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                                                                  Exhibit 4.1

                        COGENT COMMUNICATIONS GROUP, INC.

                              AMENDED AND RESTATED
                             STOCKHOLDERS AGREEMENT


         STOCKHOLDERS AGREEMENT made this 16th day of October, 2001 by and
among (i) Cogent Communications Group, Inc., a Delaware corporation (the
"Company"), (ii) David Schaeffer (the "Founder"), and each other Person
(other than a Purchaser, as defined below) who, after the date hereof,
acquires at least one percent (1%) of the number of shares of Common Stock or
other equity securities of the Company outstanding and joins in and becomes a
party to this Agreement by executing and delivering to the Company an
Instrument of Accession in the form of Schedule II hereto (the Founder and
such other persons being referred to collectively as the "Holders" and
singularly as a "Holder"), and (iii) those persons whose names are set forth
under the heading "Purchasers" on Schedule I hereto (the "Purchasers").

                                   WITNESSETH:

         WHEREAS, simultaneously herewith, the Company and certain of the
Purchasers (the "Series C Purchasers") have consummated the transactions
contemplated by that certain Series C Participating Convertible Preferred Stock
Purchase Agreement by and among the Company and the Series C Purchasers, dated
as of the date hereof (the "Purchase Agreement"), pursuant to which the Series C
Purchasers have agreed, subject to the terms and conditions set forth therein,
to purchase up to 52,137,643 shares of the Company's Series C Participating
Convertible Preferred Stock, par value $.001 per share (the "Series C Preferred
Stock");

         WHEREAS, the Founder and certain of the Purchasers who purchased the
Series A Participating Convertible Preferred Stock, par value $.001 per share,
of the Company (the "Series A Preferred Stock"), and Series B Participating
Convertible Preferred Stock, par value $.001 per share, of the Company (the
"Series B Preferred Stock," and together with the "Series A Preferred Stock" and
the "Series C Preferred Stock," the "Preferred Stock"), are parties to that
certain Stockholders Agreement, dated as of March 14, 2001 (the "Original
Stockholders Agreement"), and in connection with the consummation of the
transactions contemplated by the Purchase Agreement, the Company, the Founder
and such Purchasers, constituting signatories sufficient under Section 15 of the
Original Stockholders Agreement to amend the Original Stockholders Agreement,
desire to amend and restate the Original Stockholders Agreement as set forth
herein and execute and deliver this Agreement, setting forth herein certain
terms and conditions governing their relative ownership of the Shares (as
hereinafter defined).

         NOW THEREFORE, in consideration of the mutual covenants herein
contained and other good and valuable consideration, the receipt and sufficiency
of which is hereby acknowledged, the Company, the Holders and the Purchasers
hereby agree as follows:

                  1.       PROHIBITED TRANSFERS.

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                           (a)  TRANSFERS BY HOLDERS.  The Holders shall not
sell, assign, transfer, pledge, hypothecate, mortgage or dispose of, by gift or
otherwise, or in any way encumber, all or any part of the Shares (as hereinafter
defined) owned by them except in compliance with the terms of this Agreement.
For purposes of this Agreement, the term "Shares" shall mean and include all
shares of Common Stock of the Company and all shares of any class or series of
equity securities or equity-backed securities of the Company or any subsidiary,
including without limitation, capital stock (including any shares of treasury
stock) or rights, options, warrants or other securities convertible into or
exercisable or exchangeable for capital stock or any debt security which by its
terms is convertible into or exchangeable for any equity security or has any
other equity feature or any security that is a combination of debt and, in any
event that is owned by the Holders, whether presently held or hereafter
acquired. Notwithstanding the foregoing, after the date on which the Company
becomes obligated to file reports pursuant to the Securities Exchange Act of
1934, as amended (the "Public Company Date"), this Section 1(a) shall apply only
to the Founder and no other Holder.

                           (b)  TRANSFER BY THE FOUNDER WHILE AN EMPLOYEE.
Notwithstanding the provisions of Section 1(a) and except as set forth in
Section 4, for so long as the Founder is employed by the Company or Cogent
Communications, Inc., the Founder shall not sell, assign or otherwise transfer
any shares of Common Stock held by the Founder (the "Founder's Common") for a
period of three (3) years from February 7, 2000; provided, that the foregoing
restriction on sales by the Founder shall terminate on the first to occur of (i)
the closing of a firmly underwritten public offering pursuant to an effective
registration statement under the Securities Act of 1933, as amended, covering
the offer and sale of Common Stock of the Company in which (a) the pre-money
valuation of the Company is at least $500,000,000 and (b) the gross cash
proceeds (before underwriting discounts, commissions and fees) are at least
$50,000,000 (a "Qualified Offering"), (ii) the sale of the Company or control
thereof, whether by merger, sale, recapitalization or similar corporate event or
the transfer of more than a majority of its capital stock (calculated on an as
converted, fully diluted basis) or assets (collectively, a "Transfer of
Control"), or (iii) conversion into Common Stock of all then outstanding shares
of Preferred Stock (each of the event set forth in clauses (i)-(iii) hereof, a
"Corporate Event").

                  (c) TRANSFERS BY THE FOUNDER WHILE NOT AN EMPLOYEE.
Notwithstanding the provisions of Section 1(a), if the Founder is no longer
employed by the Company or Cogent Communications, Inc. for whatever reason, the
foregoing restrictions on transfers of Founder's Common shall be lifted as to
25% of the Founder's Common plus such additional percentage of as is obtained by
dividing the actual number of days elapsed from February 7, 2000 by 1460 (as
adjusted for stock splits, stock dividends, reclassifications, recapitalizations
or other similar events). The restrictions contained in this Section 1(c) shall
be of no further force and effect from and after the first to occur of (i) a
Qualified Offering, (ii) a Transfer of Control or (iii) conversion into Common
Stock of a majority of all then outstanding shares of Preferred Stock

         2. RIGHT OF REFUSAL ON DISPOSITIONS BY THE HOLDERS. Except as set forth
in Section 4, if at any time prior to the consummation of a Qualified Offering
any of the Holders wishes to sell, assign, transfer or otherwise dispose of any
or all Shares owned by such Holder pursuant to the terms of a bona fide offer
received from a third party, the Holder shall submit a written offer



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to sell such Shares to the Purchasers (with a copy to the Company) on terms and
conditions, including price, not less favorable to the Purchasers than those on
which he proposes to sell such Shares to such third party (the "Offer"). The
Offer shall disclose the identity of the proposed purchaser or transferee, the
Shares proposed to be sold or transferred, the agreed terms of the sale or
transfer and any other material facts relating to the sale or transfer. Within
thirty (30) days after receipt of the Offer, each Purchaser and each Qualified
Transferee, if any, shall give notice to the Holder of its intent to purchase
all or any portion of the offered Shares on the same terms and conditions as set
forth in the Offer. Each Purchaser and Qualified Transferee shall have the right
to purchase that number of the Shares as to which the Offer applies as shall be
equal to the aggregate number of such Shares multiplied by a fraction, the
numerator of which is the number of shares of Common Stock of the Company then
owned by such Purchaser or Qualified Transferee (as applicable) (calculated on
an as converted basis, and including any shares of Common Stock deemed to be
beneficially owned by such Purchaser pursuant to Rule 13d-3 promulgated under
the Securities Exchange Act of 1934 ("Rule 13d-3")) and the denominator of which
is the aggregate number of shares of said Common Stock then issued and
outstanding and held by (and deemed to be beneficially owned by) all the
Purchasers (calculated on an as converted basis). The amount of Shares each
Purchaser or Qualified Transferee, as that term is defined below, is entitled to
purchase under this Section 2 shall be referred to as such Purchaser's "Pro Rata
Fraction." Each Purchaser shall have the right to transfer his right to any Pro
Rata Fraction or part thereof to any Qualified Transferee. If any Purchaser or
Qualified Transferee does not wish to purchase or to transfer his right to
purchase his Pro Rata Fraction, then any Purchasers or Qualified Transferees who
so elect shall have the right to purchase, on a pro rata basis with any other
Purchasers or Qualified Transferees who so elect, any Pro Rata Fraction not
purchased by a Purchaser or Qualified Transferee. Each Purchaser or Qualified
Transferee shall act upon the Offer as soon as practicable after receipt from
the Company of notice that it has not elected to purchase all of the offered
Shares, and in all events within fifteen (15) days after receipt thereof. Each
Purchaser and Qualified Transferee shall have the right to accept the Offer as
to all or part of the Remaining Offered Shares offered thereby. If a Purchaser
or Qualified Transferee shall elect to purchase all or part of such Purchaser's
or Qualified Transferee's Pro rata Fraction, said Purchaser or Qualified
Transferee shall individually communicate in writing such election to purchase
to whichever of the Holders has made the Offer, which communication shall be
delivered by hand or delivered to such Holder at the address set forth in
Section 8 below and shall, when taken in conjunction with the Offer be deemed to
constitute a valid, legally binding and enforceable agreement for the sale and
purchase of the Shares covered thereby.

         If the Purchasers, taken together, do not agree to purchase all of the
Shares offered by a Holder pursuant to and within thirty (30) days after receipt
of the Offer, and consummate such purchase within forty-five (45) days after
receipt of the Offer, such Shares subject to the Offer as shall not have been
purchased may be sold by such Holder at any time within 90 days after the
expiration of the Offer, but subject to the provisions of Section 3 below. Any
such sale shall be at not less than the price and upon other terms and
conditions, if any, not more favorable to the purchaser than those specified in
the Offer. Any Shares not sold within such 90-day period shall continue to be
subject to the requirements of a prior offer and re-sale pursuant to this
Section.



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         For purposes hereof, a "Qualified Transferee' shall mean any person (i)
who is a Purchaser, (ii) who is an "affiliated person" of a Purchaser, as that
term is defined in the Investment Company Act of 1940, (iii) who is a partner,
member or stockholder of a Purchaser that is a partnership, limited liability
company or corporation, as applicable, and who is offered a pro rata right,
based on his, her or its interest in the Purchaser, to acquire the Shares
offered by a Holder pursuant to this Section 2, or (iv) who acquires at least
twenty five percent (25%) of the shares of Preferred Stock issued by the Company
to any Purchaser (as adjusted for stock splits, stock dividends,
reclassifications, recapitalizations or other similar events). With respect to
any transfers of Shares by any Holder other than the Founder, the Founder shall
be deemed to be a Purchaser for purposes of this Section 2. In addition,
beginning on the Public Company Date, the term "Holder" in this Section 2 shall
be deemed to mean the Founder.

             3. RIGHT OF PARTICIPATION IN SALES BY THE FOUNDER. Except as set
forth in Section 4, if at any time the Founder wishes to sell, transfer or
otherwise dispose of any Shares owned by him to any person (the "Acquiror") in a
transaction which is subject to the provisions of Section 2 hereof, and such
sale, transfer or other disposition would, when combined with all prior sales,
transfers and other dispositions by the Founder, result in the transfer by the
Founder of Shares representing more than twenty-five percent (25%) of the total
number of shares of Founder's Common with respect to which the restrictions on
transfer set forth herein have elapsed or otherwise do not apply, each Purchaser
shall have the right to require, as a condition to such sale or disposition,
that the Acquiror purchase from said Purchaser at the same price per Share and
on the same terms and conditions as involved in such sale or disposition by the
Founder the same percentage of shares of Common Stock owned (and deemed to be
beneficially owned under Rule 13d-3) by such Purchaser as such sale or
disposition represents with respect to the number of shares of Founder's Common
(calculated on an as converted, fully diluted basis) owned by the Founder
immediately prior to such sale. Each Purchaser wishing so to participate in any
such sale or disposition shall notify the Founder of such intention as soon as
practicable after receipt of the Offer made pursuant to Section 2, and in all
events within fifteen (15) days after receipt thereof. If a Purchaser shall
elect to participate in such sale or disposition, said Purchaser shall
individually communicate such election to the Founder, which communication shall
be delivered by hand or mailed to the Founder at the address set forth in
Section 8 below. The Founder and/or each participating Purchaser shall sell to
the Acquiror all, or at the option of the Acquiror, any part of the Stock (as
defined in Section 5 below) proposed to be sold by them at not less than the
price and upon other terms and conditions, if any, not more favorable to the
Acquiror than those set forth in the Offer; PROVIDED, HOWEVER, that any purchase
of less than all of such Stock by the Acquiror shall be made from the Founder
and/or each participating Purchaser based upon a fraction, the numerator of
which is the number of shares of Stock of the Company then owned by the Founder
or such participating Purchaser (including any shares of Common Stock deemed to
be owned under Rule 13d-3) and the denominator of which is the aggregate number
of shares of Stock held by (and deemed to be held by) the Founder and all of the
participating Purchasers. The Founder shall use his best efforts to obtain the
agreement of the Acquiror to the participation of the participating Purchasers
in the contemplated sale, and shall not sell any Stock to such Acquiror if such
Acquiror declines to permit the participating Purchasers to participate pursuant
to the terms of this Section 3. The provisions of this Section 3



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shall not apply to the sale of any Shares by the Founder (i) to a Purchaser
pursuant to an Offer under Section 2 or (ii) made upon or after the occurrence
of a Corporate Event.

         4. PERMITTED TRANSFERS. Anything herein to the contrary
notwithstanding, the provisions of Sections 1, 2 and 3 shall not apply to: (a)
any transfer of Shares by a Holder by gift or bequest or through inheritance to,
or for the benefit of, any member or members of his immediate family; (b) any
transfer of Shares by a Holder to a trust in respect of which he serves as
trustee, provided that the trust instrument governing said trust shall provide
that such Holder, as trustee, shall retain sole and exclusive control over the
voting and disposition of said Shares until the termination of the applicable
restrictions on transfer under this Agreement; (c) any sale of Common Stock in a
public offering pursuant to a registration statement filed by the Company with
the Securities and Exchange Commission; (d) any repurchase of shares of Common
Stock from officers, employees, directors or consultants of the Company which
are subject to restrictive stock purchase agreements under which the Company has
the option to repurchase such shares upon the occurrence of certain events,
including termination of employment; and (e) any pledge, hypothecation or other
similar financing transaction in which the transferring Holder continues to have
the sole and exclusive authority and right to vote the shares subject to such
pledge, hypothecation or other financing transaction. In the event of any such
transfer, other than pursuant to subsection (c) of this Section 4, the
transferee of the Shares shall hold the Shares so acquired with all the rights
conferred by, and subject to all the restrictions imposed by, this Agreement on
the party from whom the transferee received the Shares, and as a condition to
such transfer, each such transferee shall execute and deliver a written
agreement agreeing to be bound by the provisions of this Agreement.

         5. ELECTION OF DIRECTORS; ISSUANCE OF OPTIONS.

                  (a) ELECTION OF DIRECTORS. Each of the parties hereto agrees
to vote all of the Stock (as hereinafter defined) of the Company now owned or
hereafter acquired by such party (and attend, in person or by proxy, all
meetings of stockholders called for the purpose of electing directors), and the
Company agrees to take all actions (including, but not limited to the nomination
of specified persons) to cause and maintain the election to the Board of
Directors of the Company, to the extent permitted pursuant to the Company's
certificate of incorporation, of the following:

                           (i)      two (2) individuals designated by the
holders of a majority of the shares of Common Stock (other than any shares
received on conversion of the Preferred Stock) (the designees of the holders of
Common Stock under this subsection shall initially be David Schaeffer and H.
Helen Lee);

                           (ii)     two (2) individuals designated by the
holders of a majority in interest of the then outstanding Series A Preferred
Stock (the designees of the holders of Series A Preferred Stock under this
subsection shall initially be Erel Margalit and James Wei);



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                           (iii)    one (1) individual designated by the holders
of a majority in interest of the then outstanding Series B Preferred Stock (the
designee of the holders of Series B Preferred Stock under this subsection shall
initially be Edward Glassmeyer);

                           (iv)     one (1) individual designated by the holders
of a majority in interest of the then outstanding Series C Preferred Stock; and

                           (v)      a three (3) member Compensation Committee,
one of the members of which shall be nominated by the directors elected pursuant
to subparagraph (i) above and who shall not be the Founder and one of the
members of which shall be nominated by the directors elected pursuant to
subparagraphs (ii), (iii) and (iv) above.

         Each of the parties further covenants and agrees to vote, to the extent
possible, all Shares of Stock of the Company now owned or hereafter acquired by
such party so that (i) the Company's Board of Directors shall consist of six (6)
members, each of whom shall be nominated as set forth above and (ii) the
Compensation Committee thereof shall consist of three (3) members, each of whom
shall be nominated as set forth above, (iii) the holders of the Series A
Preferred Stock, Series B Preferred Stock, Series C Preferred Stock and the
Founder's Common shall be entitled, in the aggregate, to have up to three
persons as observers at each meeting of the Board of Directors and any committee
(other than the Compensation Committee) thereof. For the purposes of this
Agreement, "Stock" shall mean and include all Preferred Stock and Common Stock
and all other securities of the Company which may be exchangeable for or issued
in exchange for or in respect of shares of Common Stock (whether by way of stock
split, stock dividends, combination, reclassification, reorganization or any
other means).

         In the absence of any designation from the persons or groups so
designating directors as specified above, the director previously designated by
them and then serving shall be reelected if still eligible to serve as provided
herein.

         No party hereto shall vote to remove any member of the Board of
Directors or the Compensation Committee thereof designated in accordance with
the aforesaid procedure unless the persons or groups so designating directors as
specified above so vote, and, if such persons or groups so vote then the
non-designating party or parties shall likewise so vote.

         Any vacancy on the Board of Directors or the Compensation Committee
thereof created by the resignation, removal, incapacity or death of any person
designated under this Section 5 shall be filled by another person designated in
a manner so as to preserve the constituency of the Board or such Committee as
provided above.

         (b) ISSUANCE OF OPTIONS TO HOLDERS OF PREFERRED STOCK. Each of the
parties hereto agrees that the Company shall not, and each agrees to vote all of
their Stock of the Company now owned or hereafter acquired by such party (and
attend, in person or by proxy, all meetings of stockholders called for the
purpose of electing directors) to preclude the Company from issuing any options
under the Company's stock option plans as in effect from time to time to any
holder of Preferred Stock or any person employed by or controlled by or under
common control



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with any such holder or any affiliate thereof without first obtaining the
unanimous approval of the Board of Directors of the Company.

         6. RIGHT OF PARTICIPATION IN SALES BY THE COMPANY.

         (a) RIGHT OF PARTICIPATION. Except as provided in Section 6(f) of this
Agreement, the Company shall not issue, sell or exchange, agree or obligate
itself to issue, sell or exchange, or reserve or set aside for issuance, sale or
exchange, any (i) shares of Common Stock, (ii) any other equity security of the
Company, including without limitation, shares of Preferred Stock, (iii) any debt
security of the Company (other than debt with no equity feature) including
without limitation, any debt security which by its terms is convertible into or
exchangeable for any equity security of the Company, (iv) any security of the
Company that is a combination of debt and equity, or (v) any option, warrant or
other right to subscribe for, purchase or otherwise acquire any such equity
security or any such debt security of the Company, unless in each case the
Company shall have first offered to sell such securities (the "Offered
Securities") to the Purchasers who hold individually or together with their
affiliates at least 2,500,000 Shares of the Preferred Stock then outstanding
and, for so long as the Founder holds not less than fifty percent (50%) of the
number of shares of Founder's Common held by him on the date hereof (in both
cases, as adjusted for stock splits, stock dividends, reclassifications,
recapitalizations or other similar events), the holders of the Founder's Common
(such Purchasers and, if applicable, the holders of the Founders' Common being
referred to as the "Participating Stockholders") as follows: The Company shall
offer to sell to each Participating Stockholder (a) that portion of the Offered
Securities as the number of shares of Common Stock (including all shares of
capital stock convertible into Common Stock, on a fully-diluted basis) then held
by such Participating Stockholder, as the case may be, bears to the total number
of shares of Common Stock (including all shares of capital stock convertible
into Common Stock, on a fully-diluted basis) of the Company then outstanding
(the "Basic Amount," and the aggregate of the Basic Amounts of all Participating
Stockholders being referred to as the "Aggregate Basic Amount"), and (b) such
additional portion of the Aggregate Basic Amount as such Participating
Stockholder shall indicate it will purchase should the other Participating
Stockholders subscribe for less than their Basic Amounts (the "Undersubscription
Amount"), at a price and on such other terms as shall have been specified by the
Company in writing delivered to such Participating Stockholder (the "Offer"),
which Offer by its terms shall remain open and irrevocable for a period of
twenty (20) days from receipt of the offer.

         (b) NOTICE OF ACCEPTANCE. Notice of each Participating Stockholder's
intention to accept, in whole or in part, any Offer made pursuant to Section
6(a) shall be evidenced by a writing signed by such Participating Stockholder
and delivered to the Company prior to the end of the 20-day period of such
offer, setting forth such of the Participating Stockholder's Basic Amount as
such Participating Stockholder elects to purchase and, if such Participating
Stockholder shall elect to purchase all of its Basic Amount, such
Undersubscription Amount as such Participating Stockholder shall elect to
purchase (the "Notice of Acceptance"). If the Basic Amounts subscribed for by
all Participating Stockholders are less than the total Aggregate Basic Amount,
then each Participating Stockholder who has set forth Undersubscription Amounts
in its Notice of Acceptance shall be entitled to purchase, in addition to the
Basic Amounts subscribed



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for, all Undersubscription Amounts it has subscribed for; PROVIDED, HOWEVER,
that should the Undersubscription Amounts subscribed for exceed the difference
between the Aggregate Basic Amount and the Basic Amounts subscribed for (the
"Available Undersubscription Amount"), each Participating Stockholder who has
subscribed for any Undersubscription Amount shall be entitled to purchase only
that portion of the Available Undersubscription Amount as the Undersubscription
Amount subscribed for by such Participating Stockholder bears to the total
Undersubscription Amounts subscribed for by all Participating Stockholders,
subject to rounding by the Board of Directors to the extent it reasonably deems
necessary.

         (c) CONDITIONS TO ACCEPTANCES AND PURCHASE.

                           (i)      PERMITTED SALES OF REFUSED SECURITIES.  If
Notices of Acceptance are not given by the Participating Stockholders in respect
of all the Aggregate Basic Amount, the Company shall have ninety (90) days from
the expiration of the period set forth in Section 6(a) to close the sale of all
or any part of such Aggregate Basic Amount as to which a Notice of Acceptance
has not been given by the Participating Stockholders (the "Refused Securities")
to the person or persons specified in the Offer, but only for cash and otherwise
in all respects upon terms and conditions, including, without limitation, unit
price and interest rates, which are no more favorable, in the aggregate, to such
other person or persons or less favorable to the Company than those set forth in
the Offer.

                           (ii)     REDUCTION IN AMOUNT OF OFFERED SECURITIES.
If the Company shall propose to sell less than all the Refused Securities (any
such sale to be in the manner and on the terms specified in Section 6(c)(i)
above), then each Participating Stockholder may, at its sole option and in its
sole discretion, reduce the number of, or other units of the Offered Securities
specified in its respective Notices of Acceptance to an amount which shall be
not less than the amount of the Offered Securities which the Participating
Stockholder elected to purchase pursuant to Section 6(b) multiplied by a
fraction, (A) the numerator of which shall be the amount of Offered Securities
which the Company actually proposes to sell, and (B) the denominator of which
shall be the amount of all Offered Securities. In the event that any
Participating Stockholder so elects to reduce the number or amount of Offered
Securities specified in its respective Notices of Acceptance, the Company may
not sell or otherwise dispose of more than the reduced amount of the Offered
Securities until such securities have again been offered to the Participating
Stockholders in accordance with Section 6(a).

                           (iii)    CLOSING.  Upon the closing, which shall
include full payment to the Company, of the sale to such other person or persons
of all or less than all the Refused Securities, the Participating Stockholders
shall purchase from the Company, and the Company shall sell to the Participating
Stockholders, the number of Offered Securities specified in the Notices of
Acceptance, as reduced pursuant to Section 6(c)(ii) if the Participating
Stockholders have so elected, upon the terms and conditions specified in the
Offer. The purchase by the Participating Stockholders of any Offered Securities
is subject in all cases to the preparation, execution and delivery by the
Company and the Participating Stockholders of a purchase agreement relating to
such Offered Securities reasonably satisfactory in form and substance to the
Participating Stockholders and their respective counsel.



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         (d) FURTHER SALE. In each case, any Offered Securities not purchased by
the Participating Stockholders or other person or persons in accordance with
Section 6(c) may not be sold or otherwise disposed of until they are again
offered to the Participating Stockholders under the procedures specified in
Sections 6(a), 6(b) and 6(c).

         (e) TERMINATION OF RIGHT OF PARTICIPATION. The rights of the
Participating Stockholders under this Section 6 shall terminate immediately
prior to the consummation of a Qualified Offering. In addition, the rights of
holders of the Founder's Common under this Section 6 shall terminate when the
Founder owns less than 50% of the shares of Founder's Common held by the Founder
on the date first above written (as adjusted for stock splits, stock dividends,
reclassifications, recapitalizations or other similar events). Upon the
termination of the rights of an individual or entity pursuant to this subsection
(e), such individual or entity shall no longer be deemed to be a "Participating
Stockholder" under this Section 6.

         (f) EXCEPTION. The rights of the Participating Stockholders under this
Section 6 shall not apply to:

                           (i)      Common Stock issued as a stock dividend to
holders of Common Stock or upon any subdivision or combination of shares of
Common Stock,

                           (ii)     shares of Series A Preferred Stock issued as
a dividend to holders of Series A Preferred Stock upon any subdivision or
combination of shares of such series of Series A Preferred Stock,

                           (iii)    shares of Series B Preferred Stock issued as
a dividend to holders of Series B Preferred Stock upon any subdivision or
combination of shares of such series of Series B Preferred Stock,

                           (iv)     shares of Series C Preferred Stock issued as
a dividend to holders of Series C Preferred Stock upon any subdivision or
combination of shares of such series of Series C Preferred Stock,

                           (v)      shares of Common Stock issued or issuable
upon conversion of the Series A, Series B and Series C Preferred Stock,

                           (vi)     up to 14,900,000 shares of Common Stock
issued or issuable pursuant to options, warrants or other rights (as adjusted
for any stock dividends, combinations, splits, recapitalizations and the like)
issued to employees, officers or directors of, or consultants or advisors to the
Corporation or any subsidiary pursuant to stock purchase or stock option plans
or other arrangements that are approved by the Board of Directors,

                           (vii)    Common Stock issued pursuant to the
acquisition of another corporation by the Company by merger (whereby the Company
owns no less than 51% of the voting power of such corporation) or purchase of
substantially all of its stock or assets, if such



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acquisition is approved by a majority of the Directors nominated by the holders
of the Preferred Stock in the manner set forth in Section 5 hereof,

                           (viii)   Common Stock offered to the public pursuant
to a registration statement filed under the Securities Act,

                           (ix)     the issuance Common Stock, or options or
warrants to purchase Common Stock, issued to financial institutions or lessors
in connection with commercial credit arrangements, equipment financings or
similar transactions, as approved by the two-thirds (2/3rds) of the then sitting
members of the Board of Directors,

                           (x)      shares of Series C Preferred Stock issued
pursuant to the Purchase Agreement, and

                           (xi)     the issuance of (X) Common Stock in
accordance with the exchange ratio set forth in the Agreement and Plan of Merger
for the acquisition of Allied Riser Communications Corporation, as amended prior
to the date hereof, and (Y) convertible debt ("Exchange Debt") in connection
with the acquisition of Allied Riser Communications Corporation issued in
exchange for or as replacement of and on substantially the same terms and
conditions as the convertible debt of Allied Riser Communications Corporation
outstanding at the time of the acquisition or the issuance of additional
convertible debt or equity as a paid-in-kind interest payment on such Exchange
Debt approved by the Board of Directors.

         (g) WAIVER. The rights of the Purchasers under this Section 6 may be
waived in any instance, on behalf of all of the Purchasers, prospectively or
retroactively, by the written agreement of the holders of a majority in interest
of the Preferred Stock owned beneficially or of record by the Purchasers. The
rights of holders of the Founder's Common under this Section 6 may be waived in
any instance, on behalf of all such holders, prospectively or retroactively, by
the written agreement of the holders of a majority of the Founder's Common then
outstanding. Upon waiver of the rights of the Purchasers or holders of Founder's
Common in accordance with this subsection (g) with respect to a particular
issuance, sale or exchange of Offered Securities, the Purchasers or such holder,
as the case may be, shall be excluded from the definition of "Participating
Stockholders" for purposes of this Section 6 with respect to such issuance, sale
or exchange.

         7. TERMINATION. This Agreement, and the respective rights and
obligations of the parties hereto, shall terminate upon the earliest to occur of
the following: (i) the completion of a Qualified Offering, provided that the
obligations of Section 9 shall survive such termination; or (ii) the sale of the
Company, whether by merger, sale, or transfer of more than ninety percent (90%)
of its capital stock, or sale of substantially all of its assets. In addition,
any Purchaser or Qualified Transferee may elect to terminate its rights and
obligations with respect to any or all of Sections 2, 3, 5 or 6 by providing
written notice of such election to the Company at any time after the Public
Company Date.



                                       10
<Page>


         8. NOTICES. All notices and other communications hereunder shall be in
writing and shall be deemed to have been given when delivered or mailed by first
class, registered or certified mail (air mail if to or from outside the United
States), return receipt requested, postage prepaid, or by internationally,
recognized overnight courier service (two business days after deposit with such
overnight courier service in the case of deliveries to non-U.S. residents), if
to each Holder at his respective address set forth on Schedule I hereto or on
the Instrument of Accession pursuant to which he became a party to this
Agreement, and if to the Purchasers, at their respective addresses set forth on
Schedule I hereto or to such other address as the addressee shall have furnished
to the other parties hereto in the manner prescribed by this Section 8.

         9. LOCK-UP AGREEMENT. Each of the Holders and the Purchasers hereby
agrees in connection with the Company's Qualified Offering, upon the request of
the principal underwriter managing the Qualified Offering of the Company, not to
sell publicly any Shares now owned or hereafter acquired by him, her or it and
subject to this Agreement (other than Shares being registered in such offering
or any shares purchased in the open market after the Company's initial public
offering) without the prior written consent of such underwriter for a period of
time (not to exceed one hundred eighty (180) days) from the consummation of such
Qualified Offering as the underwriter may specify, in all events subject to the
provisions of Section 13(f) of a certain Amended and Restated Registration
Rights Agreement dated as of the date hereof.

         10. FAILURE TO DELIVER SHARES. If a Holder becomes obligated to sell
any Shares owned by, or held for the benefit of, such Holder to the Founder, a
Purchaser or a Qualified Transferee under this Agreement and fails to deliver
such shares in accordance with the terms of this Agreement, the Founder or such
Purchaser, as applicable, may, at his or its option, in addition to all other
remedies it may have, send to the Company for the benefit of such Holder the
purchase price for such Shares as is herein specified. Thereupon, the Company
upon written notice to said Holder, (a) shall cancel on its books the
certificate(s) representing the Shares to be sold and (b) shall issue, in lieu
thereof, in the name of the Founder or such Purchaser, as applicable, a new
certificate(s) representing such Shares, and thereupon all of said Holder's
rights in and to such shares shall terminate. The Company may exercise a similar
remedy in enforcing its rights under Section 2. If a Holder transfers any shares
to the Founder or a Purchaser in violation of this Agreement, the Company may,
at the election of a majority of the disinterested members of the Board of
Directors, cancel on the books of the Company any shares of capital stock then
held by such Holder, and compel such Holder to purchase from the Founder or
Purchaser, as applicable, and any transferee a number of shares of capital stock
equal to the amount so transferred in violation of this Agreement.

         11. SPECIFIC PERFORMANCE. The rights of the parties under this
Agreement are unique and, accordingly, the parties shall, in addition to such
other remedies as may be available to any of them at law or in equity, have the
right to enforce their rights hereunder by actions for specific performance to
the extent permitted by law.

         12. LEGEND. Until this Agreement terminates in full, the certificates
representing the Shares shall bear on their face a legend indicating the
existence of the restrictions imposed hereby. After the Qualified Offering, the
Company shall not issue or deliver to any transfer



                                       11
<Page>


agent a stop transfer notice with respect to any Shares, the transfer of which
is permitted pursuant to Rule 144(k) and the Securities Act of 1933.

         13. ENTIRE AGREEMENT. This Agreement (including any and all exhibits,
schedules and other instruments contemplated thereby) constitutes the entire
agreement among the parties with respect to the subject matter hereof and
supersedes all prior agreements and understandings between them or any of them
as to such subject matter.

         14. WAIVERS AND FURTHER AGREEMENTS. Except as otherwise expressly set
forth herein, the rights of the Purchasers under this Agreement may be waived by
an instrument in writing executed and delivered by Purchasers holding at least
two-thirds in interest of the Common Stock (including shares of Common Stock
into which any shares of Preferred Stock are convertible) then held or deemed to
be held by all Purchasers; PROVIDED, HOWEVER, that the rights set forth in
SECTION 5 with respect to the designation of the Board of Directors of the
Company may not be waived without the prior written consent of the constituency
affected by such waiver, which waiver shall be obtained in a manner consistent
with, and shall require the same percentages prescribed in, SECTION 5. Any
waiver by any party of a breach of any provision of this Agreement shall not
operate or be construed as a waiver of any subsequent breach of that provision
or of any other provision hereof. Each of the parties hereto agrees to execute
all such further instruments and documents and to take all such further action
as any other party may reasonably require in order to effectuate the terms and
purposes of this Agreement. Notwithstanding the foregoing, no waiver approved in
accordance herewith shall be effective if and to the extent that such waiver
grants to any one or more Purchasers any rights more favorable than any rights
granted to all other Purchasers or otherwise treats any one or more Purchasers
differently than all other Purchasers.

         15. AMENDMENTS. Except as otherwise expressly provided herein, this
Agreement may not be amended except by an instrument in writing executed by (i)
Purchasers holding at least two-thirds in interest of the shares of Common Stock
issued or issuable to the Purchasers (including shares of Common Stock into
which any shares of Preferred Stock are convertible), (ii) the Company, (iii)
Holders holding a majority of the Shares subject to this Agreement and (iv)
holders of a majority of the Founder's Common. Notwithstanding the foregoing, no
amendment approved in accordance with clause (i) above shall be effective if and
to the extent that such amendment creates any additional affirmative obligations
to be complied with by any or all of the Purchasers unless approved by holders
of all of the Preferred Stock then outstanding.

         16. ASSIGNMENT; SUCCESSORS AND ASSIGNS. This Agreement shall be binding
upon and shall inure to the benefit of the parties hereto and their respective
heirs, executors, legal representatives, successors and permitted transferees,
except as may be expressly provided otherwise herein, AND PROVIDED, FURTHER,
that no Purchaser may transfer its rights or obligations hereunder except to a
Qualified Transferee. Notwithstanding anything contained herein to the contrary,
until the first to occur of (i) termination of this Agreement and (ii) a
Qualified Offering, any transferee of Preferred Stock shall, as a condition to
such transfer, deliver to the Company a written instrument by which such
transferee agrees to be bound by the obligations imposed



                                       12
<Page>


hereunder on holders of Preferred Stock to the same extent as if such transferee
had signed this Agreement.

         17. SEVERABILITY. In case any one or more of the provisions contained
in this Agreement shall for any reason be held to be invalid, illegal or
unenforceable in any respect, such invalidity, illegality or unenforceability
shall not affect any other provision of this Agreement and such invalid, illegal
and unenforceable provision shall be reformed and construed so that it will be
valid, legal, and enforceable to the maximum extent permitted by law.

         18. COUNTERPARTS.  This Agreement may be executed in two or more
counterparts, each of which shall be deemed an original, but all of which
together shall constitute one and the same instrument.

         19. ADDITIONAL PARTIES. Prior to the Public Company Date, the Company
shall require each executive officer who shall, after the date hereof, acquire
any shares of Common Stock, or any other person (other than a Purchaser or
Qualified Transferee) who acquires in excess of one percent (1%) of the shares
of Common Stock or other equity securities of the Company then outstanding, in
each case as a condition to such acquisition, to become a party to this
Agreement by executing and delivering to the Company an Instrument of Accession
in the form of Schedule II hereto.

         20. SECTION HEADINGS.  The headings contained in this Agreement are for
reference purposes only and shall not in any way affect the meaning or
interpretation of this Agreement.

         21. GOVERNING LAW.  This Agreement shall be construed and enforced in
accordance with and governed by the laws of the State of New York.

         22. ORIGINAL STOCKHOLDERS AGREEMENT.  Upon and after the Closing (as
defined in the Purchase Agreement), the Original Stockholders Agreement shall be
terminated and of no further force and effect.


                  [REMAINDER OF PAGE INTENTIONALLY LEFT BLANK]



                                       13
<Page>


         IN WITNESS WHEREOF, the parties hereto have executed this Agreement as
of the date first above written.

                                   THE COMPANY:

                                   COGENT COMMUNICATIONS GROUP, INC.

                                   By: /s/ Dave Schaeffer
                                      -----------------------------
                                          Name: Dave Schaeffer
                                          Title: Chief Executive Officer



                                   PURCHASERS:

                                   OAK INVESTMENT PARTNERS IX,
                                   LIMITED PARTNERSHIP

                                   By:      Oak Associates IX, LLC,
                                            its General Partner

                                   By: /s/ Edward Glassmeyer
                                      -----------------------------
                                          Name:
                                          Title:

                                   OAK IX AFFILIATES FUND, LIMITED PARTNERSHIP

                                   By:      Oak IX Affiliates, LLC,
                                            its General Partner

                                   By: /s/ Edward Glassmeyer
                                      -----------------------------
                                          Name:
                                          Title:

                                   OAK IX AFFILIATES FUND-A, LIMITED PARTNERSHIP

                                   By:      Oak Associates IX, LLC,
                                            its General Partner

                                   By: /s/ Edward Glassmeyer
                                      -----------------------------
                                          Name:
                                          Title:



                                       14
<Page>


   [SIGNATURE PAGE TO AMENDED AND RESTATED STOCKHOLDERS AGREEMENT - CONTINUED]



                                   JERUSALEM VENTURE PARTNERS III, L.P.

                                   By:   Jerusalem Partners III, L.P.,
                                         its General Partner

                                   By:   Jerusalem Venture Partners Corporation,
                                         its General Partner

                                   By: /s/ Erel N. Margalit
                                      -----------------------------
                                        Name: Erel N. Margalit
                                        Title:

                                   JERUSALEM VENTURE PARTNERS III
                                   (ISRAEL), L.P.

                                   By:   Jerusalem Venture Partners III (Israel)
                                         Management Company Ltd.,
                                         its General Partner

                                   By: /s/ Erel N. Margalit
                                      -----------------------------
                                        Name: Erel N. Margalit
                                        Title:

                                   JERUSALEM VENTURE PARTNERS
                                   ENTREPRENEURS FUND III, L.P.

                                   By:   Jerusalem Partners III, L.P.,
                                         its General Partner

                                   By:   Jerusalem Venture Partners Corporation,
                                         its General Partner

                                   By: /s/ Erel N. Margalit
                                      -----------------------------
                                        Name: Erel N. Margalit
                                        Title:



                                       15
<Page>


   [SIGNATURE PAGE TO AMENDED AND RESTATED STOCKHOLDERS AGREEMENT - CONTINUED]

                                   JERUSALEM VENTURE PARTNERS IV, L.P.

                                   By:   Jerusalem Partners IV, L.P.,
                                         its General Partner

                                   By:   Jerusalem Venture Partners Corporation
                                         IV, its General Partner

                                   By: /s/ Erel N. Margalit
                                      -----------------------------
                                        Name: Erel N. Margalit
                                        Title:

                                   JERUSALEM VENTURE PARTNERS IV (Israel), L.P.

                                   By:   Jerusalem Partners IV - Venture
                                         Capital, L.P., its General Partner

                                   By:   Jerusalem Venture Partners Corporation
                                         IV,its General Partner

                                   By: /s/ Erel N. Margalit
                                      -----------------------------
                                        Name: Erel N. Margalit
                                        Title:

                                   JERUSALEM VENTURE PARTNERS IV-A, L.P.

                                   By:   Jerusalem Venture Partners IV, L.P.,
                                         its General Partner

                                   By:   Jerusalem Venture Partners Corporation
                                         IV, its General Partner

                                   By: /s/ Erel N. Margalit
                                      -----------------------------
                                        Name: Erel N. Margalit
                                        Title:



                                       16
<Page>


   [SIGNATURE PAGE TO AMENDED AND RESTATED STOCKHOLDERS AGREEMENT - CONTINUED]

                                   WORLDVIEW TECHNOLOGY
                                   PARTNERS III, L.P.

                                   By:      Worldview Capital III, L.P.,
                                            its General Partner

                                   By:      Worldview Equity I, L.L.C.,
                                            its General Partner

                                   By: /s/ James Wei
                                      -----------------------------
                                          Name: James Wei
                                          Title: Member

                                   WORLDVIEW TECHNOLOGY
                                   INTERNATIONAL III, L.P.

                                   By:      Worldview Capital III, L.P.,
                                            its General Partner

                                   By:      Worldview Equity I, L.L.C.,
                                            its General Partner

                                   By: /s/ James Wei
                                      -----------------------------
                                          Name: James Wei
                                          Title: Member

                                   WORLDVIEW STRATEGIC PARTNERS III, L.P.

                                   By:      Worldview Capital III, L.P.,
                                            its General Partner

                                   By:      Worldview Equity I, L.L.C.,
                                            its General Partner

                                   By: /s/ James Wei
                                      -----------------------------
                                          Name: James Wei
                                          Title: Member

                                   WORLDVIEW III CARRIER FUND, L.P.

                                   By:      Worldview Capital III, L.P.,
                                            its General Partner

                                   By:      Worldview Equity I, L.L.C.,
                                            its General Partner

                                   By: /s/ James Wei
                                      -----------------------------
                                          Name: James Wei
                                          Title: Member



                                       17
<Page>


   [SIGNATURE PAGE TO AMENDED AND RESTATED STOCKHOLDERS AGREEMENT - CONTINUED]


                                   BROADVIEW CAPITAL PARTNERS L.P.

                                   By:      Broadview Capital Partners
                                            Management LLC, its General Partner

                                   By: /s/ Stephen J. Bachmann
                                      -----------------------------
                                            Name:    Stephen J. Bachmann
                                            Title:   Managing Director

                                   BROADVIEW CAPITAL PARTNERS
                                   QUALIFIED PURCHASER FUND L.P.

                                   By:      Broadview Capital Partners
                                            Management LLC, its General Partner

                                   By: /s/ Stephen J. Bachmann
                                      -----------------------------
                                            Name:    Stephen J. Bachmann
                                            Title:   Managing Director

                                   BROADVIEW CAPITAL PARTNERS
                                   AFFILIATES FUND LLC

                                   By:      Broadview Capital LLC,
                                            its Manager

                                   By: /s/ Stephen J. Bachmann
                                      -----------------------------
                                            Name:    Stephen J. Bachmann
                                            Title:   Managing Director



                                       18
<Page>


   [SIGNATURE PAGE TO AMENDED AND RESTATED STOCKHOLDERS AGREEMENT - CONTINUED]

                                   BOULDER VENTURES III, L.P.

                                   By: /s/ Andrew E. Jones
                                      -----------------------------
                                          Name: Andrew E. Jones
                                          Title: General Partner

                                   BOULDER VENTURES III (ANNEX), L.P.

                                   By: /s/ Andrew E. Jones
                                      -----------------------------
                                          Name: Andrew E. Jones
                                          Title: General Partner



                                       19
<Page>


   [SIGNATURE PAGE TO AMENDED AND RESTATED STOCKHOLDERS AGREEMENT - CONTINUED]

                                   NAS PARTNERS I L.L.C.

                                   By: /s/ Randall A. Hack
                                      -----------------------------
                                          Name: Randall A. Hack
                                          Title: Member


                                   NASSAU CAPITAL PARTNERS IV L.P.

                                   By:      Nassau Capital LLC,
                                            its General Partner

                                   By: /s/ Randall A. Hack
                                      -----------------------------
                                          Name: Randall A. Hack
                                          Title: Member



                                       20
<Page>


   [SIGNATURE PAGE TO AMENDED AND RESTATED STOCKHOLDERS AGREEMENT - CONTINUED]

                                   SMALLCAP WORLD FUND, INC.

                                   By: /s/ Vincent P. Costi
                                      -----------------------------
                                          Name: Vincent P. Costi
                                          Title: Vice President



                                       21
<Page>


   [SIGNATURE PAGE TO AMENDED AND RESTATED STOCKHOLDERS AGREEMENT - CONTINUED]


                                      /s/ David Schaeffer
                                      -----------------------------
                                      David Schaeffer



                                       22
<Page>


   [SIGNATURE PAGE TO AMENDED AND RESTATED STOCKHOLDERS AGREEMENT - CONTINUED]

                                   2M TECHNOLOGY VENTURES, L.P.

                                   By:      2M Technology Group LLC,
                                            its General Partner

                                   By: /s/ A. Scott Letier
                                      -----------------------------
                                          Name: A. Scott Letier
                                          Title: Vice President



                                       23
<Page>


                                   SCHEDULE I


Dave Schaeffer
Denise Shen
Ruth E. Schaeffer, Trustee of the Schaeffer Descendents Trust
Barry Morris
Scott Welker
Thaddeus Weed
Edward Lu
Bradley Griggs
Scott Stewart
C. Blair Partners, LP
C. Blair Partners II, LP
C. Blair Fund, Ltd.

Jerusalem Venture Partners III (Israel) LP:      Jerusalem Technology Park
                                                 Building One
                                                 Mahla, Jerusalem 91847
                                                 Attn: Erel Margalit

Jerusalem Venture Partners III LP                666 Fifth Avenue
Jerusalem Venture Partners Entrepreneurs Fund    Suite 195
LP:                                              New York, NY 10103

Oak Investment Partners IX, LP                   One Gorham Island
Oak IX Affiliates Fund, LP                       Westport, CT 06880
Oak IX Affiliates Fund-A, LP                     Attn: Ed Glassmeyer


Worldview Technology Partners III, LP            435 Tasso Street #120
Worldview Technology  International III, LP      Palo Alto, CA 94301
Worldview Strategic Partners III, LP             Attn: James Wei
Worldview III Carrier Fund, LP

Boulder Ventures III, LP                         4750 Owings Mills Blvd.
Boulder Ventures III (Annex), LP                 Owings Mills, MD 21117
                                                 Attn:  Andy Jones

Comdisco, Inc.                                   3rd Floor South
                                                 Totten Pond Office Center
                                                 400-1 Totten Pond Road, Suite 5
                                                 Waltham, MA 02451
                                                 Attn: Jan Haas



                                       24
<Page>


ACON Venture Partners, LP                        345 California Street
                                                 Suite 3300
                                                 San Francisco, CA 94104
                                                 Attn: Jon Levinson

Clipperbay & Co.                                 3000 K Street. NW
                                                 Suite 230
                                                 Washington, DC 20007
                                                 Attn: Brad Vogt

Covestco-Venteura, LLC                           c/o Jura Trust
                                                 Mitteldorf 1
                                                 Vaduz, Liechtenstein, FL-9490
                                                 Attn: Albin A. Johann

Nassau Capital Partners IV, LP                   22 Chambers Street
NAS Partners I, LLC                              Princeton, NJ 08542
                                                 Attn:  Randall A. Hack
Broadview Capital Partners Qualified Purchaser   950 Tower Lane, 18th Floor
Fund LP                                          Foster City, CA  94404
Broadview Capital Partners LP                    Attn:  David Kapnick
Broadview Capital Partners Affiliates Fund LLC
Broadview BCPSBS Fund LP

2M Technology Ventures, L.P.                     3401 Armstrong Ave.
                                                 Dallas, TX  75205
                                                 Attn:  Scott Letier


Paul Johnson

Spencer Punter

Scappoose Portland, LLC

Brian Rich

Constantine Scontras

David Steinberg



<Page>


Raj Mehra

Edward Pollack

John D. Watson, Jr.

Latham & Watkins, a California general partnership

Brooke Coburn

Colin Stern

Robert Nabholz

Rafi Gidron

Robert Barron

Louis E. Martinage

R. Brad Kummer

University of Maryland Foundation for UMBC

Friedman Kaplan Seiler & Adelman LLP

Jeff Barrows

Jim Dertzbaugh

Gordon P. Griggs, Trustee, Declaration of Trust of Gordon P. Griggs

Brian Griggs and Melissa Griggs, Trustees for Griggs Family Trust

Jeffrey Allen Knepp

Kevin Pavuk

Melvin Young

Andrew Morrison

Bridget Oppenheimer

Keith Steinberg



<Page>


Samuel Parker

Kevin Gallagher

Karen Chow

Michael Van Vleck

Behdad Eghbali

Paul Hauser

Matthew Whalen

Hans Wittich

David J. Daigle

Larry Collins

John Leone

Dave Diller

William Currer

Kenneth Klamm

David Ordonio

Jeffrey Megrue

H. Helen Lee

Comdisco, Inc.

Applegreen Capital, Inc.

Clipperbay & Co.



<Page>


                                   SCHEDULE II

                        COGENT COMMUNICATIONS GROUP, INC.

                             INSTRUMENT OF ACCESSION


         The undersigned, _________________, as a condition precedent to
becoming the owner or holder of record of ___________________ (______) shares of
the Common Stock, par value $.001 per share, of Cogent Communications Group,
Inc., a Delaware corporation (the "Company"), hereby agrees to become a Holder
party to and bound by that certain Stockholders Agreement dated as of _________
___, 2001 by and among the Company and other stockholders of the Company. This
Instrument of Accession shall take effect and shall become an integral part of
the said Stockholders Agreement immediately upon execution and delivery to the
Company of this Instrument.

         IN WITNESS WHEREOF, this INSTRUMENT OF ACCESSION has been duly executed
by or on behalf of the undersigned, as a sealed instrument under the laws of the
State of Delaware, as of the date below written.

                                   Signature:

                                   --------------------------------------
                                   (Print Name)

                                   Address:

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

                                   Accepted:

                                   COGENT COMMUNICATIONS GROUP , INC.


                                   By:
                                        ---------------------------------
                                     Name:
                                           ------------------------------
                                     Title:
                                            -----------------------------
                                   Date:
                                         --------------------------------