Phát triển các yêu cầu về mạngTrước khi tìm kiếm các chi tiết hơn tại SDNs, chúng ta hãy xem xét các yêu cầu về mạng phát triển dẫn đến một nhu cầu cho một phương pháp phản ứng linh hoạt, để kiểm soát dòng chảy giao thông trong mạng hoặc Internet.One key leading factor is the increasingly widespread use of Server Virtualization. In essence, server virtualization masks server resources, including the number and identity of individual physical servers, processors, and operating systems, from server users. This masking makes it possible to partition a single machine into multiple, independent servers, conserving hardware resources. It also makes it possible to migrate a server quickly from one machine to another for load balancing or for dynamic switchover in the case of machine failure. Server virtualization has become a central element in dealing with "big data" applications and in implementing cloud computing infrastructures. But it creates problems with traditional network architectures (for example, refer to [2]). One problem is configuring Virtual LANs (VLANs). Network managers need to make sure the VLAN used by the Virtual Machine is assigned to the same switch port as the physical server running the virtual machine. But with the virtual machine being movable, it is necessary to reconfigure the VLAN every time that a virtual server is moved. In general terms, to match the flexibility of server virtualization, the network manager needs to be able to dynamically add, drop, and change network resources and profiles. This process is difficult to do with conventional network switches, in which the control logic for each switch is co-located with the switching logic.
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