Radia Perlman's Interconnections: Bridges, Routers Switches, and Internetworking Protocols is recognized as a leading text on networking theory and practice. It provides authoritative and comprehensive information on general networking concepts, routing algorithms and protocols, addressing, and the mechanics of bridges, routers, switcher, and hubs. This second edition is expanded and updated to cover the newest developments in the field, including advances in switching and bridge technology, VLANs, Fast Ethernet, DHCP, ATM, and Ipv6. Additional new topics include IPX,AppleTalk, and DECnet. You will gain a deeper understanding of the range of solutions possibIe and find vaIuableinformation on protocols for which documentation is not readiIy availabIe elsewhere.
　　Whitten by the inventor of many of the aIgorithms that make switching and routing robust and efficient, this book oftbrs an expert's insight into how and why networks operate as they do. PerIman describes all of the major networking algorithms and protocols in use today in cIear and concise terms, while exploring the engineering trade-offs that the different approaches represent.

InterconnectiOns, Second Edtion is about what goes on inside the boxes that move dataaround the Internet. These boxes are variously called bridges, routers, switches, and hubs. The book also describes the devices that connect to the network.
　　There is considerable confusion in this area. Most of the terminology is ill defined and is used in conflicting ways. The terdrino1ogy and the specifications tend to be daunting.Some knowledge is spread among many different documents; much is unwritten folk wisdom. Adding to the confusion is dogma. Beliefs are accepted as trUth, and questioning any of the dogma is often greeted with hostility. But good engineering demands that we under stand what we're doing and why, keep an open ndnd, and 1earn from exPerience.
　　In Interconnections, Second Edition, instead of diving right into the details of one protocol, I first focus on the prob1ems to be soIved. I examine various solutions to each of these problems and discuss the engineering trade-off s invoIved. Then I look at a variety of solutions that have been deployed and compare the approaches. I give technical arguments for any opinions, and if you think I have missed any arguments I welcome email discussion. My email address is at the back of the book, which I hope you will find after having read the book cover to cover.
　　In the first edition, my intention was to help people understand the prob1ems and the general types of so1utions, assuming that they would read the specifications to get the deails of specific protocols. But people used the book as a reference in addition to using it to understand the issues. So in this edition l have documented many more of the protocols in detail.
　　I believe that to understand something deeply you need to compare it to something else. The first edition was "minimalist" in that I always used only two examples' two types of bridges, bridges versus routers, connection-oriented versus connectionless network layer protocols, and two examples of connectionless protocols (CLNP and lP). In this edition I add a 1ot more examples, including ATM, IPv6, IPX, AppleTalk, and DECnet. I did this in part because these protocols exist, and it is hard to get information about them. But mostly I did it because the protocols embody interesting ideas that should not be lost. When we design new protocols, we should learn frorn previous ideas,both good and bad. Also, it takes very little additional effOrt, after the problem is described generically, to describe several examp1es.
　　The Tao of network protocols: If all you see is IP, you see nothing.
　　　　　　　　　　　　　　　　　　　　　--Greg Minshall
Roadmap to the Book
　　The first fOur chapters are not significantly different from their counterParts in the first edition, but the rest of the book has been largely rewritten. Chapters l through 4 cover general networking concepts, data link issues such as addressing and multiplexing, transparent bridges and the spanning tree algorithm, and source routing bridges. Chapter 5 is completely new and explains how the notion of a switch evolved into a rediscovery of the bridge. It also covers VLANs and fast Ethemet.
　　The remainder of the book concentrates on layer 3 (the network layer). Chapter 6 gives an overview of the network layer. ChaPter 7 covers connection-oriented networks, including ATM and X.25. Chapter 8 discusses the issues in a generic connectionless network layer. Chapter 9 covers layer 3 addressing generica1ly and gives a detailed comparison of IP IPv6, CLNP DECnet, AppleTalk, and IPX. ChaPter 10 covers the infOrmation that should appear in a network layer header and contrasts the headers of several protocols.
　　Chapter 11 covers autoconfiguration and neighbor discovery, including protocols such as ARP and DHCP Chapter 12 covers routing algorithms generically.
　　Chapter 13 discusses the problem of doing longest-prefix matching, which is required in order to fOrward IP packets quickly. Chapter 14 discusses the specifics of various routing protocols including RIP IS-IS, OSPF PNNI, NLSP and BGP Chapter 15 covers network layer multicast. Chapter 16 explains how to design a network that is invulnerable to sabotage, an idea whose time may come.
　　The final two chapters summarize the book, and I hope they will be mostly light and entertaining reading. ChaPter 17 probes the mystery of what, if anything, distinguishes a router from a bridge. Chapter 18 attempts to capture folk wisdom about how to design a protocol.
　　Finally, there is an extensive glossary. I try to define terms when I first use them, but if I ever fail to do that, you will probably find them in the glossary.

Acknowledgments
　　Writing this section is scare because I am afraid I will leave people out. I'd like to thank the people who reviewed all or paf't of the book' Peter Memishian, Paul Koning, Tony Lauck,Craig Pallridge, Dan Pitt, Brian Kernighan, Paul Bottorff Joe1 Halpern, Charlie Kaufman.Mike Speciner, Andy Tanenbaum, Phil Rosenzweig, Dan Senie, William Welch, Craig Labovitz, Chase Bailey, George Varghese, and Suchi Raman. Other people who have been helpful by answering questions are Ariel Hendel, Rich Kubota, Stuar-t Cheshire,Tom Maufef, Steve Deering, and John Moy. The first time I sent an email question in the middle of the night (when I did most of my work on this book) to Craig Partridge, the co-series editor fOr this book, the beep indicating incoming mail happened so immediately that I assumed it was an automatic mail responder informing me he was on vacation. But it was an answer to my question. I assume he doesn't have an automatic mail responder so clever that it can answer technical questions, so l thank him for being so prompt and available. Brian Kernighan, the other series editor, also had detailed and helpful comments on the entire book.
　　The people at Addison-Wesley have been amazingly patient with me for the many years in which I've been working on this edition. I'm not sure they had any alternative besides patience, but it was nicP that they believed I'd finish even when I wasn't so sure.So thank you to Mary Hart, Karen Gettman, Jacquelyn Doucette, and Jason Jones. And I'd also like to thank my copy editor, Betsy Hardinger. She of all people will have read every word of the book, while maintaining the concentration to note inconsistencies and ways of removing excess words here and there. I know it's her job, but I'm still impressed.
　　Mike Speciner helped me figure out the mysteries of Framemaker. Ray Perlner made sure that I maintained some humor in the book and watched over my shoulder while I typed the last chapter to see that l had enough funny bad real-life protocols. Dawn Perlner has been terrifical1y supportive, convincing her friends and even strangers in bookstores to buy my books. She used to be my child. Now she's a wonderful friend.

Chapter 1 Essential Networking Concepts
l . l Layers
l . 2 Service Models
l . 3 Important Properties of a Network
l . 4 Reliable Data Transfer Protocols
Chapter 2 Data Link Layer Issues
2. I Generic LANs
2. 2 IEEE 802 LANs
2. 3 Names, Addresses. Routes
2. 4 LAN Addresses
2. 5 Multicast versus Unicast Addresses
2. 6 The Broadcast Address
2. 7 Multiplexing Field
2. 8 Bit Order
2. 9 Logical Link Control
2. IO Issues in 802.3
2. ll Issues in 802.5
2. 12 Packet Bursts
2. l3 Reasons for Bridges
2. I4 Point-to-Point Links
Chapter 3 Traneparent Bridges
3. I The No-Frills Bridge
3. 2 The Learning Bridge
3. 3 Spanning Tree Algorithm
3. 4 Spanning Tree Algorithm Refinements
3.5 Bridge Message Formats
3.6 Other Bridge Issues
3.7 Remote Bridges
Chapter 4 Source Routing Bridges
4.l Pure Source Routing
4.2 SR-TB Bridges
4.3 SRT Bridges
4.4 End-system Algorithms
4.5 Source Routing versus Transparent Bridging
4.6 Ideas for Improving Source Route Bridging
Chapter 5 Hubs, Switches, Virtual LANs, and Fast Ethernet
5.l Hubs
5.2 Faster LANs
5.3 Virtual LANs (VLANs)
Chapter 6 Network Interface: Service Models
6.l What Is the Network Layer
6.2 Network Service Types
Chapter 7 Connection-oriented Nets: X.25 and ATM
7.l Generic Connection-oriented Network
7.2 X.25: Reliable Connection-oriented Service
7.3 Implementing X.25 Inside the Net
7.4 Asynchronous Transfer Mode
Chapter 8 Generic Connectionless Service
8.I Data Transfer
8.2 Addresses
8.3 Hop Count
8.4 Service Class Information
8.5 Network Feedback
8.6 Fragmentation and Reassembly
8.7 Maximum Packet Size Discovery
Chapter 9 Network Layer Addresses
9.I Hierarchical Addresses with Fixed Boundaries
9.2 Hierarchical Addresses with Flexible Boundaries
9.3 Owning versus Renting Addresses
9.4 Types of Addresses
9.5 IP
9.6 IPX
9.7 IPX+
9.S IPv6
9.9 CLNP Network Layer Addresses
9. IO AppleTalk Network Layer Addresses
9. ll DECnet Phases III and IV
9. l2 NAT/NAPT
Chapter 10 Connectionless Data Packet Formats
IO.I Pieces of a Connectionless Network Layer
lO.2 Data Packets
IO.3 Sammary of Packet Formats for Easy Reference
IO.4 Technical Issues and Comparisons in Data Packet Formats
I0.5 Source Routing
IO.6 The Great IPX Frame Format Mystery
IO.7 Error Reports and Other Network Feedback to the Endnode
Chapter 11 Neighbor Greeting and Autoconfiguration
lI .l Endnodes Attached via Point-to-Point Links
ll .2 Endnodes Attached via LANs
lI .3 Endnodes Attached via Nonbroadcast Multiaccess Media
ll .4 Finding Things
Chapter 12 Routing Algorithm Coneepts
l2.I Distance Vector Routing
12.2 Link State Routing
12.3 Comparison of Link State and Distance Vector Roating
12.4 Load Splitting
12.5 Link Costs
I2.6 Migrating Routing Algorithms
12.7 LANs
12.8 Types of Service
12.9 Partition Repair: Level l Subnetwork Partition
Chapter 19 Fast Packet Fowarding
13.l Using an Additional Header
13.2 Address Prefix Matching
13.3 Longest Prefix Match with Trie
I3.4 Binary Search
Chapter 14 Specific Routing Protocols
14.l A Brief History of Intradomain Routing Protocols
14.2 RIP
14.3 RTMP, IPX-RIP, and DECnet
14.4 IS-IS, OSPF, NLSP, and PNNI
14.5 Interdomain Routing Protocols
Chapter 15 WAN Multicast
15.l Introduction
15.2 Multicast in IP
Chapter 16 Sabotage-proof Routing
16.l The Problem
16.2 AII You Need to Know about Cryptography
l6.3 Overview of the Approach
16.4 Detailed Description of the Approach
l6.5 Summary
16.6 For Further Reading
Chapter 17 To Route, Bridge, or Switch: Is That the Question
I7.l Switches
l7.2 Bridges versus Routers
l7.3 Extensions to Bridges
17.4 Extensions to Routers
Chapter 18 Protocol Design Folklore
18.l Simplicity versus nexibility versus Optimality
l8.2 Knowing the Problem You're Trying to Solve
l8.3 Overhead and Scaling
l8.4 Operation Above Capacity
l8.5 Compact IDs versus Object Identifiers
18.6 Optimizing for the Most Common or Important Case
I8. 7 Forward Compatibility
l8.8 Migration: Roating Algorithms and Addressing
l8.9 Parameters
18.IO Making Multiprotocol Operation Possible
18.ll Ronning over Layer 3 versus Layer 2
18.12 Robustness
18.13 Determinism versus Stability
18.14 Performance for Correctness
18.15 In Closing
Glossary
Index