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                                                                     Exhibit 5.1
                                                                     -----------

                                  HALE AND DORR
                               Counsellors at Law
                                 60 State Street
                           Boston, Massachusetts 02109

                               September 27, 1996

Shiva Corporation
28 Crosby Drive
Bedford, Massachusetts 01730

Ladies and Gentlemen:

     We have assisted in the preparation of a Registration Statement on Form S-8
(the "Registration Statement") to be filed with the Securities and Exchange
Commission relating to an aggregate of 2,059 shares (the "Shares") of Common
Stock, $.01 par value per share, of Shiva Corporation, a Massachusetts
corporation ("Shiva"), issued to Sunil Bopardikr and Richard Maddox and Celia
Maddox pursuant to options granted under the Airsoft, Inc. ("Airsoft") 1993
Stock Plan and assumed by Shiva pursuant to the Agreement and Plan of Merger
dated as of June 16, 1996 by and among Shiva, SV Acquisition Corp. and Airsoft
(collectively, the "Options").

     We have examined the Restated Articles of Organization of the Company, as
amended, the Restated By-laws of the Company, as amended, and originals, or
copies certified to our satisfaction, of all pertinent records of the meetings
of the directors and stockholders of the Company, the Registration Statement and
such other documents relating to the Company as we have deemed material for the
purposes of this opinion.

     In examination of the foregoing documents, we have assumed the genuineness
of all signatures and the authenticity of all documents submitted to us as
originals, the conformity to original documents of all documents submitted to us
as certified, photostatic or facsimile copies, and the authenticity of the
originals of any such documents.

     Based upon and subject to the foregoing, we are of the opinion that the
Shares were duly authorized and legally issued and are fully paid and
nonassessable.

     We hereby consent to the filing of this opinion with the Securities and
Exchange Commission in connection with the Registration Statement.

                                                     Very truly yours,

                                                     /s/ Hale and Dorr
                         
                                                     HALE AND DORR