 as open shortest path first (OSPF). The main problem with the shortest-path routing policy is that it does not consider the network resilience (protection) factor. To maximize the routing, one can develop an algorithm with the objective of constructing a shortest-path tree. Among all possible shortest-path trees, we can find the one that results in best resilience compared to other shortest-path trees. The effect of protection depends on both on the selection of the pri- mary paths and the choice of the controller location. To get a sense of how these two factors affect the protection metrics in an SDN, we make some calculations in two example networks, with the topology of Internet2 [88] network in Figure 4.12 and a typical Fat-tree like data center network in Figure 4.13. Figure 4.12 shows the Internet2 topology with 10 nodes and 13 edges. Here we illustrate two examples of controller selection, 4 Software-Defined Networks Principles and Applications Unprotected Controller Tree of primary paths Edges Figure 4.12 Example of Internet2 network protection. Unprotected Controller Tree of primary paths Edges Figure 4.13 Example of Fat-tree network protection. deploying controller on node 2 and node 3. The location of the controller is shown in rectangular box. For each controller deploy- ment, we compute the shortest path tree to all other nodes (switches), rooted in the controller. The primary paths in the tree are shown in solid lines. For each switch, we compute its backup path. The nodes without any protection are shown in circles. In this example, we 4.4 SDN Management observe that the upper case is a better solution, since only two nodes are unprotected. In particular, node 5 is protected by node 8 in the upper figure but not in the bottom figure since it is the parent of node 8 in the primary path. OpenFlow type of SDN also raises a large amount of interests in enterprise and data center networks. Figure 4.13 shows another example in Fat-tree like data center networks, containing 20 nodes and 32 links. Simila