than one
                    Carrier-MFN Lateral Extension exists into the same
                    Building.

                 c) The Disposition documents shall prohibit the Fiber
                    Customer from selling, assigning, leasing, licensing,
                    granting an indefeasible right to use, or otherwise
                    transferring, the fiber strands at any time (but may
                    borrow against it or pledge its interest therein).

          4.3.11 Dispositions of Excess Carrier-MFN Lateral Fibers can be made
                 at MFN's discretion for a lateral/building access fee
                 determined by MFN in its sole discretion. If Excess Carrier-MFN
                 Lateral Fibers are Disposed of at a lateral/building access
                 price less than the price set forth in the matrix attached as
                 EXHIBIT D to this Amendment ("MINIMUM BASE LATERAL/BUILDING
                 ACCESS PRICE"), then the Minimum Base Lateral/Building Access
                 Price will be used to calculate the Fiber Proceeds (as defined
                 in Section 4.3.13 below). If Excess Carrier-MFN Lateral Fibers
                 are Disposed of at a lateral/building access price more than
                 the price set forth in the matrix attached as EXHIBIT D to
                 this Amendment ("MAXIMUM BASE LATERAL/BUILDING ACCESS PRICE"),
                 then the Maximum Base Lateral/Building Access Price will be
                 used to calculate the Fiber Proceeds (as defined in
                 Section 4.3.13 below).

          4.3.12 Any future Dispositions of Excess Carrier-MFN Lateral Fibers
                 for which an initial lease has terminated shall be done in
                 accordance with the terms and conditions of this Amendment, up
                 through and until such Excess Carrier-MFN Lateral Fibers are no
                 longer commercially viable.

                                      6
<Page>

          4.3.13 Revenues received for lateral/building access fees in
                 connection with the Disposition of Excess Carrier-MFN Lateral
                 Fibers shall be split fifty (50)/fifty (50) between Carrier and
                 MFN ("FIBER PROCEEDS"). Only one-time/non-recurring fees (i.e.,
                 for installation, upfront costs, etc.) received in connection
                 with the Disposition of Excess Carrier-MFN Lateral Fibers,
                 which are over and above MFN's out-of pocket costs (for
                 splicing, etc. performed as part of the Disposition) plus
                 [*], shall be amortized over a period of
                 sixty (60) months for purposes of making the Exhibit D
                 calculations of the revenue received by MFN pursuant to this
                 Amendment; (but, they shall be paid out as received). MFN shall
                 remit to Carrier all Fiber Proceeds received during any
                 calendar quarter within forty-five (45) days from the end of
                 such quarter.

          4.3.14 Carrier shall have the right, upon prior reasonable written
                 notice to MFN, to audit, MFN's accounting records and to
                 inspect fiber terminations at fiber distribution panels/OCEFs
                 in Buildings subject to this Amendment, to determine if MFN has
                 adhered to the terms of this Amendment with respect to the
                 sharing of the Fiber Proceeds. Such audit shall be conducted by
                 a mutually acceptable independent accounting firm, provided
                 that such accountant shall hold MFN's accounting records in
                 strictest confidence except as necessary to report to Carrier
                 on MFN's compliance with Section 4.3.13 of this Amendment. Such
                 audit and inspection shall be conducted during MFN's normal
                 business hours, with minimal interruption to MFN's business,
                 with reasonable prior notice to MFN, and may require MFN
                 personnel to be present at all times. Any sum owed by MFN to
                 the Carrier as a result of such audit shall be due and payable,
                 with annual interest thereon of twelve percent (12%) from the
                 date such sum should have been remitted to Carrier. Carrier
                 shall bear all expenses for the audit unless MFN is determined
                 to have underpaid Carrier by more than ten percent (10%) of the
                 sum due hereunder from Fiber Proceeds, in which case MFN shall
                 reimburse Carrier for the expenses of such audit.

5.   BUILDINGS WHICH ARE OFF-NET AND ON THE CARRIER TARGET BUILDING LIST AND
     BUT NOT ON THE MFN TARGET BUILDING LIST.

     5.1  If the Building is Off-Net and is listed in the Carrier Target
          Building List but not in the MFN Target Building List, MFN will
          construct, upon Carrier's written request, a MFN Lateral Extension
          for a charge of MFN's actual cost to construct plus [*]
          [*] ("MFN CONSTRUCTION COST"). Carrier will pay seventy five
          percent (75%) of the MFN Construction Cost upon execution of the
          applicable product order Supplement and twenty five percent (25%)
          upon MFN's completion of construction of the Carrier Lateral
          Extension. Carrier will receive a credit equal to (i) twenty-five
          (25%) of the MFN Construction Cost for the first new MFN customer
          using such MFN Lateral Extension; (ii) twenty-five (25%) of the MFN
          Construction Cost for the second new MFN customer using such MFN
          Lateral Extension; and (iii) twenty-five (25%) of the MFN
          Construction Cost for the third new MFN customer using such MFN
          Lateral Extension. For the fourth and for each subsequent new MFN
          customer using such MFN Lateral Extension, Carrier will receive
          fifty (50%) of all amounts received by MFN from such customer for
          use of such MFN Lateral Extension. Any such credit due hereunder
          will be applied towards any monthly charges due pursuant to the
          Agreement unless otherwise agreed by the Parties.

     5.2 Carrier may also elect to construct its own lateral to the Building by
         itself or through a third party. Any such lateral extensions
         constructed under this Section 5.1 shall be Carrier's property, shall
         be considered a Carrier Lateral Extension, and shall be subject to the
         provisions of Section 4.2.4 of this Amendment, including MFN's splice
         obligation.

[*] Indicates confidential treatment requested.

                                      7
<Page>

     IN WITNESS WHEREOF, the parties hereto have each caused this Amendment to
     be signed and delivered as of the Effective Date.

     Metromedia Fiber Network Services, Inc.      Cogent Communications, Inc.

     Name    Thomas D. Byrnes                    Name   David Schaeffer
          ---------------------------------           -------------------------

     Title   President Carrier Services          Title  Chief Executive Officer
           --------------------------------            -------------------------

     Signature    /s/ Thomas D. Byrnes           Signature  /s/ Donald Schaeffer
               ----------------------------                ---------------------

     Date      July 19, 2001                     Date         July 19, 2001
          ---------------------------------           --------------------------

                                      8

<Page>

                                    EXHIBIT A

                      INITIAL CARRIER TARGET BUILDING LIST

[To be supplied by Carrier]

<Page>

                                    EXHIBIT B

                        INITIAL MFN TARGET BUILDING LIST

[To be supplied by MFN]

<Page>

                                    EXHIBIT C

                REJECTED AND CANCELLED PRODUCT ORDER SUPPLEMENTS

[To be supplied by MFN]

<Page>

                                    EXHIBIT D

                           FIBER STRAND PRICING MATRIX

Minimum and Maximum Base Lateral/Building Access Price for Excess Carrier-MFN
Lateral Fibers Disposed of pursuant to this Amendment are as follows:

<Table>
<Caption>

NUMBER OF FIBERS:                        MIN. BASE LATERAL/BUILDING           MAXIMUM BASE LATERAL/BUILDING
-----------------                        --------------------------           -----------------------------
                                         ACCESS PRICE                         ACCESS PRICE
                                         ------------                         ------------
                                         MONTHLY RECURRING ($)                MONTHLY RECURRING ($)
                                         ---------------------                ---------------------

         <S>                             <C>                                    <C>
         2                               [***]                                  [***]

         4                               [***]                                  [***]

         6                               [***]                                  [***]

         8                               [***]                                  [***]

         10                              [***]                                  [***]

         12                              [***]                                  [***]

         14                              [***]                                  [***]

         16                              [***]                                  [***]

</Table>

[*] Indicates confidential treatment requested.

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