Many of the network applications today are demanding QoS guaranteed paths which the best effort routing protocols e.g. OSPF cannot calculate, because these protocols are topology driven, do not address many of the constraints by these applications and only calculate shortest paths. In this thesis offline constraint based routing is studied for Open Shortest Path First (OSPFv2) protocol single area network and an offline server is proposed for QoS guaranteed routing. The server builds traffic engineering (TE) database and calculates QoS guaranteed paths on behalf of all the routers in that area. The client routers only do best effort routing for normal data flows with no requirement for QoS guaranteed paths. The client routers use NETCONF protocol to download QoS routes from the offline server (OS). The offline server besides calculating QoS paths also reduces congestion and helps in efficiently utilizing the network resources, for example bandwidth.