SDN交换机转发规则TCAM存储优化综述  

A Survey on TCAM Storage Optimization for SDN Switch Forwarding Rules

作　　者：陈志鹏 徐明伟[1,2] 杨芫 CHEN Zhi-Peng;XU Ming-Wei;YANG Yuan(Department of Computer Science&Technology,Tsinghua University,Beijing 100084;Beijing National Research Center for Information Science and Technology,Beijing 100084)

机构地区：[1]清华大学计算机科学与技术系,北京100084 [2]北京信息科学与技术国家研究中心,北京100084

出　　处：《计算机学报》2021年第7期1341-1362,共22页Chinese Journal of Computers

基　　金：国家自然科学基金(61625203,61832013);国家重点研发计划(2017YFB0801701)资助.

摘　　要：软件定义网络(SDN)将传统网络的控制平面和数据平面解耦,通过控制平面的控制器灵活地对网络进行管理,目前应用最广泛的控制协议是OpenFlow.三态内容寻址存储器(TCAM)查找速度快、支持三态掩码存储,在SDN网络中应用广泛.但TCAM成本高、功耗大,并且在存储含有范围字段匹配域的规则时候存在范围膨胀问题,因此交换机中可存储的转发规则数量,尤其是匹配域的数量和类型都比较多的OpenFlow规则数目非常有限,这成为约束SDN网络大规模扩展和应用的瓶颈.研究机构从不同角度提出了针对SDN中交换机转发规则的TCAM存储优化方案.本文从转发规则存储架构优化、本地交换机转发规则压缩、全局转发规则动态优化以及控制器参与的网络转发规则管理四个角度总结了相关研究工作,并提出了适合未来SDN网络的转发规则存储的综合优化方案.Software Defined Networking(SDN)makes network control more convenient and more flexible by decoupling the control plane and the data plane.An controller interacts with switches through specific control protocols such as OpenFlow,and rules for forwarding packets will be installed or updated in the switches.Ternary Content Addressable Memory(TCAM)is the most widely used storage medium for forwarding rules in modern SDN switches due to its fast lookup.TCAM supports parallel lookup and outputs the results in one clock cycle.Besides,TCAM can store rules with wildcard directly,which is common in OpenFlow networks.However,TCAM suffers the shortcomings of high cost,high power consumption,and the problem of range expansion when storing range-field-contained forwarding rules.As is known to all,OpenFlow has been the most widely used control protocol at present,and the OpenFlow protocol standard has specified more than 40 match fields according to its latest version.The number of match fields is still growing to achieve more qualitive network functions.Therefore,forwarding rules in an OpenFlow switch specify longer bits and occupy more room in TCAM than those in a traditional L2 or L3 switch.Therefore,the number of forwarding rules that TCAM can store is very limited,especially the OpenFlow forwarding rules with various match fields.This becomes a bottleneck of the SDN network development.In order to efficiently utilize the limited TCAM storage resources for forwarding rules,it is necessary to optimize the storage of forwarding rules in SDN networks.This paper mainly analyses and summarizes the storage optimization mechanisms of forwarding rules in SDN networks from such four perspectives as forwarding rule storage architecture optimization,compression of forwarding rules locally and globally,management of forwarding rules with the participation of controller(s).First,forwarding rule storage architecture optimization aims at improving lookup circuit structure in switches,replacing TCAM with other storage media,or applying a

关 键 词：软件定义网络(SDN) 三态内容寻址存储器(TCAM) 转发规则存储优化 

分 类 号：TP393[自动化与计算机技术—计算机应用技术]