This EMPLOYMENT AGREEMENT (this "Agreement") is dated as of June 16, 2000 and effective as of the
consummation of the merger among Concentric Network Corporation ("Concentric"), NEXTLINK
Communications, Inc. ("Nextlink") and NM Acquisition Corp. ("Employer") pursuant to the Agreement and Plan
of Merger and Share Exchange Agreement, dated as of January 9, 2000 and as amended and restated as of May
10, 2000, by and among Concentric, Employer, Eagle River Investments, L.L.C., Craig O. McCaw and NM
Acquisition Corp. (the "Effective Date"), between Henry R. Nothhaft ("Executive") and Employer.
In consideration of the premises and the mutual covenants hereinafter set forth and other good and valuable
consideration, the receipt and sufficiency of which is hereby acknowledged, the parties hereto hereby agree as
1. EMPLOYMENT OF EXECUTIVE
Employer hereby agrees to employ Executive, and Executive hereby agrees to be and remain in the employ of
Employer, upon the terms and conditions hereinafter set forth.
2. EMPLOYMENT PERIOD
Subject to earlier termination as provided in section 5, the term of Executive's employment under this Agreement
shall commence as of the Effective Date and shall continue for a period of two (2) years (the "Initial Employment
Period"). Unless either party gives written notice of an intent not to extend the Initial Employment Period, or any
extension thereof, at least one year prior to the expiration of the Initial Employment Period, or any extension
thereof, the Initial Employment Period, and any extension thereof, shall be automatically extended for an
additional one-year period such that until a notice of intent not to extend is given by either party, the unexpired
term of the Agreement is always at least one full year (the Initial Employment Period and any extension thereof is
hereafter referred to as the "Employment Period").
3. DUTIES AND RESPONSIBILITIES
During the Employment Period, Executive shall d