<PAGE>


                                                                    EXHIBIT 10.3


                          REGISTRATION RIGHTS AGREEMENT


     THIS REGISTRATION RIGHTS AGREEMENT (the "Agreement") is made as of June 15,
2001, among NEON COMMUNICATIONS, INC., a Delaware corporation ("Neon") and MODE
1 COMMUNICATIONS, INC., a Connecticut corporation ("Mode 1").


                              B A C K G R O U N D:


     Pursuant to a certain Subordinated Convertible Note Purchase Agreement
dated as of the date hereof by and between Neon and Mode 1 (the "Mode 1 Purchase
Agreement"), Mode 1 is purchasing and Neon is selling an 18% Subordinated
Convertible Note (the "Mode 1 Note"), all as more fully described in the Mode 1
Purchase Agreement.

     NOW THEREFORE, in consideration of the foregoing and of the mutual promises
and covenants set forth herein, the parties hereto, intending to be legally
bound, agree as follows:

     1. CERTAIN DEFINITIONS. As used in this Agreement, the following terms
shall have the meanings set forth below:

        (a) "APPLICABLE PERIOD" shall mean the time between the date on which a
Registration Statement covering the Registrable Securities has been declared
effective by the Commission and the earlier of (i) the date on which each Seller
has completed the distribution of the Registrable Securities described in the
Registration Statement or (ii) the date on which all of the Registrable
Securities held by the Sellers shall be eligible to be sold pursuant to Rule
144(h) (or any similar successor provision).

        (b) "BUSINESS DAY" shall mean a day that is not a Saturday, a Sunday, or
a day on which banking institutions in New York, New York are required to be
closed.

        (c) "CLOSING" shall mean the closing of the transactions contemplated by
the Mode 1 Purchase Agreement.

        (d) "CLOSING DOCUMENTS" shall mean this Agreement, the Mode 1 Purchase
Agreement and each of the other agreements and documents delivered by Neon at
Closing.

        (e) "COMMISSION" shall mean the United States Securities and Exchange
Commission or any other federal agency at the time administering the Securities
Act.

        (f) "COMMON STOCK" shall mean the common stock, par value $.01 per
share, of Neon.

        (g) "EXCHANGE ACT" shall mean the Securities Exchange Act of 1934, as
amended, and the rules and regulations thereunder, all as the same shall be in
effect from time to time.


<PAGE>


        (h) "MODE 1 SHARES" shall mean the shares of Common Stock issuable upon
conversion of the Mode 1 Note.

        (i) "NASDAQ" shall mean The Nasdaq Stock Market or any market successor
thereto.

        (j) "PERMITTED TRANSFER" shall mean (i) a sale, assignment, pledge or
transfer of the interest of Mode 1 in all or any part of the Registrable
Securities to any third party, (ii) a Transfer by Mode 1 to a subsidiary,
limited partnership or limited liability company, which subsidiary, limited
partnership or limited liability company is controlled by Mode 1; PROVIDED,
HOWEVER, that each Transferee shall, prior to the Transfer of Registrable
Securities to such Transferee, execute and deliver to Neon a valid and binding
agreement in the form attached hereto as EXHIBIT A.

        (k) "PERMITTED TRANSFEREE" shall mean a transferee in a transaction
constituting a Permitted Transfer.

        (l) "PERSON" means an individual, partnership, limited liability
company, corporation, trust or unincorporated organization or government or
agency or political subdivision thereof.

        (m) "PROSPECTUS" shall mean (i) each preliminary prospectus included in
the Registration Statement filed prior to the time it becomes effective; (ii)
the form of prospectus first filed with the Commission pursuant to Rule 424(b);
(iii) all supplements thereto; and (iv) amendments thereto which shall have been
declared effective by the Commission.

        (n) "REGISTRABLE SECURITIES" shall mean (i) the Mode 1 Shares and (ii)
any Common Stock and any other security issued as an interest payment or other
distribution with respect to or in exchange for or in replacement of the Mode 1
Shares, PROVIDED, HOWEVER, that Registrable Securities shall not include any
shares of Common Stock which have been sold to the public either pursuant to the
Registration Statement or pursuant to Rule 144, which are eligible for resale
pursuant to Rule 144(k) under the Securities Act, or which have been sold in any
other transaction in which the transferor's rights under this Agreement are not
assigned.

        (o) The terms "REGISTER," "REGISTERED" and "REGISTRATION" shall refer to
a registration effected by preparing and filing with the Commission a
registration statement in compliance with the Securities Act and applicable
rules and regulations thereunder, and the declaration or ordering of the
effectiveness of such registration statement by the Commission.

        (p) "REGISTRATION EXPENSES" shall mean all expenses incurred by Neon in
effecting any registration pursuant to this Agreement, including all
registration, qualification and filing fees, reproduction and printing expenses,
expenses incurred by Neon in the preparation of any registration statement, fees
and disbursements of counsel for Neon and those of Neon's other independent
professional advisors and experts, listing fees and other costs incurred in
listing Registrable Securities for trading on Nasdaq or on any stock exchange,
blue sky fees and expenses (if any), expenses of any regular or special
accounting services provided to Neon or required by any such registration, and
the reasonable fees and disbursements of one counsel selected by Mode 1, but
shall not include Selling Expenses.


                                       2


<PAGE>


        (q) "REGISTRATION STATEMENT" shall mean any registration statement to be
filed or filed by Neon with the Commission pursuant to Section 2, below
(including (a) all amendments and supplements thereto, (b) each Prospectus
contained therein, and (c) all exhibits thereto or incorporated by reference
therein).

        (r) "RULE 144" shall mean Rule 144 as promulgated by the Commission
under the Securities Act, as such rule may be amended from time to time, or any
similar successor rule that may be promulgated by the commission.

        (s) "SECURITIES ACT" shall mean the Securities Act of 1933, as amended,
and regulations thereunder, all as the same shall be in effect from time to
time.

        (t) "SELLER" shall mean Mode 1, each Permitted Transferee thereof, and
any other holder of Registrable Securities to whom the registration rights
conferred by this Agreement have been transferred in compliance with Section
11(a) hereof, in each case who are offering for resale Registrable Securities on
a Registration Statement.

        (u) "SELLING EXPENSES" shall mean all brokerage fees, selling
commissions and underwriting discounts (if any), and stock transfer taxes
applicable to the sale of Registrable Securities and fees and disbursements of
counsel for any Seller (other than the fees and disbursements of such counsel
included in Registration Expenses).

        (v) "TRANSFER" shall mean any sale, transfer, encumbrance, gift,
donation, assignment, pledge, hypothecation or other disposition of any Common
Stock or any interest therein, whether voluntary or involuntary, including, but
not limited to, any disposition by operation of law, by court order, by judicial
process or by foreclosure, levy or attachment.

     2. REGISTRATION.

        (a) INITIAL REGISTRATION. As soon as practicable after the Closing, Neon
shall use its best efforts to effect the registration for offer and sale under
the Securities Act of all of the Mode 1 Shares. In furtherance thereof, Neon
shall file with the Commission within one hundred and eighty (180) days of
Closing a registration statement on an appropriate form (which form shall comply
as to form in all material respects with the requirements of the applicable
form) under the Securities Act covering the Mode 1 Shares and that number of
additional shares of Common Stock which represent interest payments that would
become due on the Mode 1 Note through August 15, 2004 if such interest payments
were to be paid in the form of additional shares of Common Stock or additional
convertible notes in accordance with the terms of the Mode 1 Note.

        (b) ADDITIONAL REGISTRATION. Neon shall file an additional registration
statement no later than January 15, 2005, to the extent necessary to register
the offer and sale under the Securities Act of that number of additional shares
of Common Stock which represent interest payments that would become due under
the Mode 1 Note through its maturity date if such interest payments were to be
paid in the form of additional shares of Common Stock or additional convertible
notes in accordance with the terms of the Mode 1 Note.

     3. REGISTRATION EXPENSES. All Registration Expenses shall be borne by Neon.


                                       3


<PAGE>


     4. REGISTRATION  PROCEDURES. If and whenever Neon is required by the
provisions of this Agreement to use its best efforts to effect the registration
of any Registrable Securities under the Securities Act, Neon shall, at Neon's
expense:

        (a) notify each Seller as to: (i) the initial filing of the Registration
Statement; (ii) the receipt of any comments thereon from the Commission; (iii)
any request from the Commission or any state regulatory authority for amendment
of the Registration Statement or for supplement to any Prospectus or for any
additional information in connection therewith; (iv) the filing of each
amendment thereto, including any post-effective amendment; (v) the effectiveness
of the Registration Statement or any post-effective amendment thereto; and (vi)
the issuance by the Commission or any state regulatory authority of any stop
order suspending the effectiveness of the Registration Statement or the use of
any Prospectus or the institution of any proceedings for that purpose;

        (b) use its best efforts to prevent the issuance of any stop order
preventing or suspending the use of any Prospectus and to obtain as soon as
possible the lifting or withdrawal thereof, if issued;

        (c) keep the Registration Statement effective from the effective date
thereof to and including the first to occur: (i) ninety-six (96) months from the
Closing Date; (ii) the date on which all Sellers have completed the distribution
of Registrable Securities described in the Registration Statement; or (iii) the
date on which all of the Registrable Securities held by the Sellers shall be
eligible to be sold pursuant to Rule 144(k) (or any similar successor
provision);

        (d) promptly prepare and file with the Commission such amendments and
supplements to the Registration Statement and the prospectus used in connection
with the Registration Statement as shall be necessary to comply with the
provisions of the Securities Act with respect to the disposition of all
securities covered by the Registration Statement and thereafter use its
reasonable best efforts to cause any such post-effective amendment to be
declared effective by the Commission as promptly as permitted by the Commission;

        (e) furnish to each Seller: (i) such number of Prospectuses and other
documents incident thereto, including any amendment of or supplement to the
Prospectus, as such Seller may reasonably request (for dissemination or
otherwise) from time to time; (ii) two signed copies of the Registration
Statement and all amendments thereto, including all exhibits filed therewith;
and (iii) such number of conformed copies of the Registration Statement
(including such number of copies of the exhibits filed therewith as may
reasonably be requested), including documents incorporated by reference therein,
as such Seller may reasonably request from time to time;

        (f) notify each Seller of Registrable Securities covered by the
Registration Statement at any time

            (i) when a Prospectus relating thereto is required to be delivered
under the Securities Act of the happening of any event or the failure of any
event to occur or the discovery of any facts as a result of which the Prospectus
included in the Registration Statement, as then in effect, includes any untrue
statement of a material fact or omits to state a material fact required to be
stated therein or necessary to make the statements therein not misleading or


                                       4


<PAGE>


incomplete in the light of the circumstances then existing, and at the request
of a Seller, prepare and furnish to such Seller, a reasonable number of copies
of a supplement to or an amendment of such Prospectus as may be necessary so
that, as thereafter delivered to the purchaser(s) of such shares, such
Prospectus shall not include any 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 or incomplete in the light of the
circumstances then existing;

            (ii) if, during the Applicable Period, the representations and
warranties of Neon contained in this Agreement or in the Mode 1 Purchase
Agreement, as the case may be, cease to be true and correct in any material
respect;

            (iii) if Neon receives any notification of the issuance of a stop
order or the suspension of the registration or qualification of the Registrable
Securities in any jurisdiction or the initiation of any proceeding for such
purpose; and

            (iv) that, in Neon's reasonable determination, a post-effective
amendment to the Registration Statement would be appropriate;

        (g) use its best efforts to register or qualify the Registrable
Securities covered by the Registration Statement under the securities or Blue
Sky laws of such states as the Seller shall reasonably request, and do any and
all other acts and things that may be necessary or desirable to enable the
Seller to consummate the public sale or other disposition in such states of the
Registrable Securities owned by such Seller; PROVIDED, HOWEVER that Neon shall
not be required in connection with this paragraph (g) to qualify as a foreign
corporation or execute a general consent to service of process in any
jurisdiction;

        (h) use its best efforts to list the Registrable Securities registered
pursuant to this Agreement on Nasdaq and any securities exchange on which shares
of the Common Stock are then listed;

        (i) make generally available to its security holders, as soon as
reasonably practicable, an earnings statement covering the period of at least
twelve (12) months, but not more than eighteen (18) months, beginning with the
first month after the effective date of the Registration Statement, which
earnings statement shall satisfy the provisions of Section 11(a) of the
Securities Act and Rule 158 thereunder (or any similar rule promulgated under
the Securities Act); and

        (j) Neon shall provide one copy of each notice or document given or
furnished to each Seller pursuant to Section 4(a) (e) and (f) above,
concurrently with the provision thereof to each Seller and/or as promptly
thereafter as possible, to legal counsel designated by each Seller in a written
notice given to Neon.


                                       5


<PAGE>


     5. INFORMATION BY EACH SELLER.

        (a) Each Seller shall furnish to Neon such information regarding such
Seller, the Registrable Securities held by such Seller and the sale or other
Transfer thereof proposed by such Seller as Neon may request in writing and as
shall be reasonably required in connection with the Registration.

        (b) Each Seller shall furnish to Neon such certificates and documents
confirming as of the effective date of the Registration Statement the
representations and warranties and performance of the covenants made herein by
such Seller.

     6. REPRESENTATION AND WARRANTIES OF NEON. Neon represents and warrants
to each Seller as of the date hereof follows:

        (a) Neon complies with the conditions for the use of Form S-3 under the
Securities Act in connection with the resale of securities on behalf of a
selling stockholder.

        (b) The Registration Statement will contain, and the Prospectus and any
amendments or supplements thereto will contain, all statements which are
required to be stated therein by, and will conform to, the requirements of the
Securities Act. The documents incorporated by reference in the Prospectus, at
the time filed with the Commission, conformed in all material respects to the
then applicable requirements of the Exchange Act or the Securities Act. The
Registration Statement will not contain any untrue statement of a material fact
and will not omit to state any material fact required to be stated therein or
necessary to make the statements therein not misleading. The prospectus and any
amendments and supplements thereto will not contain as of the date of such
Prospectus, any untrue statement of material fact; and will not omit as of the
date of such Prospectus, to state any material fact required to be stated
therein or necessary to make the statements therein, in the light of the
circumstances under which they were made, not misleading; PROVIDED, HOWEVER,
that Neon makes no representations or warranties as to information contained in
or omitted from the Registration Statement or the Prospectus, in reliance upon,
and in conformity with, written information furnished to Neon by or on behalf of
Mode 1 or any predecessor of Mode 1 or any other Seller, specifically for use in
the preparation thereof or in any report or other document incorporated therein
by reference, including, without limitation, any Current Report on Form 8-K
under the Exchange Act which Neon may file in connection with the transactions
contemplated by the Note Purchase Agreement.

        (c) The consolidated financial statements of Neon and its subsidiaries,
together with related notes and schedules as set forth or incorporated by
reference in the Registration Statement, present fairly the financial position
and the results of operations and cash flows of Neon and the consolidated
subsidiaries, at the indicated dates and for the indicated periods. Such
financial statements and related schedules have been prepared in accordance with
generally accepted principles of accounting, consistently applied throughout the
periods involved, and all adjustments necessary for a fair presentation of
results for such periods have been made.

        (d) No approval, consent, order, authorization, designation, or filing
by or with any regulatory, administrative or other governmental body is
necessary to be made by or on


                                       6


<PAGE>


behalf of Neon in connection with the execution and delivery by Neon of this
Agreement and the consummation of the transactions herein contemplated except
(i) as required under the Securities Act or the Exchange Act; (ii) in connection
with the listing of the Registrable Securities on Nasdaq; or (iii) as may be
necessary to qualify the Registrable Securities for public offering under state
securities or Blue Sky laws.

     7. REPRESENTATION AND WARRANTIES OF EACH SELLER. Each Seller, severally
and not jointly, represents and warrants, with respect to itself only, the
following:

        (a) Seller has, and will have, upon the effectiveness of the
Registration Statement and at the time of any sale or other Transfer thereunder,
good and marketable title to the Registrable Securities held by it which it
seeks to sell pursuant to the Registration Statement, free and clear of any
liens, encumbrances and claims, at law or in equity, and full right, power and
authority to effect the sale and delivery of such Registrable Securities.

        (b) Seller has not taken, directly or indirectly, any action designed
to, or which has constituted, or which might reasonably be expected to cause or
result in the manipulation or stabilization of the price of the Common Stock
and, other than as permitted by the Securities Act, Seller will not distribute
any Prospectus (as defined in the Securities Act) or other offering material in
connection with the offering of the Registrable Securities.

     8. COVENANTS OF EACH SELLER. Each Seller, severally and not jointly
covenants and agrees, with respect to itself only, as follows:

        (a) Seller shall not make or effect any Transfer, directly or,
indirectly, of any Registrable Securities, owned of record or beneficially by
it, (i) prior to the effectiveness of the Registration Statement, or (ii)
thereafter, except as permitted by and in accordance with the respective terms
and conditions of this Agreement (including Section 6 (b), below) and the other
Closing Documents.

        (b) Subsequent to the effectiveness of the Registration Statement,
Seller shall not make or effect any Transfer of Registrable Securities except:
(i) Permitted Transfers; (ii) Transfers pursuant to the Prospectus and as
provided under the caption "Plan of Distribution" therein; and (iii) Transfers
in accordance with Rule 144(k); PROVIDED, HOWEVER, that if, for any reason, the
Registration Statement shall not have become effective prior to the first
anniversary of Closing, Transfers of Registrable Securities may be effected in
accordance with Rule 144; and PROVIDED, FURTHER, HOWEVER, that if the
Registration Statement shall become effective but the Prospectus shall
thereafter become unusable to effect sales of Registrable Securities during the
Applicable Period due to the entry of a stop order, the filing of a
post-effective amendment which has not been declared effective or for any other
reason, then Transfers of Registrable Securities may be effected pursuant to the
provisions of Rule 144.

        (c) Seller shall promptly notify Neon of each Transfer (other than
Transfers effected pursuant to the Prospectus or Rule 144) of Registrable
Securities made or effected by it, but in no event later than five (5) Business
Days after such Transfer. Each such Seller shall specify the name, address and
tax identification number of each transferee, together with the amount of
Registrable Securities transferred to such transferee.


                                       7


<PAGE>


        (d) Seller shall promptly notify Neon if it shall have become an
"affiliate" of Neon within the meaning of Rule 144(a).

        (e) Seller shall not take, directly or indirectly, any action designed
to cause or result in, or which might reasonably be expected to constitute, the
manipulation or stabilization of the price of Common Stock or of any other
securities of Neon. Seller will use its best efforts to maintain an orderly
market when distributing the Registrable Securities.

        (f) The information pertaining to Seller provided or which will be
provided to Neon by or on behalf of each such Seller for inclusion under the
caption "Selling Stockholders" in each Prospectus will be complete and accurate
in all material respects as to such Seller as of the date of such Prospectus.

     9. INDEMNIFICATION WITH RESPECT TO SECURITIES MATTERS.

        (a) Neon will indemnify each Seller, each of their respective officers,
directors and partners, agents, representatives, legal counsel, and accountants
and each Person controlling each such Seller within the meaning of Section 15 of
the Securities Act with respect to which Registration has been effected pursuant
to this Section 9 against all expenses, claims, losses, damages, and liabilities
(or actions, proceedings, or settlements in respect thereof) arising out of or
based on any untrue statement (or alleged untrue statement) of a material fact
contained in any Prospectus, offering circular, or other document (including any
related Registration Statement) incident to any such Registration, or based on
any omission (or alleged omission) to state therein a material fact required to
be stated therein or necessary to make the statement therein not misleading, or
any violation by Neon of the Securities Act or any rule or regulation thereunder
applicable to Neon and relating to action or inaction required of Neon in
connection with any such Registration, and will reimburse any such Seller, its
respective officers, directors, partners, agents, representatives, legal
counsel, and accountants and each person controlling such Seller for any legal
and any other expenses reasonably incurred in connection with investigating and
defending or settling any such claim, loss, damage, liability, or action;
PROVIDED, HOWEVER, that Neon 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 Neon by any Seller and stated to be specifically for use therein;
PROVIDED, FURTHER, THAT Neon will not be liable in any case to the extent such
claim, loss, damage, liability or action arises out of the Indemnified Party's
(as defined below) failure to send or give a copy of the final Prospectus, as
the same may be then supplemented or amended, to the Person asserting an untrue
statement or alleged untrue statement or omission or alleged omission at or
prior to the written confirmation of the sale of Registrable Securities to such
Person if such statement or omission was corrected in such final Prospectus so
long as such final Prospectus, and any amendments or supplements thereto, have
been furnished to such Indemnified Party. It is agreed that the indemnity
agreement contained in this Section 9 shall not apply to amounts paid in
settlement of any such loss, claim, damage, liability, or action if such
settlement is effected without the consent of Neon (which consent shall not be
unreasonably withheld).

        (b) Each Seller will indemnify Neon, each of its directors, officers,
partners, agents, representatives, legal counsel, and accountants and each
Person who controls Neon within the meaning of Section 15 of the Securities Act,
against all claims, losses, damages and


                                       8


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liabilities (or actions in respect thereof) arising out of or based on any
untrue statement (or alleged untrue statement) of a material fact contained in
the Registration Statement, Prospectus, offering circular, or other document, 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 Neon, directors, officers, partners, agents, representatives,
legal counsel, and accountants and control persons 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) is made in such Registration Statement,
Prospectus, offering circular, or the document in reliance upon and in
conformity with written information furnished to Neon by such Seller or
authorized by such Seller to be furnished to Neon on behalf of such Seller, and
stated to be specifically for use therein; provided, however, that the
obligations of each Seller hereunder shall not apply to amounts paid in
settlement of any such claims, losses, damages, or liabilities (or actions in
respect thereof) if such settlement is effected without the consent of such
Seller (which consent shall not be unreasonably withheld). The maximum liability
of any Seller for indemnity pursuant to this Section 9(b) shall not exceed the
net proceeds that such Seller realized from the sale of its Registrable
Securities pursuant to the Prospectus or, if such Seller has not yet sold any
Registrable Securities pursuant to the Prospectus at the time that
indemnification is required pursuant to this Agreement then such Seller's
maximum liability hereunder shall be the value of the Common Stock beneficially
held by such Seller covered by the Prospectus measured by the closing price of
such Common Stock on Nasdaq or other market or exchange on which the Common
Stock are traded, or, if not so traded, by a fair market value standard
reasonably approved by Neon's then current Board of Directors.

        (c) Each Person entitled to indemnification under this Section 9 (the
"INDEMNIFIED PARTY") shall give notice to the Person required to provide
indemnification (the "INDEMNIFYING PARTY") promptly after such Indemnified Party
has actual knowledge of any claim as to which indemnity may be sought, and shall
permit the Indemnifying Party to assume the defense of such claim or any
litigation resulting therefrom, provided that counsel for the Indemnifying
Party, who shall conduct the defense of such claim or any litigation resulting
therefrom, shall be approved by the Indemnified Party (whose approval shall not
unreasonably be withheld), and the Indemnified Party may participate in such
defense at such Indemnified Party's expense, 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 Agreement to the
extent such failure is not prejudicial. 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 to such Indemnified Party of a release from all liability in respect
to such claim or litigation. Each Indemnified Party shall furnish such
information regarding itself or the claim in question as an Indemnifying Party
may reasonably request in writing and as shall be reasonably required in
connection with defense of such claim and litigation resulting therefrom.

        (d) If the indemnification provided for in this Section 9 is unavailable
to or insufficient to hold harmless an Indemnified Party with respect to any
loss, liability, claim, damage, or expense, (or actions or proceedings in
respect thereof) referred to therein, then the Indemnifying Party, in lieu of
indemnifying such Indemnified Party hereunder, shall contribute


                                       9


<PAGE>


to the amount paid or payable by such Indemnified Party as a result of such
loss, liability, claim, damage, or expense (or actions or proceedings in respect
thereof) 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 statement or omissions that resulted in such loss,
liability, claim, damage, or expense (or actions or proceedings in respect
thereof), as well as any other relevant equitable considerations; provided,
however, that no Person guilty of fraudulent misrepresentation (within the
meaning of Section 11(f) of the Securities Act) shall be entitled to
contributions from any Person that was not guilty of such fraudulent
misrepresentation. The relative fault of the Indemnifying Party and 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.

     The parties hereto agree that it would not be just and equitable if
contributions pursuant to this Section 9(d) were determined by pro rata
allocation or by any other method, of allocation which does not take account of
the equitable considerations referred to above in this Section 9 (d). The amount
paid or payable by an Indemnified Party as a result of any loss, liability,
claim, damage, or expense (or actions or proceedings in respect thereof)
referred to above in this Section 9(d) shall be deemed to include any legal or
other expenses reasonably incurred by such Indemnified Party in connection with
investigating or defending any such action or claim.

        (e) The obligations of each Seller to indemnify and hold harmless Neon
and each other person entitled to indemnity as an Indemnified Party under
Section 9(b), above, is independent of any provision of the Mode 1 Purchase
Agreement and the right of Neon and each such other Person to be indemnified
under Section 9(b) shall not be limited by or otherwise subject to any provision
of the Mode 1 Purchase Agreement. Specifically, by way of example, and not by
way of limitation, such claims shall not be subject to any minimum amount and
such claims may not be asserted against or offset by any portion of the Mode 1
Note.

     10. REPORTING REQUIREMENTS.  Neon agrees that:

        (a) during the Applicable Period, for so long as Neon is subject to the
reporting requirements of Section 13 or 15 of the Exchange Act, Neon will file
the reports required to be filed by it under the Securities Act and Section
13(a) or 15(d) of the Exchange Act and the rules and regulations adopted by the
Commission thereunder;

        (b) if Neon shall cease to be so required to file such reports, it will,
upon the request of any Seller with Registrable Securities covered under a
Registration Statement, take such further action that is reasonable in the
circumstances, including, without limitation, the provision of current public
information as required by Rule 144(c) (or any similar successor provision), to
enable such Seller to sell its Registrable Securities pursuant to Rule 144; and

        (c) periodically furnish to each Seller with Registrable Securities
covered under a Registration Statement forthwith upon written request a written
statement by Neon as to its


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<PAGE>


compliance with the reporting requirements of the Securities Act, the Exchange
Act and/or Rule 144, as appropriate.

     11. MISCELLANEOUS.

        (a) BENEFITS NON-TRANSFERABLE. Notwithstanding anything to the contrary
contained elsewhere in this Agreement or in any other Closing Document, the
obligation of Neon to effect the Registration and, thereafter, to maintain the
effectiveness of the Registration Statement is solely for the benefit of Mode 1
and, subject to Section 1(g), its Permitted Transferees.

        (b) GOVERNING LAW. This Agreement shall be governed by and interpreted
and enforced in accordance with the laws of the State of Delaware as applied to
contracts made and fully performed therein.

        (c) SECTION HEADINGS. All section headings are for convenience only and
shall in no way modify or restrict any of the terms or provisions hereof.

        (d) INTERPRETATION. The masculine (or neuter) pronoun and the singular
number shall include the masculine, feminine and neuter genders and the singular
and plural numbers. All references in the singular or plural shall be deemed to
have been made, respectively, in the plural or singular number as well, as the
context may require.

        (e) COUNTERPARTS. This Agreement may be executed in two or more
counterparts, including, without limitation, execution by facsimile, each of
which shall be deemed an original, and all of which when taken together shall be
deemed to be one and the same instrument. It shall not be necessary in making
proof of this Agreement or any counterpart hereof to produce or account for any
of the other counterparts.

        (f) AMENDMENTS AND WAIVERS. The provisions of this Agreement, including
provisions of this Section 9(f), may not be amended, modified or supplemented,
otherwise than with the prior written consent of Neon and Mode 1.

        (g) NOTICES. All notices and other communications provided for or
permitted hereunder shall be made in writing by hand delivery, registered first
class mail, telex, telecopier, or any courier guaranteeing overnight delivery:
(i) if to Mode 1 addressed as follows: 107 Selden Street, Berlin, Connecticut
06037 and (ii) if to Neon, addressed to Neon's address as set forth in the Mode
1 Purchase Agreement, and thereafter at such other address, notice of which is
given in accordance with the provisions of this Section 9(g).

     All such notices and communications shall be deemed to have been duly
given at the time delivered by hand, if personally delivered; five Business Days
after being deposited in the mail, postage prepaid, if mailed; when answered
back, if telexed; when receipt is acknowledged, if telecopied; and on the next
Business Day, if timely delivered to an air courier guaranteeing overnight
delivery.

        (h) SUCCESSORS AND ASSIGNS. This Agreement shall inure to the benefit of
and be binding upon the successors, assigns and transferees of the parties
hereto, subject to Section 9(a), above, provided, however, that nothing herein
shall be deemed to permit any assignment,


                                       11


<PAGE>


transfer or other disposition of Registrable Securities in violation of the
terms of this Agreement, the Note Purchase Agreement or applicable law. If any
transferee of any Seller shall acquire Registrable Securities, in any manner,
whether by operation of law or otherwise, such Registrable Securities shall be
held subject to all of the terms of this Agreement, and by taking and holding
such Registrable Securities, such Person shall be conclusively deemed to have
agreed to be bound by and to perform all of the terms and provisions of this
Agreement and such Person shall be entitled to receive the benefits hereof.


                  [REMAINDER OF PAGE LEFT INTENTIONALLY BLANK]








                                       12


<PAGE>


         IN WITNESS WHEREOF, the parties hereto, intending to be legally bound
hereby, have duly executed this Registration Rights Agreement on the date first
above written.


Attest:                                  NEON COMMUNICATIONS, INC.


/s/ Barbara Johnson                      By:  /s/ Stephen E. Courter
---------------------------------            ---------------------------------
Name: Barbara Johnson                         Name:  Stephen E. Courter
Admin Assistant and                           Title: Chief Executive Officer
Assistant Secretary


Attest:                                  MODE 1 COMMUNICATIONS, INC.


/s/ Leonard Rodriguez                    By:  /s/ John H. Forsgren
---------------------------------            ---------------------------------
Name: Leonard Rodriguez                       Name:  John H. Forsgren
in house Counsel                              Title: Exec VP and CFO of NU
                                                     as Agent for Mode 1




                         REGISTRATION RIGHTS AGREEMENT
                                 SIGNATURE PAGE


<PAGE>


                                                                       EXHIBIT A


                               ADOPTION AGREEMENT


        This Adoption Agreement ("ADOPTION AGREEMENT") is executed by the
undersigned (the "TRANSFEREE") pursuant to the terms of that certain
Registration Rights Agreement dated as of June 15, 2001 (the "AGREEMENT") by and
among Neon Communications, Inc. and the other parties thereto. Capitalized terms
used but not defined herein shall have the respective meanings ascribed to such
terms in the Agreement. By the execution of this Adoption Agreement, the
Transferee agrees as follows:

        1. ACKNOWLEDGMENT. Transferee acknowledges that Transferee is acquiring
certain securities of the Company (the "Securities"), subject to the terms and
conditions of the Agreement.

        2. AGREEMENT. Transferee (i) agrees that the Securities acquired by
Transferee shall be bound by and subject to the terms of the Agreement, and (ii)
hereby adopts the Agreement with the same force and effect as if Transferee were
originally a party thereto, with the effect that Transferee shall hereafter be
deemed a "Seller" for the purposes of the Agreement.

        3. NOTICE. Any notice required or permitted by the Agreement shall be
given to Transferee at the address listed beside Transferee's signature below.

        EXECUTED AND DATED as of this ____ day of __________________.


                             [NAME OF TRANSFEREE]



                             By:________________________________________________
                             Name:______________________________________________
                             Title:_____________________________________________


                             Social Security Number or Tax ID Number:___________
                             Address:___________________________________________
                             Fax:_______________________________________________