This paper is divided into four parts: the first part of the SDN overview; the second part: Openflow technology and its related components and research progress; the third part: SDN problems and solutions; the fourth part: SDN application deployment.
Part 1: Overview of SDN:SDN, software-defined network, separates the control plane and data plane of the network, providing a new solution for R&D network new applications and future Internet technologies.
Why is SDN appearing?1. The drawbacks of traditional networks
Internet access methods and network role positioning have undergone fundamental changes. Mobile access and Internet of Things have become the main access methods for the Internet. Cloud computing has become the main Internet computing model. Multimedia sharing applications and social networks have become new applications for the Internet. The network has become an information platform for information collection, transmission, storage and processing. However, this makes the IP/address-centric, TCP/IP architecture of peer-to-peer communication face enormous challenges in terms of scalability, dynamics, and security controllability.
Scalability: The proliferation of traffic and the rapid expansion of routing tables have affected the scalability of traditional networks. The root cause lies in the peer-to-peer communication mode with the IP address as the core. NDN/CDN
Dynamic: The increasing popularity of portable mobile terminals and the emergence of the Internet of Things have led to explosive growth in the number of low-smart terminals. Mobile-centric network structure (security mechanism + global name resolution)
Security Controllability: By extending network protocols (IPsec, SSL), adding security devices (firewalls).
PS: In the peer-to-peer architecture where the IP address is the core, the service resources and the physical network lack mutual mutual understanding, such as the problems encountered by P2P.
2, the defect of the router
The core routers of the network continue to expand the functions of bearers, such as packet filtering, differentiated services, multicast, quality of service, traffic engineering, etc. The "dumb" and "simple" data forwarding units originally defined by routers have become bloated. Today's routers can only open a small number of functions through command line interfaces, etc. It is difficult for researchers to test and deploy new network architectures and network technologies in real networks.
Part II: Progress of penflow technology and its related components and researchOpenflow, narrowly defined SDN, refers to one of the various communication protocols between the SDN control plane and the data plane, and is a specific implementation of SDN. When SDN was originally proposed as a prototype of SDN, it was mainly composed of Openflow switch and controller. Initially proposed SDN is to try to use a centralized controller, so that network administrators can easily define network flow-based security control policies and apply these policies to various network devices to achieve security for the entire network. control.
The Openflow switch consists of three parts: a flow table, a secure channel, and an openflow protocol.
1. Flow table: In order to improve the query efficiency of the traffic, the current flow table query obtains the corresponding operation through the multi-level flow table and the pipeline mode. The flow table entry mainly includes: a matching domain, a counter, and an operation. The structure of the matching domain contains many matches, covering most of the identity of the link layer, network layer, and transport layer.
2, Openflow protocol, with the continuous development of Openflow protocol, VLAN, MPLS, ipv6 and other protocols have gradually expanded to the Openflow standard.
3, Openflow adopts the matching and forwarding mode of the flow, so the router and the switch are no longer distinguished in Openflow, and the second is collectively referred to as the Openflow switch.
The secure channel is the interface that connects the Openflow switch to the controller. Through this interface, the controller configures and manages the openflow switch according to the format specified by the Openflow protocol.
Currently, there are two versions of Openflow switches based on software, which are deployed in Linux systems: User space-based software Openflow switches are easy to operate and easy to modify, but have poor performance; based on kernel space software, Openflow switches are faster. Virtualization services are provided, but the actual modifications and operations are complex.
Controller:
1. In the NOX-based Openflow network, NOX is the control center. The application running on the NOX manages and controls the entire network by calling the global data in the network view and operating the Openflow switch. NOX implements the basic control functions of the network, provides the API's basic control platform for the Openflow network, but fails to provide sufficient reliability and flexibility to meet the scalable requirements.
2. In order to enable the controller to be deployed directly in the real network, to solve the problem of control sharing of multiple controllers to the openflow switch, and to meet the actual needs of network virtualization, the flowvisor implements network virtualization between the switch and the controller. Layers, a solid hardware forwarding plane can be shared by multiple logical network slices, each with different forwarding policies. In this mode, multiple controllers can simultaneously control one switch, and multiple test networks can run simultaneously on a real network.
SDN features:
The application layer invokes the northbound interface of the control layer to implement applications with different functions according to the application requirements of the network. Through this software model, network administrators can configure, manage, and optimize the underlying network resources through dynamic SDN applications to achieve a flexible and controllable network. This is also the most important manifestation of SDN openness and programmability.
Part III: Problems and Solutions for SDN1. The design problem of the SDN forwarding plane. As the Openflow protocol is released continuously, the flow table of the switch also changes from the original single-table structure to the multi-table structure. The matching entries of the flow table entries also support ipv6, MPLS, etc., which means The structure of Openflow switches is more complicated.
2. Scalability of the control plane: As the network traffic increases, a multi-controller solution is needed, and how the number of control units and the network state between them are achieved and how to achieve interaction requires further research.
3. Consistency of SDN control logic. Although the control plane can centrally deploy control logic to the entire network, the data plane forwarding device is still a distributed system. There may be delays, it is difficult to ensure consistency, and it may cause problems of open circuit and packet loss.
4. The computing pressure is high, the software complexity is high, and the system stability has hidden dangers: in order to realize the programmability of the network, the application will be given a lot of control over the environment, which easily leads to system collapse.
5, the controller interface has not been standardized
6. The inherent security risks of centralized network control. The uniqueness of SDN security issues lies in the concentration and openness of SDN management. Control plane security (listening), application layer security (worms, malware), through the authorization, access control, etc. to solve the problem of the control level, through the programming interface provided by the controller to identify the application layer application.
7. Market interest
Part IV: Application Deployment of SDN:Application for campus network: realize network virtual partitioning and mobile management.
Data center-oriented deployment
Application for network management
Application for security control
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