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use this common connection “gets on” or “gets off” the bus. Because NICs share a common bus, each NIC can “hear” other NICs. NICs have built-in rules for using this common area, which is discussed further in Hour 9, “Ethernet Basics,” and Hour 10, “Token-Ring Basics.” For the moment, you just need to know that each NIC has been schooled in “netiquette” and has been taught in the factory to play well with others and to share the wire nicely—that is, most of the time. Be aware that if a network card does not obey these rules, this can cause problems on the entire shared segment. (See Figure 1.2 for an illustration of shared versus dedicated telephone lines and network segments.) Figure 1.2 Shared versus dedicated lines. Computers on older networks were actually connected together on the same wire, much like older Christmas lights used to be. Therefore, a physical break in the wire meant that all the computers on one side of the break went down. A hub-based segment fixes this, because each computer has its own physical connection, and the hub ties them all together. The newer method of sharing the wire is called a star topology, because it looks like a star. The older method is called bus topology—the line from PC to PC is the common bus area. A new technology called switching allows each network card to have its own private line; however, a lot of hub-based shared networks are still in existence (and don’t look for them to go away any time soon). You’ll find switching to be more and more exciting as you get into network troubleshooting. Similar to the way hubs allow users to get away from the “Christmas light bulb” problem, switches allow users to get away from many of the problems of shared networks. Instead of each computer having to compete for the right to talk when it wants to, each computer can transmit pretty much when it needs to—as long as the computer on the other end is available, of course. Others in the network neighborhood no longer compete for the right to talk on the wire, because each computer has its own connection. How does this work? In a nutshell, a switch looks at the MAC addresses of two workstations on the network that want to communicate, and it opens up a high-speed private channel for them. A hub has one common channel, but a switch has many, many channels, as well as the intelligence to switch conversations between them. With a fast enough switch (called a wire speed switch), workstations conversing on the switch are not affected whatsoever by other workstations talking away at full speed. Although prices on hubs are very low, switching has become very cheap as well; you can look to this
technology as the future of local area networks. Although shared hubs have their virtues (for example, it’s easy to see the conversations on a shared line, which is good for troubleshooting), the fact remains that they are more trouble-prone than switched networks (switched networks are much faster and more reliable). As switches get even cheaper, you can expect to deploy them instead of hubs. Previous Table of Contents Next
Page 1 and 2: To access the contents, click the c
Page 3 and 4: Workshop Q&A Quiz Answers to Quiz Q
Page 5 and 6: Eminent Domain TCP/IP Graffiti DHCP
Page 7 and 8: Configuring Your Proxy Proxy Troubl
Page 9 and 10: Socks Stuff AOL Instant Messenger A
Page 11 and 12: Table of Contents Introduction: Get
Page 13 and 14: about your more complex network iss
Page 15 and 16: Tell Us What You Think! Table of Co
Page 17 and 18: with me when I was first getting st
Page 19 and 20: NIC (network interface card) The te
Page 21 and 22: MAC Attack Previous Table of Conten
Page 23: Routers Previous Table of Contents
Page 27 and 28: for a TCP/IP address in a large net
Page 29 and 30: Sprechen Sie DLC? Previous Table of
Page 31 and 32: socket 80 of the TCP/IP address 167
Page 33 and 34: program in a name entry; entering t
Page 35 and 36: WINS Previous Table of Contents Nex
Page 37 and 38: kind and spit them out as fast as p
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Page 41 and 42: Figure 2.1 A simple logical map. If
Page 43 and 44: Figure 2.4 A physical documentation
Page 45 and 46: the room). This way, you can read t
Page 47 and 48: un on the server at 9:50 on Monday
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Page 51 and 52: Beware of Vendor Your vendor probab
Page 53 and 54: call the risk/benefit ratio—the a
Page 55 and 56: Workshop Q&A Previous Table of Cont
Page 59 and 60: If you determine that it’s just o
Page 61 and 62: (see Figure 4.2). Figure 4.2 An Eth
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Page 65 and 66: just that the network itself is at
Page 67 and 68: A Each situation is obviously diffe
Page 71 and 72: Ruling out is particularly effectiv
Page 73 and 74: Drive duplication can be a big help
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Previous Table of Contents Next Aft
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5. When you log problems on a given
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if they have a plan, they are going
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Is It a Virus, Doc? Previous Table
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O: Only have tried two other Intern
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A Remember that what a user says is
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Previous Table of Contents Next Hou
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Previous Table of Contents Next Loo
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Figure 7.1 Searching several sites
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You’ll also find forums run by th
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Previous Table of Contents Next
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a server but you think it should be
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Workshop Q&A Previous Table of Cont
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Previous Table of Contents Next Par
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Name Brand Versus Generic PCs The c
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static electricity that may have bu
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SIMMs and DIMMs There are two kinds
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This is called looping back, becaus
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Windows Previous Table of Contents
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Figure 8.4 The NT Task Manager’s
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UNIX Previous Table of Contents Nex
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Probably the most important thing t
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Hour 9 Ethernet Basics Previous Tab
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which translates into lots of colli
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it currently requires fiber-optic c
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designation is simply an industry-s
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Down, Down, Down Previous Table of
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A Collisions cause other errors, su
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Follow the Rules: Share and Enjoy!
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Previous Table of Contents Next Err
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Token Analyzers Finding a NAUN is r
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Token-Ring does not have any hard-a
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Down Town Previous Table of Content
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C. 1, 16 D. 4, 16 Answers to Quiz Q
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Going Native Although Windows allow
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Eminent Domain Previous Table of Co
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machine with the username Administr
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protocol. They therefore relied on
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Previous Table of Contents Next Fol
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Most of the time, you’ll not want
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allows you to manage them and check
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Binding Previous Table of Contents
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Figure 11.6 Showing bindings for al
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Informational Commands Previous Tab
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Figure 11.8 A monitor session. We k
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case you need them. 2. What does SM
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a great example of client/server. W
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Previous Table of Contents Next Alt
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The first number is the process ID
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tcp 0 0 frotz.frob.com.telnet 200.1
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Name Game Previous Table of Content
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The next thing you need to find out
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A UNIX security and file permission
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the amount of time used or data sen
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NLMs In addition to accepting comma
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NLM Party Previous Table of Content
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Again, make sure you are running th
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Big Monitor Is Watching Previous Ta
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Then, eureka! During one session of
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Protocol Problems Previous Table of
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Figure 13.10 UNICON will configure
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Summary Previous Table of Contents
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7. The TCP/IP protocol and basic se
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ivory-tower stuff, but some of it i
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Configuring in Comfort Previous Tab
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Router 1 in Figure 14.3 is shown in
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to that network. Instead, the next
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Route in Peace: Routing Protocols P
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get to a network segment that until
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Figure 14.4 How two stations talk v
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Tree Trunks Previous Table of Conte
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garbage characters like these on a
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A. Add Router 99 to Router 88’s r
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Let’s lay out some definitions he
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Packet-Filtering Routers Previous T
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eceptionist hangs up one line (the
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from the proxy server without causi
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Proxy Trouble Previous Table of Con
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3. The proxy server resolves the na
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Q My vendor says that its firewall
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Previous Table of Contents Next Par
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• Make checklists of tasks that m
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Joe User Previous Table of Contents
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groups | grep -q -w network && { ec
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If you’re going to add or replace
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Policies Previous Table of Contents
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in this hour—will pay off as you
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Q Which duplication software is rig
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Hour 17 Where Do I Start? Previous
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As optimistic as we’d all like to
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• PCAnywhere • ReachOut • Rem
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IPX/SPX Previous Table of Contents
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Q What happens if I ping the loopba
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correlations? A. netstat -a B. trac
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equire that the application files t
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The File and Print Blues Previous T
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With five potential points of failu
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In some cases, a slight difference
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Application Celebration Previous Ta
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Proto Local Address Foreign Address
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printer 515 Line Printer Daemon (ne
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Connected to 167.195.160.6. Escape
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Workshop Q&A Q What in the blazes i
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3. A 4. B 5. False 6. B 7. True 8.
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Intranet = Internal The word intran
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Internet Identification Previous Ta
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If an outside machine is “on the
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Here I Ping Again Previous Table of
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Figure 19.6 DNS zones, like the fol
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[rs.internic.net] Registrant: John
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For example, I ran an NFS server on
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• SMTP—Simple Mail Transfer Pro
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Dialout DNS Previous Table of Conte
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3. What does DMZ stand for? A. DNS
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• It’s a way to avoid a Dilbert
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Socks Stuff Previous Table of Conte
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Figure 20.2 The AOL Instant Messeng
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RealPlayer Previous Table of Conten
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external client for proxy support,
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Typical Operation Previous Table of
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scantily, and still others are not
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Not every kind of filter is availab
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important. Your relative or interpa
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Application Antics Previous Table o
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Broken Ring Previous Table of Conte
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creating a segment between the swit
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Q Where can I get an Ethernet mini-
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Figure 22.1 The MG-Soft MIB browser
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the probe has picked up what’s go
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Previous Table of Contents Next Her
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information without the overhead th
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A. Broadcast B. Baseline C. Brag D.
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• Application efficiency • Serv
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Application and Protocol Efficiency
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and so on—is to measure. Everythi
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it a point to say, “Would you sho
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Here are the two types of performan
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Network Statistics Previous Table o
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Q About that latency analysis metho
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Router Configuration Previous Table
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For the second option, you’ll hav
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Automatic for the People Previous T
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are in an unknown location) to conn
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Previous Table of Contents Next The
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C. SYS:SYSTEM\AUTOEXEC.BAT D. SYS:P
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active hub An active hub is one tha
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A TCP-based authentication service
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applications and protocols are base
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An extremely fast network cable tha
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See Internet Group Management Proto
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A device that converts (modulates)
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providers. Point-to-Point Tunneling
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security audit An examination (ofte
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An essential part of a network inte
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Index Symbols A 100 Megabit Etherne
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C new product, 45-46 burned-in addr
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DLC (Data Link Control), 17 DMZ (de
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F fat finger factor, 42-43, 46 fata
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ICQ, 335-336 IMAP (Internet Mail Ap
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M filters, 347-352 LANDecoder, 347
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NetBIOS (Network Basic Input/Output
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network card. See NIC Network Contr
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power supply check, 66 troubleshoot
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Q-R qualitative problems, 58 quanti
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names, 393-394 NetWare, 202 paging
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T dumb terminal mode, 211, 224 full
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isolating soft errors, 135-136 LANa
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U standardizing configuration, 245
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V W upstream, 134 Usenet newsgroups
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autodetection problems, 159 broadca
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