探索SDN：软件定义网络的革命

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软件定义网络（Software Defined Network，SDN）是一种新兴的网络架构理念，它将网络控制平面与转发平面分离，使得网络设备的控制功能可以由软件进行集中管理和配置。这一创新思想旨在提高网络灵活性、可编程性和效率。《SDN：软件定义网络》是由Thomas D. Nadeau和Ken Gray合著的一本书，于2013年出版，版权归两人所有。该书深入探讨了SDN的核心概念和技术细节，包括但不限于以下几个方面： 1. **网络架构变革**：传统网络设计中，控制和转发功能通常在硬件设备上紧密耦合。SDN通过引入软件控制层，允许网络管理员通过统一的接口对网络进行全局管理和配置，打破了这种耦合，提高了网络的可扩展性和易管理性。 2. **开放标准与API**：SDN强调标准化和开放接口，如OpenFlow是其中最著名的API，它定义了控制器如何与网络设备通信，实现灵活的流量控制和策略部署。 3. **网络自动化**：SDN使得网络配置变得自动化，能够快速响应业务需求变化，减少了人为错误和配置复杂性。 4. **网络服务和灵活性**：通过软件定义，网络服务可以更容易地被创建、修改和删除，提高了网络服务的动态性，支持了云计算和虚拟化环境的需求。 5. **安全性与隔离**：SDN提供了新的安全视角，允许对网络流量进行更精细的控制和监控，有助于更好地防止恶意攻击和数据包泄露。 6. **实践案例和部署指南**：书中还可能包含实际的部署案例和最佳实践，帮助读者理解和应用SDN技术到实际网络环境中。《SDN：软件定义网络》作为一本权威的教程，不仅适合网络工程师、系统管理员，也对那些关注网络演进的IT专业人士具有参考价值。该书的英文原版无水印，表明其内容严谨且专业，同时提供了在线版本供读者方便查阅。如果你对SDN的理论背景、实施方法或未来趋势感兴趣，这本书将是你的理想学习资源。如果你正在寻找关于SDN技术的深入理解或者希望通过实践来掌握这个领域的知识，这本书的First Edition发布日期为2013年8月7日，修订历史记录显示其持续更新以反映最新的技术和行业进展。

on the controller that can speak to many different devices. Different vendors, eras of

equipment, and classes of equipment (e.g., transport, simple switches, wireless base

stations, subscriber termination gateways, peering routers, core routers, and servers)

all are on the trajectory to be able to be programmed by the SDN protocols that plug

into the bottom of the controller. The programmer only uses the APIs on the top of the

controller to automate, orchestrate, and operate the network. This doesn’t necessarily

mean there is a grand unification theory of controllers and one to serve all layers and

functions of networking, but what it does mean is that the network now has been ab‐

stracted and is being programmed off box. Thus, when integrated into an IaaS (Infra‐

structure as a Service) layer in a stack, OSS, or IT system, the network is being automated

and orchestrated as fast as users log onto the net and as fast as workloads are being spun

up on servers.

The use of new tooling practices typically utilized by system administrators and new

available to network operators are related to the whole SDN movement. Tools such as

Puppet, Chef, CFEngine, and others are being used to automate and orchestrate the

network in new ways as plug-ins can now be created to utilize the network data via the

open interfaces of the network. Controller APIs also allow for easier and faster ways to

build and apply policy across the network in multiple languages and with integration

into existing tools such as IDEs (NetBeans, Eclipse, et al.). This allows for a better user

experience for network engineers versus the traditionally used CLI model.

Before we dig into examples, it’s important to understand what SDN actually solves and

why there is a shift to this particular architecture. As networks evolve and new services

are deployed, it’s critical to implement new ways for users to more easily provision and

orchestrate network resources in real time. By implementing this, cost can be reduced

by the automation of moving resources around faster and more reliably, and by allowing

the network to respond directly to a request from an application (versus the intervention

by a human). This allows for operators to use programmatic (scalable) control versus

manual to create and apply these services in a way that is simpler than a command-line

interface. Additionally, it enables the ability to utilize new resources from the network

(user data, traffic path information, etc.) and create new types of applications that can

control policy for the network in a scalable fashion. It also allows for the optimization

of infrastructure, services, and applications by allowing for new network data and ca‐

pabilities to be extended and applied into the aforementioned architecture, creating new

ways to not only optimize existing applications but also to insert new services or offer‐

ings that can provide a better user experience or create a new offering or advanced

feature that could be monetized.

As SDN evolves, it’s important to look at some implementations to understand why it’s

so critical for multiple industries (e.g., video delivery, user services and mobile, cable

and broadband, security, and provider edge) to embrace. Where SDN reaches its po‐

tential, however, is when you look at it for not just programming the network functions

and scaling those across your infrastructure, but also for actually tying server, storage,

xiv | Foreword by David Ward

and the network together for new use cases. In this case, systems can actually interact

with each other, allowing for more infrastructure flexibility, whether physical, virtual,

or hybrid.

Traffic policy and rerouting based on network conditions and/or regulation shifts are

also common applications, as are the insertion of new services or data into applications

that may be able to more clearly prioritize bandwidth for a user that pays a premium

amount for faster connection speeds. When you apply SDN and a centralized manage‐

ment plane that is separate from the data plane, you can more quickly make decisions

on where data traffic can be rerouted, as this can occur programmatically with software

interfaces (APIs), versus on-the-box CLI methodology.

One advanced use case is the hybrid cloud. In this case, an application may run in a

private cloud or data center yet utilize the public cloud when the demand for computing

capacity spikes or cost can be reduced. Historically, cloud bursting was typically used

only in environments with non-mission critical applications or services, but with the

network tie-in and software principles applied, the use case shifts. Applications now

remain in compliance with the IT organizations’ policies and regulations. The applica‐

tion can also retain its dependency model if it is reliant on different data or information

that it typically has on premises versus off, or in the public cloud environment. It also

allows for the application to run across different platforms regardless of where the ap‐

plication was built.

As we look at SDN, we must also consider Network Functions Virtualization and how

this ties into the broader infrastructure and virtualization picture. The transition from

physical to virtual is one that is leading many of these changes in the industry. By tying

the hardware (physical) to software (virtual), including network, server, and storage,

there’s the opportunity to virtualize network services and have them orchestrated as fast

as any other workload. Tie this via programmatic interfaces to the WAN, and you can

absolutely guarantee service delivery. SDN coupled with NFV is a pivotal architectural

shift in both computing and networking. This shift is marked by dynamic changes to

infrastructure to closely match customer demand, analytics to assist in predicting per‐

formance requirements, and a set of management and orchestration tools that allow

network functions and applications to scale up, down, and out with greater speed and

less manual intervention. This change affects how we build cloud platforms for appli‐

cations and at the most basic level must provide the tools and techniques that allow the

network to respond to changing workload requirements as quickly as the platforms that

leverage them. It also allows workload requirements to include network requirements

and have them satisfied.

It’s important to note that not all networks are the same, and that’s why it’s critical to

understand the importance of the underlying infrastructure when abstracting control

from the network—either from physical or virtual devices. Network Functions Virtu‐

alization is simply the addition of virtual or off-premises devices to augment traditional

Foreword by David Ward | xv

infrastructure. However, the tie to both the on- and off-premises offerings must be

considered when running applications and services to ensure a seamless experience not

just for the organization running the applications or services but also for the consumer

of the services (whether they be enterprise and in-house users or external customers).

So why should you care? From a technical perspective, SDN allows for more flexibility

and agility as well as options for your infrastructure. By allowing data to be controlled

centrally and tied into not just the network, but also the storage and server, you get a

more cohesive view on performance, speed, traffic optimization, and service guarantees.

With programmatic interfaces (APIs) that can be exposed in multiple languages and

utilized with tools, your operators and administrators can more quickly respond to the

demand of the business side of the house or external customer needs. They can now

apply policies for other development organizations in-house to allow them network

data to more effectively spin up server farms or even build applications with network

intelligence built in for faster, better performing applications. By allowing for the data

to be exposed in a secure and scalable way, the entire IT organization benefits, and with

faster development and deployment cycles and easier delivery of new services, so too

does the business. The promise that SOA gave developers—write once, run anywhere

—can now be fully realized with the underlying network’s ability to distribute infor‐

mation across the enterprise, access, WAN, and data center (both physical and virtual).

This allows for applications to break free from the boundaries of the OSS and manage‐

ment platforms that had previously limited their ability to run in different environments.

The IT industry is going through a massive shift that will revolutionize the way users

build, test, deploy, and monetize their applications. With SDN, the network is now closer

to applications (and vice versa), allowing for a new breed of smarter, faster, and better

performing applications. It enables the network to be automated in new ways, providing

more flexibility and scalability for users, and unleashes the potential for business cost

savings and revenue-generating opportunities. It’s a new era in networking and the IT

industry overall, and it will be a game-changing one. Check out this book—it’s required

reading.

—David Ward

CTO, Cisco Systems

xvi | Foreword by David Ward

2. http://www.gartner.com/technology/research/methodologies/hype-cycle.jsp

you can’t easily see. Under the waterline, some very muscular feet are paddling away to

move that duck along. In many ways, this is analogous to the progress of software-

defined networks.

The surface view of SDN might lead the casual observer to conclude a few things. First,

defining what SDN is, or might be, is something many organizations are frantically

trying to do in order to resuscitate their business plans or revive their standards-

developing organizations (SDOs). Second, that SDN is all about the active rebranding

of existing products to be this mythical thing that they are not. Many have claimed that

products they built four or five years ago were the origins of SDN, and therefore ev‐

erything they have done since is SDN, too.

Along these lines, the branding of seemingly everything anew as SDN and the expected

hyperbole of the startup community that SDN has been spawning for the past three or

four years have also contributed negatively toward this end.

If observers are predisposed by their respective network religions and politics to dismiss

SDN, it may seem like SDN is an idea adrift.

Now go ahead and arm yourself with a quick pointer to the Gartner hype-cycle.

understand that perspective and can see where that cycle predicts things are at.

Some of these same aspects of the present SDN movement made us lobby hard for the

glitter-horned unicorn just to make a point—that we see things differently.

For more than two years, our involvement in various customer meetings, forums, con‐

sortia, and SDOs discussing the topic, as well as our work with many of the startups,

converts, and early adopters in the SDN space, leads us to believe that something worth

noting is going on under the waterline. This is where much of the real work is going on

to push the SDN effort forward toward a goal of what we think is optimal operational

efficiency and flexibility for networks and applications that utilize those networks.

There is real evidence that SDN has finally started a new dialogue about network pro‐

grammability, control models, the modernization of application interfaces to the net‐

work, and true openness around these things.

In that light, SDN is not constrained to a single network domain such as the data center

—although it is true that the tidal wave of manageable network endpoints hatched via

virtualization is a prime mover of SDN at present. SDN is also not constrained to a single

customer type (e.g., research/education), a single application (e.g., data center orches‐

tration), or even a single protocol/architecture (e.g., OpenFlow). Nor is SDN constrain‐

ed to a single architectural model (e.g., the canonical model of a centralized controller

and a group of droid switches). We hope you see that in this book.

xviii | Preface

www.allitebooks.com

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