Cisco - Network Consultants Handbook

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During the course of a typical day—if there is such a thing as a "typical" day—network consultants are bombarded with questions coming from all directions. These questions come from customers, peers, sales and marketing teams, network administrators, and so on, and the list seems neverending at times. Network consultants, designers, engineers, managers, and so on have developed an instinct over time and sometimes cringe or develop other nervous habits when the phrase, "You got a second?" is uttered. To the uninitiated, this question seems innocent enough, but after a while they, too, develop the same cringe or nervous habit. ...

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  1. Network Consultants Handbook
  2. About the Author.......................................................................................................................................................................... 10 About the Technical Reviewers .................................................................................................................................................. 11 Acknowledgments ....................................................................................................................................................................... 12 Foreword ...................................................................................................................................................................................... 13 Introduction................................................................................................................................................................................... 14 Purpose of This Book................................................................................................................................................................. 16 How This Book Can Be Used ..................................................................................................................................................... 17 The Twelve Networking Truths .................................................................................................................................................. 17 Feedback.................................................................................................................................................................................... 19 Chapter 1. Open System Interconnection (OSI) Model ........................................................................................................... 20 OSI Reference Model ................................................................................................................................................................. 20 Summary.................................................................................................................................................................................... 31 Chapter 2. LAN Topologies ........................................................................................................................................................ 32 Unicast....................................................................................................................................................................................... 32 Multicast .................................................................................................................................................................................... 33 Broadcast ................................................................................................................................................................................... 34 LAN Addressing ........................................................................................................................................................................ 38 LAN Topologies......................................................................................................................................................................... 39 LAN Topologies......................................................................................................................................................................... 47 Routers....................................................................................................................................................................................... 56 Summary.................................................................................................................................................................................... 56 Chapter 3. Ethernet/IEEE 802.3................................................................................................................................................. 58 Ethernet Network Elements ........................................................................................................................................................ 62 Ethernet Network Topologies and Structures .............................................................................................................................. 63 IEEE 802.3 Logical Relationship to the OSI Reference Model ................................................................................................... 65 CSMA/CD Operation................................................................................................................................................................... 71 The Ethernet Physical Layers ..................................................................................................................................................... 82 10 Mbps Ethernet Operation....................................................................................................................................................... 83 100 Mbps, or Fast Ethernet......................................................................................................................................................... 92 100VG-AnyLAN........................................................................................................................................................................ 99 1000 Mbps, or Gigabit (Gbps) Ethernet .................................................................................................................................... 104
  3. 10 Gbps, or 10 Gigabit Ethernet ............................................................................................................................................... 107 Summary.................................................................................................................................................................................. 113 Chapter 4. Ethernet Documentation........................................................................................................................................ 113 Case Study: Naming Conventions............................................................................................................................................. 114 Small Ethernet (Hub-Based) Networks ..................................................................................................................................... 117 Documentation Case Study....................................................................................................................................................... 121 Summary.................................................................................................................................................................................. 150 Chapter 5. Ethernet Network Review and Analysis ............................................................................................................... 150 Cisco Router Interface Commands ........................................................................................................................................... 151 show interface ethernet number accounting .............................................................................................................................. 170 show buffers ethernet ............................................................................................................................................................... 173 Buffer Misses ........................................................................................................................................................................... 177 show processes cpu .................................................................................................................................................................. 179 CPU Utilization........................................................................................................................................................................ 181 Ethernet Network Analysis ....................................................................................................................................................... 182 Ethernet Frame Transmission ................................................................................................................................................... 182 Ethernet Baseline...................................................................................................................................................................... 187 Ethernet MTU .......................................................................................................................................................................... 191 Ethernet Throughput................................................................................................................................................................. 192 Ethernet Effective Utilization ................................................................................................................................................... 195 Ethernet with IP Networking .................................................................................................................................................... 197 Ethernet with IPX Networking ................................................................................................................................................. 204 Case Study: Ethernet Network Analyzers ................................................................................................................................. 211 Summary.................................................................................................................................................................................. 216 Chapter 6. Token Ring/IEEE 802.5 ......................................................................................................................................... 221 Token Ring .............................................................................................................................................................................. 221 Physical Connections................................................................................................................................................................ 224 Token Ring Operation .............................................................................................................................................................. 225 Token Holding Time (THT) ..................................................................................................................................................... 233 Frame Format ........................................................................................................................................................................... 239 Dedicated Token Ring.............................................................................................................................................................. 243
  4. Summary.................................................................................................................................................................................. 247 Chapter 7. FDDI......................................................................................................................................................................... 248 Fiber-Optic Transmission Modes.............................................................................................................................................. 249 FDDI Topology........................................................................................................................................................................ 250 FDDI LAN Applications .......................................................................................................................................................... 261 Summary.................................................................................................................................................................................. 261 Chapter 8. Token Ring and FDDI LAN Documentation......................................................................................................... 262 Case Study: Naming Conventions............................................................................................................................................. 264 Case Study: Simple Token Ring LAN ...................................................................................................................................... 267 Case Study: Simple FDDI LAN................................................................................................................................................ 271 Summary.................................................................................................................................................................................. 275 Chapter 9. Token Ring and FDDI Network Review and Analysis......................................................................................... 275 Token Ring LANs .................................................................................................................................................................... 276 FDDI LANs ............................................................................................................................................................................. 312 FDDI LANs ............................................................................................................................................................................. 348 Summary.................................................................................................................................................................................. 385 Chapter 10. ATM LAN Emulation (LANE)............................................................................................................................... 385 Emulated LAN Environments................................................................................................................................................... 387 LAN Emulation Clients (LECs)................................................................................................................................................ 394 LAN Emulation Servers (LESs)................................................................................................................................................ 395 LAN Emulation Applications ................................................................................................................................................... 417 Summary.................................................................................................................................................................................. 418 Chapter 11. ATM LANE Documentation, Review, and Analysis........................................................................................... 419 Effective Operating Rate .......................................................................................................................................................... 420 ATM LANE Traffic Classes..................................................................................................................................................... 421 IOS Commands ........................................................................................................................................................................ 427 ATM LANE Documentation .................................................................................................................................................... 443 Summary.................................................................................................................................................................................. 450 Chapter 12. Telecommunications and Telephony ................................................................................................................. 451 Voice Signaling ........................................................................................................................................................................ 451 ANI .......................................................................................................................................................................................... 460
  5. Lines and Trunks...................................................................................................................................................................... 463 ISDN........................................................................................................................................................................................ 473 DSL.......................................................................................................................................................................................... 483 Summary.................................................................................................................................................................................. 494 Chapter 13. Private Line WANs ............................................................................................................................................... 496 T1 Basics ................................................................................................................................................................................. 496 TDM ........................................................................................................................................................................................ 500 T1 Documentation.................................................................................................................................................................... 515 T1 Access................................................................................................................................................................................. 520 T1 Testing and Analysis ........................................................................................................................................................... 523 DS0 Basics ............................................................................................................................................................................... 526 DS3 .......................................................................................................................................................................................... 530 Summary.................................................................................................................................................................................. 533 Chapter 14. Fiber-Optic Technology ....................................................................................................................................... 534 Optic Bands and Transmission Windows.................................................................................................................................. 536 SONET/SDH............................................................................................................................................................................ 541 DWDM .................................................................................................................................................................................... 550 Summary.................................................................................................................................................................................. 554 Chapter 15. Frame Relay ......................................................................................................................................................... 557 Frame Relay Terms and Concepts ............................................................................................................................................ 559 Frame Relay Applications ........................................................................................................................................................ 599 Frame Relay Traffic Shaping.................................................................................................................................................... 631 Traffic Policing and Shaping .................................................................................................................................................... 639 Summary.................................................................................................................................................................................. 651 Chapter 16. Frame Relay Documentation............................................................................................................................... 656 Case Study: Naming Conventions............................................................................................................................................. 658 Frame Relay DLCI Table ......................................................................................................................................................... 697 Summary.................................................................................................................................................................................. 700 Chapter 17. Frame Relay WAN Analysis ................................................................................................................................ 702 Frame Relay Traffic Shaping.................................................................................................................................................... 702 Frame Relay Oversubscription.................................................................................................................................................. 708
  6. Frame Relay Data Delivery Ratio (DDR) ................................................................................................................................. 713 Frame Relay SLAs ................................................................................................................................................................... 719 Summary.................................................................................................................................................................................. 720 Chapter 18. ATM Wide-Area Networking (WAN) and MPOA ............................................................................................... 722 ATM Network Architecture ..................................................................................................................................................... 725 ATM WAN Interfaces .............................................................................................................................................................. 727 PNNI Signaling ........................................................................................................................................................................ 732 ATM Connections .................................................................................................................................................................... 733 ATM Cells and Cell Relay........................................................................................................................................................ 734 ATM Service Classes ............................................................................................................................................................... 736 ATM Service Architecture........................................................................................................................................................ 737 ATM Service Categories Description ....................................................................................................................................... 741 ATM Functional Layers ........................................................................................................................................................... 748 ATM Addressing...................................................................................................................................................................... 755 ATM Applications.................................................................................................................................................................... 757 Multiprotocol Over ATM (MPOA)........................................................................................................................................... 761 Three Elements of MPOA ........................................................................................................................................................ 763 MPOA Logical Components .................................................................................................................................................... 765 Caching .................................................................................................................................................................................... 766 Virtual Subnets......................................................................................................................................................................... 766 Network Layer Mapping........................................................................................................................................................... 767 Taking a Shortcut: The Basic Concept ...................................................................................................................................... 768 MPOA Packet Flow.................................................................................................................................................................. 770 Migration and Coexistence ....................................................................................................................................................... 772 Inverse Multiplexing for ATM (IMA) ...................................................................................................................................... 773 Summary.................................................................................................................................................................................. 775 Chapter 19. ATM WAN Documentation .................................................................................................................................. 777 Case Study: Naming Conventions............................................................................................................................................. 778 ATM VPI/VCI Table................................................................................................................................................................ 804 Summary.................................................................................................................................................................................. 807 Chapter 20. Voice Technology................................................................................................................................................. 807
  7. VoIP Network Elements ........................................................................................................................................................... 808 Session Initiation Protocol (SIP)............................................................................................................................................... 839 VoIP Equipment Adjustment .................................................................................................................................................... 844 VoX Call Establishment ........................................................................................................................................................... 848 VoX Summary ......................................................................................................................................................................... 849 Voice over ATM (VoATM)...................................................................................................................................................... 850 VoATM Expectations............................................................................................................................................................... 861 VoATM Summary.................................................................................................................................................................... 870 Voice over Frame Relay (VoFR) .............................................................................................................................................. 871 VoIP......................................................................................................................................................................................... 876 VoX Circuit Sizing................................................................................................................................................................... 877 Summary.................................................................................................................................................................................. 880 Chapter 21. Remote Access and VPNs .................................................................................................................................. 882 Remote Access......................................................................................................................................................................... 882 LAN-to-LAN VPN................................................................................................................................................................... 890 Authentication .......................................................................................................................................................................... 890 Encryption Alternatives ............................................................................................................................................................ 898 Telecommunications Access Methods to a Local ISP ............................................................................................................... 907 Policy and Administrative Management ................................................................................................................................... 910 VPN Network Requirements .................................................................................................................................................... 916 Remote Access VPN Network Design ...................................................................................................................................... 922 VPN User-Access Requirements .............................................................................................................................................. 927 VPN Performance Requirements .............................................................................................................................................. 928 VPN Client Essentials, Security Guidelines, and Vulnerabilities............................................................................................... 931 DHCP Support ......................................................................................................................................................................... 936 Summary.................................................................................................................................................................................. 938 Chapter 22. Network Management Introduction..................................................................................................................... 938 Network Management Architecture.......................................................................................................................................... 939 Network Management Model ................................................................................................................................................... 941 Network Management Functional Architecture......................................................................................................................... 953 MIB.......................................................................................................................................................................................... 957
  8. Summary.................................................................................................................................................................................. 965 Chapter 23. IP VPN WAN Documentation.............................................................................................................................. 967 Remote Access Documentation Template................................................................................................................................. 969 IOS Commands ........................................................................................................................................................................ 977 Summary.................................................................................................................................................................................. 982 Chapter 24. Routing Protocols, Part I .................................................................................................................................... 982 Routing: Static Versus Dynamic ............................................................................................................................................... 983 Routing Information Protocol (RIP).......................................................................................................................................... 991 RIP Routing Protocol Summary.............................................................................................................................................. 1006 RIP Version 2 (RIPv2) ........................................................................................................................................................... 1006 RIPv2 Summary ..................................................................................................................................................................... 1010 IGRP ...................................................................................................................................................................................... 1010 IGRP Summary ...................................................................................................................................................................... 1020 EIGRP.................................................................................................................................................................................... 1021 EIGRP Summary.................................................................................................................................................................... 1028 OSPF...................................................................................................................................................................................... 1029 OSPF Summary...................................................................................................................................................................... 1042 Summary................................................................................................................................................................................ 1042 Chapter 25. Routing Protocols, Part II................................................................................................................................... 1047 Intermediate System to Intermediate System (IS-IS)............................................................................................................... 1047 IS-IS Summary....................................................................................................................................................................... 1057 Border Gateway Protocol, Version 4 (BGP4).......................................................................................................................... 1058 BGP Summary ....................................................................................................................................................................... 1082 EGP........................................................................................................................................................................................ 1086 EGP Summary........................................................................................................................................................................ 1088 Summary............................................................................................................................................................................... 1089 Chapter 26. IPv6 Introduction................................................................................................................................................. 1091 IPv6 Terms............................................................................................................................................................................. 1095 IPv6 Addressing ..................................................................................................................................................................... 1096 IPv6 Neighbor Discover Protocol (NDP) ................................................................................................................................ 1109 IPv4/IPv6 Transition .............................................................................................................................................................. 1110
  9. IPv4/IPv6 Network Address Translation (NAT) ..................................................................................................................... 1112 IPv6 Header ........................................................................................................................................................................... 1112 IPv6/IPv4 Tunneling .............................................................................................................................................................. 1115 6to4 Tunnel Management ....................................................................................................................................................... 1117 6to4 Case Study...................................................................................................................................................................... 1118 Summary................................................................................................................................................................................ 1126 Chapter 27. Multiprotocol Label Switching (MPLS).............................................................................................................. 1127 Label-Edge Routers (LERs) and Label\_Switching Routers (LSRs)........................................................................................ 1129 Forward Equivalence Classes (FECs) ..................................................................................................................................... 1129 Labels and Label Bindings ..................................................................................................................................................... 1130 MPLS Fundamentals ............................................................................................................................................................. 1131 Multilayer Switching .............................................................................................................................................................. 1134 MPLS Evolution..................................................................................................................................................................... 1139 MPLS Model.......................................................................................................................................................................... 1140 MPLS and Layer 3 Forwarding .............................................................................................................................................. 1143 MPLS Operation .................................................................................................................................................................... 1144 MPLS Enhanced Routing ....................................................................................................................................................... 1147 MPLS Applications ................................................................................................................................................................ 1148 MPLS Virtual Private Networks (MPLS-VPNs) ..................................................................................................................... 1152 IP/MPLS Network.................................................................................................................................................................. 1154 BGP-Extended Community Attributes.................................................................................................................................... 1155 MPLS VPN Operational Model.............................................................................................................................................. 1156 Summary................................................................................................................................................................................ 1162 Appendix A. LAN/WAN Network Assessment ...................................................................................................................... 1163 Introduction........................................................................................................................................................................... 1163 Executive Summary of Findings ............................................................................................................................................. 1163 Current Network Topology and Characterization.................................................................................................................... 1164 Recommendations .................................................................................................................................................................. 1173 Network Health ...................................................................................................................................................................... 1173 Network Provisioning............................................................................................................................................................. 1195 Subnet Masks ......................................................................................................................................................................... 1197
  10. Data Transmission Throughput............................................................................................................................................... 1200 Mesh Network Connectivity ................................................................................................................................................... 1205 VoIP Bandwidth Consumption ............................................................................................................................................... 1210 Appendix B. Protocol List.................................................................................................................................................... 1212 Appendix C. List of ITU-T X.121 Data Country or Geographical Area Codes................................................................... 1242 Appendix E. Bibliography........................................................................................................................................................ 1255 About the Author Matthew "Cat" Castelli has more than 13 years of experience in the telecommunications networking industry, starting as a cryptologic technician (communications) in the United States Navy. Cat has since been working as a principal consultant for a Cisco Professional Services partner and as a senior technical consultant/enterprise network design engineer for a global telecommunications integrator. Cat has broad exposure to LAN/WAN, Internet, and Alternative technologies (VoX) for service provider and enterprise networks of all sizes, including implementation, application, configuration, integration, network management, and security solutions. Cat currently holds CCNA, CCDA, CCNP, and CCDP certifications and recently completed Technical Review for Advanced MPLS Design and Implementation (Cisco Press). When Cat is not involved with network design or engineering, he can be found pursuing his degree, reading, cheering for the Los Angeles Dodgers, or simply enjoying a cigar and scotch. Cat is currently a network architect engineer for Global Crossing. He can be contacted at mjcastelli@earthlink.net.
  11. About the Technical Reviewers Belinda Goldsmith is a senior network engineer. She has 10 years of experience in the networking industry. She has worked in small/medium/enterprise environments supporting LAN/WAN/VOIP networks. She is a CCIE candidate, and currently holds the CCNP, CCDA, CCNA, and MCSE certifications. Ron Milione, Ph.D., is one of the leading senior software staff developers at Computer Associates International, a Cisco developer partner and world-leading software company that develops eBusiness infrastructure software. Ron has MSEE and BSEE degrees from City College of New York with a major in telecommunications. Ron also holds CCDA, CCNA, CCDP, and CCNP certifications with Cisco. In addition to Cisco certification, Ron holds certifications in Compaq, Microsoft, and Novell and is an adjunct professor of computer science and telecommunications at St. John’s University in New York. Ron has been published in several industry publications and other books. He can be reached via e-mail at ronald.milione@ca.com. Barb Nolley is the president and principal consultant for BJ Consulting, Inc., a small consulting firm that specializes in networking education. Since starting BJ Consulting, Barb has developed and taught training courses for Novell’s Master CNE certification, as well as several courses for Cisco Systems’ Engineering Education group. Barb also likes to deliver high-energy presentations about networking technologies and recently started teaching the CCNA track for the University of California-Riverside Extension. Barb stays current on networking technologies by constantly reading published books and perusing more than 50 industry publications each month. Prior to starting her own company in 1993, Barb worked for Apple Computer, Tandem Computer, and Tymnet (now part of MCI), where she held positions in everything from technical support to project management. John Tiso, CCIE #5162, is one of the senior technologists of NIS, a Cisco Systems silver partner. He has a BS degree from Adelphi University. John also holds the CCDP certification; the Cisco Security and Voice Access
  12. Specializations; and Sun Microsystems, Microsoft, and Novell certifications. John has been published in several industry publications. He can be reached via e-mail at johnt@jtiso.com. Jeff Whittemore is the director of advanced technology for The Systems House, a supply chain software and data center services provider. Jeff has been involved in IT for 25 years and began his networking career in the early 1980s with the design of the first network server system in the Midwest to host a multiuser database. Recently, Jeff built a national network and central data center from the ground up for a multi-billion dollar office supply company. Jeff incorporates a special emphasis on fault tolerance and resiliency into his network and data center designs. He is UNIX AIX and Microsoft MCSE certified and can be reached via e-mail at jeff.whittemore@tsh.com. Acknowledgments I would like to thank the following individuals for their unending support in the making of this book. It is these individuals who had me sometimes wondering if writing the book wasn’t the easiest part. John Kane, your humor, good nature, encouragement, support, and friendship have been invaluable. It all started about a year ago when you asked if I had any ideas for a book. You’ve done it now and I thank you. Amy Lewis, as much as any one person should have to work with me through combinations of caffeine and cotton candy, I say thank you because you deserve a medal. Your endless support, encouragement, motivation, and patience kept me going as deadlines loomed ever more intimidating. Your humor and friendship, however, may very well be one of the best things to come from this project. To Jeff Whittemore, Belinda Goldsmith, John Tiso, Ron Millione and Barb Nolley, I say thank you for keeping my straight. It is through the efforts of these individuals that what you hold in your hands was verified as being "honest and true."
  13. To Megan Crouch and Melissa Thornton, I say thank you for your hard work and determination, and our countless late nights as the deadline loomed near. To Karen Gill, "What is she doing again?" … Thank you for your hard work and dedication to this book. Foreword Many large projects in the networking industry, especially in the professional services or consulting arenas, have started with the statements: "There's something wrong in the network!" or the famous "The network is slow!" A large part of a networking consultant's working life can be devoted to identifying and resolving the underlying cause of those statements. When asked to resolve a networking issue, a consultant must grasp the problem (both actual and perceived), understand the environment of the problem (networking as well as organizational), and make intelligent guesses about the nature of the problem. The consultant must then drill down to find the exact nature of the problem, test the hypotheses, and then recommend or implement a solution. The author of this book, Matt Castelli, and I have collaborated on a number of such projects. The challenge to the networking consultant is not only to have technical expertise, but to apply this expertise efficiently in an environment that is both complex and dynamic. Not only do today's networks entail transmission of data to and from a myriad of hosts, but also over a collection of different media, even within one network. If one looks at another network, many facets of the network will be different. Such is the result of the widespread application of standards in networks. There are now many ways to get a result. Matt not only understands the ins and outs of these complex issues, but he presents the issues in a manner that makes it more manageable for a consultant to apply the knowledge to the problem.
  14. Cisco Press has numerous books on networking. What Matt offers in this book is something that I have not seen presented elsewhere. Network Consultants Handbook is a must-have for those professionals who need to solve various complex networking problems on a daily basis. The reader gets a general overview, followed by building blocks for bringing a consulting project to a successful resolution. As a fellow networking professional, I am pleased to see Matt bring his years of experience in consulting and breadth of knowledge to bear on this book. Jeffrey F. Stevenson Director, Systems Engineering Quarry Technologies, Inc. Introduction During the course of a typical day—if there is such a thing as a "typical" day—network consultants are bombarded with questions coming from all directions. These questions come from customers, peers, sales and marketing teams, network administrators, and so on, and the list seems neverending at times. Network consultants, designers, engineers, managers, and so on have developed an instinct over time and sometimes cringe or develop other nervous habits when the phrase, "You got a second?" is uttered. To the uninitiated, this question seems innocent enough, but after a while they, too, develop the same cringe or nervous habit. The reason is this: Networks are like snowflakes; no two are alike. This is the challenge that network consultants, engineers, managers, designers, and anyone else involved with a telecommunications network must face every day.
  15. The question "You got a second?" is often followed by the question’s recipient researching through several volumes, Web sites, old e-mails, rolodexes of contacts, and so on in an effort to find the answer to that seemingly simple question. During this flurry of books, paper, Web sites, phone calls, and voice mails, the questioner sometimes says to himself, "I thought this person knew it all" or "What’s the big deal?" The big deal is that the telecommunications industry is in such a dynamic and fluid state that it is nearly impossible for someone to keep up with everything, leaving many individuals to become Subject Matter Experts, or SMEs, in one or several technologies. This specialization does not relieve the consultant (or whoever was the recipient of the "seemingly simple" question) of the responsibility of knowing something about everything. A "Jack of all trades, master of none" mentality begins to develop. Not only do network consultants, engineers, managers, and so on face the everyday challenging task of managing and maintaining these networks and answering questions about past, current, or future (proposed) technology, but consultants and others must also document, review, analyze, and find ways to improve these networks. They are often looking for ways to cut costs, while maintaining the same, if not better, level of service to their users. Before a consultant or another can review a network, he must have a clear understanding of the network in question, whether it is a current or planned implementation. Just as no two networks are alike, documentation of such networks follows suit. Often networks are not so much documented as they are drawn—on white boards or with drawing software packages—with little supporting configuration information. In the course of a single morning, I was the recipient of such questions including, but not limited to the following: Ethernet standards and limitations, Voice over Frame Relay, differences between and history of AMI and B8ZS line coding (and limitations of AMI), FRASI, and review of a customer's network document—and all this before lunch! One of the questions asked was: "Isn't there a book or Web site that has all of this stuff?" That was the most poignant question of all, and one that caught my attention above all the others.
  16. There was no single resource that I could read through and get what I needed, quickly and easily. Just as there was no single resource that helped me prepare documentation for my customer’s current or proposed networks. This same question further spawned an idea, an idea that was kicked around for a few years that resulted from my suffering through a "typical" day. I began to gather these books, Web sites, and old e-mails. I further created some document templates, and amassed what amounted to a labor of love: a collection of this information that, although organized in a fashion that would make Dewey Decimal cry, was still useful and served as my everyday resource. What you hold in your hands, and can view on the Internet at www.ciscopress.com/1587050390, is the result of that fateful question "Isn’t there a book or Web site that has all of this stuff?" Purpose of This Book The purpose of this book is to provide a resource to consultants and engineers to audit (assess), analyze, and evaluate any current or future network environment. Resources include form templates to complete during a network audit, necessary device commands to aid in obtaining necessary information, and consistent forms to aid in documentation. This book is intended for anyone who designs, manages, sells, administrates, or desires to understand various internetworking technologies, without wading through the sometimes intense discussions, standards documents, books, or white papers involved. This book is presented as a "greatest hits" of internetworking technologies, augmenting Cisco Press’s Internetworking Technologies Handbook: Third Edition, with the addition of insight into some of the technology’s infrastructure, as well as documentation templates and analysis guidelines.
  17. How This Book Can Be Used This book is intended to be used as a resource in whatever fashion the reader sees fit, either as a desktop reference resource or in the field where the tables and calculations help provide near-real time answers to internetworking issues and challenges. The Twelve Networking Truths One last note: I invite you to read the following, RFC 1925 by Ross Callon, perhaps ironically published April 1, 1996. Herein are the Twelve Networking Truths. Those in the know will nod silently, smirk, and perhaps chuckle. The uninitiated should consider themselves encouraged and shown the light. The Twelve Networking Truths Status of This Memo This memo provides information for the Internet community. This memo does not specify an Internet standard of any kind. Distribution of this memo is unlimited. Abstract This memo documents the fundamental truths of networking for the Internet community. This memo does not specify a standard, except in the sense that all standards must implicitly follow the fundamental truths. Acknowledgments
  18. The truths described in this memo result from extensive study over an extended period of time by many people, some of whom did not intend to contribute to this work. The editor merely has collected these truths, and would like to thank the networking community for originally illuminating these truths. 1. Introduction This Request For Comments (RFC) provides information about the fundamental truths underlying all networking. These truths apply to networking in general, and are not limited to TCP/IP, the Internet, or any other subset of the networking community. 2. The Fundamental Truths 1. It Has To Work. 2. No matter how hard you push and no matter what the priority, you can’t increase the speed of light. (2A) (corollary). No matter how hard you try, you can’t make a baby in much less than 9 months. Trying to speed this up *might* make it slower, but it won’t make it happen any quicker. 3. With sufficient thrust, pigs fly just fine. However, this is not necessarily a good idea. It is hard to be sure where they are going to land, and it could be dangerous sitting under them as they fly overhead. 4. Some things in life can never be fully appreciated nor understood unless experienced firsthand. Some things in networking can never be fully understood by someone who neither builds commercial networking equipment nor runs an operational network. 5. It is always possible to agglutinate multiple separate problems into a single complex interdependent solution. In most cases, this is a bad idea. 6. It is easier to move a problem around (for example, by moving the problem to a different part of the overall network architecture) than it is to solve it.
  19. (6A) (corollary). It is always possible to add another level of indirection. 7. It is always something. (7A) (corollary). Good, Fast, Cheap: Pick any two (you can’t have all three). 8. It is more complicated than you think. 9. For all resources, whatever it is, you need more. (9A) (corollary) Every networking problem always takes longer to solve than it seems like it should. 10. One size never fits all. 11. Every old idea will be proposed again with a different name and a different presentation, regardless of whether it works. (11A) (corollary). See rule 6a. 12. In protocol design, perfection has been reached not when there is nothing left to add, but when there is nothing left to take away. Feedback Feedback, as always, is appreciated. This book is intended to be a living volume, with updates and modifications as current standards change and new standards are introduced. The templates herein are designed as a starting point, and I certainly encourage you to use these, create your own, or use some combination of the two. If you find a method or document design that works better than what is presented here and would like to share it, I wholeheartedly encourage you to do so.
  20. I can be contacted either in care of Cisco Press, or directly at mjcastelli@earthlink.net. Chapter 1. Open System Interconnection (OSI) Model Although practically every networking book on the market today discusses the Open System Interconnection (OSI) model, its importance should not be taken for granted. For this reason, the OSI model will be discussed here as it pertains to local-area networks (LANs) and wide-area networks (WANs). OSI Reference Model The OSI reference model describes how information from a user or client application in one host or computer moves through an internetwork to an application on another host. The OSI model is a conceptual model composed of seven layers, each specifying particular network functions (see Figure 1-1). Figure 1-1. OSI Reference Model
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