Concepts and technologies disclosed herein are directed to a multi-tier fault tolerant network design with Quality of Service (“QoS”) considerations. According to one aspect, a network planning system can identify at least one critical site of a plurality of sites. The critical site is considered to be critical for survivability of a network. The network planning system can construct a topology that connects the plurality of sites. The network planning system can determine a shortest path for each network link in the topology. The network planning system can check a service level agreement to determine a reliability requirement for each link in the topology that is not connected to the critical site. The network planning system can implement a reliable adaptive multipath provisioning algorithm to adaptively determine a bandwidth allocation on each link in the topology based, at least in part, upon the shortest path and the reliability requirement.