《软件定义网络：全面方法第二版》详解与最新发展

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《软件定义网络：全面方法第二版》是一本深入探讨Software Defined Networking (SDN)技术的专业书籍。作者Paul Göransson、Chuck Black和Timothy Culver在书中全面解析了SDN的核心概念，旨在帮助商业决策者理解将部分网络迁移到SDN模型的好处与风险，以及何时适当地集成SDN技术，并如何开发或获取SDN应用。该书强调了开放网络的核心理念，讨论了随着市场成熟，SDN技术如何逐渐与主流网络供应商的产品兼容，特别提到了OpenDaylight控制器的更新内容。控制器章节扩展了对多种南向协议的支持，NETCONF在控制器和设备讨论中的纳入，以及网络功能虚拟化(NFV)的更全面覆盖。此外，书中还涵盖了最新OpenFlow规范版本1.5.1的详细信息。新增的一章专门探讨了NETCONF在SDN中的应用，这有助于读者理解这两种技术的融合。同时，书中也加强了对SDN在光网络中的应用介绍，为计算机网络课程提供了配套的教学支持材料。本书的重要价值在于它不仅提供理论知识，还紧跟行业动态，确保读者能够了解到最新的SDN技术发展和实践。通过阅读这本书，无论是网络专业人员还是对SDN技术感兴趣的读者，都能获得全面而深入的理解，以便在实际项目中有效地应用和管理SDN。

Preface

When we initially conceived of the idea of writing this book, we were motivated in part by the lack of a

single good reference for a comprehensive overview of SDN. Although we were involved professionally

with SDN technologies, even we found information related to SDN to be largely unavailable in any

single comprehensive source. We realized that for the very large numbers of professionals that were

not directly working with SDN but who needed to learn about it, this was a big problem. Thus, our

broad-brush goal in writing this book is to describe the setting that gave rise to SDN, the deﬁning

characteristics that distinguish it from competing technologies, and to explain the numerous signiﬁcant

commercial impacts that this nascent technology is already having. One of the challenges in writing an

early book about such a rapidly evolving technology is that it is a moving target.

The preceding paragraph, written for our ﬁrst edition published 3 years ago, still rings true today.

So many technologies that were off our ﬁrst edition radar are now commonly considered part of SDN.

We have selected to use the words A Comprehensive Approach as part of our title. There are many

competing ideas in use today, all of which wish to jump on the SDN bandwagon. Indeed, the size

of that bandwagon seems ever-expanding. Whatever aspect or type of SDN technology with which

our reader may be required to work, we at least hope that he or she will be able to place it into the

broader SDN context through the reading of this book. For this purpose, we try to discuss a variety of

deﬁnitions of SDN. We hope that no reader takes offense that we were not dogmatic in our application

of the deﬁnition of SDN in this work.

Individuals interested in learning about Software Deﬁned Networks or having a general interest in

any of the following topics:

• networking

• switching

• Software Deﬁned Networks

• OpenFlow

• OpenStack

• OpenDaylight

• Network Virtualization

• Network Functions Virtualization

will ﬁnd this book useful.

Software Deﬁned Networking is a broad ﬁeld that is rapidly expanding. While we have attempted

to be as comprehensive as possible, the interested reader may need to pursue certain technical topics

via the references provided. We do not assume the reader has any special knowledge other than a

basic understanding of computer concepts. Some experience in computer programming and computer

networking will be helpful for understanding the material presented. The book contains a large number

of ﬁgures and diagrams to explain and to illustrate networking concepts that are being deﬁned or

discussed. These graphics help the reader to continue straight through the text without feeling the need

to reach for other references.

The ﬁrst edition of this work was very well received. Over the 3 years since its initial publication,

we have received numerous inquiries from university faculty using the text as the basis for a course.

xxiii

CHAPTER

INTRODUCTION

It is not often that an author of a technology text gets to read about his subject matter in a major

story in a current issue of a leading news magazine. The tempest surrounding Software Deﬁned

Networking (SDN) is indeed intense enough to make mainstream news [1]. The modern computer

network has evolved into a complex beast that is challenging to manage and which struggles to scale

to the requirements of some of today’s environments. SDN represents a new approach to computer

networking that attempts to address these weaknesses of the current paradigm. SDN is a fundamentally

novel way to program the switches utilized in modern data networks. SDN’s move to a highly scalable

and centralized network control architecture is better suited to the extremely large networks prevalent

in today’s mega-scale data centers. Rather than trying to crowbar application-speciﬁc forwarding into

legacy architectures ill-suited to the task, SDN is designed from the outset to perform ﬁne-grained

trafﬁc forwarding decisions. Interest in SDN goes far beyond the research and engineering communities

intrigued by this new Internet switching technology. Another of the early drivers of SDN was to

facilitate experimentation with and the development of novel protocols and applications designed to

address problems related to an Internet bogged down by the weight of three decades of incremental

technological ﬁxes—a problem sometimes called Internet Ossiﬁcation. If SDN’s technological promise

is realized, this will represent nothing short of a tectonic shift in the networking industry, as long-

term industry incumbents may be unseated and costs to consumers may plummet. Along with this

anticipation, though, surely comes a degree of overhype, and it is important that we understand not

only the potentials of this new networking model, but also its limitations. In this work we will endeavor

to provide a technical explanation of how SDN works, an overview of those networking applications

for which it is well-suited and those for which it is not, a tutorial on building custom applications on top

of this technology, and a discussion of the many ramiﬁcations it has on the networking business itself.

This introductory chapter provides background on the fundamental concepts underlying current

state-of-the-art Internet switches, where data plane, control plane and management plane will be deﬁned

and discussed. These concepts are key to understanding how SDN implements these core functions

in a substantially different manner than the traditional switch architecture. We will also present how

forwarding decisions are made in current implementations and the limited ﬂexibility this offers network

administrators to tune the network to varying conditions. At a high level, we provide examples of how

more ﬂexible forwarding decisions could greatly enhance the business versatility of existing switches.

We illustrate how breaking the control plane out of the switch itself into a separate, open-platform

controller can provide this greater ﬂexibility. We conclude by drawing parallels between how the Linux

operating system has enjoyed rapid growth by leveraging the open source development community and

how the same efﬁciencies can be applied to the control plane on Internet switches.

Software Deﬁned Networks. http://dx.doi.org/10.1016/B978-0-12-804555-8.00001-6

2 CHAPTER 1 INTRODUCTION

We next look at some basic packet switching terminology that will be used throughout the text, and

following that we provide a brief history of the ﬁeld of packet switching and its evolution.

1.1 BASIC PACKET SWITCHING TERMINOLOGY

This section deﬁnes much of the basic packet switching terminology used throughout the book. Our

convention is to italicize a new term on its ﬁrst use. For more specialized concepts that are not deﬁned

in this section, they will be deﬁned on their ﬁrst use. Many packet switching terms and phrases have

several and varied meanings to different groups. Throughout the book we try to use the most-accepted

deﬁnition for terms and phrases. Acronyms are also deﬁned and emphasized on their ﬁrst use, and

the appendix on acronyms provides an alphabetized list of all of the acronyms used in this work. An

advanced reader may decide to skip over this section. Others may want to skim this material, and later

look back to refer to speciﬁc concepts.

This terminology is an important frame of reference as we explain how SDN differs from traditional

packet switching. To some degree, though, SDN does away with some of these historic concepts or

changes their meaning in a fundamental way. Throughout this book, we encourage the reader to look

back at these deﬁnitions and consider when the term’s meaning is unchanged in SDN, when SDN

requires a nuanced deﬁnition, and when a discussion of SDN requires entirely new vocabulary.

A Wide Area Network (WAN) is a network that covers a broad geographical area, usually larger

than a single metropolitan area.

A Local Area Network (LAN) is a network that covers a limited geographical area, usually not more

than a few thousand square meters in area.

A Metropolitan Area Network (MAN) is a network that ﬁlls the gap between LANs and WANs.

This term came into use because LANs and WANs were originally distinguished not only by their

geographical areas of coverage, but also by the transmission technologies and speeds that they used.

With the advent of technologies resembling LANs in terms of speed and access control, but with the

capability of serving a large portion of a city, the term MAN came into use to distinguish these networks

as a new entity distinct from large LANs and small WANs.

A Wireless Local Area Network (WLAN) is a LAN in which the transmission medium is air. The

typical maximum distance between any two devices in a wireless network is on the order of 50 m.

While it is possible to use transmission media other than air for wireless communication, we will not

consider these in our use of this term in this work.

The Physical Layer is the lowest layer of the seven layer Open Systems Interconnection (OSI) model

of computer networking [2]. It consists of the basic hardware transmission technology to move bits of

data on a network.

The Data Link Layer is the second lowest layer of the OSI model. This is the layer that provides the

capability to transfer data from one device to another on a single network segment. For clarity, here we

equate a LAN network segment with a collision domain. A strict deﬁnition of LAN network segment

is an electrical or optical connection between network devices. For our deﬁnition of data link layer we

will consider multiple segments linked by repeaters as a single LAN segment. Examples of network

segments are a single LAN, such as an Ethernet, or a point-to-point communications link between

adjacent nodes in a WAN. The link layer includes: (1) mechanisms to detect sequencing errors or bit-

errors that may occur during transmission, (2) some mechanism of ﬂow control between the sender

1.1 BASIC PACKET SWITCHING TERMINOLOGY 3

and receiver across that network segment, and (3) a multiplexing ability that allows multiple network

protocols to use the same communications medium. These three functions are considered to be part of

the logical link control (LLC) component of the data link layer. The remaining functions of the data

link layer are part of the Media Access Control (MAC) component, described separately below.

The MAC layer is the part of the data link layer that controls when a shared medium may be accessed

and provides addressing in the case that multiple receivers will receive the data yet only one should

process it. For our purposes in this book, we will not distinguish between data link layer and MAC

layer.

The Network Layer provides the functions and processes that allow data to be transmitted from

sender to receiver across multiple intermediate networks. To transit each intermediate network involves

the data link layer processes described above. The network layer is responsible for stitching together

those discrete processes such that the data correctly makes its way from the sender to the intended

receiver.

Layer one is the same as the physical layer deﬁned above.

Layer two is the same as the data link layer deﬁned above. We will also use the term L2

synonymously with layer two.

Layer three is the same as the network layer deﬁned above. L3 will be used interchangeably with

layer three in this work.

A port is a connection to a single communications medium, including the set of data link layer and

physical layer mechanisms necessary to correctly transmit and receive data over that link. This link

may be of any feasible media type. We will use the term interface interchangeably with port throughout

this text. Since this book will also deal with virtual switches, the deﬁnition of port will be extended to

include virtual interfaces, which are the endpoints of tunnels.

A frame is the unit of data transferred over a layer two network.

A packet is the unit of data transferred over a layer three network. Sometimes this term is used

more generally to refer to the units of data transferred over either a layer two network (frames) as well,

without distinguishing between layers two and three. When the distinction is important, a packet is

always the payload of a frame.

A MAC address is a unique value that globally identiﬁes a piece of networking equipment. While

these addresses are globally unique, they serve as layer two addresses, identifying a device on a layer

two network topology.

An IP Address is a nominally unique value assigned to each host in a computer network that uses

the Internet Protocol for layer three addressing.

An IPv4 Address is an IP address that is a 32-bit integer value conforming to the rules of Internet

Protocol Version 4. This 32-bit integer is frequently represented in dotted notation, with each of the

4 bytes comprising the address represented by a decimal number from 0 to 255, separated by periods

(e.g., 192.168.1.2).

An IPv6 Address is an IP address that is a 128-bit integer conforming to the rules of Internet Protocol

Version 6, introducing a much larger address space than IPv4.

A switch is a device that receives information on one of its ports and transmits that information out

one or more of its other ports, directing this information to a speciﬁed destination.

A circuit switch is a switch where contextual information specifying where to forward the data

belonging to a circuit (i.e., connection) is maintained in the switch for a prescribed duration, which

may span lapses of time when no data belonging to that connection is being processed. This context

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