[Exhibit 10.1]

             REGISTRATION RIGHTS AND TRANSFER RESTRICTION AGREEMENT

        This AGREEMENT (this "Agreement"), dated as of May 31, 2006,
among Level 3 Communications, Inc., a Delaware corporation ("Company"), MCCC ICG
Holdings LLC, a Delaware limited liability Company ("Seller"), Columbia Capital
Equity Partners III (QP), L.P., a Delaware limited partnership ("Columbia III"),
Columbia Capital Equity Partners III (Cayman), L.P., a Cayman Islands exempted
limited partnership ("Columbia Cayman"), Columbia Capital Equity Partners III
(AI), L.P., a Delaware limited partnership ("Columbia AI"), Columbia Capital
Equity Investors III, L.L.C., a Delaware limited liability company ("Columbia
LLC"), Columbia Capital Employees Investors III, L.L.C., a Delaware limited
liability company ("Columbia Employees"), M/C Venture Partners V, L.P., a
Delaware limited partnership ("M/C V"), M/C Venture Investors, L.L.C., a
Delaware limited liability company ("M/C LLC"), Chestnut Venture Partners, L.P.,
a Delaware limited partnership ("Chestnut") and Bear Investments, LLLP, a
Colorado limited liability limited partnership ("Bear" and together with
Columbia III, Columbia Cayman, Columbia AI, Columbia LLC, Columbia Employees,
M/C V, M/C LLC and Chestnut, the "Seller Owners")

                              W I T N E S S E T H:
                               - - - - - - - - - -

        WHEREAS, Company and Seller are parties to a Purchase
Agreement, dated as of April 14, 2006 (the "Purchase Agreement"), pursuant to
which Company will acquire from the Seller all of the issued and outstanding
shares of common stock of ICG Communications, Inc., a Delaware corporation (the
"Acquisition");

        WHEREAS, in connection with the Acquisition, Seller will
receive an aggregate of 25,975,088 shares (such shares, the "Shares") of common
stock, par value $.01 per share of Company ("Company Common Stock"), including
3,272,452 shares to be held in escrow pursuant to the Escrow Agreement;

        WHEREAS, the Seller Owners, directly or indirectly, own all of
the outstanding capital stock of the Seller;

        WHEREAS, it is a condition to consummation of the Acquisition
that Company enter into this Agreement providing for the registration of the
shares of Company Common Stock to be received by Seller in the Acquisition; and

        WHEREAS, the Company is willing to prepare and file a
registration statement under the Securities Act of 1933, as amended (the
"Securities Act"), with the Securities and Exchange Commission (the "SEC") with
respect to the Shares and to maintain the effectiveness of such registration
statement, upon the terms and subject to the conditions set forth herein;

        NOW THEREFORE, in consideration of the foregoing and the
respective covenants and agreements hereinafter contained, the parties hereby
agree as follows:

     SECTION 1. Definitions. All terms used in this Agreement which are defined
in the Purchase Agreement shall have the meanings specified in the Purchase
Agreement unless the context otherwise requires.




     SECTION 2. Registration of the Shares.

     2.1 Shelf Registration Statement. As soon as reasonably practicable after
the date hereof and in any event within five (5) business days following the
consummation of the Acquisition, the Company shall prepare and file with the SEC
a shelf registration statement, relating to the offer and sale by Seller and
Seller Owners at any time and from time to time on a delayed or continuous basis
in accordance with Rule 415 under the Securities Act and in accordance with this
Agreement, of all the Shares (the "Registration Statement"). If, at the time of
filing of the Registration Statement, the Registration Statement is eligible to
become effective upon filing pursuant to Rule 462(e) (or any successor rule)
under the Securities Act, the Company shall file the Registration Statement as
an automatic shelf registration statement pursuant to such rule. If the
Registration Statement is not so eligible to become effective upon filing, the
Company shall use its reasonable best efforts to have the Registration Statement
declared effective as promptly as practicable (with such date on which the
Registration Statement becomes effective referred to as the "Effective Date").
Promptly (i) upon the filing thereof in the case of an automatic shelf or (ii)
upon receipt of an order of the SEC declaring the Registration Statement
effective, the Company shall deliver to Seller and any of the Seller Owners
included in the Registration Statement a copy of such Registration Statement and
any amendments thereto together with an opinion of counsel representing the
Company for the purposes of such Registration, in form and substance reasonably
acceptable to Seller and the Seller Owners, addressed to Seller and the Seller
Owners, including, confirming that the Registration Statement is effective and
that all of the Shares have been duly registered and, subject to the transfer
restrictions contained in this Agreement, are freely transferable and that all
of the shares have been admitted for listing on the NASDAQ Stock Market.

     2.2 Adjustment. If at any time the Shares as a class shall have been
increased, decreased, changed into or exchanged for a different number or class
of shares or securities as a result of a reorganization, recapitalization,
reclassification, stock dividend, stock split, reverse stock split, combination
or exchange of shares or other similar change in capitalization, then an
appropriate and proportionate adjustment shall be made to the number of Shares
for all purposes under this Agreement.

     SECTION 3. Maintenance of Registration Statement and Prospectuses.

     3.1 The Company shall use its reasonable best efforts to keep the
Registration Statement and the prospectus contained therein (as amended or
supplemented from time to time, the "Prospectuses" and each a "Prospectus")
continuously effective until the Termination Date (as defined below). In the
event the Registration Statement cannot be kept effective for such period, the
Company shall use its reasonable best efforts to prepare and file with the SEC
and have declared effective as promptly as practicable another registration
statement on the same terms and conditions as the initial Registration Statement
and such registration statement shall be considered the Registration Statement
for purposes hereof. The Company shall furnish to Seller and the Seller Owners
such number of copies of a Prospectus in conformity with the requirements of the
Act, and an electronic copy of the Prospectus to facilitate the disposition of
the Shares owned by Seller and the Seller Owners.

                                       2


     3.2 The Company shall advise Seller and the Seller Owners promptly in
writing when the Registration Statement, or any post-effective amendment
thereto, has been declared effective by the SEC. The Company shall advise Seller
and the Seller Owners in writing of the receipt by the Company of any stop order
from the SEC suspending the effectiveness of the Registration Statement, and if
at any time there shall be a stop order suspending the effectiveness of the
Registration Statement, the Company shall use its reasonable best efforts to
obtain promptly the withdrawal of such order. The Company shall advise Seller
and the Seller Owners promptly in writing of the existence of any fact and the
happening of any event that makes any statement of a material fact made in the
Registration Statement or Prospectus untrue, or that requires the making of any
additions to or changes in the Registration Statement or Prospectus in order to
make the statements therein not misleading and in such event the Company shall
prepare and file with the SEC, as soon as reasonably practicable, an amendment
to such Registration Statement or an amendment or supplement to such Prospectus
so that, as so amended or supplemented, such Registration Statement and such
Prospectus will not contain an untrue statement of a material fact or omit to
state a material fact required to be stated therein or necessary to make the
statements therein, in light of the circumstances then existing, not misleading.
Upon receipt of such written advice, each of Seller and the Seller Owners shall
discontinue and refrain from making any sales of Shares, until such time as the
Company advises Seller and the Seller Owners that such Registration Statement or
such Prospectus no longer contains an untrue statement or omission of a material
fact.

     3.3 Each of Seller and the Seller Owners shall furnish to the Company such
information regarding such party and the distribution of the Shares as the
Company may from time to time reasonably request in writing in order to comply
with the Securities Act. Each of Seller and the Seller Owners shall notify the
Company as promptly as practicable of any inaccuracy or change in information
previously furnished by such party to the Company or of the happening of any
event in either case as a result of which any Prospectus relating to the
Registration Statement contains an untrue statement of a material fact regarding
such party or the distribution of such Shares, or omits to state any material
fact regarding such party or the distribution of such Shares required to be
stated therein or necessary to make the statements therein not misleading in
light of the circumstances then existing, and to furnish promptly to the Company
any additional information required to correct or update any previously
furnished information or required so that such Prospectus shall not contain,
with respect to such party or the distribution of such Shares an untrue
statement of a material fact or omit to state a material fact required to be
stated therein or necessary to make the statements therein not misleading in
light of the circumstances then existing.

     3.4 Notwithstanding anything to the contrary contained herein, for a period
not to exceed forty-five (45) consecutive calendar days and not to exceed
seventy (70) aggregate calendar days in any twelve-month period (each a "Black
Out Period"), the Company will not be required to file any registration
statement pursuant to this Agreement, file any amendment thereto, furnish any
supplement to a prospectus included in a registration statement pursuant to this
Agreement, make any other filing with the SEC required pursuant to this
Agreement, cause any registration statement or other filing with the SEC to
become effective, or take any similar action, and any and all sales of Shares by
Seller and the Seller Owners pursuant to an effective registration statement
shall be suspended: (i) if an event has occurred and is continuing as a result
of which any such registration statement or prospectus would, in the Company's
good faith

                                       3


judgment, contain an untrue statement of a material fact or omit to state a
material fact required to be stated therein or necessary to make the statements
therein not misleading, (ii) if the Company notifies Seller and the Seller
Owners that such actions would, in the Company's good faith judgment, require
the disclosure of material non-public information which the Board of Directors
of the Company has determined would be seriously detrimental to the Company to
disclose and which the Company would not otherwise be required to disclose or
(iii) if the Company notifies Seller and the Seller Owners that, in the
Company's good faith judgment, it is necessary to suspend sales of Shares by
Seller and the Seller Owners, to facilitate a pending or proposed public or Rule
144A offering by the Company of Company Common Stock or Common Stock Equivalents
(as defined below), provided, however, that any such suspension of sales shall
be not longer than twenty-one (21) consecutive calendar days. Upon the
termination of the condition described in clauses (i), (ii) or (iii) above, the
Company shall promptly give written notice to Seller and the Seller Owners and
shall promptly file any registration statement or amendment thereto required to
be filed by it pursuant to this Agreement, furnish any prospectus supplement or
amendment required to be furnished pursuant to this Agreement, make any other
filing with the SEC required of it or terminate any suspension of sales it has
put into effect and shall take such other actions to permit registered sales of
Shares as contemplated by this Agreement. For purposes of this Agreement,
"Common Stock Equivalents" shall mean any rights, warrants, options, convertible
securities or indebtedness, exchangeable securities or indebtedness, or other
rights, exercisable for or convertible or exchangeable into, directly or
indirectly, Company Common Stock and securities convertible or exchangeable into
Company Common Stock, whether at the time of issuance or upon the passage of
time or the occurrence of any future event.

     3.5 Company shall take all actions necessary to execute such documents and
cause all of the Shares to be admitted for listing on the NASDAQ Stock Market,
which listing shall be effective on the Effective Date.

     SECTION 4. Restrictions on Transfer.

     4.1 On or prior to the Effective Date, none of Seller or the Seller Owners
shall, nor shall they permit any of their Affiliates or the Escrow Agent in its
capacity as such under the Escrow Agreement to sell, contract to sell, pledge,
grant any option to purchase, acquire any option to sell, hypothecate, loan,
make a short sale or otherwise transfer to any Person or dispose of (each a
"Transfer") any shares of Company Common Stock. For a period of 180 days
following the Effective Date (the "Transfer Period"), Seller and the Seller
Owners shall not, and shall not permit any of their Affiliates or the Escrow
Agent in its capacity as such under the Escrow Agreement to, Transfer in the
aggregate on any given day (a "Transfer Date") such number of shares of Company
Common Stock that exceeds (i) the product of (x) 4,360,507 shares of Company
Common Stock and (y) the number of trading days in the period from and including
the Effective Date to and including the Transfer Date less (ii) the aggregate
number of shares of Company Common Stock Transferred by Seller, the Seller
Owners and any of their Affiliates in accordance with this section during the
period from and including the Effective Date to, but excluding, the Transfer
Date; provided, however, that Seller and the Seller Owners shall not, and shall
not permit any of their Affiliates or the Escrow Agent in its capacity as such
under the Escrow Agreement to, Transfer, whether directly or indirectly, more
than 13,081,520 shares of Company Common Stock on any such Transfer Date, and
provided further, that in

                                       4


determining the maximum number of shares of Company Common Stock that may be
Transferred in any one day as provided above, any Transfers permitted by the
succeeding sentence shall not be included in such calculation. Notwithstanding
anything herein to the contrary, the transfer restrictions set forth in this
section shall not apply to: (1) any Transfer of shares of Company Common Stock
by Seller to the Seller Owners; (2) any Transfer to holders of membership units
in Seller other than the Seller Owners, provided, however, that such holders
shall agree with the Company in writing prior to such Transfer to be bound by
the terms of this Agreement; and (3) any Transfer of all or part of the Shares
to one or more persons (a "Negotiated Transaction"), provided, however, that
such person or persons shall agree with the Company in writing prior to such
Transfer to be bound by the terms of this Agreement and provided further that
the maximum number of shares of Company Common Stock that may be sold by all
such persons, together with the Seller Owners and Affiliates, shall not exceed
in the aggregate the maximum number of shares of Company Common Stock that may
be sold as provided above. In addition to the foregoing, (i) at any time after
the Effective Date and prior to June 30, 2006, Seller and the Seller Owners
shall not, and shall not permit any of their Affiliates to knowingly make any
direct Transfer in a Negotiated Transaction that would result in the acquirer
holding economic or voting ownership in excess of five percent (5%) or more of
Company Common Stock and (ii) at any time after the Effective Date, Seller and
the Seller Owners shall not knowingly (after due inquiry of the transferee) and
shall not knowingly permit any of their Affiliates to knowingly (after due
inquiry of the transferee) make any direct Transfer in a Negotiated Transaction
that would result in the acquirer holding economic or voting ownership in excess
of ten percent (10%) or more of Company Common Stock. For purposes of this
Section 4, neither Seller nor the Seller Owners shall be deemed to have made a
transfer that would result in the acquirer holding economic or voting ownership
in excess of five percent (5%) or ten percent (10%) of Company Common Stock as
provided in clauses (i) and (ii) above, if such transfer is made in an open
market broker sale transaction without knowledge of the identity of the acquiror
at the time of the sale transaction by Seller or Seller Owners.

     4.2 Seller and Seller Owners (and any subsequent transferee who agrees to
be bound by the terms of this Section 4) agree that within five (5) business
days after the consummation of any Transfer referred to in this Section 4, such
transferring party shall deliver documentation to the Purchaser that identifies
the transferee, the number of shares of Company Common Stock transferred and the
date of such Transfer.

     SECTION 5. Blue Sky. In connection with the registration under Section 2
hereof, the Company shall take all actions necessary to permit the resale by
Seller and the Seller Owners of any Company Common Stock under the blue sky laws
of the several states, except that the Company shall not for any such purpose be
required to qualify generally to do business as a foreign corporation in any
jurisdiction wherein it would not but for the requirements of this Section 5 be
obligated to be so qualified, subject itself to taxation in any such
jurisdiction or to consent to general service of process in any such
jurisdiction.

     SECTION 6. Expenses. All expenses incident to the Company's performance of
or compliance with this Agreement will be borne by the Company, including,
without limitation, all: (i) registration and filing fees and expenses; (ii)
expenses of printing; (iii) fees and expenses of counsel for the Company; and
(iv) fees and expenses of one counsel for Seller and the Seller Owners,
provided, however, such fees pursuant to this clause (iv) shall not exceed
$5,000.

                                       5


Notwithstanding the foregoing, the Company shall not be liable for and
shall not pay any expenses or fees of more than one counsel for Seller or the
Seller Owners or any commissions to be paid in connection with any sale of the
Shares by Seller or the Seller Owners.

     SECTION 7. Termination. The obligations of the Company hereunder, with
respect to the Shares, shall terminate upon the earlier of (i) the date on which
all Shares covered by the Registration Statement have been disposed of by Seller
and the Seller Owners and (ii) the second anniversary of the Acquisition. The
date on which such obligations shall terminate shall be referred to as the
"Termination Date."

     SECTION 8. Indemnification.

     8.1 The Company will, and does hereby agree to, indemnify and hold harmless
each of Seller and the Seller Owners, and each of their directors, officers,
employees and agents and each person controlling Seller or a Seller Owner with
respect to any registration effected pursuant to this Agreement against all
claims, losses, damages, and liabilities (or actions in respect thereto)
including any of the foregoing incurred in settlement of any litigation,
commenced or threatened, to which Seller and the Seller Owners may become
subject under the Securities Act, the Securities Exchange Act of 1934 (the
"Exchange Act"), or other federal or state law insofar as such claims, losses,
damages or liabilities (or actions in respect thereto) arise out of or are based
on any untrue statement (or alleged untrue statement) of a material fact
contained in any registration statement or prospectus relating to the Shares, or
other document, or any amendment or supplement thereto, or any omission (or
alleged omission) to state therein a material fact required to be stated therein
or necessary to make the statements therein not misleading, and will reimburse
each such party for any legal and any other expenses reasonably incurred in
connection with investigating or defending any such claim, loss, damage,
liability, or action; provided that the Company will not be liable in any such
case to the extent that any such claim, loss, damage, liability or expense
arises out of or is based on any untrue statement or omission based upon written
information furnished to the Company by such party and stated to be specifically
for use therein and provided further, that the Company shall only reimburse such
parties for the fees and expenses of a single legal counsel for all such
parties.

     8.2 Each of Seller and the Sellers Owners will, severally based on Shares
sold pursuant to a registration effected pursuant to this Agreement, but not
jointly, if Shares held by or issuable to such party are included in a
registration effected pursuant to this Agreement, indemnify the Company, each of
its directors and officers, each person controlling the Company and the officers
and directors of each such controlling person against all claims, losses,
damages, and liabilities (or actions in respect thereof) including any of the
foregoing incurred in settlement of any litigation, commenced or threatened,
arising out of or based on any untrue statement (or alleged untrue statement) of
a material fact contained in the Registration Statement or the Prospectus
included therein, or any omission (or alleged omission) to state therein a
material fact required to be stated therein or necessary to make the statements
therein not misleading, and will reimburse the Company, and each such director,
officer and controlling person, for any legal or any other expenses reasonably
incurred in connection with investigating or defending any such claim, loss,
damage, liability, or action, in each case to the extent, but only to the extent
that such untrue statement (or alleged untrue statement) or omission (or alleged
omission) was made in such Registration Statement or Prospectus, in reliance
upon and in conformity with written

                                       6


information furnished to the Company by such party and stated to be specifically
for use therein. Notwithstanding the foregoing, the liability of each Seller and
the Seller Owners under this Section shall be limited in an amount equal to the
per share sales price (less any underwriting discounts and commissions)
multiplied by the number of Shares sold by such party pursuant to the
Registration Statement.

     8.3 Each party entitled to indemnification under this Section 8 (the
"Indemnified Party") shall give written notice to the party required to provide
such indemnification (the "Indemnifying Party") of any claim as to which
indemnification may be sought promptly after such Indemnified Party has actual
knowledge thereof, and shall permit the Indemnifying Party to assume the defense
of any such claim or any litigation resulting therefrom; provided that counsel
for the Indemnifying Party, who shall conduct the defense of such claim or
litigation, shall be subject to approval by the Indemnified Party (whose
approval shall not be unreasonably withheld) and after the Indemnifying Party
assumes the defense thereof, the Indemnifying Party shall not be liable to such
Indemnified Party for any legal or other expenses subsequently incurred by the
latter in connection with the defense thereof, unless in the reasonable judgment
of the Indemnified Party, representation of such Indemnified Party by such
counsel would be inappropriate due to actual or potential differing interests
between such Indemnified Party and the Indemnifying Party in such proceeding in
which case such Indemnified Party shall have the right to employ separate
counsel to participate in such defense at the expense of the Indemnifying Party;
it being understood that the Indemnifying Party shall not, in connection with
any one such action or separate but substantially similar or related actions in
the same jurisdiction arising out of the same general allegations, be liable for
the reasonable fees and expenses of more than one separate firm of attorneys at
any time for all such Indemnified Parties provided, however, that the
Indemnifying Party shall bear the expenses of independent counsel for the
Indemnified Party if the Indemnified Party reasonably determines that
representation of more than one party by the same counsel would be inappropriate
due to actual or potential conflicts of interest between the Indemnified Party
and the Indemnifying Party; and provided further that the failure of any
Indemnified Party to give notice as provided herein shall not relieve the
Indemnifying Party of its obligations under this Section 8, except to the extent
that such failure to give notice shall materially adversely affect the
Indemnifying Party in the defense of any such claim or any such litigation. No
Indemnifying Party, in the defense of any such claim or litigation, shall,
except with the consent of each Indemnified Party, consent to entry of any
judgment or enter into any settlement that does not include as an unconditional
term thereof the giving by the claimant or plaintiff therein, to such
Indemnified Party, of a release from all liability in respect to such claim or
litigation.

     8.4 If the indemnification provided for in subsection (a) or (b) of this
Section 8 is for any reason unavailable to a party to be indemnified with
respect to any claims, actions, demands, losses, damages, liabilities, costs or
expenses referred to therein, then each Indemnifying Party under any such
subsection, in lieu of indemnifying such Indemnified Party thereunder, hereby
agrees to contribute to the amount paid or payable by such Indemnified Party as
a result of such claims, actions, demands, losses, damages, liabilities, cost or
expenses in such proportion as is appropriate to reflect the relative fault of
the Indemnifying Party on the one hand and of the Indemnified Party on the other
in connection with the statements or omissions which resulted in such claims,
actions, demands, losses, damages, liabilities, costs or expenses, as well as
any other relevant equitable considerations. The relative fault of the
Indemnifying Party and

                                       7


of the Indemnified Party shall be determined by reference to, among other
things, whether the untrue or alleged untrue statement of a material fact or the
omission or alleged omission to state a material fact relates to information
supplied by the Indemnifying Party or by the Indemnified Party and the parties'
relative intent, knowledge, access to information and opportunity to correct or
prevent such statement or omission. Notwithstanding the foregoing, the amount
Seller shall be obligated to contribute pursuant to this subsection (d) shall be
limited to an amount equal to the per share sale price (less any underwriting
discount and commissions) multiplied by the number of Shares sold by such party
pursuant to the Registration Statement which gives rise to such obligation to
contribute (less aggregate amount of any damages which such party has otherwise
been required to pay in respect of such claim, action, demand, loss, damage,
liability, cost or expense or any substantially similar claim, action, demand,
loss, damage, liability, cost or expense arising from the sale of such Shares).
No person guilty of fraudulent misrepresentation (within the meaning of Section
11(f) of the Securities Act) shall be entitled to contribution hereunder from
any person who was not guilty of such fraudulent misrepresentation. The
obligations of Seller and the Seller Owners under this paragraph will be several
(based on Shares sold pursuant to a registration effected pursuant to this
Agreement) and not joint.

     SECTION 9. Rule 144 Reporting. With a view to making available to Seller
and the Seller Owners the benefits of certain rules and regulations of the SEC
which may permit the sale of the Shares to the public without registration, the
Company agrees to use its best efforts to:

     9.1 comply, on a timely basis with all the reporting requirements of the
Exchange Act, and comply with all other public information reporting
requirements of the SEC as a condition to the availability of an exemption from
the Securities Act under Rule 144 thereunder, as amended from time to time, or
successor rule thereto, for the sale of Shares by Seller or the Seller Owners;

     9.2 provide, at the Company's expense, such opinion of counsel as may be
reasonably requested by the transfer agent for the Shares in connection with
each sale of Registrable Securities pursuant to an exemption from the
registration requirements of the Securities Act (under Rule 144 thereunder, as
amended from time to time, or successor rule thereto or otherwise) or otherwise,
so long as the Seller Owners have furnished to counsel documentation reasonably
acceptable to such counsel related to the transfer and the Shares; and

     9.3 whenever Seller or the Seller Owners are able to demonstrate to the
Company that the provisions of Rule 144(k) (or any successor rule) under the
Securities Act are available to them and have furnished to the Company such
documentation in connection therewith as the Company may reasonably request,
provide, at the Company's expense, new certificates that do not bear a
restrictive legend.

     9.4 So long as any of Seller and the Seller Owners own any Shares, furnish
to such party forthwith upon request, a copy of the most recent annual or
quarterly report of the Company, and such other reports and documents as such
party may reasonably request in availing itself of any rule or regulation of the
SEC allowing it to sell any such Shares without registration; provided that such
reports are not otherwise available to Seller or the Seller Owners on the SEC's
Edgar web site.

                                       8


     SECTION 10. Amendments. This Agreement may not be amended without the
written consent of the Company and the holders of at least two-thirds (2/3rds)
of the aggregate of the Shares.

     SECTION 11. Miscellaneous.

     11.1 Benefits of Agreement. Except as otherwise provided herein, nothing in
this Agreement, expressed or implied, shall give or be construed to give any
person, firm or corporation, other than the parties hereto, any legal or
equitable right, remedy or claim under any covenant, condition or provision
contained in this Agreement being for the sole benefit of the parties hereto.

     11.2 Successors and Assigns. This Agreement shall be binding upon the
Company and its successors and assigns and shall inure to the benefit of Seller
and the Seller Owners and to the benefit of their successors and permitted
assigns.

     11.3 Assignment of Registration Rights. The rights to have the Company
register Shares pursuant to this Agreement shall be assignable by Seller only in
connection with a transfer of Shares pursuant to Section 4.

     11.4 Notices. Any notice, request, instruction or other document to be
given hereunder shall be in writing and delivered personally or sent by
registered or certified mail, postage prepaid, by reputable national express
courier or shipping cost prepaid, according to the instructions set forth below.
Such notices shall be deemed given: at the time delivered by hand, if personally
delivered; three business days after having been sent by registered or certified
mail; and one business day after having been sent by express courier.

                  If to Seller or any Seller Owner:

                           MCCC ICG Holdings LLC
                           2010 8th Street
                           Boulder, CO 80302
                           Attn: Manager

                  Copy to:

                           Kendall, Koenig & Oelsner PC
                           1675 Broadway, Suite 750
                           Denver, CO 80202
                           Attn:  David J. Kendall

                  If to the Company:

                           Level 3 Communications, Inc.
                           1025 Eldorado Blvd.
                           Building 2000
                           Broomfield, CO 80021
                           Attn: General Counsel

                                       9


                  Copy to:

                           Willkie Farr & Gallagher LLP
                           787 Seventh Ave.
                           New York, New York 10019
                           Attn:  David K. Boston

     11.5 Governing Law. THIS AGREEMENT SHALL BE GOVERNED BY AND CONSTRUED IN
ACCORDANCE WITH THE LAWS OF THE STATE OF NEW YORK, WITHOUT REGARD TO PRINCIPLES
OF CONFLICTS OF LAW.

     11.6 Counterparts.; Facsimile. This Agreement may be executed in two or
more counterparts, each of which will be deemed an original, but all such
counterparts taken together will constitute one and the same Agreement. Any
facsimile copies hereof or signature hereon shall, for all purposes, be deemed
originals

     11.7 Severability. In the event any provision in this Agreement shall be
held invalid, illegal or unenforceable in any respect for any reason, the
validity, legality and enforceability of any such provision in every other
respect and the remaining provisions shall not in any way be affected or
impaired thereby.

                                       10


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

                 LEVEL 3 COMMUNICATIONS, INC.


                 By:/s/ Robert M. Yates
                    ----------------------------
                 Name: Robert M. Yates
                 Title: Senior Vice President



                 MCCC ICG HOLDINGS, LLC

                 By:/s/ Robert J. Schmiedeler
                 Name: Robert J. Schmiedeler
                 Title: Chief Financial Officer and Secretary

                   COLUMBIA CAPITAL EQUITY PARTNERS III (QP), L.P.

                   By:          COLUMBIA CAPITAL EQUITY   PARTNERS
                   III, L.P., as general          partner


                   By: /s/ Donald A. Doering
                       ---------------------
                       Name:    Donald A. Doering
                       Title: Chief Financial Officer

                   COLUMBIA CAPITAL EQUITY PARTNERS III (CAYMAN), L.P.

                   By: COLUMBIA CAPITAL EQUITY    PARTNERS (CAYMAN)
                   III, LTD, as general partner


                   By: /s/ Donald A. Doering
                       ---------------------
                       Name:    Donald A. Doering
                       Title: Chief Financial Officer


                 [Registration Rights Agreement Signature Page]


                                       11



                      COLUMBIA CAPITAL EQUITY PARTNERS III (AI), L.P.

                      By: COLUMBIA CAPITAL EQUITY    PARTNERS III, L.P.,
                      as general   partner


                      By: /s/ Donald A. Doering
                          ---------------------
                          Name:    Donald A. Doering
                          Title: Chief Financial Officer

                      COLUMBIA CAPITAL INVESTORS III, L.L.C.

                      By:      COLUMBIA CAPITAL EQUITY PARTNERS III, L.P.,
                      as managing member


                      By:      /s/ Donald A. Doering___________
                               ---------------------
                               Name:____Donald A. Doering
                               Title: Chief Financial Officer

                      COLUMBIA CAPITAL EMPLOYEE INVESTORS III, L.L.C.

                      By:      COLUMBIA CAPITAL EQUITY    PARTNERS III, L.P.,
                      as managing member


                      By:      /s/ Donald A. Doering
                               ---------------------
                               Name:____Donald A. Doering
                               Title: Chief Financial Officer

                      M/C VENTURE PARTNERS V, L.P.


                      By:      /s/ James F. Wade
                               -----------------
                               Name: James F. Wade
                               Title: Managing Partner

                 [Registration Rights Agreement Signature Page]

                                       12



                      M/C VENTURE INVESTORS, L.L.C.


                      By:      /s/ James F. Wade
                               -----------------
                               Name: James F. Wade
                               Title: Managing Partner

                      CHESTNUT VENTURE PARTNERS, L.P.


                      By:      /s/ James F. Wade
                               -----------------
                               Name: James F. Wade
                               Title: Managing Partner
                 [Registration Rights Agreement Signature Page]

                          BEAR INVESTMENTS, LLLP


                          By:      /s/ Daniel P. Caruso
                                   --------------------
                                   Name: Daniel P. Caruso
                                   Title:


                 [Registration Rights Agreement Signature Page]

                                       13