Flow Table Timeout And Path Tracing For SDN

Software defined network(SDN)is an emerging network architecture which decouples control plane from forwarding plane.In the forwarding plane,the switches and other network equipment are responsible for packet forwarding and processing.In the control plane,there is a logic centralized controller.It interfaces with the switch over a unified protocol such as OpenFlow protocol and installs the flow entries into the switch to guide the packet forwarding and processing.With the rapid development of SDN,it benefits a lot to the network management,while it also introduces many problems and challenges,like scalability,network fault diagnosis,etc.All need to be addressed and optimized.For the scalability of the forwarding plane,this paper mainly studies the timeout of the flow entry,and puts forward a dynamic optimization scheme.For the fault diagnosis of the network,this paper focuses on the path tracing of the network flow,and proposes the implementation scheme based on multiple flow tables.The contributions of this work are as follows:OpenFlow protocol uses timeout mechanism to manage the lifetime of flow entries.If there is no matching flow within a specified time,the flow entry will be removed.For too large timeout,the flow entries will stay in the flow table for too long time and result in unnecessary occupation of flow table.For too small timeout,it will produce too many packet-in events and cause overload on the controller.In practical application,the flow table resources are very precious and the controller processing capacity is also quite limited.Hence,the fixed timeout mechanism will bring a lot of disadvantages inevitably.For this,this paper embarking from the actual network traffic,puts forward the dynamic timeout algorithm which is different from the previous algorithms.This algorithm is not against the OpenFlow protocol and does not need to collect the data which is hard to obtain,but can assign suitable timeout to different flows.Finally,based on real network traffic,we do a series of experiments.The results show that the dynamic timeout algorithm proposed in this paper will not increase the pressure of the controller obviously,but can significantly reduce the consumption of the flow table resources.The emergence of SDN makes the network control more fine-grained.SDN allows network operators to use the controller to well translate the abstract strategy into the specific function,which is installed in the corresponding switches in the form of flow entries.Therefore,the network operator is very necessary to confirm that the specific function is consistent with the high-level strategy.It is badly in need of new tools to detect and locate the problem especially in the network error configuration or fault.In the past,a lot of researches locate the network fault by collecting the details of the flow entries.But it is too idealistic because the actual operation in the network will be different from what is expected.To solve these problems,this paper puts forward the path tracing scheme based on the multiple flow tables.The scheme distinguishes the probe packet from the normal work flow with flag bit.Based on the characteristics of multiple flow tables,this scheme uses the probe packet to obtain the real trajectory of the work flow without changing its original forwarding behavior so as to quickly locate the fault of the network.