EXHIBIT 5.1

                    [Letterhead of Kelley Drye & Warren LLP]



                                February 9, 2001

Nx Networks, Inc.
13595 Dulles Technology Drive
Herndon, Virginia  20171

        Re:  REGISTRATION STATEMENT ON FORM S-3

Ladies and Gentlemen:

                  We have  acted as  special  counsel to Nx  Networks,  Inc.,  a
Delaware  corporation  (the  "Company"),  in connection with the filing with the
Securities  and  Exchange   Commission  (the  "Commission")  of  a  Registration
Statement on Form S-3 (the "Registration Statement") under the Securities Act of
1933, as amended (the "Securities Act"),  pertaining to the proposed offering of
an aggregate of 7,317,022 shares of the Company's  common stock,  $.05 par value
per share (the  "Shares"),  including  an  aggregate  of  237,613  shares of the
Company's  common stock issuable upon exercise of certain warrants issued by the
Company (the "Warrants"), as described in the Registration Statement.

                  In  connection  with  this  opinion,  we  have  examined  such
documents and have  reviewed such matters of law as we have deemed  necessary or
appropriate  for the purpose of  rendering  this  opinion.  For purposes of this
opinion,  we have assumed the  authenticity of all documents  submitted to us as
originals,  the  conformity  to  originals of all  documents  submitted to us as
certified or  photostatic  copies and the  authenticity  of the originals of all
documents  submitted to us as copies. We have also assumed the legal capacity of
all natural persons, the genuineness of all signatures on all documents examined
by us, the  authority of such persons  signing on behalf of the parties  thereto
other than the Company and the due authorization,  execution and delivery of all
documents by the parties  thereto other than the Company.  As to certain factual
matters material to the opinion  expressed  herein, we have relied to the extent
we deemed proper upon representations, warranties and statements of officers and
other  representatives of the Company. Our opinion expressed below is subject to
the  qualification  that we express no opinion as to any law of any jurisdiction
other than the corporation laws of the State of Delaware and the federal laws of
the United  States of America.  Without  limiting the  foregoing,  we express no
opinion with respect to the applicability thereto or effect of municipal laws or
the  rules,  regulations  or orders of any  municipal  agencies  within any such





Nx Networks, Inc.
February 9, 2001
Page 2



state. Our opinion expressed below is further subject to the qualification  that
the  issuance  of  1,717,960  of the Shares is subject  to the  approval  of the
stockholders  of the Company in  accordance  with the rules of the Nasdaq  Stock
Market and the corporation laws of the State of Delaware.

                  Based  upon  and  subject  to  the  foregoing  qualifications,
assumptions and  limitations and the further  limitations set forth below, it is
our opinion  that the Shares  previously  issued by the  Company  have been duly
authorized,  validly issued, fully paid and are non-assessable,  that the Shares
underlying the Warrants have been duly  authorized and, upon proper exercise and
proper  payment  of the  exercise  price  thereof  pursuant  to the terms of the
Warrants,  will be validly issued,  fully paid and non-assessable,  and that the
1,717,960  Shares to be issued upon approval of the stockholders of the Company,
have been duly  authorized  and, upon such approval in accordance with the rules
of the Nasdaq  Stock Market and the  corporation  laws of the State of Delaware,
will be validly issued, fully paid and non-assessable.

                  This  opinion  is  limited to the  specific  issues  addressed
herein,  and no opinion may be inferred or implied beyond that expressly  stated
herein.  We assume no obligation to revise or supplement this opinion should the
present  corporation  laws of the State of Delaware  or the federal  laws of the
United States of America be changed by legislative action,  judicial decision or
otherwise.

                  We hereby  consent to the filing of this  letter as an exhibit
to the Registration  Statement.  In giving such consent, we do not admit that we
are in the category of persons whose consent is required  under Section 7 of the
Securities  Act or the  rules  and  regulations  of the  Commission  promulgated
thereunder.

                  This opinion is furnished to you in connection with the filing
of the  Registration  Statement  and is not to be used,  circulated,  quoted  or
otherwise relied upon for any other purpose.

                                           Very truly yours,

                                           Kelley Drye & Warren LLP




                                           By:  Randi-Jean Hedin
                                                ________________________________
                                                A Member of the Firm