Beginning with 4.4.0, the licensing text in ISC DHCP source files needs to be updated to reflect the change to MPL Licensing:

/*
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
*/