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Exhibit 10.21    
  


[COGENT LETTERHEAD]  


1015 31st Street, NW Suite 330

Washington, DC 20007

Tel: 202-295-4208

Fax: 202-338-8798 


September 18,
2000 


Mark
Allen Schleifer

13400 Briarwood Drive

Laurel, MD 20708-1410 


Dear
Mark: 


        Thank
you for your interest in Cogent Communications! We would like to extend to you the position of Director Network Engineer. The current cash compensation for this position will be a
base salary of $208,000. Base salary will be paid semi-monthly. Additionally, you will receive a signing bonus of $20,800 to be paid on November 1st, 2000. 


        In
addition to the cash compensation you receive, Cogent will issue 175,000 shares of options to purchase common equity in the company at a strike price of $1.50. 100% of these options
will vest on a quarterly basis over a 4-year period with a 1-year cliff. Based upon the targeted capitalization of the company, there will be 70 million shares
outstanding. 


        Cogent
will periodically perform employee evaluations at minimum intervals of 12 months commencing within 18 months of your employment. These reviews will be utilized to
evaluate your compensation
package relative to the market for similar level professionals at organizations of comparable stage of development and market opportunity to Cogent. The findings of these reviews will be submitted to
the company's compensation committee for final decision and appropriate compensation adjustments. 


        In
the event of Constructive Termination Without Cause, you will receive one months salary against $208,000, six months of benefits coverage, all vested shares and shares to be vested in
the quarter of termination. In the event of a Change of Control and either Termination Without Cause or Constructive Termination, in addition to the conditions mentioned above, you will receive 50% of
your unvested shares at the $1.50 strike price. 


        As
a member of the Cogent team, you will be entitled to company funded health care insurance, dental coverage, and life insurance. The company has also implemented a 401(k) retirement
plan that is corporately administered, however, it will require individual contributions on a non-matching basis by individual participants. Cogent is prepared to offer 4 weeks of paid
vacation. Additionally, the company has implemented 6 fixed major holidays and 2 discretionary floating holidays to be chosen from other less recognized holidays. 


        Your
employment date is expected to be October 3rd, 2000 or at a mutually agreed to date between yourself and the company. Also, upon acceptance of this offer of
employment, you will be required to sign a standard non-compete and non-disclosure agreement and a Federal I-9 form. Also, by signing this offer letter you warrant
that you are not currently bound by any contract that would conflict with this document or our non-compete and non-disclosure agreement. 








        We
look forward to having you join our team and build the most advanced next generation network for high-speed Internet services. If you have any further questions, please
give me a call at 202-295-4208. 



	

Sincerely,	
 	

 	
 	

 
	

/s/ Shawn Guzzo	
 	

 	
 	

 
	

Shawn Guzzo

Director of Human Resources	
 	

 	
 	

 
	

Agreed and Accepted	
 	

 	
 	

 
	

/s/ Mark A. Schleifer
 Mark Allen Schleifer	
 	

10/3/2000
 Date	
 	

 











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Exhibit 10.21