1997 Stock Plan - Concentric Network Corp.


                        CONCENTRIC NETWORK CORPORATION
                                1997 STOCK PLAN


     1.   Purposes of the Plan.  The purposes of this Stock Plan are:
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          .    to attract and retain the best available personnel for positions
               of substantial responsibility,

          .    to provide additional incentive to Employees, Directors and
               Consultants, and

          .    to promote the success of the Company's business.

     Options granted under the Plan may be Incentive Stock Options or
Nonstatutory Stock Options, as determined by the Administrator at the time of
grant. Stock Purchase Rights may also be granted under the Plan.

     2.   Definitions.  As used herein, the following definitions shall apply:
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          (a)  "Administrator" means the Board or any of its Committees as 
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shall be administering the Plan, in accordance with Section 4 of the Plan.

          (b)  "Applicable Laws" means the requirements relating to the
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administration of stock option plans under U. S. state corporate laws, U.S.
federal and state securities laws, the Code, any stock exchange or quotation
system on which the Common Stock is listed or quoted and the applicable laws of
any foreign country or jurisdiction where Options or Stock Purchase Rights are,
or will be, granted under the Plan.

          (c)  "Board" means the Board of Directors of the Company.
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          (d)  "Code" means the Internal Revenue Code of 1986, as amended.
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          (e)  "Committee"  means a committee of Directors appointed by the 
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Board in accordance with Section 4 of the Plan.

          (f)  "Common Stock" means the common stock of the Company.
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          (g)  "Company" means Concentric Network Corporation, a Delaware
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corporation.

          (h)  "Consultant" means any person, including an advisor, engaged by
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the Company or a Parent or Subsidiary to render services to such entity.

          (i)  "Director" means a member of the Board.
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          (j)  "Disability" means total and permanent disability as defined in
                ----------                                                    
Section 22(e)(3) of the Code.

          (k)  "Employee" means any person, including Officers and Directors,
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employed by the Company or any Parent or Subsidiary of the Company. A Service
Provider shall not cease to be an Employee in the case of (i) any leave of
absence approved by the Company or (ii) transfers between locations of the
Company or between any of the Company, its Parent, any Subsidiary, or any
successor. For purposes of Incentive Stock Options, no such leave may exceed
ninety days, unless reemployment upon expiration of such leave is guaranteed by
statute or contract. If reemployment upon expiration of a leave of absence
approved by the Company is not so guaranteed, on the 181st day of such leave any
Incentive Stock Option held by the Optionee shall cease to be treated as an
Incentive Stock Option and shall be treated for tax purposes as a Nonstatutory
Stock Option. Neither service as a Director nor payment of a director's fee by
the Company shall be sufficient to constitute "employment" by the Company.

          (l)  "Exchange Act" means the Securities Exchange Act of 1934, as
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amended.

          (m)  "Fair Market Value" means, as of any date, the value of Common
                -----------------    
 Stock determined as follows:

               (i)    If the Common Stock is listed on any established stock
exchange or a national market system, including without limitation the Nasdaq
National Market or The Nasdaq SmallCap Market of The Nasdaq Stock Market, its
Fair Market Value shall be the closing sales price for such stock (or the
closing bid, if no sales were reported) as quoted on such exchange or system for
the last market trading day prior to the time of determination, as reported in
The Wall Street Journal or such other source as the Administrator deems
reliable;

               (ii)   If the Common Stock is regularly quoted by a recognized
securities dealer but selling prices are not reported, the Fair Market Value of
a Share of Common Stock shall be the mean between the high bid and low asked
prices for the Common Stock on the last market trading day prior to the day of
determination, as reported in The Wall Street Journal or such other source as
the Administrator deems reliable; or

               (iii)  In the absence of an established market for the Common
Stock, the Fair Market Value shall be determined in good faith by the
Administrator.

          (n)  "Incentive Stock Option" means an Option intended to qualify as
                ----------------------          
an incentive stock option within the meaning of Section 422 of the Code and the
regulations promulgated thereunder.

          (o)  "Nonstatutory Stock Option" means an Option not intended to 
                -------------------------
qualify as an Incentive Stock Option.

                                      -2-

 
          (p)  "Notice of Grant" means a written or electronic notice evidencing
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certain terms and conditions of an individual Option or Stock Purchase Right
grant. The Notice of Grant is part of the Option Agreement.

          (q)  "Officer" means a person who is an officer of the Company within
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the meaning of Section 16 of the Exchange Act and the rules and regulations
promulgated thereunder.

          (r)  "Option" means a stock option granted pursuant to the Plan.
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          (s)  "Option Agreement" means an agreement between the Company and an
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Optionee evidencing the terms and conditions of an individual Option grant.  The
Option Agreement is subject to the terms and conditions of the Plan.

          (t)  "Option Exchange Program" means a program whereby outstanding
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Options are surrendered in exchange for Options with a lower exercise price.

          (u)  "Optioned Stock" means the Common Stock subject to an Option or
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Stock Purchase Right.

          (v)  "Optionee" means the holder of an outstanding Option or Stock
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Purchase Right granted under the Plan.

          (w)  "Parent" means a "parent corporation," whether now or hereafter
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existing, as defined in Section 424(e) of the Code.

          (x)  "Plan" means this Concentric Network Corporation 1997 Stock Plan.
                ----                                                            

          (y)  "Restricted Stock" means shares of Common Stock acquired 
                ----------------    
pursuant to a grant of Stock Purchase Rights under Section 11 of the Plan.

          (z)  "Restricted Stock Purchase Agreement" means a written agreement
                -----------------------------------                           
between the Company and the Optionee evidencing the terms and restrictions
applying to stock purchased under a Stock Purchase Right.  The Restricted Stock
Purchase Agreement is subject to the terms and conditions of the Plan and the
Notice of Grant.

          (aa) "Rule 16b-3" means Rule 16b-3 of the Exchange Act or any 
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successor to Rule 16b-3, as in effect when discretion is being exercised with
respect to the Plan.

          (bb) "Section 16(b)" means Section 16(b) of the Exchange Act.
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          (cc) "Service Provider" means an Employee, Director or Consultant.
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                                      -3-

 
          (dd) "Share" means a share of the Common Stock, as adjusted in 
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accordance with Section 13 of the Plan.

          (ee) "Stock Purchase Right" means the right to purchase Common Stock
                --------------------                                          
pursuant to Section 11 of the Plan, as evidenced by a Notice of Grant.

          (ff) "Subsidiary" means a "subsidiary corporation," whether now or
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hereafter existing, as defined in Section 424(f) of the Code.

     3.   Stock Subject to the Plan.  Subject to the provisions of Section 13 of
          -------------------------                                             
the Plan, the maximum aggregate number of Shares that may be optioned and sold
under the Plan is 1,500,000 Shares. The Shares may be authorized, but unissued,
or reacquired Common Stock.

          If an Option or Stock Purchase Right expires or becomes unexercisable
without having been exercised in full, or is surrendered pursuant to an Option
Exchange Program, the unpurchased Shares that were subject thereto shall become
available for future grant or sale under the Plan (unless the Plan has
terminated); provided, however, that Shares that have actually been issued under
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the Plan, whether upon exercise of an Option or Right, shall not be returned to
the Plan and shall not become available for future distribution under the Plan,
except that if Shares of Restricted Stock are repurchased by the Company at
their original purchase price, such Shares shall become available for future
grant under the Plan.

     4.   Administration of the Plan.
          -------------------------- 

          (a)  Procedure.
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               (i)  Multiple Administrative Bodies.  The Plan may be 
                    ------------------------------    
administered by the Board and/or different Committees with respect to different
groups of Service Providers.

              (ii)  Section 162(m). To the extent that the Administrator 
                    --------------            
determines it to be desirable to qualify Options granted hereunder as
"performance-based compensation" within the meaning of Section 162(m) of the
Code, the Plan shall be administered by a Committee of two or more "outside
directors" within the meaning of Section 162(m) of the Code.

             (iii)  Rule 16b-3.  To the extent desirable to qualify transactions
                    ----------       
hereunder as exempt under Rule 16b-3, the transactions contemplated hereunder
shall be structured to satisfy the requirements for exemption under Rule 16b-3.

              (iv)   Other Administration.  Other than as provided above, the 
                     --------------------          
Plan shall be administered by (A) the Board or (B) a Committee, which committee
shall be constituted to satisfy Applicable Laws.

                                      -4-

 
          (b)  Powers of the Administrator.  Subject to the provisions of the 
               ---------------------------      
Plan, and in the case of a Committee, subject to the specific duties delegated
by the Board to such Committee, the Administrator shall have the authority, in
its discretion:

               (i)  to determine the Fair Market Value;

              (ii)  to select the Service Providers to whom Options and Stock
Purchase Rights may be granted hereunder;

             (iii)  to determine the number of shares of Common Stock to be
covered by each Option and Stock Purchase Right granted hereunder;

              (iv)  to approve forms of agreement for use under the Plan;

               (v)  to determine the terms and conditions, not inconsistent
with the terms of the Plan, of any Option or Stock Purchase Right granted
hereunder. Such terms and conditions include, but are not limited to, the
exercise price, the time or times when Options or Stock Purchase Rights may be
exercised (which may be based on performance criteria), any vesting acceleration
or waiver of forfeiture restrictions, and any restriction or limitation
regarding any Option or Stock Purchase Right of the shares of Common Stock
relating thereto, based in each case on such factors as the Administrator, in
its sole discretion, shall determine;

              (vi)  to reduce the exercise price of any Option or Stock
Purchase Right to the then current Fair Market Value if the Fair Market Value of
the Common Stock covered by such Option or Stock Purchase Right shall have
declined since the date the Option or Stock Purchase Right was granted;

             (vii)  to institute an Option Exchange Program;

            (viii)  to construe and interpret the terms of the Plan and awards
granted pursuant to the Plan;

              (ix)  to prescribe, amend and rescind rules and regulations
relating to the Plan, including rules and regulations relating to sub-plans
established for the purpose of qualifying for preferred tax treatment under
foreign tax laws;

               (x)  to modify or amend each Option or Stock Purchase Right
(subject to Section 15(c) of the Plan), including the discretionary authority to
extend the post-termination exercisability period of Options longer than is
otherwise provided for in the Plan;

              (xi)  to allow Optionees to satisfy withholding tax obligations by
electing to have the Company withhold from the Shares to be issued upon exercise
of an Option or Stock Purchase Right that number of Shares having a Fair Market
Value equal to the amount required to be withheld. 

                                      -5-

 
The Fair Market Value of the Shares to be withheld shall be determined on the
date that the amount of tax to be withheld is to be determined. All elections by
an Optionee to have Shares withheld for this purpose shall be made in such form
and under such conditions as the Administrator may deem necessary or advisable;

             (xii)  to authorize any person to execute on behalf of the Company
any instrument required to effect the grant of an Option or Stock Purchase Right
previously granted by the Administrator;

            (xiii)  to make all other determinations deemed necessary or
advisable for administering the Plan.

          (c)  Effect of Administrator's Decision.  The Administrator's 
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decisions, determinations and interpretations shall be final and binding on all
Optionees and any other holders of Options or Stock Purchase Rights.

     5.   Eligibility.  Nonstatutory Stock Options and Stock Purchase Rights may
          -----------                                                           
be granted to Service Providers. Incentive Stock Options may be granted only to
Employees.

     6.   Limitations.
          ----------- 

          (a)  Each Option shall be designated in the Option Agreement as either
an Incentive Stock Option or a Nonstatutory Stock Option. However,
notwithstanding such designation, to the extent that the aggregate Fair Market
Value of the Shares with respect to which Incentive Stock Options are
exercisable for the first time by the Optionee during any calendar year (under
all plans of the Company and any Parent or Subsidiary) exceeds $100,000, such
Options shall be treated as Nonstatutory Stock Options. For purposes of this
Section 6(a), Incentive Stock Options shall be taken into account in the order
in which they were granted. The Fair Market Value of the Shares shall be
determined as of the time the Option with respect to such Shares is granted.

          (b)  Neither the Plan nor any Option or Stock Purchase Right shall
confer upon an Optionee any right with respect to continuing the Optionee's
relationship as a Service Provider with the Company, nor shall they interfere in
any way with the Optionee's right or the Company's right to terminate such
relationship at any time, with or without cause.

          (c)  The following limitations shall apply to grants of Options:

               (i)  No Service Provider shall be granted, in any fiscal year of
the Company, Options to purchase more than 500,000 Shares.

              (ii)  In connection with his or her initial service, a Service
Provider may be granted Options to purchase up to an additional 500,000 Shares
that shall not count against the limit set forth in subsection (i) above.

                                      -6-

 
             (iii)  The foregoing limitations shall be adjusted proportionately
in connection with any change in the Company's capitalization as described in
Section 13.

              (iv)  If an Option is canceled in the same fiscal year of the
Company in which it was granted (other than in connection with a transaction
described in Section 13), the canceled Option will be counted against the limits
set forth in subsections (i) and (ii) above. For this purpose, if the exercise
price of an Option is reduced, the transaction will be treated as a cancellation
of the Option and the grant of a new Option.

     7.   Term of Plan.  Subject to Section 19 of the Plan, the Plan shall 
          ------------         
become effective upon its adoption by the Board. It shall continue in effect for
a term of ten years unless terminated earlier under Section 15 of the Plan.

     8.   Term of Option.  The term of each Option shall be stated in the Option
          --------------                                                        
Agreement. In the case of an Incentive Stock Option, the term shall be ten years
from the date of grant or such shorter term as may be provided in the Option
Agreement. Moreover, in the case of an Incentive Stock Option granted to an
Optionee who, at the time the Incentive Stock Option is granted, owns stock
representing more than ten percent of the total combined voting power of all
classes of stock of the Company or any Parent or Subsidiary, the term of the
Incentive Stock Option shall be five years from the date of grant or such
shorter term as may be provided in the Option Agreement.

     9.   Option Exercise Price and Consideration.
          --------------------------------------- 

          (a)  Exercise Price.  The per share exercise price for the Shares to
               --------------         
be issued pursuant to exercise of an Option shall be determined by the
Administrator, subject to the following:

               (i)  In the case of an Incentive Stock Option

                    (A)  granted to an Employee who, at the time the Incentive
Stock Option is granted, owns stock representing more than ten percent of the
voting power of all classes of stock of the Company or any Parent or Subsidiary,
the per Share exercise price shall be no less than 110% of the Fair Market Value
per Share on the date of grant.

                    (B)  granted to any Employee other than an Employee
described in paragraph (A) immediately above, the per Share exercise price shall
be no less than 100% of the Fair Market Value per Share on the date of grant.

              (ii)  In the case of a Nonstatutory Stock Option, the per Share
exercise price shall be determined by the Administrator. In the case of a
Nonstatutory Stock Option intended to qualify as "performance-based
compensation" within the meaning of Section 162(m) of the Code, the per Share
exercise price shall be no less than 100% of the Fair Market Value per Share on
the date of grant.

                                      -7-

 
              (iii)  Notwithstanding the foregoing, Options may be granted with
a per Share exercise price of less than 100% of the Fair Market Value per Share
on the date of grant pursuant to a merger or other corporate transaction.

          (b)  Waiting Period and Exercise Dates.  At the time an Option is
               ---------------------------------                           
granted, the Administrator shall fix the period within which the Option may be
exercised and shall determine any conditions that must be satisfied before the
Option may be exercised.

          (c)  Form of Consideration.  The Administrator shall determine the
               ---------------------                                        
acceptable form of consideration for exercising an Option, including the method
of payment. In the case of an Incentive Stock Option, the Administrator shall
determine the acceptable form of consideration at the time of grant. Such
consideration may consist entirely of:

               (i)  cash;

              (ii)  check;

             (iii)  promissory note;

              (iv)  other Shares that (A) in the case of Shares acquired upon
exercise of an option, have been owned by the Optionee for more than six months
on the date of surrender, and (B) have a Fair Market Value on the date of
surrender equal to the aggregate exercise price of the Shares as to which said
Option shall be exercised;

               (v)  consideration received by the Company under a cashless
exercise program implemented by the Company in connection with the Plan;

              (vi)  a reduction in the amount of any Company liability to the
Optionee, including any liability attributable to the Optionee's participation
in any Company-sponsored deferred compensation program or arrangement;

             (vii)  any combination of the foregoing methods of payment; or

            (viii)  other consideration and method of payment for the issuance
of Shares to the extent permitted by Applicable Laws.

     10.  Exercise of Option.
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          (a)  Procedure for Exercise; Rights as a Shareholder. Any Option 
               -----------------------------------------------     
granted hereunder shall be exercisable according to the terms of the Plan and at
such times and under such conditions as determined by the Administrator and set
forth in the Option Agreement. Unless the Administrator provides otherwise,
vesting of Options granted hereunder shall be tolled during any unpaid leave of
absence. An Option may not be exercised for a fraction of a Share.

                                      -8-

 
               An Option shall be deemed exercised when the Company receives:
(i) written or electronic notice of exercise (in accordance with the Option
Agreement) from the person entitled to exercise the Option, and (ii) full
payment for the Shares with respect to which the Option is exercised. Full
payment may consist of any consideration and method of payment authorized by the
Administrator and permitted by the Option Agreement and the Plan. Shares issued
upon exercise of an Option shall be issued in the name of the Optionee or, if
requested by the Optionee, in the name of the Optionee and his or her spouse.
Until the Shares are issued (as evidenced by the appropriate entry on the books
of the Company or of a duly authorized transfer agent of the Company), no right
to vote or receive dividends or any other rights as a stockholder shall exist
with respect to the Optioned Stock, notwithstanding the exercise of the Option.
The Company shall issue (or cause to be issued) such Shares promptly after the
Option is exercised. No adjustment will be made for a dividend or other right
for which the record date is prior to the date the Shares are issued, except as
provided in Section 13 of the Plan.

               Exercising an Option in any manner shall decrease the number of
Shares thereafter available, both for purposes of the Plan and for sale under
the Option, by the number of Shares as to which the Option is exercised.

          (b)  Termination of Relationship as a Service Provider.  If an 
               -------------------------------------------------       
Optionee ceases to be a Service Provider, other than upon the Optionee's death
or Disability, the Optionee may exercise his or her Option within such period of
time as is specified in the Option Agreement to the extent that the Option is
vested on the date of termination (but in no event later than the expiration of
the term of such Option as set forth in the Option Agreement). In the absence of
a specified time in the Option Agreement, the Option shall remain exercisable
for three months following the Optionee's termination. If, on the date of
termination, the Optionee is not vested as to his or her entire Option, the
Shares covered by the unvested portion of the Option shall revert to the Plan.
If, after termination, the Optionee does not exercise his or her Option within
the time specified by the Administrator, the Option shall terminate, and the
Shares covered by such Option shall revert to the Plan.

          (c)  Disability of Optionee.  If an Optionee ceases to be a Service
               ----------------------                                        
Provider as a result of the Optionee's Disability, the Optionee may exercise his
or her Option within such period of time as is specified in the Option Agreement
to the extent the Option is vested on the date of termination (but in no event
later than the expiration of the term of such Option as set forth in the Option
Agreement). In the absence of a specified time in the Option Agreement, the
Option shall remain exercisable for twelve months following the Optionee's
termination. If, on the date of termination, the Optionee is not vested as to
his or her entire Option, the Shares covered by the unvested portion of the
Option shall revert to the Plan. If, after termination, the Optionee does not
exercise his or her Option within the time specified herein, the Option shall
terminate, and the Shares covered by such Option shall revert to the Plan.

          (d)  Death of Optionee.  If an Optionee dies while a Service Provider,
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the Option may be exercised within such period of time as is specified in the
Option Agreement (but in no event later 

                                      -9-

 
than the expiration of the term of such Option as set forth in the Notice of
Grant), by the Optionee's estate or by a person who acquires the right to
exercise the Option by bequest or inheritance, but only to the extent that the
Option is vested on the date of death. In the absence of a specified time in the
Option Agreement, the Option shall remain exercisable for twelve months
following the Optionee's termination. If, at the time of death, the Optionee is
not vested as to his or her entire Option, the Shares covered by the unvested
portion of the Option shall immediately revert to the Plan. The Option may be
exercised by the executor or administrator of the Optionee's estate or, if none,
by the person(s) entitled to exercise the Option under the Optionee's will or
the laws of descent or distribution. If the Option is not so exercised within
the time specified herein, the Option shall terminate, and the Shares covered by
such Option shall revert to the Plan.

          (e)  Buyout Provisions.  The Administrator may at any time offer to
               -----------------        
buy out for a payment in cash, Shares or otherwise an Option previously granted
based on such terms and conditions as the Administrator shall establish and
communicate to the Optionee at the time that such offer is made.

          (f)  Other Provisions.  The Option Agreement shall contain such other
               ----------------                                                
terms, provisions and conditions not inconsistent with the Plan as may be
determined by the Administrator in its sole discretion.
 
     11.  Stock Purchase Rights.
          --------------------- 

          (a)  Rights to Purchase.  Stock Purchase Rights may be issued either
               ------------------                                             
alone, in addition to, or in tandem with other awards granted under the Plan
and/or cash awards made outside of the Plan.  After the Administrator determines
that it will offer Stock Purchase Rights under the Plan, it shall advise the
offeree in writing or electronically, by means of a Notice of Grant, of the
terms, conditions and restrictions related to the offer, including the number of
Shares that the offeree shall be entitled to purchase, the price to be paid, and
the time within which the offeree must accept such offer.  The offer shall be
accepted by execution of a Restricted Stock Purchase Agreement in the form
determined by the Administrator.

          (b)  Repurchase Option.  Unless the Administrator determines 
               -----------------       
otherwise, the Restricted Stock Purchase Agreement shall grant the Company a
repurchase option exercisable upon the voluntary or involuntary termination of
the purchaser's service with the Company for any reason (including death or
Disability). The purchase price for Shares repurchased pursuant to the
Restricted Stock Purchase Agreement shall be the original price paid by the
purchaser and may be paid by cancellation of any indebtedness of the purchaser
to the Company. The repurchase option shall lapse at a rate determined by the
Administrator.

          (c)  Buyout Provisions.  The Administrator may at any time offer to 
               -----------------        
buy out for a payment in cash, Shares or otherwise an Option previously granted
based on such terms and conditions as the Administrator shall establish and
communicate to the Optionee at the time that such offer is made.

                                     -10-

 
          (d)  Other Provisions.  The Restricted Stock Purchase Agreement shall
               ----------------                                                
contain such other terms, provisions and conditions not inconsistent with the
Plan as may be determined by the Administrator in its sole discretion.

          (e)  Rights as a Shareholder.  Once the Stock Purchase Right is
               -----------------------                                   
exercised, the purchaser shall have the rights equivalent to those of a
stockholder, and shall be a stockholder when his or her purchase is entered upon
the records of the duly authorized transfer agent of the Company. No adjustment
will be made for a dividend or other right for which the record date is prior to
the date the Stock Purchase Right is exercised, except as provided in Section 13
of the Plan.

     12.  Non-Transferability of Options and Stock Purchase Rights.  An Option 
          --------------------------------------------------------      
or Stock Purchase Right may not be sold, pledged, assigned, hypothecated,
transferred, or disposed of in any manner other than by will or by the laws of
descent or distribution and may be exercised, during the lifetime of the
Optionee, only by the Optionee.

     13.  Adjustments Upon Changes in Capitalization, Dissolution, Merger or 
          ------------------------------------------------------------------
          Asset Sale.
          ----------

          (a)  Changes in Capitalization.  Subject to any required action by the
               -------------------------                                        
stockholders of the Company, the number of shares of Common Stock covered by
each outstanding Option and Stock Purchase Right, and the number of shares of
Common Stock that have been authorized for issuance under the Plan but as to
which no Options or Stock Purchase Rights have yet been granted or that have
been returned to the Plan upon cancellation or expiration of an Option or Stock
Purchase Right, as well as the price per share of Common Stock covered by each
such outstanding Option or Stock Purchase Right, shall be proportionately
adjusted for any increase or decrease in the number of issued shares of Common
Stock resulting from a stock split, reverse stock split, stock dividend,
combination or reclassification of the Common Stock, or any other increase or
decrease in the number of issued shares of Common Stock effected without receipt
of consideration by the Company; provided, however, that conversion of any
convertible securities of the Company shall not be deemed to have been "effected
without receipt of consideration."  Such adjustment shall be made by the Board,
whose determination in that respect shall be final, binding and conclusive.
Except as expressly provided herein, no issuance by the Company of shares of
stock of any class, or securities convertible into shares of stock of any class,
shall affect, and no adjustment by reason thereof shall be made with respect to,
the number or price of shares of Common Stock subject to an Option or Stock
Purchase Right.

          (b)  Dissolution or Liquidation.  In the event of the proposed
               --------------------------                               
dissolution or liquidation of the Company, the Administrator shall notify each
Optionee as soon as practicable prior to the effective date of such proposed
transaction. The Administrator in its discretion may provide for an Optionee to
have the right to exercise his or her Option until ten days prior to such
transaction as to all of the Optioned Stock covered thereby, including Shares as
to which the Option would not otherwise be exercisable. In addition, the
Administrator may provide that any Company repurchase option applicable to any
Shares purchased upon exercise of an Option or Stock Purchase Right shall lapse
as to all such Shares, provided the proposed dissolution or liquidation takes
place at the time 

                                     -11-

 
and in the manner contemplated. To the extent it has not been previously
exercised, an Option or Stock Purchase Right will terminate immediately prior to
the consummation of such proposed action.

          (c)  Merger or Asset Sale.  In the event of a merger of the Company 
               --------------------                                           
with or into another corporation, or the sale of substantially all of the assets
of the Company, each outstanding Option and Stock Purchase Right shall be
assumed or an equivalent option or right substituted by the successor
corporation or a Parent or Subsidiary of the successor corporation. In the event
that the successor corporation refuses to assume or substitute for the Option or
Stock Purchase Right, the Optionee shall fully vest in and have the right to
exercise the Option or Stock Purchase Right as to all of the Optioned Stock,
including Shares as to which it would not otherwise be vested or exercisable. If
an Option or Stock Purchase Right becomes fully vested and exercisable in lieu
of assumption or substitution in the event of a merger or sale of assets, the
Administrator shall notify the Optionee in writing or electronically that the
Option or Stock Purchase Right shall be fully vested and exercisable for a
period of fifteen days from the date of such notice, and the Option or Stock
Purchase Right shall terminate upon the expiration of such period. For the
purposes of this paragraph, the Option or Stock Purchase Right shall be
considered assumed if, following the merger or sale of assets, the option or
right confers the right to purchase or receive, for each Share of Optioned Stock
subject to the Option or Stock Purchase Right immediately prior to the merger or
sale of assets, the consideration (whether stock, cash, or other securities or
property) received in the merger or sale of assets by holders of Common Stock
for each Share held on the effective date of the transaction (and if holders
were offered a choice of consideration, the type of consideration chosen by the
holders of a majority of the outstanding Shares); provided, however, that if
such consideration received in the merger or sale of assets is not solely common
stock of the successor corporation or its Parent, the Administrator may, with
the consent of the successor corporation, provide for the consideration to be
received upon the exercise of the Option or Stock Purchase Right, for each Share
of Optioned Stock subject to the Option or Stock Purchase Right, to be solely
common stock of the successor corporation or its Parent equal in fair market
value to the per share consideration received by holders of Common Stock in the
merger or sale of assets.

     14.  Date of Grant.  The date of grant of an Option or Stock Purchase Right
          -------------                                                         
shall be, for all purposes, the date on which the Administrator makes the
determination granting such Option or Stock Purchase Right, or such other later
date as is determined by the Administrator. Notice of the determination shall be
provided to each Optionee within a reasonable time after the date of such grant.

     15.  Amendment and Termination of the Plan.
          ------------------------------------- 

          (a)  Amendment and Termination.  The Board may at any time amend, 
               -------------------------       
alter, suspend or terminate the Plan.

          (b)  Stockholder Approval.  The Company shall obtain stockholder 
               --------------------          
approval of any Plan amendment to the extent necessary and desirable to comply
with Applicable Laws.

                                     -12-

 
          (c)  Effect of Amendment or Termination.  No amendment, alteration,
               ----------------------------------                            
suspension or termination of the Plan shall impair the rights of any Optionee,
unless mutually agreed otherwise between the Optionee and the Administrator,
which agreement must be in writing and signed by the Optionee and the Company.
Termination of the Plan shall not affect the Administrator's ability to exercise
the powers granted to it hereunder with respect to Options granted under the
Plan prior to the date of such termination.

     16.  Conditions Upon Issuance of Shares.
          ---------------------------------- 

          (a)  Legal Compliance.  Shares shall not be issued pursuant to the
               ----------------                                             
exercise of an Option or Stock Purchase Right unless the exercise of such Option
or Stock Purchase Right and the issuance and delivery of such Shares shall
comply with Applicable Laws and shall be further subject to the approval of
counsel for the Company with respect to such compliance.

          (b)  Investment Representations.  As a condition to the exercise of an
               --------------------------                                       
Option or Stock Purchase Right, the Company may require the person exercising
such Option or Stock Purchase Right to represent and warrant at the time of any
such exercise that the Shares are being purchased only for investment and
without any present intention to sell or distribute such Shares if, in the
opinion of counsel for the Company, such a representation is required.

     17.  Inability to Obtain Authority.  The inability of the Company to obtain
          -----------------------------                                         
authority from any regulatory body having jurisdiction, which authority is
deemed by the Company's counsel to be necessary to the lawful issuance and sale
of any Shares hereunder, shall relieve the Company of any liability in respect
of the failure to issue or sell such Shares as to which such requisite authority
shall not have been obtained.

     18.  Reservation of Shares.  The Company, during the term of this Plan, 
          ---------------------         
will at all times reserve and keep available such number of Shares as shall be
sufficient to satisfy the requirements of the Plan.

     19.  Stockholder Approval.  The Plan shall be subject to approval by the
          --------------------                                           
stockholders of the Company within twelve months after the date the Plan is
adopted. Such stockholder approval shall be obtained in the manner and to the
degree required under Applicable Laws.

                                     -13-

 
                        CONCENTRIC NETWORK CORPORATION
                                1997 STOCK PLAN

                            STOCK OPTION AGREEMENT


     Unless otherwise defined herein, the terms defined in the Plan shall have
the same defined meanings in this Option Agreement.

I.   NOTICE OF STOCK OPTION GRANT
     ----------------------------

[Optionee's Name and Address]

     You have been granted an option to purchase Common Stock of the Company,
subject to the terms and conditions of the Plan and this Option Agreement, as
follows:

     Grant Number                    ___________________________

     Date of Grant                   ___________________________

     Vesting Commencement Date       ___________________________

     Exercise Price per Share        $__________________________

     Total Number of Shares Granted  ___________________________

     Total Exercise Price            $___________________________

     Type of Option:                 ___   Incentive Stock Option

                                     ___   Nonstatutory Stock Option

     Term/Expiration Date:           _________________________


     Vesting Schedule:
     ---------------- 

     This Option may be exercised, in whole or in part, in accordance with the
following schedule:

     Twenty-five percent of the Shares subject to the Option shall vest twelve
months after the Vesting Commencement Date, and thereafter the Shares subject to
the Option shall vest in 36 equal increments over 36 months, at the end of each
month, subject to the Optionee continuing to be a Service Provider on such
dates.

 
     Termination Period:
     ------------------ 

     This Option may be exercised for three months after Optionee ceases to be a
Service Provider. Upon the death or Disability of the Optionee, this Option may
be exercised for such longer period as provided in the Plan.  In no event shall
this Option be exercised later than the Term/Expiration Date as provided above.

II.  AGREEMENT
     ---------

     1.   Grant of Option.  The Plan Administrator of the Company hereby grants
          ---------------                                                      
to the Optionee named in the Notice of Grant attached as Part I of this
Agreement (the "Optionee") an option (the "Option") to purchase the number of
Shares, as set forth in the Notice of Grant, at the exercise price per share set
forth in the Notice of Grant (the "Exercise Price"), subject to the terms and
conditions of the Plan, which is incorporated herein by reference. Subject to
Section 15(c) of the Plan, in the event of a conflict between the terms and
conditions of the Plan and the terms and conditions of this Option Agreement,
the terms and conditions of the Plan shall prevail.

          If designated in the Notice of Grant as an Incentive Stock Option
("ISO"), this Option is intended to qualify as an Incentive Stock Option under
Section 422 of the Code. However, if this Option is intended to be an Incentive
Stock Option, to the extent that it exceeds the $100,000 rule of Code Section
422(d) it shall be treated as a Nonstatutory Stock Option ("NSO").

     2.   Exercise of Option.
          ------------------ 

          (a)  Right to Exercise.  This Option is exercisable during its term in
               -----------------                                                
accordance with the Vesting Schedule set out in the Notice of Grant and the
applicable provisions of the Plan and this Option Agreement.

          (b)  Method of Exercise.  This Option is exercisable by delivery of an
               ------------------                                               
exercise notice, in the form attached as Exhibit A (the "Exercise Notice"),
which shall state the election to exercise the Option, the number of Shares in
respect of which the Option is being exercised (the "Exercised Shares"), and
such other representations and agreements as may be required by the Company
pursuant to the provisions of the Plan. The Exercise Notice shall be completed
by the Optionee and delivered to the Corporate Secretary of the Company. The
Exercise Notice shall be accompanied by payment of the aggregate Exercise Price
as to all Exercised Shares. This Option shall be deemed to be exercised upon
receipt by the Company of such fully executed Exercise Notice accompanied by
such aggregate Exercise Price.

          No Shares shall be issued pursuant to the exercise of this Option
unless such issuance and exercise complies with Applicable Laws. Assuming such
compliance, for income tax purposes the Exercised Shares shall be considered
transferred to the Optionee on the date the Option is exercised with respect to
such Exercised Shares.

                                      -2-

 
     3.   Method of Payment.  Payment of the aggregate Exercise Price shall be 
          -----------------        
by any of the following, or a combination thereof, at the election of the
Optionee:

          (a)  cash; or

          (b)  check; or

          (c)  consideration received by the Company under a cashless exercise
program implemented by the Company in connection with the Plan; or

          (d)  surrender of other Shares that (i) in the case of Shares acquired
upon exercise of an option, have been owned by the Optionee for more than six
months on the date of surrender, AND (ii) have a Fair Market Value on the date
of surrender equal to the aggregate Exercise Price of the Exercised Shares; or

          (e)  with the Administrator's consent, delivery of Optionee's
promissory note (the "Note") in the form attached hereto as Exhibit C, in the
amount of the aggregate Exercise Price of the Exercised Shares together with the
execution and delivery by the Optionee of the Security Agreement attached hereto
as Exhibit B. The Note shall bear interest at the "applicable federal rate"
prescribed under the Code and its regulations at time of purchase, and shall be
secured by a pledge of the Shares purchased by the Note pursuant to the Security
Agreement.

     4.   Non-Transferability of Option.  This Option may not be transferred in
          -----------------------------                                        
any manner otherwise than by will or by the laws of descent or distribution and
may be exercised during the lifetime of Optionee only by the Optionee. The terms
of the Plan and this Option Agreement shall be binding upon the executors,
administrators, heirs, successors and assigns of the Optionee.

     5.   Term of Option.  This Option may be exercised only within the term set
          --------------                                                        
out in the Notice of Grant, and may be exercised during such term only in
accordance with the Plan and the terms of this Option Agreement.

     6.   Tax Consequences.  Some of the federal tax consequences relating to
          ----------------        
this Option, as of the date of this Option, are set forth below. THIS SUMMARY IS
NECESSARILY INCOMPLETE, AND THE TAX LAWS AND REGULATIONS ARE SUBJECT TO CHANGE.
THE OPTIONEE SHOULD CONSULT A TAX ADVISER BEFORE EXERCISING THIS OPTION OR
DISPOSING OF THE SHARES.

          (a)  Exercising the Option.
               --------------------- 

               (i)  Nonstatutory Stock Option.  The Optionee may incur regular
                    -------------------------       
federal income tax liability upon exercise of a NSO. The Optionee will be
treated as having received compensation income (taxable at ordinary income tax
rates) equal to the excess, if any, of the Fair Market Value of the Exercised
Shares on the date of exercise over their aggregate Exercise Price. If the
Optionee is 

                                      -3-


an Employee or a former Employee, the Company will be required to withhold from
his or her compensation or collect from Optionee and pay to the applicable
taxing authorities an amount in cash equal to a percentage of this compensation
income at the time of exercise, and may refuse to honor the exercise and refuse
to deliver Shares if such withholding amounts are not delivered at the time of
exercise.

               (ii) Incentive Stock Option.  If this Option qualifies as an 
                    ----------------------                                  
ISO, the Optionee will have no regular federal income tax liability upon its
exercise, although the excess, if any, of the Fair Market Value of the Exercised
Shares on the date of exercise over their aggregate Exercise Price will be
treated as an adjustment to alternative minimum taxable income for federal tax
purposes and may subject the Optionee to alternative minimum tax in the year of
exercise. In the event that the Optionee ceases to be an Employee but remains a
Service Provider, any Incentive Stock Option of the Optionee that remains
unexercised shall cease to qualify as an Incentive Stock Option and will be
treated for tax purposes as a Nonstatutory Stock Option on the date three months
and one day following such change of status.

          (b)  Disposition of Shares.
               --------------------- 

               (i)  NSO.  If the Optionee holds NSO Shares for at least one 
                    --- 
year, any gain realized on disposition of the Shares will be treated as long-
term capital gain for federal income tax purposes.

               (ii) ISO.  If the Optionee holds ISO Shares for at least one year
                    ---                                                         
after exercise and two years after the grant date, any gain realized on
disposition of the Shares will be treated as long-term capital gain for federal
income tax purposes. If the Optionee disposes of ISO Shares within one year
after exercise or two years after the grant date, any gain realized on such
disposition will be treated as compensation income (taxable at ordinary income
rates) to the extent of the lesser of (A) the difference between the Fair Market
Value of the Shares acquired on the date of exercise and the aggregate Exercise
Price, or (B) the difference between the sale price of such Shares and the
aggregate Exercise Price. Any additional gain will be taxed as capital gain,
short-term or long-term depending on the period that the ISO Shares were held.

          (c)  Notice of Disqualifying Disposition of ISO Shares.  If the 
               -------------------------------------------------    
Optionee sells or otherwise disposes of any of the Shares acquired pursuant to
an ISO on or before the later of (i) two years after the grant date, or (ii) one
year after the exercise date, the Optionee shall immediately notify the Company
in writing of such disposition. The Optionee agrees that he or she may be
subject to income tax withholding by the Company on the compensation income
recognized from such early disposition of ISO Shares by payment in cash or out
of the current earnings paid to the Optionee.

     7.   Entire Agreement; Governing Law.  The Plan is incorporated herein by
          -------------------------------                                     
reference. The Plan and this Option Agreement constitute the entire agreement of
the parties with respect to the subject matter hereof and supersede in their
entirety all prior undertakings and agreements of the Company and Optionee with
respect to the subject matter hereof, and may not be modified adversely 

                                      -4-

 
to the Optionee's interest except by means of a writing signed by the Company
and Optionee. This agreement is governed by the internal substantive laws, but
not the choice of law rules, of the State of California.

     8.   NO GUARANTEE OF CONTINUED SERVICE.  OPTIONEE ACKNOWLEDGES AND AGREES
          ---------------------------------                                   
THAT THE VESTING OF SHARES PURSUANT TO THE VESTING SCHEDULE HEREOF IS EARNED
ONLY BY CONTINUING AS A SERVICE PROVIDER AT THE WILL OF THE COMPANY (AND NOT
THROUGH THE ACT OF BEING HIRED, BEING GRANTED AN OPTION OR PURCHASING SHARES
HEREUNDER). OPTIONEE FURTHER ACKNOWLEDGES AND AGREES THAT THIS AGREEMENT, THE
TRANSACTIONS CONTEMPLATED HEREUNDER AND THE VESTING SCHEDULE SET FORTH HEREIN DO
NOT CONSTITUTE AN EXPRESS OR IMPLIED PROMISE OF CONTINUED ENGAGEMENT AS A
SERVICE PROVIDER FOR THE VESTING PERIOD, FOR ANY PERIOD, OR AT ALL, AND SHALL
NOT INTERFERE WITH OPTIONEE'S RIGHT OR THE COMPANY'S RIGHT TO TERMINATE
OPTIONEE'S RELATIONSHIP AS A SERVICE PROVIDER AT ANY TIME, WITH OR WITHOUT
CAUSE.

     By your signature and the signature of the Company's representative below,
you and the Company agree that this Option is granted under and governed by the
terms and conditions of the Plan and this Option Agreement. Optionee has
reviewed the Plan and this Option Agreement in their entirety, has had an
opportunity to obtain the advice of counsel prior to executing this Option
Agreement and fully understands all provisions of the Plan and Option Agreement.
Optionee hereby agrees to accept as binding, conclusive and final all decisions
or interpretations of the Administrator upon any questions relating to the Plan
and Option Agreement. Optionee further agrees to notify the Company upon any
change in the residence address indicated below.

OPTIONEE:                                    CONCENTRIC NETWORK CORPORATION

___________________________________      By: ______________________________
Signature                                    Signature

___________________________________          __________________________________
Print Name                                   Print Name

___________________________________          __________________________________
Residence Address                            Title
___________________________________

___________________________________
Telephone        OPTION AGREEMENT - 1997 STOCK PLAN

                                      -5-

 
                                   EXHIBIT A
                                   ---------

                        CONCENTRIC NETWORK CORPORATION
                                1997 STOCK PLAN

                                EXERCISE NOTICE


Concentric Network Corporation
10590 North Tantau Avenue
Cupertino, CA 95014

Attention:  Corporate Secretary

     1.   Exercise of Option.  Effective as of today, ________________, 199__,
          ------------------                                                  
the undersigned ("Purchaser") hereby elects to purchase ______________ shares
(the "Shares") of the Common Stock of Concentric Network Corporation (the
"Company") under and pursuant to the 1997 Stock Plan (the "Plan") and the Stock
Option Agreement dated _____________, 19___ (the "Option Agreement"). The
purchase price for the Shares shall be $_____________, as required by the Option
Agreement.

     2.   Delivery of Payment.  Purchaser herewith delivers to the Company the
          -------------------                                                 
full purchase price for the Shares.

     3.   Representations of Purchaser.  Purchaser acknowledges that Purchaser
          ----------------------------                      
has received, read and understood the Plan and the Option Agreement and agrees
to abide by and be bound by their terms and conditions.

     4.   Rights as Stockholder.  Until the issuance (as evidenced by the
          ---------------------                                          
appropriate entry on the books of the Company or of a duly authorized transfer
agent of the Company) of the Shares, no right to vote or receive dividends or
any other rights as a stockholder shall exist with respect to the Optioned
Stock, notwithstanding the exercise of the Option. The Shares so acquired shall
be issued to the Optionee as soon as practicable after exercise of the Option.
No adjustment will be made for a dividend or other right for which the record
date is prior to the date of issuance, except as provided in Section 13 of the
Plan.

     5.   Tax Consultation.  Purchaser understands that Purchaser may suffer
          ----------------                                                  
adverse tax consequences as a result of Purchaser's purchase or disposition of
the Shares. Purchaser represents that Purchaser has consulted with any tax
consultants Purchaser deems advisable in connection with the purchase or
disposition of the Shares and that Purchaser is not relying on the Company for
any tax advice.

     6.   Entire Agreement; Governing Law.  The Plan and Option Agreement are
          -------------------------------                                    
incorporated herein by reference. This Agreement, the Plan and the Option
Agreement constitute the entire agreement of the parties with respect to the
subject matter hereof and supersede in their entirety all prior undertakings and
agreements of the Company and Purchaser with respect to the subject matter
hereof, and may not be modified adversely to the Purchaser's interest except by
means of a writing 

 
signed by the Company and Purchaser. This agreement is governed by the internal
substantive laws, but not the choice of law rules, of the State of California.


Submitted by:                          Accepted by:

PURCHASER:                             CONCENTRIC NETWORK CORPORATION


________________________________    By:_____________________________
Signature                              Signature

________________________________       __________________________________
Print Name                             Print Name

                                       __________________________________
                                       Title



Address:                               Address:
-------                                ------- 

________________________________       Concentric Network Corporation
________________________________       10590 North Tantau Avenue
________________________________       Cupertino, CA 95014

________________________________       __________________________________
Telephone                              Date Received

                   OPTION EXERCISE NOTICE - 1997 STOCK PLAN

                                      -2-

 
                                   EXHIBIT B
                                   ---------

                              SECURITY AGREEMENT


     This Security Agreement is made as of __________, 19___ between Concentric
Network Corporation, a Delaware corporation ("Pledgee"), and
_________________________ ("Pledgor").


                                   Recitals
                                   --------

     Pursuant to Pledgor's election to purchase Shares under the Option
Agreement dated ________ (the "Option"), between Pledgor and Pledgee under
Pledgee's 1997 Stock Plan, and Pledgor's election under the terms of the Option
to pay for such shares with a promissory note (the "Note"), Pledgor has
purchased _________ shares of Pledgee's Common Stock (the "Shares") at a price
of $________ per share, for a total purchase price of $__________. The Note and
the obligations thereunder are as set forth in Exhibit C to the Option.

     NOW, THEREFORE, it is agreed as follows:

     1.   Creation and Description of Security Interest.  In consideration of 
          ---------------------------------------------   
the transfer of the Shares to Pledgor under the Option Agreement, Pledgor,
pursuant to the California Commercial Code, hereby pledges all of such Shares
(herein sometimes referred to as the "Collateral") represented by certificate
number ______, duly endorsed in blank or with executed stock powers, and
herewith delivers said certificate to the Secretary of Pledgee ("Pledgeholder"),
who shall hold said certificate subject to the terms and conditions of this
Security Agreement.

     The pledged stock (together with an executed blank stock assignment for use
in transferring all or a portion of the Shares to Pledgee if, as and when
required pursuant to this Security Agreement) shall be held by the Pledgeholder
as security for the repayment of the Note, and any extensions or renewals
thereof, to be executed by Pledgor pursuant to the terms of the Option, and the
Pledge  holder shall not encumber or dispose of such Shares except in accordance
with the provisions of this Security Agreement.

     2.   Pledgor's Representations and Covenants.  To induce Pledgee to enter
          ---------------------------------------                             
into this Security Agreement, Pledgor represents and covenants to Pledgee, its
successors and assigns, as follows:

          a.   Payment of Indebtedness.  Pledgor will pay the principal sum of
               -----------------------  
the Note secured hereby, together with interest thereon, at the time and in the
manner provided in the Note.

          b.   Encumbrances.  The Shares are free of all other encumbrances,
               ------------                                                 
defenses and liens, and Pledgor will not further encumber the Shares without the
prior written consent of Pledgee.

          c.   Margin Regulations.  In the event that Pledgee's Common Stock is
               ------------------                                            
now or later becomes margin-listed by the Federal Reserve Board and Pledgee is
classified as a "lender" within the 

 
meaning of the regulations under Part 207 of Title 12 of the Code of Federal
Regulations ("Regulation G"), Pledgor agrees to cooperate with Pledgee in making
any amendments to the Note or providing any additional collateral as may be
necessary to comply with such regulations.

     3.   Voting Rights.  During the term of this pledge and so long as all
          -------------                                                    
payments of principal and interest are made as they become due under the terms
of the Note, Pledgor shall have the right to vote all of the Shares pledged
hereunder.

     4.   Stock Adjustments.  In the event that during the term of the pledge
          -----------------                                                  
any stock dividend, reclassification, readjustment or other changes are declared
or made in the capital structure of Pledgee, all new, substituted and additional
shares or other securities issued by reason of any such change shall be
delivered to and held by the Pledgee under the terms of this Security Agreement
in the same manner as the Shares originally pledged hereunder. In the event of
substitution of such securities, Pledgor, Pledgee and Pledgeholder shall
cooperate and execute such documents as are reasonable so as to provide for the
substitution of such Collateral and, upon such substitution, references to
"Shares" in this Security Agreement shall include the substituted shares of
capital stock of Pledgor as a result thereof.

     5.   Options and Rights.  In the event that, during the term of this 
          ------------------      
pledge, subscription Options or other rights or options shall be issued in
connection with the pledged Shares, such rights, Options and options shall be
the property of Pledgor and, if exercised by Pledgor, all new stock or other
securities so acquired by Pledgor as it relates to the pledged Shares then held
by Pledgeholder shall be immediately delivered to Pledgeholder, to be held under
the terms of this Security Agreement in the same manner as the Shares pledged.

     6.   Default.  Pledgor shall be deemed to be in default of the Note and of
          -------                                                              
this Security Agreement in the event:

          a.   Payment of principal or interest on the Note shall be delinquent
for a period of ten days or more; or

          b.   Pledgor fails to perform any of the covenants set forth in the
Option or contained in this Security Agreement for a period of ten days after
written notice thereof from Pledgee.

     In the case of an event of Default, as set forth above, Pledgee shall have
the right to accelerate payment of the Note upon notice to Pledgor, and Pledgee
shall thereafter be entitled to pursue its remedies under the California
Commercial Code.

     7.   Release of Collateral.  Subject to any applicable contrary rules under
          ---------------------                                                 
Regulation G, there shall be released from this pledge a portion of the pledged
Shares held by Pledgeholder hereunder upon payments of the principal of the
Note. The number of the pledged Shares that shall be released shall be that
number of full Shares that bears the same proportion to the initial number of
Shares pledged hereunder as the payment of principal bears to the initial full
principal amount of the Note.

                                      -1-

 
     8.   Withdrawal or Substitution of Collateral.  Pledgor shall not sell,
          ----------------------------------------                          
withdraw, pledge, substitute or otherwise dispose of all or any part of the
Collateral without the prior written consent of Pledgee.

     9.   Term.  The within pledge of Shares shall continue until the payment of
          ----                                                                  
all indebtedness secured hereby, at which time the remaining pledged stock shall
be promptly delivered to Pledgor, subject to the provisions for prior release of
a portion of the Collateral as provided in paragraph 7 above.

     10.  Insolvency.  Pledgor agrees that if a bankruptcy or insolvency
          ----------                                                    
proceeding is instituted by or against it, or if a receiver is appointed for the
property of Pledgor, or if Pledgor makes an assignment for the benefit of
creditors, the entire amount unpaid on the Note shall become immediately due and
payable, and Pledgee may proceed as provided in the case of default.

     11.  Pledgeholder Liability.  In the absence of willful or gross 
          ----------------------    
negligence, Pledgeholder shall not be liable to any party for any of
Pledgeholder's acts, or omissions to act, as Pledgeholder.

     12.  Invalidity of Particular Provisions.  Pledgor and Pledgee agree that 
          -----------------------------------     
the enforceability or invalidity of any provision or provisions of this Security
Agreement shall not render any other provision or provisions herein contained
unenforceable or invalid.

     13.  Successors or Assigns.  Pledgor and Pledgee agree that all of the 
          ---------------------    
terms of this Security Agreement shall be binding on their respective successors
and assigns, and that the term "Pledgor" and the term "Pledgee" as used herein
shall be deemed to include, for all purposes, the respective designees,
successors, assigns, heirs, executors and administrators.

     14.  Governing Law.  This Security Agreement shall be interpreted and
          -------------                                                   
governed under the internal substantive laws, but not the choice of law rules,
of the State of California.

                                      -2-

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



     "PLEDGOR"                     _______________________________________
                                   Signature
                                   _______________________________________
                                   Print Name

                 Address:          _______________________________________

                                   _______________________________________

                                   _______________________________________
                                   Telephone


     "PLEDGEE"                     Concentric Network Corporation,
                                   a Delaware corporation


                               By: ___________________________________
                                   Signature
 
                                   ______________________________________
                                   Print Name

                                   ______________________________________
                                   Title


     "PLEDGEHOLDER"                ______________________________________
                                   Corporate Secretary
                                   Concentric Network Corporation



                                1997 STOCK PLAN
                           OPTION SECURITY AGREEMENT
                                   EXHIBIT C
                                   ---------

 
                                      NOTE


$_______________                                           Cupertino, California

                                                           ______________, 19___

     FOR VALUE RECEIVED, _______________ promises to pay to Concentric Network
Corporation, a Delaware corporation (the "Company"), or order, the principal sum
of _______________________ ($_____________), together with interest on the
unpaid principal hereof from the date hereof at the rate of _______________
percent (____%) per annum, compounded semiannually.

     Principal and interest shall be due and payable on __________, 19___.
Payment of principal and interest shall be made in lawful money of the United
States of America.

     The undersigned may at any time prepay all or any portion of the principal
or interest owing hereunder.

     This Note is subject to the terms of the Option, dated as of
________________.  This Note is secured in part by a pledge of the Company's
Common Stock under the terms of a Security Agreement of even date herewith and
is subject to all the provisions thereof.

     The holder of this Note shall have full recourse against the undersigned,
and shall not be required to proceed against the collateral securing this Note
in the event of default.

     In the event the undersigned shall cease to be an employee, director or
consultant of the Company for any reason, this Note shall, at the option of the
Company, be accelerated, and the whole unpaid balance on this Note of principal
and accrued interest shall be immediately due and payable.

     Should any action be instituted for the collection of this Note, the
reasonable costs and attorneys' fees therein of the holder shall be paid by the
undersigned.

                              ____________________________________
                              Signature

                              ____________________________________
                              Print Name

                                      -2-

 
                        CONCENTRIC NETWORK CORPORATION 
                               1997 STOCK PLAN 
                    NOTICE OF GRANT OF STOCK PURCHASE RIGHT

     Unless otherwise defined herein, the terms defined in the 1997 Stock Plan
(the "Plan") shall have the same defined meanings in this Notice of Grant.

[Grantee's Name and Address]

     You have been granted the right to purchase Common Stock of the Company,
subject to the Company's Repurchase Option and your ongoing status as a Service
Provider (as described in the Plan and the attached Restricted Stock Purchase
Agreement), as follows:

     Grant Number                         _________________________

     Date of Grant                        _________________________

     Price Per Share                      $________________________

     Total Number of Shares Subject       _________________________
      to This Stock Purchase Right

     Expiration Date:                     _________________________

     YOU MUST EXERCISE THIS STOCK PURCHASE RIGHT BEFORE THE EXPIRATION DATE OR
IT WILL TERMINATE AND YOU WILL HAVE NO FURTHER RIGHT TO PURCHASE THE SHARES. By
your signature and the signature of the Company's representative below, you and
the Company agree that this Stock Purchase Right is granted under and governed
by the terms and conditions of the 1997 Stock Plan and the Restricted Stock
Purchase Agreement, attached hereto as Exhibit A-1, both of which are made a
part of this document. You further agree to execute the attached Restricted
Stock Purchase Agreement as a condition to purchasing any shares under this
Stock Purchase Right.

GRANTEE:                                  CONCENTRIC NETWORK CORPORATION

_____________________________         By: __________________________________
Signature                                 Signature

_____________________________             ____________________________________
Print Name                                Print Name
                                          _____________________________________
                                          Title

                                      -3-

 
                                  EXHIBIT A-1
                                  -----------

                        CONCENTRIC NETWORK CORPORATION
                                1997 STOCK PLAN

                      RESTRICTED STOCK PURCHASE AGREEMENT

     Unless otherwise defined herein, the terms defined in the Plan shall have
the same defined meanings in this Restricted Stock Purchase Agreement.

     WHEREAS the Purchaser named in the Notice of Grant (the "Purchaser") is an
Service Provider, and the Purchaser's continued participation is considered by
the Company to be important for the Company's continued growth; and

     WHEREAS in order to give the Purchaser an opportunity to acquire an equity
interest in the Company as an incentive for the Purchaser to participate in the
affairs of the Company, the Administrator has granted to the Purchaser a Stock
Purchase Right subject to the terms and conditions of the Plan and the Notice of
Grant, which are incorporated herein by reference, and pursuant to this
Restricted Stock Purchase Agreement (the "Agreement");

     NOW THEREFORE, the parties agree as follows:

     15.  Sale of Stock.  The Company hereby agrees to sell to the Purchaser and
          -------------                                                         
the Purchaser hereby agrees to purchase shares of the Company's Common Stock
(the "Shares") at the per Share purchase price and as otherwise described in the
Notice of Grant.

     16.  Payment of Purchase Price.  The purchase price for the Shares may be
          -------------------------                                           
paid by delivery to the Company at the time of execution of this Agreement of
cash, a check, or some combination thereof.

     17.  Repurchase Option.
          ----------------- 

          (a)  In the event the Purchaser ceases to be a Service Provider for
any or no reason (including death or disability) before all of the Shares are
released from the Company's Repurchase Option (see Section 4), the Company
shall, upon the date of such termination (as reasonably fixed and determined by
the Company) have an irrevocable, exclusive option (the "Repurchase Option") for
a period of sixty days from such date to repurchase up to that number of shares
that constitute the Unreleased Shares (as defined in Section 4) at the original
purchase price per share (the "Repurchase Price"). The Repurchase Option shall
be exercised by the Company by delivering written notice to the Purchaser or the
Purchaser's executor (with a copy to the Escrow Holder) AND, at the Company's
option, (i) by delivering to the Purchaser or the Purchaser's executor a check
in the amount of the aggregate Repurchase Price, or (ii) by canceling an amount
of the Purchaser's indebtedness to the Company equal to the aggregate Repurchase
Price, or (iii) by a combination of (i) and (ii) so that the combined payment
and cancellation of indebtedness equals the aggregate Repurchase Price. Upon
delivery of such notice and the payment of the aggregate Repurchase Price, the
Company shall become the legal and beneficial owner of the Shares being
repurchased and all 

 
rights and interests therein or relating thereto, and the Company shall have the
right to retain and transfer to its own name the number of Shares being
repurchased by the Company.

          (b)  Whenever the Company shall have the right to repurchase Shares
hereunder, the Company may designate and assign one or more employees, officers,
directors or stockholders of the Company or other persons or organizations to
exercise all or a part of the Company's purchase rights under this Agreement and
purchase all or a part of such Shares. If the Fair Market Value of the Shares to
be repurchased on the date of such designation or assignment (the "Repurchase
FMV") exceeds the aggregate Repurchase Price of such Shares, then each such
designee or assignee shall pay the Company cash equal to the difference between
the Repurchase FMV and the aggregate Repurchase Price of such Shares.

     18.  Release of Shares From Repurchase Option.
          ---------------------------------------- 

          (a)  Twenty-five percent of the Shares shall be released from the
Company's Repurchase Option one year after the Date of Grant and thereafter the
Shares shall be released in 36 equal increments over 36 months, at the end of
each month, provided that the Purchaser does not cease to be a Service Provider
prior to the date of any such release.

          (b)  Any of the Shares that have not yet been released from the
Repurchase Option are referred to herein as "Unreleased Shares."

          (c)  The Shares that have been released from the Repurchase Option
shall be delivered to the Purchaser at the Purchaser's request (see Section 6).

     19.  Restriction on Transfer.  Except for the escrow described in Section 6
          -----------------------                                               
or the transfer of the Shares to the Company or its assignees contemplated by
this Agreement, none of the Shares or any beneficial interest therein shall be
transferred, encumbered or otherwise disposed of in any way until such Shares
are released from the Company's Repurchase Option in accordance with the
provisions of this Agreement, other than by will or the laws of descent and
distribution.

     20.  Escrow of Shares.
          ---------------- 

          (a)  To ensure the availability for delivery of the Purchaser's
Unreleased Shares upon repurchase by the Company pursuant to the Repurchase
Option, the Purchaser shall, upon execution of this Agreement, deliver and
deposit with an escrow holder designated by the Company (the "Escrow Holder")
the share certificates representing the Unreleased Shares, together with the
stock assignment duly endorsed in blank, attached hereto as Exhibit A-2.  The
Unreleased Shares and stock assignment shall be held by the Escrow Holder,
pursuant to the Joint Escrow Instructions of the Company and Purchaser attached
hereto as Exhibit A-3, until such time as the Company's Repurchase Option
expires.

                                      -5-

 
          (b)  The Escrow Holder shall not be liable for any act it may do or
omit to do with respect to holding the Unreleased Shares in escrow while acting
in good faith and in the exercise of its judgment.

          (c)  If the Company or any assignee exercises the Repurchase Option
hereunder, the Escrow Holder, upon receipt of written notice of such exercise
from the proposed transferee, shall take all steps necessary to accomplish such
transfer.

          (d)  When the Repurchase Option has been exercised or expires
unexercised or a portion of the Shares has been released from the Repurchase
Option, upon request the Escrow Holder shall promptly cause a new certificate to
be issued for the released Shares and shall deliver the certificate to the
Company or the Purchaser, as the case may be.

          (e)  Subject to the terms hereof, the Purchaser shall have all the
rights of a stockholder with respect to the Shares while they are held in
escrow, including without limitation, the right to vote the Shares and to
receive any cash dividends declared thereon. If, from time to time during the
term of the Repurchase Option, there is (i) any stock dividend, stock split or
other change in the Shares, or (ii) any merger or sale of all or substantially
all of the assets or other acquisition of the Company, any and all new,
substituted or additional securities to which the Purchaser is entitled by
reason of the Purchaser's ownership of the Shares shall be immediately subject
to this escrow, deposited with the Escrow Holder and included thereafter as
"Shares" for purposes of this Agreement and the Repurchase Option.

     21.  Legends.  The share certificate evidencing the Shares, if any, issued
          -------                                                               
hereunder shall be endorsed with the following legend (in addition to any legend
required under applicable state securities laws):

     THE SHARES REPRESENTED BY THIS CERTIFICATE ARE SUBJECT TO CERTAIN
RESTRICTIONS UPON TRANSFER AND RIGHTS OF REPURCHASE AS SET FORTH IN AN AGREEMENT
BETWEEN THE COMPANY AND THE STOCKHOLDER, A COPY OF WHICH IS ON FILE WITH THE
SECRETARY OF THE COMPANY.

     22.  Adjustment for Stock Split.  All references to the number of Shares 
          --------------------------                                          
and the purchase price of the Shares in this Agreement shall be appropriately
adjusted to reflect any stock split, stock dividend or other change in the
Shares that may be made by the Company after the date of this Agreement.

     23.  Tax Consequences.  The Purchaser has reviewed with the Purchaser's own
          ----------------                                                      
tax advisors the federal, state, local and foreign tax consequences of this
investment and the transactions contemplated by this Agreement. The Purchaser is
relying solely on such advisors and not on any statements or representations of
the Company or any of its agents. The Purchaser understands that the Purchaser
(and not the Company) shall be responsible for the Purchaser's own tax liability
that may arise as a result of the transactions contemplated by this Agreement.
The Purchaser understands that Section 83 of the Internal Revenue Code of 1986,
as amended (the "Code"), taxes as ordinary

                                      -6-

 
income the difference between the purchase price for the Shares and the Fair
Market Value of the Shares as of the date any restrictions on the Shares lapse.
In this context, "restriction" includes the right of the Company to buy back the
Shares pursuant to the Repurchase Option. The Purchaser understands that the
Purchaser may elect to be taxed at the time the Shares are purchased rather than
when and as the Repurchase Option expires by filing an election under Section
83(b) of the Code with the IRS within 30 days from the date of purchase. The
form for making this election is attached as Exhibit A-4 hereto.

          THE PURCHASER ACKNOWLEDGES THAT IT IS THE PURCHASER'S SOLE
RESPONSIBILITY AND NOT THE COMPANY'S TO FILE TIMELY THE ELECTION UNDER SECTION
83(b), EVEN IF THE PURCHASER REQUESTS THE COMPANY OR ITS REPRESENTATIVES TO MAKE
THIS FILING ON THE PURCHASER'S BEHALF.

     24.  General Provisions.
          ------------------ 

          (a)  This Agreement shall be governed by the internal substantive
laws, but not the choice of law rules of the State of California. This
Agreement, subject to the terms and conditions of the Plan and the Notice of
Grant, represents the entire agreement between the parties with respect to the
purchase of the Shares by the Purchaser. Subject to Section 15(c) of the Plan,
in the event of a conflict between the terms and conditions of the Plan and the
terms and conditions of this Agreement, the terms and conditions of the Plan
shall prevail. Unless otherwise defined herein, the terms defined in the Plan
shall have the same defined meanings in this Agreement.

          (b)  Any notice, demand or request required or permitted to be given
by either the Company or the Purchaser pursuant to the terms of this Agreement
shall be in writing and shall be deemed given when delivered personally or
deposited in the U.S. mail, First Class with postage prepaid, and addressed to
the parties at the addresses of the parties set forth at the end of this
Agreement or such other address as a party may request by notifying the other in
writing.

          Any notice to the Escrow Holder shall be sent to the Company's address
with a copy to the other party hereto.

          (c)  The rights of the Company under this Agreement shall be
transferable to any one or more persons or entities, and all covenants and
agreements hereunder shall inure to the benefit of, and be enforceable by the
Company's successors and assigns. The rights and obligations of the Purchaser
under this Agreement may only be assigned with the prior written consent of the
Company.

          (d)  Either party's failure to enforce any provision of this Agreement
shall not in any way be construed as a waiver of any such provision, nor prevent
that party from thereafter enforcing any other provision of this Agreement. The
rights granted both parties hereunder are cumulative and shall not constitute a
waiver of either party's right to assert any other legal remedy available to it.

          (e)  The Purchaser agrees upon request to execute any further
documents or instruments necessary or desirable to carry out the purposes or
intent of this Agreement.

                                      -7-

 
          (f)  PURCHASER ACKNOWLEDGES AND AGREES THAT THE VESTING OF SHARES
PURSUANT TO SECTION 4 HEREOF IS EARNED ONLY BY CONTINUING SERVICE AS A SERVICE
PROVIDER AT THE WILL OF THE COMPANY (AND NOT THROUGH THE ACT OF BEING HIRED OR
PURCHASING SHARES HEREUNDER). PURCHASER FURTHER ACKNOWLEDGES AND AGREES THAT
THIS AGREEMENT, THE TRANSACTIONS CONTEMPLATED HEREUNDER AND THE VESTING SCHEDULE
SET FORTH HEREIN DO NOT CONSTITUTE AN EXPRESS OR IMPLIED PROMISE OF CONTINUED
ENGAGEMENT AS A SERVICE PROVIDER FOR THE VESTING PERIOD, FOR ANY PERIOD, OR AT
ALL, AND SHALL NOT INTERFERE WITH PURCHASER'S RIGHT OR THE COMPANY'S RIGHT TO
TERMINATE PURCHASER'S RELATIONSHIP AS A SERVICE PROVIDER AT ANY TIME, WITH OR
WITHOUT CAUSE.

     By Purchaser's signature below, Purchaser represents that he or she is
familiar with the terms and provisions of the Plan, and hereby accepts this
Agreement subject to all of the terms and provisions thereof. Purchaser has
reviewed the Plan and this Agreement in their entirety, has had an opportunity
to obtain the advice of counsel prior to executing this Agreement and fully
understands all provisions of this Agreement. Purchaser agrees to accept as
binding, conclusive and final all decisions or interpretations of the
Administrator upon any questions arising under the Plan or this Agreement.
Purchaser further agrees to notify the Company upon any change in the residence
indicated in the Notice of Grant.

DATED:  ______________________

PURCHASER:                                CONCENTRIC NETWORK CORPORATION


______________________________         By:___________________________
Signature                                 Signature

______________________________            ________________________________
Print Name                                Print Name
 
                                          ________________________________
                                          Title



                                1997 STOCK PLAN
                      RESTRICTED STOCK PURCHASE AGREEMENT

                                      -8-

 
                                  EXHIBIT A-2
                                  -----------

                     ASSIGNMENT SEPARATE FROM CERTIFICATE



     FOR VALUE RECEIVED I, __________________________, hereby sell, assign and
transfer unto
________________________________________________________________________________
________________ (__________) shares of the Common Stock of Concentric Network
Corporation standing in my name of the books of said corporation represented by
Certificate No. _____ herewith and do hereby irrevocably constitute and appoint
_____________________________________________ to transfer the said stock on the
books of the within named corporation with full power of substitution in the
premises.

     This Stock Assignment may be used only in accordance with the Restricted
Stock Purchase Agreement (the "Agreement") between________________________ and
the undersigned dated ______________, 19__.


Dated: _______________, 19__


                                     Signature:______________________________



INSTRUCTIONS:  Please do not fill in any blanks other than the signature line.
The purpose of this assignment is to enable the Company to exercise the
Repurchase Option, as set forth in the Agreement, without requiring additional
signatures on the part of the Purchaser.

 
                                  EXHIBIT A-3
                                  -----------

                           JOINT ESCROW INSTRUCTIONS
                           -------------------------


                                                                   _______, 19__
                                                             

Corporate Secretary
Concentric Network Corporation
10590 North Tantau Avenue
Cupertino, CA 95014


Dear _________________:

     As Escrow Agent for both Concentric Network Corporation, a Delaware
corporation (the "Company"), and the undersigned purchaser of stock of the
Company (the "Purchaser"), you are hereby authorized and directed to hold the
documents delivered to you pursuant to the terms of that certain Restricted
Stock Purchase Agreement ("Agreement") between the Company and the undersigned,
in accordance with the following instructions:

     1.   In the event the Company and/or any assignee of the Company (referred
to collectively as the "Company") exercises the Company's Repurchase Option set
forth in the Agreement, the Company shall give to Purchaser and you a written
notice specifying the number of shares of stock to be purchased, the purchase
price, and the time for a closing hereunder at the principal office of the
Company. Purchaser and the Company hereby irrevocably authorize and direct you
to close the transaction contemplated by such notice in accordance with the
terms of said notice.

     2.   At the closing, you are directed (a) to date the stock assignments
necessary for the transfer in question, (b) to fill in the number of shares
being transferred, and (c) to deliver same, together with the certificate
evidencing the shares of stock to be transferred, to the Company or its
assignee, against the simultaneous delivery to you of the purchase price (by
cash, a check, or some combination thereof) for the number of shares of stock
being purchased pursuant to the exercise of the Company's Repurchase Option.

     3.   Purchaser irrevocably authorizes the Company to deposit with you any
certificates evidencing shares of stock to be held by you hereunder and any
additions and substitutions to said shares as defined in the Agreement.
Purchaser does hereby irrevocably constitute and appoint you as Purchaser's
attorney-in-fact and agent for the term of this escrow to execute with respect
to such securities all documents necessary or appropriate to make such
securities negotiable and to complete any transaction herein contemplated,
including but not limited to the filing with any applicable state blue sky
authority of any required applications for consent to, or notice of transfer of,
the securities. Subject to the provisions of this paragraph 3, Purchaser shall
exercise all rights and privileges of a stockholder of the Company while the
stock is held by you.

     4.   Upon written request of the Purchaser, but no more than once per
calendar year, unless the Company's Repurchase Option has been exercised, you
shall deliver to Purchaser a certificate or 

 
certificates representing so many shares of stock as are not then subject to the
Company's Repurchase Option. Within 90 days after Purchaser ceases to be a
Service Provider, you shall deliver to Purchaser a certificate or certificates
representing the aggregate number of shares held or issued pursuant to the
Agreement and not purchased by the Company or its assignees pursuant to exercise
of the Company's Repurchase Option.

      5.  If at the time of termination of this escrow you should have in your
possession any documents, securities, or other property belonging to Purchaser,
you shall deliver all of the same to Purchaser and shall be discharged of all
further obligations hereunder.

     6.   Your duties hereunder may be altered, amended, modified or revoked
only by a writing signed by all of the parties hereto.

     7.   You shall be obligated only for the performance of such duties as are
specifically set forth herein and may rely and shall be protected in relying or
refraining from acting on any instrument reasonably believed by you to be
genuine and to have been signed or presented by the proper party or parties.
You shall not be personally liable for any act you may do or omit to do
hereunder as Escrow Agent or as attorney-in-fact for Purchaser while acting in
good faith, and any act done or omitted by you pursuant to the advice of your
own attorneys shall be conclusive evidence of such good faith.

     8.   You are hereby expressly authorized to disregard any and all warnings
given by any of the parties hereto or by any other person or corporation,
excepting only orders or process of courts of law, and are hereby expressly
authorized to comply with and obey orders, judgments or decrees of any court.
In case you obey or comply with any such order, judgment or decree, you shall
not be liable to any of the parties hereto or to any other person, firm or
corporation by reason of such compliance, notwithstanding any such order,
judgment or decree being subsequently reversed, modified, annulled, set aside,
vacated or found to have been entered without jurisdiction.

     9.   You shall not be liable in any respect on account of the identity,
authorities or rights of the parties executing or delivering or purporting to
execute or deliver the Agreement or any documents or papers deposited or called
for hereunder.

     10.  You shall not be liable for the outlawing of any rights under the
statute of limitations with respect to these Joint Escrow Instructions or any
documents deposited with you.

     11.  You shall be entitled to employ such legal counsel and other experts
as you may deem necessary properly to advise you in connection with your
obligations hereunder, may rely upon the advice of such counsel, and may pay
such counsel reasonable compensation therefor.

     12.  Your responsibilities as Escrow Agent hereunder shall terminate if you
shall cease to be an officer or agent of the Company or if you shall resign by
written notice to each party.  In the event of any such termination, the Company
shall appoint a successor Escrow Agent.

                                      -2-

 
     13.  If you reasonably require other or further instruments in connection
with these Joint Escrow Instructions or obligations in respect hereto, the
necessary parties hereto shall join in furnishing such instruments.

     14.  It is understood and agreed that should any dispute arise with respect
to the delivery and/or ownership or right of possession of the securities held
by you hereunder, you are authorized and directed to retain in your possession
without liability to anyone all or any part of said securities until such
disputes shall have been settled either by mutual written agreement of the
parties concerned or by a final order, decree or judgment of a court of
competent jurisdiction after the time for appeal has expired and no appeal has
been perfected, but you shall be under no duty whatsoever to institute or defend
any such proceedings.

     15.  Any notice required or permitted hereunder shall be given in writing
and shall be deemed effectively given upon personal delivery or upon deposit in
the United States Post Office, by registered or certified mail with postage and
fees prepaid, addressed to each of the other parties thereunto entitled at the
following addresses or at such other addresses as a party may designate by ten
days' advance written notice to each of the other parties hereto.


          COMPANY:         Concentric Network Corporation    
                           10590 North Tantau Avenue         
                           Cupertino, CA 95014               
                                                             
          PURCHASER:       ________________________________  
                                                             
                           ________________________________  
                                                             
                           ________________________________   

          ESCROW AGENT:    Corporate Secretary
                           Concentric Network Corporation
                           10590 North Tantau Avenue
                           Cupertino, CA 95014

     16.  By signing these Joint Escrow Instructions, you become a party hereto
only for the purpose of said Joint Escrow Instructions; you do not become a
party to the Agreement.

     17.  This instrument shall be binding upon and inure to the benefit of the
parties hereto, and their respective successors and permitted assigns.

     18.  These Joint Escrow Instructions shall be governed by, and construed
and enforced in accordance with, the internal substantive laws, but not the
choice of law rules, of the State of California.

                                      -3-

 
                              Very truly yours,

                              CONCENTRIC NETWORK CORPORATION


                          By: ___________________________________
                              Signature

                              ______________________________________
                              Print Name

                              ______________________________________
                              Title


                              PURCHASER:

                              ______________________________________
                              Signature

                              ______________________________________
                              Print Name


ESCROW AGENT:


__________________________________
Corporate Secretary Signature

__________________________________
Print Name


                           JOINT ESCROW INSTRUCTIONS

                                      -4-

 
                                  EXHIBIT A-4
                                  -----------
                         ELECTION UNDER SECTION 83(b)
                         ----------------------------
                     OF THE INTERNAL REVENUE CODE OF 1986
                     ------------------------------------

The undersigned taxpayer hereby elects, pursuant to Section 83(b) of the
Internal Revenue Code of 1986, as amended, to include in taxpayer's gross income
for the current taxable year the amount of any compensation taxable to taxpayer
in connection with his or her receipt of the property described below:

1.   The name, address, taxpayer identification number and taxable year of the
undersigned are as follows:

NAME:                    TAXPAYER:            SPOUSE:

ADDRESS:

IDENTIFICATION NO.:      TAXPAYER:            SPOUSE:

TAXABLE YEAR:

2.   The property with respect to which the election is made is described as
     follows: __________ shares (the "Shares") of the Common Stock of Concentric
     Network Corporation (the "Company").

3.   The date on which the property was transferred is: ______________, 19__.

4.   The property is subject to the following restrictions:

     The Shares may be repurchased by the Company, or its assignee, upon certain
     events. This right lapses with regard to a portion of the Shares based on
     the continued performance of services by the taxpayer over time.

5.   The fair market value at the time of transfer, determined without regard to
     any restriction other than a restriction that by its terms will never
     lapse, of such property is:
     $_______________.

6.   The amount (if any) paid for such property is:

     $_______________.

The undersigned has submitted a copy of this statement to the person for whom
the services were performed in connection with the undersigned's receipt of the
above-described property.  The transferee of such property is the person
performing the services in connection with the transfer of said property.

The undersigned understands that the foregoing election may not be revoked
--------------------------------------------------------------------------
except with the consent of the Commissioner.
------------------------------------------- 

Dated:  ___________________, 19_________________________________________________
                                 Taxpayer

The undersigned spouse of taxpayer joins in this election.

Dated:  ___________________, 19_________________________________________________
                                 Spouse of Taxpayer