Top-Down Network Design / Edition 3

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Overview

Top-Down Network Design, Second Edition, is a practical and comprehensive guide to designing enterprise networks that are reliable, secure, and manageable. Using illustrations and real-world examples, it teaches a systematic method for network design that can be applied to campus LANs, remote-access networks, WAN links, and large-scale internetworks.

You will learn to analyze business and technical requirements, examine traffic flow and QoS requirements, and select protocols and technologies based on performance goals. You will also develop an understanding of network performance factors such as network utilization, throughput, accuracy, efficiency, delay, and jitter. Several charts and job aids will help you apply a top-down approach to network design.

This Second Edition has been revised to include new and updated material on wireless networks, virtual private networks (VPNs), network security, network redundancy, modularity in network designs, dynamic addressing for IPv4 and IPv6, new network design and management tools, Ethernet scalability options (including 10-Gbps Ethernet, Metro Ethernet, and Long-Reach Ethernet), and networks that carry voice and data traffic.

Top-Down Network Design, Second Edition, has a companion website at http://www.topdownbook.com, which includes updates to the book, links to white papers, and supplemental information about design resources.


Keeping in mind customer's needs, goals and constraints, this practical, comprehensive network design guide provides an excellent starting point for CCIE design solutions. Author Priscilla Oppenheimer takes a top-down approach to logical and physical network design criteria, as she analyzes business and technical goals. This is not an introductory networking publication by any means; it is intended for network professionals with experience in troubleshooting, administering or managing heterogeneous internetworks. Readers should be past the Cisco Certified Design Associate (CCDA) stage and into CCDP or CCNP certification.

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Product Details

  • ISBN-13: 9781587202834
  • Publisher: Cisco Press
  • Publication date: 9/8/2010
  • Series: Networking Technology Series
  • Edition number: 3
  • Pages: 447
  • Sales rank: 380,736
  • Product dimensions: 7.40 (w) x 9.20 (h) x 1.20 (d)

Meet the Author

Priscilla Oppenheimer has been developing data communications and networking systems since 1980 when she earned her master’s degree in information science from the University of Michigan. After many years as a software developer, she became a technical instructor and training developer and has taught more than 3000 network engineers from most of the Fortune 500 companies. Her employment at such companies as Apple Computer, Network General, and Cisco gave her a chance to troubleshoot real-world network design problems and the opportunity to develop a practical methodology for enterprise network design. Priscilla was one of the developers of the Cisco Internetwork Design course and the creator of the Designing Cisco Networks course. Priscilla teaches network design, configuration, and troubleshooting around the world and practices what she preaches in her network consulting business.

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Read an Excerpt


Chapter 5: Designing a Network Topology

Designing a backup path that has the same capacity as the primary path can beexpensive and is only appropriate if the customer's business requirements dictate abackup path with the same performance characteristics as the primary path.

If switching to the backup path requires manual reconfiguration of any components,then Users will notice disruption. For mission-critical applications, disruption isprobably not acceptable. An automatic fallover is necessary for mission-criticalapplications. BY using redundant, partial-mesh network designs, you can speedautomatic recovery time when a link falls.

One other important consideration with backup paths is that they must be tested.Sometimes network designers develop backup solutions that are never tested until acatastrophe happens. When the catastrophe occurs, the backup links do not work. Insome network designs, the backup links are used for load balancing as well asredundancy. This has the advantage that the backup path is a tested solution that isregularly used and monitored as a part of day-to-day operations. Load balancing isdiscussed in more detail in the next section.

Load Balancing

The primary purpose of redundancy is to meet availability requirements. A secondarygoal is to improve performance by supporting load balancing across parallel links.

Load balancing must be planned and in some cases configured. Some protocols do notsupport load balancing by default. For example, when running Novell's Routing Protocol(RIP), an Internetwork Packet Exchange (IPX) router can remember only one route to aremote network. You can change this behavior on a Ciscorouter by using the ipx maximum-paths command.

In ISDN environments, You can facilitate load balancing by configuring channelaggregation. Channel aggregation on means that a router can automatically bring upmultiple ISDN B channels as bandwidth requirements increase. The Multilink Point-to-Point Protocol (MPPP) is an Internet Engineering Task Force (IETF) standard for ISDN B-channel aggregation. MPPP ensures that packets arrive in sequence at the receivingrouter. To accomplish this, data is encapsulated within the Point-to-point Protocol (PPP)and datagrams are given a sequence number. At the receiving router, PPP uses thesequence number to re-create the original data stream. Multiple channels appear as onelogical link to upper-layer protocols.Most vendor's implementations of IP routing protocols support load balancing acrossparallel links that have equal cost. (Cost values are used by routing protocols todetermine the most favorable path to a destination. Depending on the routing protocol,cost can be based on hop count, bandwidth, delay, or other factors.) Cisco supports loadbalancing across six parallel paths. With the IGRP and Enhanced [GRP protocols, Ciscosupports load balancing even when the paths do not have the same bandwidth (which isthe main metric used for measuring cost for those protocols). Using a feature calledvariance, IGRP and Enhanced IGRP can load balance across paths that do not haveprecisely the same aggregate bandwidth. Cost, metrics, and variance are discussed inmore detail in Chapter 7, "Selecting Bridging, Switching, and Routing Protocols."

Some routing protocols base cost on the number of hops to a particular destinationsThese routing protocols load balance over unequal bandwidth paths as long as thehop count is equal. Once a slow link becomes saturated, however higher capacitylinks cannot be filled. This is called Pinhole congestion. Pinhole congestion can be avoided by designing equal bandwidth links within one layer of the hierarchyusing a routing protocol that bases cost on bandwidth and has the variance feature.

Load balancing can be affected by advanced switching (forwarding) mechanismsimplemented in routers. Advanced switching processes often cache the path to remotedestinations to allow fast forwarding of subsequent packets to that destination. (Thecache obviates the need for the router CPU to look in the routing table for a path. Theresult of caching is that all packets destined to a particular destination take the same path.In this case, load balancing occurs across traffic flows to different destinations, but not ona packet-per-packet basis. Some newer technologies, such as Cisco Express Forwarding(CEF), can be configured to do packet-per-packet or destination-per-destination loadbalancing. Chapter 12, "Optimizing Your Network Design," covers CEF in more detail.

DESIGNING A CAMPUS NETWORK DESIGN TOPOLOGY

Campus network design topologies should meet a customer's goals for availability andperformance by featuring small broadcast domains, redundant distribution-laversegments, mirrored servers, and multiple ways for a workstation to reach a router for off-net communications. Campus networks should be designed using a hierarchical model sothat the network offers good performance, maintainability, and scalability.

Virtual LANs

A virtual LAN (VLAN) is an emulation of a standard LAN that allows data transfer totake place without the traditional physical restraints placed on a network. A networkadministrator can use management software to group users into a VLAN so they cancommunicate as if they were attached to the same wire, when in fact they are located ondifferent physical LAN segments. Because VLANs are based on logical instead ofphysical connections, they are very flexible.

Companies that are growing quickly cannot guarantee that employees working on thesame project will be located together. With VLANs, the physical location of a user doesnot matter. A network administrator can assign a user to a VLAN regardless of the user'slocation. In theory, VLAN assignment can be based on applications, protocols,performance requirements, security requirements, traffic-loading characteristics, or otherfactors.

VLANs allow a large flat network to be divided into subnets. This feature can be used todivide up broadcast domains. Instead of flooding all broadcasts out every port, a VLAN-enabled switch can flood a broadcast out only the ports that are part of the I same subnetas the sending station.

In the past, some companies implemented large switched campus networks with fewrouters. The goals were to keep costs down by using switches instead of routers, andprovide good performance because presumably switches were faster than routers. Withoutthe router capability of containing broadcast traffic, however, the companies neededVLANs. VLANs allow the large flat network to be divided into subnets. A router (or arouting module within a switch) was still needed for inter-subnet communication.

As routers become as fast as switches and Layer-3 functionality is added to switches,fewer companies will implement large, flat, switched networks, and there will be less of aneed for VLANs.

VLAN-based networks can be hard to manage and optimize. Also, when a VLAN isdispersed across many physical networks, traffic must flow to each of those networks,which affects the performance of the networks and adds to the capacity requirements oftrunk networks that connect VLANs....

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Table of Contents

Ch. 1 Analyzing business goals and constraints 5
Ch. 2 Analyzing technical goals and tradeoffs 27
Ch. 3 Characterizing the existing internetwork 63
Ch. 4 Characterizing network traffic 95
Ch. 5 Designing a network topology 133
Ch. 6 Designing models for addressing and naming 185
Ch. 7 Selecting switching and routing protocols 221
Ch. 8 Developing network security strategies 267
Ch. 9 Developing network management strategies 299
Ch. 10 Selecting technologies and devices for campus networks 319
Ch. 11 Selecting technologies and devices for enterprise networks 363
Ch. 12 Testing your network design 403
Ch. 13 Optimizing your network design 429
Ch. 14 Documenting your network design 457
App. A Characterizing network traffic when workstations boot 471
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Customer Reviews

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Sort by: Showing all of 5 Customer Reviews
  • Anonymous

    Posted October 4, 2007

    Primary Reference

    This book should be the primary reference for any who seek to be a network design engineer. Priscilla is a network expert and an excellent writer. There's not much I can add to the other reviews--except to say that I've owned both editions of this and refer to it on a regular basis.

    1 out of 1 people found this review helpful.

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  • Anonymous

    Posted August 30, 2004

    Measure Twice, Cut Once

    Like the carpenter, the network designer does well to develop a plan before he or she purchases. The title, Top-Down Network Design, is accurate because the author¿s key approach throughout the book is to consider what works best for the end user while meeting the goals for a Request for Proposal. Priscilla Oppenheimer has presented a well structured textbook that covers every facet of networking in general with the intent of training the reader in the best practices of network design. The point of this book is to discourage going straight to product catalogs and picking out hardware when assigned a network project. Even if the customer has not given an RFP, the designer should present an overview of the project that includes the goals and how those goals will be measured. The reader should have some basic knowledge of networking. However, this would make an excellent text book for an introductory class at a university or technical school since Oppenheimer covers all of the logical concepts and physical aspects of modern networking. The well read and experienced network engineer will also find it a good review with a unique insight or tip sprinkled just often enough to make the read worthwhile. The text is also an excellent resource for writing network design documents for all occasions. For those preparing for certification the book would most help the aspiring Cisco Certified Design Professional candidate. The book however, is primarily a supplement to the student and a most useful reference for the consulting and design professional. Oppenheimer gives well thought through, easy to read descriptions of technologies. For example, her description of the Aggregatable Global Unicast Address Format, on pages 207-8, is the most succinct explanation of how IPv6 works I have ever read. Another jewel in this book is the walk-through of designing a real campus network in Chapter 10. The author had a college¿s permission to publish it¿s network topology. This means that you are learning how a network was designed and implemented that actually worked in real life. Another practical lesson is her definition of the 'Heisenberg uncertainty principle' as 'the act of observing something can alter what is observed.' Consultants should be careful that their analysis doesn¿t become a problem in itself. The extras are appendix A, a detailed description of a workstation booting. Each protocol is charted showing the traffic it creates. Appendix B is a reading list. There is also a glossary, which is always a bonus. I am going to be looking out for other titles from this author because there is a quality in the way this book is written that I am not accustomed to in computer books. Priscilla Oppenheimer, a teacher at Southern Oregon University, at the time of the books publishing date, merits the credit for raising the bar in her genre.

    1 out of 1 people found this review helpful.

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  • Anonymous

    Posted August 13, 2004

    Times -- and Networking -- have changed: get up to date

    Top-Down Network Design, Second Edition is both a new terrific book and still a terrific book. The original took a systems approach to designing a network which could provide the service the people paying for it expected, partly by getting them to clarify their expectations and needs. The new Second Edition does this, too, but it includes material relevant to the networks being implemented today, and they are very different networks than we saw even three or four years ago. New technologies, such as VPNs, VoIP, IPv6 as well as v4, Gigabit Ethernet and 10GigE, etc. are covered as part of a networking solution, not just as cool and sexy technologies to be rolled out for that reason. Likewise, new business emphases like reliability, redundancy, resiliency (which are not the same thing), security, and even survivability are addressed. Not all new technologies will help solve these problems, and, more often than not, they aren¿t even necessary. Thoughtful planning is far more important, and working with the network as it is now, toward what it is desired to become, is how you can really solve these problems. I think one of the greatest techniques you can learn from TDND, 2e is to characterize the flows of traffic on the network. Priscilla Oppenheimer gives several examples of developing such analyses in a variety of situations ¿ campus networks, WANs, a design testing scenario, and so forth. The Appendix with workstation bootup traffic information is especially helpful ¿ the only thing I would have liked to see that I didn¿t was a little more detail on the contents of the various packets involved, but it is an Appendix, and using a sniffer will let you see them for yourself. I have both the original and the new Second Edition ¿ and getting the new one is definitely worth it. Networking has changed, and this book will help you handle the new material.

    1 out of 1 people found this review helpful.

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  • Posted September 1, 2010

    more from this reviewer

    comprehensive coverage

    [This is a review of the 3rd edition.]

    Oppenheimer directs the book at a network analyst who might have to design a large scale network for a client company. The discussion starts by suggesting an analysis of the client's industry and needs. This is reinforced by definitions of various network performance metrics, like MTBF, MTTR, capacity, throughput, delay (latency), delay variation, etc. Chapter 2 is distinguished by a comprehensive explanation of each metric. The explanations are fairly non-technical. You don't need a degree in computer science or electrical engineering to follow it.

    The text then goes into how to characterise any existing network. This is a pragmatic recognition that you typically do not have a blank slate, with no pre-existing network. These days, a company is likely to already have a network, which presumably is developing bottlenecks or other problems, such that you have been called in to suggest upgrades.

    Later in the book, the narrative does get more involved, delving into the design of a network topology, with associated switches and routers. Various common protocols are briefly but succinctly covered. As a network designer, you need thorough acquaintance with these and the text is an excellent discourse.

    I have never seen the 1st or 2nd editions, so I'm unsure exactly how the 3rd differs. I am guessing that much of the text is unchanged. For example, the protocols have been largely stable for several years. While the advice about network topologies could also have been largely unaltered. The most recent portions of this text may pertain to the latest capabilities of switches and routers.

    The text is also admirably ecumenical in its hardware descriptions. No lock in for Cisco hardware.

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  • Anonymous

    Posted June 8, 2010

    No text was provided for this review.

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