Cogent Communications Group, Inc.

Exhibit 4.3

Cogent Communications Group, Inc.

1.00 % Convertible Senior Notes due 2027

June 11, 2007

Ladies and Gentlemen:

Cogent Communications Group, Inc., a Delaware corporation (the “Company”), proposes to issue and sell to the Initial Purchasers (as defined herein) upon the terms set forth in the Purchase Agreement (as defined herein) its 1.00% Convertible Senior Notes due 2027 (the “Securities”). As an inducement to the Initial Purchasers to enter into the Purchase Agreement and in satisfaction of a condition to the obligations of the Initial Purchasers thereunder, the Company (and, for the purposes of Section 5 only, Cogent Communications, Inc., a Delaware corporation (the “Principal Subsidiary”) agrees with the Initial Purchasers for the benefit of Holders (as defined herein) from time to time of the Registrable Securities (as defined herein) as follows:

1. Definitions.

(a) Capitalized terms used herein without definition shall have the meanings ascribed to them in the Purchase Agreement. As used in this Agreement, the following defined terms shall have the following meanings:

“Affiliate” of any specified person means any other person which, directly or indirectly, is in control of, is controlled by, or is under common control with such specified person. For purposes of this definition, control of a person means the power, direct or indirect, to direct or cause the direction of the management and policies of such person whether by contract or otherwise; and the terms “controlling” and “controlled” have meanings correlative to the foregoing.

“Closing Date” means the Closing Date as defined in the Purchase Agreement.

“Commission” means the United States Securities and Exchange Commission, or any other federal agency at the time administering the Exchange Act or the Securities Act, whichever is the relevant statute for the particular purpose.

“Common Stock” means the Company’s common stock, par value $.001 per share together with any associated preferred share purchase rights.

“DTC” means The Depository Trust Company.

“Effective Date” has the meaning assigned thereto in Section 2(b)(i) hereof.

“Effective Time” means the time at which the Commission declares the Shelf Registration Statement effective under the Securities Act or at which the Shelf Registration Statement otherwise becomes effective under the Securities Act.

“Effectiveness Period” has the meaning assigned thereto in Section 2(b)(i) hereof.

“Electing Holder” has the meaning assigned thereto in Section 3(a)(iii) hereof.

“Exchange Act” means the United States Securities Exchange Act of 1934, as amended.

“Holder” means any person that is the record owner of Registrable Securities (and includes any person that has a beneficial interest in any Registrable Security in book-entry form).

“Indenture” means the Indenture, dated as of June 11, 2007 between the Company and Xxxxx Fargo Bank, N.A., as trustee (the “Trustee”), as amended and supplemented from time to time in accordance with its terms.

“Managing Underwriters” means the investment banker or investment bankers and manager or managers that shall administer an underwritten offering, if any, conducted pursuant to Section 6 hereof.

“NASD Rules” means the Rules of the National Association of Securities Dealers, Inc., as amended from time to time.

“Notice and Questionnaire” means a Notice of Registration Statement and Selling Securityholder Questionnaire substantially in the form of Appendix A hereto.

The term “person” means an individual, partnership, corporation, trust or unincorporated organization, or a government or agency or political subdivision thereof.

“Prospectus” means the prospectus (including, without limitation, any preliminary prospectus, any final prospectus and any prospectus that discloses information previously omitted from a prospectus filed as part of an effective registration statement in reliance upon Rule 430A or Rule 430B under the Securities Act) included in the Shelf Registration Statement, as amended or supplemented by any prospectus supplement with respect to the terms of the offering of any portion of the Registrable Securities covered by the Shelf Registration Statement and by all other amendments and supplements to such prospectus, including all material incorporated by reference in such prospectus and all documents filed after the date of such prospectus by the Company under the Exchange Act and incorporated by reference therein.

“Purchase Agreement” means the purchase agreement, dated June 6, 2007, between the Initial Purchasers and the Company relating to the Securities.

“Initial Purchasers” means the Initial Purchasers named in to the Purchase Agreement.

“Registrable Securities” means all or any portion of the Securities issued from time to time under the Indenture in registered form and the shares of Common Stock issuable upon conversion, repurchase or redemption of such Securities; provided, however, that a security ceases to be a Registrable Security when it is no longer a Restricted Security.

“Registration Default” has the meaning assigned thereto in Section 7(a) hereof.

“Restricted Security” means any Security or share of Common Stock issuable upon conversion thereof except any such Security or share of Common Stock that (i) has been effectively registered under the Securities Act and sold in a manner contemplated by the Shelf Registration Statement, (ii) has been transferred in compliance with Rule 144 under the Securities Act (or any successor provision thereto) or is transferable pursuant to paragraph (k) of such Rule 144 (or any successor provision thereto) or (iii) has otherwise been transferred and a new Security or share of Common Stock not subject to transfer restrictions under the Securities Act has been delivered by or on behalf of the Company in accordance with the Indenture.

“Rules and Regulations” means the published rules and regulations of the Commission promulgated under the Securities Act or the Exchange Act, as in effect at any relevant time.

“Securities Act” means the United States Securities Act of 1933, as amended.

“Shelf Registration” means a registration effected pursuant to Section 2 hereof.

“Shelf Registration Statement” means a “shelf” registration statement filed under the Securities Act providing for the registration of, and the sale on a continuous or delayed basis by the Holders of, all of the Registrable Securities pursuant to Rule 415 under the Securities Act and/or any similar rule that may be adopted by the Commission, filed by the Company pursuant to the provisions of Section 2 of this Agreement, including the Prospectus contained therein, any amendments and supplements to such registration statement, including post-effective amendments, and all exhibits and all material incorporated by reference in such registration statement, and including all information deemed to be a part thereof pursuant to Rule 430A, Rule 430B or Rule 430C under the Securities Act.

“Special Interest” has the meaning assigned thereto in Section 7(a) hereof.

“Suspension Period” has the meaning assigned thereto in Section 2(c) hereof.

“Trust Indenture Act” means the Trust Indenture Act of 1939, or any successor thereto, and the rules, regulations and forms promulgated thereunder, as the same shall be amended from time to time.

The term “underwriter” means any underwriter of Registrable Securities in connection with an offering thereof under a Shelf Registration Statement.

(b) Wherever there is a reference in this Agreement to a percentage of the “principal amount” of Registrable Securities or to a percentage of Registrable Securities, Common Stock shall be treated as representing the principal amount of Securities that was surrendered for conversion or exchange in order to receive such number of shares of Common Stock.

2. Shelf Registration.

(a) The Company shall file, as soon as practicable after the Closing Date, with the Commission a Shelf Registration Statement relating to the offer and sale of the Registrable Securities by the Holders from time to time in accordance with the methods of distribution elected by such Holders and set forth in such Shelf Registration Statement and, thereafter, shall use its commercially reasonable efforts to cause such Shelf Registration Statement to be declared effective under the Securities Act no later than 120 calendar days following the Closing Date; provided, however, that no Holder shall be entitled to be named as a selling securityholder

in the Shelf Registration Statement or to use the Prospectus forming a part thereof for resales of Registrable Securities unless such Holder is an Electing Holder.

(b) The Company shall use its commercially reasonable efforts:

(i) to keep the Shelf Registration Statement continuously effective under the Securities Act in order to permit the Prospectus forming a part thereof to be usable by Holders until the earliest of (1) the sale of all outstanding Registrable Securities registered under the Shelf Registration Statement; (2) the expiration of the period referred to in Rule 144(k) of the Securities Act with respect to all Registrable Securities held by Persons that are not Affiliates of the Company; and (3) two years from the date (the “Effective Date”) such Shelf Registration Statement is declared effective (such period being referred to herein as the “Effectiveness Period”);

(ii) after the Effective Time of the Shelf Registration Statement, promptly upon the request of any Holder of Registrable Securities that is not then an Electing Holder, to take any action reasonably necessary to enable such Holder to use the Prospectus forming a part thereof for resales of Registrable Securities, including, without limitation, any action necessary to identify such Holder as a selling securityholder in the Shelf Registration Statement; provided, however, that (i) from and after the beginning of the calendar quarter commencing after the 12-month anniversary of the Closing Date, the Company will not be required to take any action to include any holder’s registrable securities more than one time in any calendar quarter and (ii) nothing in this subparagraph shall relieve such Holder of the obligation to return a completed and signed Notice and Questionnaire to the Company in accordance with Section 3(a)(ii) hereof; and

(iii) if at any time the Securities, pursuant to the Indenture, are convertible into securities other than Common Stock, to cause, or to cause any successor under the Indenture to cause, such securities to be included in the Shelf Registration Statement no later than the date on which the Securities may then be convertible into such securities.

The Company shall be deemed not to have used its commercially reasonable efforts to keep the Shelf Registration Statement effective during the requisite period if the Company voluntarily takes any action that would result in Holders of Registrable Securities covered thereby not being able to offer and sell any of such Registrable Securities during that period, unless such action is (A) required by applicable law and the Company thereafter promptly complies with the requirements of paragraph 3(j) below or (B) permitted pursuant to Section 2(c) below.

(c) The Company may suspend the use of the Prospectus for a period (a “Suspension Period”) not to exceed 90 consecutive days or an aggregate of 120 days in any 12-month period if the Board of Directors of the Company shall have determined in good faith that because of valid business reasons (not including avoidance of the Company’s obligations hereunder), including the acquisition or divestiture of assets, pending corporate developments, public filings with the Commission and similar events, it is in the best interests of the Company to suspend such use, and prior to suspending such use the Company provides the Electing Holders with written notice of such suspension, which notice need not specify the nature of the event giving rise to such suspension.

3. Registration Procedures. In connection with the Shelf Registration Statement, the following provisions shall apply:

(a) (i) Not less than 30 calendar days prior to the Effective Time of the Shelf Registration Statement, the Company shall mail the Notice and Questionnaire to the Holders of Registrable Securities. No Holder shall be entitled to be named as a selling securityholder in the Shelf Registration Statement as of the Effective Time, and no Holder shall be entitled to use the Prospectus forming a part thereof for resales of Registrable Securities at any time, in each case unless such Holder has returned a completed and signed Notice and Questionnaire to the Company prior to the end of a period specified by the Company in such Notice, which period shall be no shorter than 20 calendar days after the date the Notice and Questionnaire were mailed.

(ii) After the Effective Time of the Shelf Registration Statement, the Company shall, upon the request of any Holder of Registrable Securities that is not then an Electing Holder (as defined herein), promptly send a Notice and Questionnaire to such Holder. Such Holder of Registrable Securities may thereafter provide the Company with a completed and signed Notice and Questionnaire, following which the Company will, within 30 days after that date (except as described below), file a supplement to the Prospectus relating to the Shelf Registration Statement, or, if required, file a post-effective amendment or a new Shelf Registration Statement in order to permit resales of such Holder’s Registrable Securities. However, if the Company receives the completed and signed Notice and Questionnaire during a Suspension Period, or if the Company initiates a Suspension Period within 30 days after the Company receives the completed and signed Notice and Questionnaire, then the Company will, except as described below, make the filing within 30 days after the end of the Suspension Period. Notwithstanding anything herein to the contrary, in no event will the Company be required to file more than one supplement to the Prospectus per 30-day period in order to name as a selling securityholder any Holder that has provided the Company with a completed and signed Notice and Questionnaire after the fifth business day before the date the initial Shelf Registration becomes effective. If the Company files a post-effective amendment or a new Shelf Registration Statement, then the Company will use reasonable efforts to cause the post-effective amendment or new Shelf Registration Statement to become effective under the Securities Act as promptly as practicable, but in any event by the 90th day after this Agreement requires the Company to file the post-effective amendment or new Shelf Registration Statement. However, if a post-effective amendment or a new Shelf Registration Statement is required in order to permit resales by Holders seeking to include Registrable Securities in the Shelf Registration statement after the effectiveness of the original Shelf Registration Statement, the Company will not be required to file more than one post-effective amendment or new Shelf Registration Statement for such purpose in any 90-day period.

(iii) The term “Electing Holder” shall mean any Holder of Registrable Securities that has returned a completed and signed Notice and Questionnaire to the Company in accordance with Section 3(a)(i) or Section 3(a)(ii) hereof.

(b) The Company shall furnish to each Electing Holder, prior to the Effective Time, a copy of the Shelf Registration Statement initially filed with the Commission, and shall furnish to such Holders, prior to the filing thereof with the Commission, copies of each amendment thereto and each amendment or supplement, if any, to the Prospectus included therein, and shall use its best efforts to reflect in each such document, at the Effective Time or when so filed with the Commission, as the case may be, such comments as such Holders and their respective counsel reasonably may propose.

(c) The Company shall promptly take such action as may be necessary so that (i) each of the Shelf Registration Statement and any amendment thereto and the Prospectus forming a part thereof and any amendment or supplement thereto (and each report or other document incorporated therein by reference in each case) complies in all material respects with the Securities Act and the Exchange Act and the respective Rules and Regulations thereunder, (ii) each of the Shelf Registration Statement and any amendment thereto does not, when it becomes effective, contain an untrue statement of a material fact or omit to state a material fact required to be stated therein or necessary to make the statements therein not misleading and (iii) each of the Prospectus forming a part of the Shelf Registration Statement, and any amendment or supplement to such Prospectus, does not at any time during the Effectiveness Period include an untrue statement of a material fact or omit to state a material fact necessary in order to make the statements therein, in the light of the circumstances under which they were made, not misleading.

(d) The Company shall promptly advise each Electing Holder and the Trustee, and shall confirm such advice in writing if so requested by any such Electing Holder or the Trustee:

(i) when a Shelf Registration Statement and any amendment thereto has been filed with the Commission and when a Shelf Registration Statement or any post-effective amendment thereto has become effective;

(ii) of any request by the Commission for amendments or supplements to the Shelf Registration Statement or the Prospectus included therein or for additional information;

(iii) of the issuance by the Commission of any stop order suspending the effectiveness of the Shelf Registration Statement or the initiation of any proceedings for such purpose;

(iv) of the receipt by the Company of any notification with respect to the suspension of the qualification of the securities included in the Shelf Registration Statement for sale in any jurisdiction or the initiation of any proceeding for such purpose; and

(v) of the occurrence of any event or the existence of any state of facts that requires the making of any changes in the Shelf Registration Statement or the Prospectus included therein so that, as of such date, such Shelf Registration Statement and Prospectus do not contain an untrue statement of a material fact and do not omit to state a material fact required to be stated therein or necessary to make the statements therein (in the case of the Prospectus, in light of the circumstances under which they were made) not misleading (which advice shall be accompanied by an instruction to such Holders to suspend the use of the Prospectus until the requisite changes have been made).

(e) The Company shall use its reasonable efforts to prevent the issuance, and if issued to obtain the withdrawal at the earliest possible time, of any order suspending the effectiveness of the Shelf Registration Statement.

(f) The Company shall furnish to each Electing Holder, without charge, at least one copy of the Shelf Registration Statement and all post-effective amendments thereto, including financial statements and schedules, and, if such Electing Holder so requests in writing, all

reports, other documents and exhibits that are filed with or incorporated by reference in the Shelf Registration Statement.

(g) The Company shall, during the Effectiveness Period, deliver to each Electing Holder, without charge, as many copies of the Prospectus (including each preliminary Prospectus) included in the Shelf Registration Statement and any amendment or supplement thereto as such Electing Holder may reasonably request; and the Company consents (except during a Suspension Period or during the continuance of any event or the existence of any state of facts described in Section 3(d)(v) above) to the use of the Prospectus and any amendment or supplement thereto by each of the Electing Holders in connection with the offering and sale of the Registrable Securities covered by the Prospectus and any amendment or supplement thereto during the Effectiveness Period.

(h) Prior to any offering of Registrable Securities pursuant to the Shelf Registration Statement, the Company shall (i) register or qualify or cooperate with the Electing Holders and their respective counsel in connection with the registration or qualification of such Registrable Securities for offer and sale under the securities or “blue sky” laws of such jurisdictions within the United States as any Electing Holder may reasonably request, (ii) keep such registrations or qualifications in effect and comply with such laws so as to permit the continuance of offers and sales in such jurisdictions for so long as may be necessary to enable any Electing Holder or underwriter, if any, to complete its distribution of Registrable Securities pursuant to the Shelf Registration Statement, and (iii) take any and all other actions necessary or advisable to enable the disposition in such jurisdictions of such Registrable Securities; provided, however, that in no event shall the Company be obligated to (A) qualify as a foreign corporation or as a dealer in securities in any jurisdiction where it would not otherwise be required to so qualify but for this Section 3(h) or (B) file any general consent to service of process in any jurisdiction where it is not as of the date hereof so subject.

(i) Unless any Registrable Securities shall be in book-entry only form, the Company shall cooperate with the Electing Holders to facilitate the timely preparation and delivery of certificates representing Registrable Securities to be sold pursuant to the Shelf Registration Statement, which certificates, if so required by any securities exchange upon which any Registrable Securities are listed, shall be penned, lithographed or engraved, or produced by any combination of such methods, on steel engraved borders, and which certificates shall be free of any restrictive legends and in such permitted denominations and registered in such names as Electing Holders may request in connection with the sale of Registrable Securities pursuant to the Shelf Registration Statement.

(j) Upon the occurrence of any event or the existence of any state of facts contemplated by paragraph 3(d)(v) above, the Company shall promptly prepare a post-effective amendment to any Shelf Registration Statement or an amendment or supplement to the related Prospectus or file any other required document so that, as thereafter delivered to Initial Purchasers of the Registrable Securities included therein, the Prospectus will not include an untrue statement of a material fact or omit to state any material fact necessary to make the statements therein, in the light of the circumstances under which they were made, not misleading. If the Company notifies the Electing Holders of the occurrence of any event or the existence of any state of facts contemplated by paragraph 3(d)(v) above, the Electing Holder shall suspend the use of the Prospectus until the requisite changes to the Prospectus have been made.

(k) Not later than the Effective Time of the Shelf Registration Statement, the Company shall provide a CUSIP number for the Registrable Securities that are debt securities.

(l) The Company shall use its best efforts to comply with all applicable Rules and Regulations, and to make generally available to its securityholders as soon as practicable, but in any event not later than eighteen months after (i) the effective date (as defined in Rule 158(c) under the Securities Act) of the Shelf Registration Statement, (ii) the effective date of each post-effective amendment to the Shelf Registration Statement, and (iii) the date of each filing by the Company with the Commission of an Annual Report on Form 10-K that is incorporated by reference in the Shelf Registration Statement, an earning statement of the Company and its subsidiaries complying with Section 11(a) of the Securities Act and the Rules and Regulations of the Commission thereunder (including, at the option of the Company, Rule 158).

(m) Not later than the Effective Time of the Shelf Registration Statement, the Company shall cause the Indenture to be qualified under the Trust Indenture Act; in connection with such qualification, the Company shall cooperate with the Trustee under the Indenture and the Holders (as defined in the Indenture) to effect such changes to the Indenture as may be required for such Indenture to be so qualified in accordance with the terms of the Trust Indenture Act; and the Company shall execute, and shall use all reasonable efforts to cause the Trustee to execute, all documents that may be required to effect such changes and all other forms and documents required to be filed with the Commission to enable such Indenture to be so qualified in a timely manner. In the event that any such amendment or modification referred to in this Section 3(m) involves the appointment of a new trustee under the Indenture, the Company shall appoint a new trustee thereunder pursuant to the applicable provisions of the Indenture.

(n) In the event of an underwritten offering conducted pursuant to Section 6 hereof, the Company shall, if requested, promptly include or incorporate in a Prospectus supplement or post-effective amendment to the Shelf Registration Statement such information as the Managing Underwriters reasonably agree should be included therein and to which the Company does not reasonably object and shall make all required filings of such Prospectus supplement or post-effective amendment as soon as practicable after it is notified of the matters to be included or incorporated in such Prospectus supplement or post-effective amendment.

(o) The Company shall enter into such customary agreements (including an underwriting agreement in customary form in the event of an underwritten offering conducted pursuant to Section 6 hereof) and take all other appropriate action in order to expedite and facilitate the registration and disposition of the Registrable Securities, and in connection therewith, if an underwriting agreement is entered into, cause the same to contain indemnification provisions and procedures substantially identical to those set forth in Section 5 hereof with respect to all parties to be indemnified pursuant to Section 5 hereof.

(p) The Company shall:

(i)(A) make reasonably available for inspection by the Electing Holders, any underwriter participating in any disposition pursuant to the Shelf Registration Statement, and any attorney, accountant or other agent retained by such Electing Holders or any such underwriter all relevant financial and other records, pertinent corporate documents and properties of the Company and its subsidiaries, and (B) cause the Company’s officers, directors and employees to supply all information reasonably requested by such Electing Holders or any such underwriter, attorney, accountant or agent in connection with the Shelf Registration Statement, in each case, as is customary for similar due

diligence examinations; provided, however, that all records, information and documents that are designated in writing by the Company, in good faith, as confidential shall be kept confidential by such Electing Holders and any such underwriter, attorney, accountant or agent, unless such disclosure is made in connection with a court proceeding or required by law, or such records, information or documents become available to the public generally or through a third party without an accompanying obligation of confidentiality; and provided further that, if the foregoing inspection and information gathering would otherwise disrupt the Company’s conduct of its business, such inspection and information gathering shall, to the greatest extent possible, be coordinated on behalf of the Electing Holders and the other parties entitled thereto by one counsel designated by and on behalf of the Electing Holders and other parties;

(ii) in connection with any underwritten offering conducted pursuant to Section 6 hereof, make such representations and warranties to the Electing Holders participating in such underwritten offering and to the Managing Underwriters, in form, substance and scope as are customarily made by the Company to underwriters in primary underwritten offerings of equity and convertible debt securities and covering matters including, but not limited to, those set forth in the Purchase Agreement;

(iii) in connection with any underwritten offering conducted pursuant to Section 6 hereof, obtain opinions of counsel to the Company (which counsel and opinions (in form, scope and substance) shall be reasonably satisfactory to the Managing Underwriters) addressed to each Electing Holder participating in such underwritten offering and the underwriters, covering such matters as are customarily covered in opinions requested in primary underwritten offerings of equity and convertible debt securities and such other matters as may be reasonably requested by such Electing Holders and underwriters (it being agreed that the matters to be covered by such opinions shall include, without limitation, as of the date of the opinion and as of the Effective Time of the Shelf Registration Statement or most recent post-effective amendment thereto, as the case may be, the absence from the Shelf Registration Statement and the Prospectus, including the documents incorporated by reference therein, of an untrue statement of a material fact or the omission of a material fact required to be stated therein or necessary to make the statements therein not misleading);

(iv) in connection with any underwritten offering conducted pursuant to Section 6 hereof, obtain “cold comfort” letters and updates thereof from the independent public accountants of the Company (and, if necessary, from the independent public accountants of any subsidiary of the Company or of any business acquired by the Company for which financial statements and financial data are, or are required to be, included in the Shelf Registration Statement), addressed to each Electing Holder participating in such underwritten offering (if such Electing Holder has provided such letter, representations or documentation, if any, required for such cold comfort letter to be so addressed) and the underwriters, in customary form and covering matters of the type customarily covered in “cold comfort” letters in connection with primary underwritten offerings;

(v) in connection with any underwritten offering conducted pursuant to Section 6 hereof, deliver such documents and certificates as may be reasonably requested by any Electing Holders participating in such underwritten offering and the Managing Underwriters, if any, including, without limitation, certificates to evidence

compliance with Section 3(j) hereof and with any conditions contained in the underwriting agreement or other agreements entered into by the Company; and

(vi) in connection with any underwritten offering conducted pursuant to Section 6 hereof, participate in any investor presentations (including customary “Road Show” presentations) as reasonably requested by the Managing Underwriter.

(q) The Company will use its commercially reasonable efforts to cause the Common Stock issuable upon conversion of the Securities to be quoted on the Nasdaq Global Market. However, if the Company’s Common Stock is not then quoted on the Nasdaq Global Market, the Company will use its commercially reasonable efforts to cause the Common Stock to be quoted or listed on whichever market or exchange its Common Stock is then primarily traded, upon the Effective Time of the Shelf Registration Statement hereunder.

(r) In the event that any broker-dealer registered under the Exchange Act shall be an “affiliate” (as defined in Rule 2720(b)(1) of the NASD Rules (or any successor provision thereto)) of the Company or has a “conflict of interest” (as defined in Rule 2720(b)(7) of the NASD Rules (or any successor provision thereto)) and such broker-dealer shall underwrite, participate as a member of an underwriting syndicate or selling group or assist in the distribution of any Registrable Securities covered by the Shelf Registration Statement, whether as a Holder of such Registrable Securities or as an underwriter, a placement or sales agent or a broker or dealer in respect thereof, or otherwise, the Company shall assist such broker-dealer in complying with the requirements of the NASD Rules, including, without limitation, by (A) engaging a “qualified independent underwriter” (as defined in Rule 2720(b)(15) of the NASD Rules (or any successor provision thereto)) to participate in the preparation of the registration statement relating to such Registrable Securities, to exercise usual standards of due diligence in respect thereto and to recommend the public offering price of such Registrable Securities, (B) indemnifying such qualified independent underwriter to the extent of the indemnification of underwriters provided in Section 5 hereof, and (C) providing such information to such broker-dealer as may be required in order for such broker-dealer to comply with the requirements of the NASD Rules.

(s) The Company shall use its reasonable efforts to take all other steps necessary to effect the registration, offering and sale of the Registrable Securities covered by the Shelf Registration Statement contemplated hereby.

4. Registration Expenses. Except as otherwise provided in Section 3, the Company shall bear all fees and expenses incurred in connection with the performance of its obligations hereof and shall bear or reimburse the Electing Holders for the reasonable fees and disbursements of a single counsel selected by a plurality of all Electing Holders who own an aggregate of not less than 33 1/3% of the Registrable Securities covered by the Shelf Registration Statement to act as counsel, which shall initially be Winston & Xxxxxx LLP, 00 Xxxx Xxxxxx Xxxxx, Xxxxxxx, Xxxxxxxx, 00000, Attention: Xxxxx X. Xxxxxxxx or other counsel, therefore in connection therewith. Each Electing Holder shall pay all underwriting discounts and commissions and transfer taxes, if any, relating to the sale or disposition of such Electing Holder’s Registrable Securities pursuant to the Shelf Registration Statement.

5. Indemnification and Contribution.

(a) Indemnification by the Company and Principal Subsidiary. Upon the registration of the Registrable Securities pursuant to Section 2 hereof, the Company and the Principal Subsidiary shall indemnify and hold harmless each Electing Holder and each underwriter, selling agent or other securities professional, if any, which facilitates the disposition of Registrable Securities, and each of their respective officers and directors and each person who controls such Electing Holder, underwriter, selling agent or other securities professional within the meaning of Section 15 of the Securities Act or Section 20 of the Exchange Act (each such person being sometimes referred to as an “Indemnified Person”) against any losses, claims, damages or liabilities, joint or several, to which such Indemnified Person may become subject under the Securities Act or otherwise, insofar as such losses, claims, damages or liabilities (or actions in respect thereof) arise out of or are based upon an untrue statement or alleged untrue statement of a material fact contained in any Shelf Registration Statement under which such Registrable Securities are to be registered under the Securities Act, or any Prospectus contained therein or furnished by the Company to any Indemnified Person, or any amendment or supplement thereto, or arise out of or are based upon the omission or alleged omission to state therein a material fact required to be stated therein or necessary to make the statements therein not misleading, and the Company and the Principal Subsidiary hereby agrees to reimburse such Indemnified Person for any legal or other expenses reasonably incurred by them in connection with investigating or defending any such action or claim as such expenses are incurred; provided, however, that neither the Company nor the Principal Subsidiary shall be liable to any such Indemnified Person in any such case to the extent that any such loss, claim, damage or liability arises out of or is based upon an untrue statement or alleged untrue statement or omission or alleged omission made in such Shelf Registration Statement or Prospectus, or amendment or supplement, in reliance upon and in conformity with written information furnished to the Company by such Indemnified Person expressly for use therein.

(b) Indemnification by the Electing Holders and any Agents and Underwriters. Each Electing Holder agrees, as a consequence of the inclusion of any of such Electing Holder’s Registrable Securities in such Shelf Registration Statement, and each underwriter, selling agent or other securities professional, if any, which facilitates the disposition of Registrable Securities shall agree, as a consequence of facilitating such disposition of Registrable Securities, severally and not jointly, to (i) indemnify and hold harmless the Company, its directors, officers who sign any Shelf Registration Statement and each person, if any, who controls the Company within the meaning of either Section 15 of the Securities Act or Section 20 of the Exchange Act, against any losses, claims, damages or liabilities to which the Company or such other persons may become subject, under the Securities Act or otherwise, insofar as such losses, claims, damages or liabilities (or actions in respect thereof) arise out of or are based upon an untrue statement or alleged untrue statement of a material fact contained in such Shelf Registration Statement or Prospectus, or any amendment or supplement, or arise out of or are based upon the omission or alleged omission to state therein a material fact required to be stated therein or necessary to make the statements therein not misleading, in each case to the extent, but only to the extent, that such untrue statement or alleged untrue statement or omission or alleged omission was made in reliance upon and in conformity with written information furnished to the Company by such Electing Holder, underwriter, selling agent or other securities professional expressly for use therein, and (ii) reimburse the Company for any legal or other expenses reasonably incurred by the Company in connection with investigating or defending any such action or claim as such expenses are incurred.

(c) Notices of Claims, Etc. Promptly after receipt by an indemnified party under subsection (a) or (b) above of notice of the commencement of any action, such indemnified party shall, if a claim in respect thereof is to be made against an indemnifying party under this

Section 5, notify such indemnifying party in writing of the commencement thereof; but the omission so to notify the indemnifying party shall not relieve it from any liability which it may have to any indemnified party otherwise than under the indemnification provisions of or contemplated by subsection (a) or (b) above. In case any such action shall be brought against any indemnified party and it shall notify an indemnifying party of the commencement thereof, such indemnifying party shall be entitled to participate therein and, to the extent that it shall wish, jointly with any other indemnifying party similarly notified, to assume the defense thereof, with counsel satisfactory to such indemnified party (who shall not, except with the consent of the indemnified party, be counsel to the indemnifying party), and, after notice from the indemnifying party to such indemnified party of its election so to assume the defense thereof, such indemnifying party shall not be liable to such indemnified party under this Section 5 for any legal expenses of other counsel or any other expenses, in each case subsequently incurred by such indemnified party, in connection with the defense thereof other than reasonable costs of investigation. No indemnifying party shall, without the written consent of the indemnified party, effect the settlement or compromise of, or consent to the entry of any judgment with respect to, any pending or threatened action or claim in respect of which indemnification or contribution may be sought hereunder (whether or not the indemnified party is an actual or potential party to such action or claim) unless such settlement, compromise or judgment (i) includes an unconditional release of the indemnified party from all liability arising out of such action or claim and (ii) does not include a statement as to, or an admission of, fault, culpability or a failure to act, by or on behalf of any indemnified party.

(d) Contribution. If the indemnification provided for in this Section 5 is unavailable to or insufficient to hold harmless an indemnified party under subsection (a) or (b) above in respect of any losses, claims, damages or liabilities (or actions in respect thereof) referred to therein, then each indemnifying party shall contribute to the amount paid or payable by such indemnified party as a result of such losses, claims, damages or liabilities (or actions in respect thereof) in such proportion as is appropriate to reflect the relative fault of the indemnifying party and the indemnified party in connection with the statements or omissions which resulted in such losses, claims, damages or liabilities (or actions in respect thereof), as well as any other relevant equitable considerations. The relative fault of such indemnifying party and indemnified party shall be determined by reference to, among other things, whether the untrue or alleged untrue statement of a material fact or omission or alleged omission to state a material fact relates to information supplied by such indemnifying party or by such indemnified party, and the parties’ relative intent, knowledge, access to information and opportunity to correct or prevent such statement or omission. The parties hereto agree that it would not be just and equitable if contribution pursuant to this Section 5(d) were determined by pro rata allocation (even if the Electing Holders or any underwriters, selling agents or other securities professionals or all of them were treated as one entity for such purpose) or by any other method of allocation which does not take account of the equitable considerations referred to in this Section 5(d). The amount paid or payable by an indemnified party as a result of the losses, claims, damages or liabilities (or actions in respect thereof) referred to above shall be deemed to include any legal or other fees or expenses reasonably incurred by such indemnified party in connection with investigating or defending any such action or claim. No person guilty of fraudulent misrepresentation (within the meaning of Section 11(f) of the Securities Act) shall be entitled to contribution from any person who was not guilty of such fraudulent misrepresentation. The obligations of the Electing Holders and any underwriters, selling agents or other securities professionals in this Section 5(d) to contribute shall be several in proportion to the percentage of principal amount or number of shares, as applicable, of Registrable Securities registered or underwritten, as the case may be, by them and not joint.

(e) Notwithstanding any other provision of this Section 5, in no event will any (i) Electing Holder be required to undertake liability to any person under this Section 5 for any amounts in excess of the dollar amount of the proceeds to be received by such Holder from the sale of such Holder’s Registrable Securities (after deducting any fees, discounts and commissions applicable thereto) pursuant to any Shelf Registration Statement under which such Registrable Securities are to be registered under the Securities Act and (ii) underwriter, selling agent or other securities professional be required to undertake liability to any person hereunder for any amounts in excess of the discount, commission or other compensation payable to such underwriter, selling agent or other securities professional with respect to the Registrable Securities underwritten by it and distributed to the public.

(f) The obligations of the Company under this Section 5 shall be in addition to any liability which the Company may otherwise have to any Indemnified Person and the obligations of any Indemnified Person under this Section 5 shall be in addition to any liability which such Indemnified Person may otherwise have to the Company. The remedies provided in this Section 5 are not exclusive and shall not limit any rights or remedies which may otherwise be available to an indemnified party at law or in equity.

6. Underwritten Offering. Any Holder of Registrable Securities who desires to do so may sell Registrable Securities (in whole or in part) in an underwritten offering; provided that (i) the Electing Holders of at least 33-1/3% in aggregate principal amount of the Registrable Securities then covered by the Shelf Registration Statement shall request such an offering and (ii) at least such aggregate principal amount of such Registrable Securities shall be included in such offering; and provided further that the Company shall not be obligated to cooperate with more than one underwritten offering during the Effectiveness Period. Upon receipt of such a request, the Company shall provide all Holders of Registrable Securities written notice of the request, which notice shall inform such Holders that they have the opportunity to participate in the offering. In any such underwritten offering, the investment banker or bankers and manager or managers that will administer the offering will be selected by, and the underwriting arrangements with respect thereto (including the size of the offering) will be approved by, the holders of a majority of the Registrable Securities to be included in such offering; provided, however, that such investment bankers and managers and underwriting arrangements must be reasonably satisfactory to the Company. No Holder may participate in any underwritten offering contemplated hereby unless (a) such Holder agrees to sell such Holder’s Registrable Securities to be included in the underwritten offering in accordance with any approved underwriting arrangements, (b) such Holder completes and executes all reasonable questionnaires, powers of attorney, indemnities, underwriting agreements, lock-up letters and other documents required under the terms of such approved underwriting arrangements, and (c) if such Holder is not then an Electing Holder, such Holder returns a completed and signed Notice and Questionnaire to the Company in accordance with Section 3(a)(ii) hereof within a reasonable amount of time before such underwritten offering. The Holders participating in any underwritten offering shall be responsible for any underwriting discounts and commissions and fees and, subject to Section 4 hereof, expenses of their own counsel. The Company shall pay all expenses customarily borne by issuers in an underwritten offering, including but not limited to filing fees, the fees and disbursements of its counsel and independent public accountants and any printing expenses incurred in connection with such underwritten offering. Notwithstanding the foregoing or the provisions of Section 3(n) hereof, upon receipt of a request from the Managing Underwriter or a representative of holders of a majority of the Registrable Securities to be included in an underwritten offering to prepare and file an amendment or supplement to the Shelf Registration Statement and Prospectus in connection with an underwritten offering, the Company may delay the filing of any such amendment or supplement for up to 90 days if the Board of Directors of the

Company shall have determined in good faith that the Company has a valid business reason for such delay.

7. Special Interest.

(a) If (i) on or prior to the 120th day following the Closing Date, a Shelf Registration Statement is not declared effective by the Commission, (ii) the Shelf Registration Statement ceases to be effective or the Holders are otherwise prevented by the Company from making sales pursuant to the Shelf Registration Statement for more than 90 consecutive days or (iii) the Shelf Registration Statement ceases to be effective or the Holders are otherwise prevented by the Company from making sales pursuant to the Shelf Registration Statement for more than 120 days, whether or not consecutive, during any 12-month period (each, a “Registration Default”), the Company shall be required to pay additional interest (“Special Interest”), from and including the day following such Registration Default to but excluding the earlier of the date (i) such Registration Default has been cured and (ii) of the earliest of (x) the sale of all outstanding Registrable Securities registered under the Shelf Registration Statement; (y) the expiration of the period referred to in Rule 144(k) of the Securities Act with respect to all Registrable Securities held by the Person that are not Affiliates of the Company and (z) two years from the Effective Date, at a rate per annum equal to an additional one-quarter of one percent (0.25%) of the principal amount of all outstanding Securities, to and including the 90th day following such Registration Default and one-half of one percent (0.50%) thereof from and after, in each case from the 91st such consecutive day or the 121st day of the 12-month period, as applicable.

(b) Following the cure of a Registration Default, Special Interest will cease to accrue with respect to that Registration Default. In addition, no Special Interest will accrue after the end of the Effectiveness Period. However, the Company shall remain liable for any previously accrued additional Special Interest.

(c) Any amounts to be paid as Special Interest pursuant to paragraph (a) of this Section 7 shall be paid in cash semi-annually in arrears, with the first semi-annual payment due on the first Interest Payment Date (as defined in the Indenture), as applicable, following the date of such Registration Default. Such Special Interest will accrue in respect of the Securities at the rates set forth in paragraph (a) of this Section 7, on the principal amount of the Securities.

(d) Except as provided in Section 8(b) hereof, the Special Interest as set forth in this Section 7 shall be the exclusive monetary remedy available to the Holders of Registrable Securities for such Registration Default. In no event shall the Company be required to pay Special Interest in excess of the applicable maximum amount of one-half of one percent (0.50%) set forth above, regardless of whether one or multiple Registration Defaults exist. In no event will Special Interest accrue on the Company’s common stock unless the Notes have been converted, in which case Special Interest will be due to the Holders as though the Holder had not converted the Notes to common stock.

8. Miscellaneous.

(a) Other Registration Rights. The Company may grant registration rights that would permit any person that is a third party the right to piggy-back on any Shelf Registration Statement, provided that if the Managing Underwriter of any underwritten offering conducted pursuant to Section 6 hereof notifies the Company and the Electing Holders that the total amount of securities which the Electing Holders and the holders of such piggy-back rights intend to include in any Shelf Registration Statement is so large as to materially threaten the success

of such offering (including the price at which such securities can be sold), then the amount, number or kind of securities to be offered for the account of holders of such piggy-back rights will be reduced to the extent necessary to reduce the total amount of securities to be included in such offering to the amount, number and kind recommended by the Managing Underwriter prior to any reduction in the amount of Registrable Securities to be included in such Shelf Registration Statement.

(b) Specific Performance. The parties hereto acknowledge that there would be no adequate remedy at law if the Company fails to perform any of its obligations hereunder and that the Initial Purchasers and the Holders from time to time may be irreparably harmed by any such failure, and accordingly agree that the Initial Purchasers and such Holders, in addition to any other remedy to which they may be entitled at law or in equity and without limiting the remedies available to the Electing Holders under Section 7 hereof, shall be entitled to compel specific performance of the obligations of the Company under this Registration Rights Agreement in accordance with the terms and conditions of this Registration Rights Agreement, in any court of the United States or any State thereof having jurisdiction.

(c) Amendments and Waivers. This Agreement, including this Section 8(c), may be amended, and waivers or consents to departures from the provisions hereof may be given, only by a written instrument duly executed by the Company and the holders of a majority in aggregate principal amount of Registrable Securities then outstanding. Each Holder of Registrable Securities outstanding at the time of any such amendment, waiver or consent or thereafter shall be bound by any amendment, waiver or consent effected pursuant to this Section 8(c), whether or not any notice, writing or marking indicating such amendment, waiver or consent appears on the Registrable Securities or is delivered to such Holder.

(d) Notices. All notices and other communications provided for or permitted hereunder shall be given as provided in the Indenture.

(e) Parties in Interest. The parties to this Agreement intend that all Holders of Registrable Securities shall be entitled to receive the benefits of this Agreement and that any Electing Holder shall be bound by the terms and provisions of this Agreement by reason of such election with respect to the Registrable Securities which are included in a Shelf Registration Statement. All the terms and provisions of this Agreement shall be binding upon, shall inure to the benefit of and shall be enforceable by the respective successors and assigns of the parties hereto and any Holder from time to time of the Registrable Securities to the aforesaid extent. In the event that any transferee of any Holder of Registrable Securities shall acquire Registrable Securities, in any manner, whether by gift, bequest, purchase, operation of law or otherwise, such transferee shall, without any further writing or action of any kind, be entitled to receive the benefits of and, if an Electing Holder, be conclusively deemed to have agreed to be bound by and to perform all of the terms and provisions of this Agreement to the aforesaid extent.

(f) Counterparts. This Agreement may be executed in any number of counterparts and by the parties hereto in separate counterparts, each of which when so executed shall be deemed to be an original and all of which taken together shall constitute one and the same agreement.

(g) Headings. The headings in this Agreement are for convenience of reference only and shall not limit or otherwise affect the meaning hereof.

(h) Governing Law. This Agreement shall be governed by and construed in accordance with the laws of the State of New York.

(i) Severability. In the event that any one or more of the provisions contained herein, or the application thereof in any circumstances, is held invalid, illegal or unenforceable in any respect for any reason, the validity, legality and enforceability of any such provision in every other respect and of the remaining provisions hereof shall not be in any way impaired or affected thereby, it being intended that all of the rights and privileges of the parties hereto shall be enforceable to the fullest extent permitted by law.

(j) Survival. The respective indemnities, agreements, representations, warranties and other provisions set forth in this Agreement or made pursuant hereto shall remain in full force and effect, regardless of any investigation (or any statement as to the results thereof) made by or on behalf of any Electing Holder, any director, officer or partner of such Holder, any agent or underwriter, any director, officer or partner of such agent or underwriter, or any controlling person of any of the foregoing, and shall survive the transfer and registration of the Registrable Securities of such Holder.

[The Remainder of this Page Intentionally Left Blank]

Please confirm that the foregoing correctly sets forth the agreement among the Company, the Initial Purchasers, and for the purposes of Section 5 only, the Principal Subsidiary.

	Very truly yours,

	COGENT COMMUNICATIONS GROUP, INC.


	By:
		Name:
		Title:


	For Section 5 only:

	COGENT COMMUNICATIONS, INC.


	By:
		Name:
		Title:

Accepted as of the date hereof:


BEAR, XXXXXXX & CO. INC.


By:
	Name:
	Title:


UBS SECURITIES LLC


By:
	Name:
	Title:

By:
	Name:
	Title:

Accepted as of the date hereof.


RBC CAPITAL MARKETS CORPORATION


By:
	Name:
	Title:

XXXXX AND COMPANY, LLC


By:
	Name:
	Title:

Appendix A

Cogent Communications Group, Inc.

INSTRUCTION TO PARTICIPANTS

(Date of Mailing)

URGENT - IMMEDIATE ATTENTION REQUESTED

DEADLINE FOR RESPONSE: [DATE]

The Depository Trust Company (“DTC”) has identified you as a DTC Participant through which beneficial interests in the Cogent Communications Group, Inc. (the “Company”) 1.00 % Convertible Senior Notes due 2027 (the “Securities”) are held.

The Company is in the process of registering the Securities under the Securities Act of 1933 for resale by the beneficial owners thereof. In order to have their Securities included in the registration statement, beneficial owners must complete and return the enclosed Notice of Registration Statement and Selling Securityholder Questionnaire.

It is important that beneficial owners of the Securities receive a copy of the enclosed materials as soon as possible as their rights to have the Securities included in the registration statement depend upon their returning the Notice and Questionnaire by [Deadline for response]. Please forward a copy of the enclosed documents to each beneficial owner that holds interests in the Securities through you. If you require more copies of the enclosed materials or have any questions pertaining to this matter, please contact Cogent Communications Group, Inc., 0000 00xx Xxxxxx, X.X., Xxxxxxxxxx, X.X., 00000, Tel. (000) 000-0000.

COGENT COMMUNICATIONS GROUP, INC.

FORM OF SELLING SECURITYHOLDER NOTICE AND QUESTIONNAIRE

The undersigned beneficial holder of 1.00% Convertible Senior Notes due 2027 (the “Notes”) of Cogent Communications Group, Inc. (the “Company”) or common stock par value $0.001 of the Company, issuable on exchange of the Notes (the “Registrable Securities”), understands that the Company has filed or intends to file with the Securities and Exchange Commission a registration statement (the “Shelf Registration Statement”) for the registration and resale under Rule 415 of the Securities Act of 1933, as amended, of the Registrable Securities in accordance with the terms of the Registration Rights Agreement (the “Registration Rights Agreement”), between the Company and the Initial Purchasers named therein. A copy of the Registration Rights Agreement is available from the Company upon request at the address set forth below. All capitalized terms not otherwise defined herein shall have the meaning ascribed thereto in the Registration Rights Agreement.

Each beneficial owner of Registrable Securities is entitled to the benefits of the Registration Rights Agreement. In order to sell or otherwise dispose of any Registrable Securities pursuant to the Shelf Registration Statement, a beneficial owner of Registrable Securities generally will be required to be named as a selling Securityholder in the related prospectus, deliver a prospectus to purchasers of Registrable Securities and be bound by those provisions of the Registration Rights Agreement applicable to such beneficial owner (including certain indemnification provisions as described below). Beneficial owners are encouraged to complete, execute and deliver this Notice and Questionnaire prior to the effectiveness of the Shelf Registration Statement so that such beneficial owners may be named as selling Securityholders in the related prospectus at the time of effectiveness. Any beneficial owner of Registrable Securities wishing to include its Registrable Securities must deliver to the Company a properly completed and signed Selling Securityholder Notice and Questionnaire.

Certain legal consequences arise from being named as Selling Securityholders in the Shelf Registration Statement and the related prospectus. Accordingly, holders and beneficial owners of Registrable Securities are advised to consult their own securities law counsel regarding the consequences of being named or not being named as a Selling Securityholder in the Shelf Registration Statement and the related prospectus.

Notice

The undersigned beneficial owner (the “Selling Securityholder”) of Registrable Securities hereby gives notice to the Company of its intention to sell or otherwise dispose of Registrable Securities beneficially owned by it and listed below in Item 3(b) pursuant to) the Shelf Registration Statement. The undersigned. by signing and returning this Notice and Questionnaire, understands that it will be bound by the terms and conditions of this Notice and Questionnaire and the Registration Rights Agreement.

Pursuant to the Registration Rights Agreement, the undersigned has agreed to indemnify and hold harmless the Company and each of its directors and officers and each person, if any, who controls the Company within the meaning of either Section 15 of the Securities Act and or Section 20 of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), from and against some losses arising in connection with statements concerning the undersigned made in the Registration Statement or the related prospectus in reliance upon the information provided in this Notice and Questionnaire. The undersigned

hereby provides the following information to the Company and represents and warrants that such information is accurate and complete:

QUESTIONNAIRE

(1)	(a)	Full Legal Name of Selling Securityholder:


	(b)	Full Legal Name of Registered Holder (if not the same as in (a) above) of Registrable Securities Listed in Item (3) Below:


	(c)	Full Legal Name of DTC Participant (if applicable and if not the same as (b) above) Through Which Registrable Securities Listed in Item (3) Below are Held:

(2)	Address for Notices to Selling Securityholder:



	Telephone
	Fax:
	Contact Person:

(3)	Beneficial Ownership of Registrable Securities:

	Except as set forth below in this Item (3), the undersigned Selling Securityholder does not beneficially own any Securities or shares of Common Stock.

	(a)	Principal amount of Securities that constitute Registrable Securities (as defined in the Registration Rights Agreement) beneficially owned:

		CUSIP No(s). of such Registrable Securities:

		Number of shares of Common Stock (if any) that constitute Registrable Securities that were issued upon conversion of Registrable Securities:

	(b)	Principal amount of Securities that do not constitute Registrable Securities beneficially owned:

		CUSIP No(s). of such other Securities:

		Number of shares of Common Stock (if any) that do not constitute Registrable Securities:

	(c)	Principal amount of Securities that constitute Registrable Securities which the undersigned wishes to have included in the Shelf Registration Statement:

		CUSIP No(s). of such Registrable Securities to be included in the Shelf Registration Statement:

		Number of shares of Common Stock (if any) that constitute Registrable Securities which the undersigned wishes to have included in the Shelf Registration Statement:

(4)	Beneficial Ownership of Other Securities of the Company:

	Except as set forth below in this Item (4), the undersigned Selling Securityholder is not the beneficial or registered owner of any shares of Common Stock or any other securities of the Company, other than the Securities and shares of Common Stock listed above in Item (3).

	State any exceptions here:


(5)	Relationships with the Company:

	Except as set forth below, neither the Selling Securityholder nor any of its affiliates, officers, directors or principal equity holders (5% or more) has held any position or office or has had any other material relationship with the Company (or its predecessors or affiliates) during the past three years.

	State any exceptions here:


(6)	Additional ownership information:

	State the names of any persons who exercise sole or shared voting or investment power over the Securities or any other securities identified in Items (3) or (4) above that the undersigned Selling Securityholder owns, specifying whether such powers are sole or shared (See Rule 13d-3 under the Securities Exchange Act of 1934 for guidance in making this determination):

	State the name of the general partner, if any, of the undersigned Selling Securityholder:


(7)	Broker-dealer information:

	State whether the undersigned Selling Securityholder is a registered broker-dealer:


	If affirmative, state whether the Securities (or any shares of Common Stock issued upon conversion of Securities) owned were received as compensation for investment banking services or were purchased as investment securities:


(8)	Broker-dealer affiliate information:

	State whether the undersigned Selling Securityholder is an affiliate of a registered broker-dealer:


	If affirmative, state whether

	(a)	the Securities were purchased in the ordinary course of business:


		and

	(b)	at the time of the purchase of the Securities (or the shares of Common Stock issued upon conversion of the Securities) to be resold, the undersigned Selling Securityholder

had any agreements or understandings, directly or indirectly, with any person to distribute the Securities (or such shares of Common Stock):

(9)	Short sales and plan of distribution:

	The Commission has published the following guidance in connection with short sales (Telephone Interp. A. 65 (July 1997)):

	“An issuer filed a Form S-3 registration statement for a secondary offering of Common Stock which is not yet effective. One of the selling shareholders wanted to do a short sale of Common Stock “against the box” and cover the short sale with registered shares after the effective date. The issuer was advised that the short sale could not be made before the registration statement becomes effective, because the shares underlying the short sale are deemed to be sold at the time such sale is made. There would, therefore, be a violation of Section 5 if the shares were effectively sold prior to the effective date.”

	The undersigned Selling Securityholder represents and agrees that the distribution of Securities and shares of Common Stock issued upon conversion of the Securities pursuant to the Shelf Registration Statement will conform with this interpretative guidance.

	State whether the undersigned Selling Securityholder has taken short positions in respect of shares of the Company’s Common Stock after November 12, 2006 and if so, state the date(s) on which such short positions were taken and for each date, the number of shares of Common Stock made subject to such short positions.


	The undersigned Selling Securityholder represents and agrees that short positions taken prior to the effective date of the Shelf Registration Statement will only be covered with shares of the Company’s Common Stock purchased in the open market and will not be covered with shares of the Company’s Common Stock obtained upon conversion of the Securities.

(10)	Plan of Distribution:

	Except as set forth below, the undersigned Selling Securityholder intends to distribute the Registrable Securities listed above in Item (3) only as follows (if at all): Such Registrable Securities may be sold from time to time directly by the undersigned Selling Securityholder or, alternatively, through broker-dealers or agents. Such Registrable Securities may be sold in one or more transactions at fixed prices, at prevailing market prices at the time of sale, at varying prices determined at the time of sale, or at negotiated prices. Such sales may be effected in transactions (which may involve crosses or block transactions) (i) on any national securities exchanges or U.S. quotation system of a registered national securities association on which the Registrable Securities may be listed or quoted at the time of sale, (ii) in the over-the-counter market, (iii) in transactions otherwise than on such exchanges or services or in the over-the-counter market, or (iv) through the writing of options. In connection with sales of the Registrable Securities or otherwise, the Selling Securityholder may enter into hedging transactions with broker-dealers, which may in turn engage in short sales of the Registrable Securities in the course of hedging the positions they assume. The Selling Securityholder may also sell Registrable Securities short and deliver Registrable Securities to close out such short positions, or loan or pledge Registrable Securities to broker-dealers that in turn may sell such securities.

	State any exceptions here:

	Note: In no event may such method(s) of distribution take the form of an underwritten offering of the Registrable Securities without the prior written agreement of the Company.

ACKNOWLEDGEMENTS

By signing below, the Selling Securityholder acknowledges that it understands its obligation to comply, and agrees that it will comply, with the prospectus delivery and other provisions of the Securities Act and the Exchange Act and the rules and respective regulations thereunder relating to stock manipulation, particularly Regulation M.

By signing below, the Selling Securityholder agrees that (i) it will only sell Registrable Securities pursuant to a Shelf Registration Statement and related Prospectus in accordance with the provisions of the Registration Rights Agreement, and (ii) It will not to sell any Registrable Securities pursuant to the Shelf Registration Statement without delivering, or causing to be delivered, a Prospectus to the purchaser thereof.

The Selling Securityholder hereby confirms its obligations under the Registration Rights Agreement to indemnify and hold harmless certain persons set forth therein. Pursuant to the Registration Rights Agreement, the Company has agreed under certain circumstances to indemnify the Selling Securityholders against certain liabilities.

In the event that the Selling Securityholder transfers all or any portion of the Registrable Securities listed in Item (3) above after the date on which such information is provided to the Company, the Selling Securityholder agrees to notify the transferee(s) at the time of the transfer of its rights and obligations under this Notice and Questionnaire and the Registration Rights Agreement.

By signing below, the Selling Securityholder consents to the disclosure of the information contained herein in its answers to Items (1) through (10) above and the inclusion of such information in the Shelf Registration Statement and related Prospectus. The Selling Securityholder understands that such information will be relied upon by the Company in connection with the preparation of the Shelf Registration Statement and related Prospectus.

In accordance with the Selling Securityholder’s obligation under Section 3(a) of the Registration Rights Agreement to provide information for inclusion in the Shelf Registration Statement, the Selling Securityholder agrees to promptly notify the Company of any inaccuracies or changes in the information provided herein which may occur subsequent to the date hereof at any time while the Shelf Registration Statement remains in effect and to provide other information regarding such Selling Securityholder as the Company may from time to time reasonably request. All notices and requests hereunder and pursuant to the Registration Rights Agreement to the Company shall be made in writing, by hand-delivery, first-class mail, or air courier guaranteeing overnight delivery as follows:

(i) To the Company:

Cogent Communications Group, Inc.
0000 00xx Xxxxxx, X.X.
Xxxxxxxxxx, X.X. 00000
Attention: Chief Legal Officer
Fax: 000-000-0000

(ii) With a copy to:

Xxxxxx & Xxxxxxx LLP
000 Xxxxxxxx Xxxxxx, XX, Xxxxx 0000
Xxxxxxxxxx, X.X. 00000
Attention: Xxxxx X. XxXxxxxxx
Fax: 000-000-0000

Once this Notice and Questionnaire is executed by the Selling Securityholder and received by the Company, the terms of this Notice and Questionnaire, and the representations and warranties contained herein, shall be binding on, shall inure to the benefit of and shall be enforceable by the respective successors, heirs, personal representatives, and assigns of the Company and the Selling Securityholder (with respect to the Registrable Securities beneficially owned by such Selling Securityholder and listed in Item (3) above). This Notice and Questionnaire shall be governed in all respects by the laws of the State of New York.

IN WITNESS WHEREOF, the undersigned, by authority duly given, has caused this Notice and Questionnaire to be executed and delivered either in person or by its duly authorized agent.

	Beneficial Owner:


	By:
		Name:
		Title:

Dated:

PLEASE RETURN THE COMPLETED AND EXECUTED NOTICE AND QUESTIONNAIRE TO THE COMPANY AT THE ADDRESS SPECIFIED ABOVE.

Exhibit 1
to Appendix A

NOTICE OF TRANSFER PURSUANT TO REGISTRATION STATEMENT

Cogent Communications Group, Inc.

0000 00xx Xxxxxx, X.X.

Xxxxxxxxxx, X.X. 00000

Attention: General Counsel

Attention: [Insert Trustee Contact]

	Re:	Cogent Communications Group, Inc. (the “Company”)
		1.00% Convertible Senior Notes due 2027 (the “Notes”)

Dear Sirs:

Please be advised that has transferred $ aggregate principal amount of the above-referenced Notes or shares of the Company’s common stock, issued upon conversion or repurchase of Notes, pursuant to an effective Registration Statement on Form S-3 (File No. 333- ) filed by the Company.

We hereby certify that the prospectus delivery requirements, if any, of the Securities Act of 1933, as amended, have been satisfied with respect to the transfer described above and that the above-named beneficial owner of the Notes or common stock is named as a selling securityholder in the Prospectus dated [date], or in amendments or supplements thereto, and that the aggregate principal amount of the Notes or number of shares of common stock transferred are [a portion of] the Notes or shares of common stock listed in such Prospectus as amended or supplemented opposite such owner’s name.

Dated:		Very truly yours,


		(Name)

	By:
		(Authorized Signature)

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Cogent Communications Group, Inc.

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