As Saurabh said; we can use static and Dynamic Routing in one network. However Dyanmic Routing is used to have the best path no matter what the status of the physical links.All routing protocols have some sort of shortest-path or lowest-cost or best-choice algorithm to help you weigh all the options available. Static routing can be used in a small network to reduce the work of the network administrator or to use a particular route only to forward the packet; we need static routing.