EXHIBIT 99.1


                                                                  EXECUTION COPY

                              AMENDMENT AND WAIVER

         AMENDMENT AND WAIVER (the "Amendment and Waiver"), dated September 8,
1999, to the Agreement and Plan of Merger, dated as of June 22, 1999 (the
"Merger Agreement"), by and among AboveNet Communications Inc., a Delaware
corporation (the "Company"), Metromedia Fiber Network, Inc., a Delaware
corporation (the "Parent"), and Magellan Acquisition, Inc., a Delaware
corporation and wholly owned subsidiary of the Parent ("Merger Sub").

         WHEREAS, the parties to the Merger Agreement desire to amend and waive
certain provisions of the Merger Agreement pursuant to and in accordance with
the terms of Sections 7.3 and 7.4 of the Merger Agreement;

         NOW THEREFORE, in consideration of the agreements contained herein, and
intending to be legally bound hereby, the parties hereto agree as follows:

1.       AMENDMENT. Section 5.21 of the Merger Agreement shall be amended and
         restated in its entirety pursuant to Section 7.3 of the Merger
         Agreement to read as follows:

         "As soon as practicable following the Effective Time and in any event
         no later than September 10, 1999, the Parent shall file with the
         Commission a registration statement on an appropriate form or a
         post-effective amendment to a previously filed registration statement
         under the Securities Act with respect to the Parent Common Stock
         issuable in respect of Company Stock Options and Company Warrants and
         shall use its reasonable best efforts to maintain the current status of
         the prospectus contained therein, as well as comply with any applicable
         state securities or "blue sky" laws, for so long as such options or
         other stock based awards remain outstanding."

2.       WAIVER. The parties hereby agree that this Amendment and Waiver shall
         constitute a waiver for purposes of Section 7.4 of the Merger Agreement
         of the covenant and the condition that the Parent comply with its
         covenant contained in Section 5.21 of the Merger Agreement at or prior
         to the Effective Time.

3.       DEFINED TERMS. Defined terms used in this Amendment and Waiver and not
         otherwise defined shall have the meaning ascribed to those terms in the
         Merger Agreement.



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         IN WITNESS WHEREOF, this Amendment and Waiver has been duly executed
and delivered by the duly authorized officers of the parties to this Amendment
and Waiver as of the date first written above.

                                  ABOVENET COMMUNICATIONS INC.


                                  By:       /s/ Sherman Tuan
                                     -----------------------------------------
                                  Name: Sherman Tuan
                                  Title: Chief Executive Officer




                                  METROMEDIA FIBER NETWORK, INC.


                                  By:       /s/ Howard Finkelstein
                                     -----------------------------------------
                                  Name: Howard Finkelstein
                                  Title: President and Chief Operating Officer



                                  MAGELLAN ACQUISITION, INC.



                                  By:       /s/ Howard Finkelstein
                                     -----------------------------------------
                                  Name: Howard Finkelstein
                                  Title: President and Chief Operating Officer