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Exhibit 10.17

CLOSING DATE AGREEMENT

        THIS CLOSING DATE AGREEMENT made this 6th day of March 2003 by and among
Cogent Communications Group, Inc., a Delaware corporation (the "Company"),
Allied Riser Communications Corporation, a Delaware corporation ("Allied
Riser"), the several noteholders (the "Noteholders") party to the Exchange
Agreement and the Settlement Agreement (each as defined below), and Gary Wolfe
as representative for the Noteholders (the "Noteholder Representative"). The
Company, Allied Riser, and the Noteholders are sometimes referred to herein
together collectively as the "Parties."

W I T N E S S E T H:

        WHEREAS, the Noteholders hold in the aggregate $106,789,000 face value
of the 7.5% Convertible Subordinated Notes Due 2007 of Allied Riser (the
"Notes").

        WHEREAS, the Company, Allied Riser and Noteholders have entered into
that certain Exchange Agreement dated as of the date hereof (the "Exchange
Agreement") pursuant to which the Noteholders have agreed to surrender to Allied
Riser 100% of the Notes in exchange for a cash payment by Allied Riser (the
"Cash Payment") and the delivery by Allied Riser to the Noteholders of shares of
the Company's Series D Preferred Stock and Series E Preferred Stock (the
"Shares") on the terms and subject to the conditions set forth therein (such
transaction is referred to herein as the "Note Exchange").

        WHEREAS, the Company, Allied Riser and Noteholders have entered into
that certain Settlement Agreement dated as of the date hereof (the "Settlement
Agreement") pursuant to which the Noteholders have agreed to dismiss with
prejudice certain claims asserted by them in a litigation pending in the Court
of Chancery of the State of Delaware (the "Litigation") against Allied Riser and
certain of its former directors and to release all claims against Allied Riser
and the Company in exchange for a cash payment by Allied Riser (the "Settlement
Payment") and the Company and Allied Riser have agreed to release all claims
against the Noteholders by the Company and Allied Riser on the terms and
conditions set forth therein (such transaction is referred to herein as the
"Settlement").

        WHEREAS, the Stipulation of Dismissal (as defined in the Settlement
Agreement) related to the dismissal of the Litigation has been filed in the
Court of Chancery of the State of Delaware in and for New Castle County.

        WHEREAS, in order to effect the release of claims in connection with the
Settlement, each of the Noteholders, Allied Riser, the Company and certain of
Allied Riser's former directors (the "Allied Riser Directors") have executed a
mutual general release (the "General Release").

        WHEREAS, pursuant to the terms of the Exchange Agreement and the
Settlement Agreement, the Cash Payment, the Settlement Payment, the Notes and
the General Release are to be placed in escrow upon the execution of the
Exchange Agreement and the Settlement Agreement.

        WHEREAS, pursuant to the terms of the Exchange Agreement and the
Settlement Agreement upon the filing with the Delaware Secretary of State of the
Third Amended and Restated Certificate of Incorporation of the Company
authorizing the Shares (the "Charter Amendment"), Allied Riser is to place the
Shares into the escrow.

        WHEREAS, the Charter Amendment has been filed with the Secretary of
State of the State of Delaware.

        WHEREAS, the parties desire to enter into this Closing Date Agreement to
provide for a closing of the Note Exchange and the Settlement without first
placing the Cash Payment, the Settlement Payment, the Notes, the General Release
or the Shares into Escrow.

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        NOW, THEREFORE, in consideration of the mutual covenants and agreements
set forth herein and in the Exchange Agreement and the Settlement Agreement, the
Parties agree as follows:

        On the date hereof:

        a)    Allied Riser shall (i) wire to the account of the Noteholder
Representative set forth in Schedule A hereto the Cash Payment of $4,997,725 and
the Settlement Payment of $4,880,256, (ii) deliver to the Noteholder
Representative duly executed certificates, in the names of each of the
Noteholders, representing the number of duly authorized, validly issued, fully
paid and non-assessable Shares set forth opposite each Noteholders name under
the headings "Series D Preferred" and "Series E Preferred" on Schedule 1.1 to
the Exchange Agreement and (iii) deliver to the Noteholder Representative the
General Release executed by Allied Riser and the Allied Riser Directors.

        b)    The Company shall deliver to the Noteholder Representative the
General Release executed by the Company.

        c)    The Noteholders shall (i) instruct their respective brokers to
instruct the Depository Trust Company ("DTC") to transfer the Notes from the
account of each Noteholder to the account of Allied Riser set forth in
Schedule B hereto, and (ii) deliver to Allied Riser the General Release executed
by each Noteholder and Angelo, Gordon & Co. L.P. The Noteholder Representative
shall provide a certification to Allied Riser that all of the Noteholders have
duly instructed their respective brokers to instruct the DTC to transfer the
Notes and such instructions have not be rescinded or amended and remain in full
force and effect.

[Signature Pages Follow]

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        IN WITNESS WHEREOF, the parties hereto have caused this CLOSING DATE
AGREEMENT to be executed as of the date first written above.

    ALLIED RISER COMMUNICATIONS CORPORATION
 
 
/s/  DAVID SCHAEFFER      

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    By: David Schaeffer     Title: Chief Executive Officer
 
 
COGENT COMMUNICATIONS GROUP, INC.
 
 
/s/  DAVID SCHAEFFER      

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    By: David Schaeffer     Title: Chief Executive Officer
 
 
/s/  GERALD K. DINSMORE      

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GERALD K. DINSMORE
 
 
/s/  R. DAVID SPRENG      

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R. DAVID SPRENG
 
 
/s/  DONALD LYNCH      

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DONALD LYNCH
 
 
/s/  BLAIR P. WHITAKER      

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BLAIR P. WHITAKER
 
 
ANDA PARTNERSHIP
By it Partners
 
 
 
THE ANN ONLY TRUST
 
 
 
/s/  MARK SLEZAK      

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      By: Mark Slezak       Title: Co-Trustee
 
 
 
THE ANN AND DESCENDANTS TRUST
 
 
 
/s/  MARK SLEZAK      

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      By: Mark Slezak       Title: Co-Trustee
 
 
CRT CAPITAL GROUP, LLC
 
 
/s/  C. MICHAEL VAUGHN      

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    By: C. Michael Vaughn     Title: Member
 
 
GUARDFISH, LLC
 
 
/s/  JOHN C. KOPCHIK      

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    By: John C. Kopchik     Title: Principal of its Manager, Providence Asset
Management LLC

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HBV MASTER REDISCOVERY OPPORTUNITIES FUND, L.P.
 
 
/s/  GEORGE J. KONOMOS      

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    By: George J. Konomos     Title: Portfolio Manager
 
 
JMG CAPITAL PARTNERS, L.P.
 
 
/s/  JOHNATHAN GLASER      

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    By: Jonathan Glaser     Title: Managing Member
 
 
JMG TRITON OFFSHORE FUND, LTD.
 
 
/s/  JOHNATHAN GLASER      

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    By: Jonathan Glaser     Title: Managing Member
 
 
MARKETUS VALUE PARTNERS, L.P.
 
 
/s/  EDMUND A. HAJIM      

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    By: Edmund A. Hajim     Title: Managing Member of its General Partner,
Marketus, L.L.C.
 
 
LA POLICE AND FIRE PENSION FUND
By its Manager,
WR HUFF & CO.
 
 
/s/  MICHAEL J. MCGUINESS      

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    By: Michael J. McGuiness     Title: Portfolio Manager
 
 
PENINSULA INVESTMENT PARTNERS, L.P.
 
 
/s/  R. TED WESCHLER      

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    By: R. Ted Weschler     Title: Managing Member of its Investment Advisor and
General Partner
 
 
SAGAMORE HILL HUB FUND LTD.
 
 
/s/  MARK MAY      

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    By: Mark May     Title:  
 
 
LC CAPITAL MASTER FUND, LTD.
 
 
/s/  STEVE LAMPE      

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    By: Steve Lampe     Title: Managing Member

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Exhibit 10.17

CLOSING DATE AGREEMENT