Linux Network Administrators Guide

564 Pages·2016·1.97 MB·English

Linux Network Administrators Guide
LinuxNetworkAdministratorsGuide
Table of Contents
Preface.....................................................................................................................................................xiv
1.PurposeandAudienceforThisBook..........................................................................................xv
2.SourcesofInformation.................................................................................................................xv
2.1.DocumentationAvailableviaFTP..................................................................................xvi
2.2.DocumentationAvailableviaWWW...........................................................................xvii
2.3.DocumentationAvailableCommercially.....................................................................xvii
2.4.LinuxJournalandLinuxMagazine.............................................................................xviii
2.5.LinuxUsenetNewsgroups...........................................................................................xviii
2.6.LinuxMailingLists........................................................................................................xix
2.7.OnlineLinuxSupport......................................................................................................xx
2.8.LinuxUserGroups..........................................................................................................xx
2.9.ObtainingLinux...............................................................................................................xx
3.FileSystemStandards...............................................................................................................xxii
4.StandardLinuxBase.................................................................................................................xxii
5.AboutThisBook......................................................................................................................xxiii
6.TheOfficialPrintedVersion......................................................................................................xxiv
7.Overview....................................................................................................................................xxv
8.ConventionsUsedinThisBook..............................................................................................xxvii
9.SubmittingChanges...............................................................................................................xxviii
10.Acknowledgments................................................................................................................xxviii
10.1.TheHallofFame........................................................................................................xxix
1.IntroductiontoNetworking..................................................................................................................1
1.1.History.........................................................................................................................................1
1.2.TCP/IPNetworks........................................................................................................................1
1.2.1.IntroductiontoTCP/IPNetworks...................................................................................2
1.2.2.Ethernets.........................................................................................................................3
1.2.3.OtherTypesofHardware...............................................................................................5
1.2.4.TheInternetProtocol......................................................................................................6
1.2.5.IPOverSerialLines.......................................................................................................8
1.2.6.TheTransmissionControlProtocol................................................................................8
1.2.7.TheUserDatagramProtocol..........................................................................................9
1.2.8.MoreonPorts.................................................................................................................9
1.2.9.TheSocketLibrary.......................................................................................................10
1.3.UUCPNetworks........................................................................................................................10
1.4.LinuxNetworking.....................................................................................................................11
1.4.1.DifferentStreaksofDevelopment................................................................................12
1.4.2.WheretoGettheCode.................................................................................................13
1.5.MaintainingYourSystem..........................................................................................................13
1.5.1.SystemSecurity............................................................................................................13
2.IssuesofTCP/IPNetworking.............................................................................................................16
2.1.NetworkingInterfaces...............................................................................................................16
2.2.IPAddresses..............................................................................................................................16
2.3.AddressResolution...................................................................................................................18
2.4.IPRouting.................................................................................................................................19
2.4.1.IPNetworks..................................................................................................................19
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2.4.2.Subnetworks.................................................................................................................19
2.4.3.Gateways......................................................................................................................21
2.4.4.TheRoutingTable........................................................................................................23
2.4.5.MetricValues................................................................................................................24
2.5.TheInternetControlMessageProtocol....................................................................................25
2.6.ResolvingHostNames..............................................................................................................25
3.ConfiguringtheNetworkingHardware...............................................................................................28
3.1.KernelConfiguration.................................................................................................................30
3.1.1.KernelOptionsinLinux2.0andHigher......................................................................31
3.1.2.KernelNetworkingOptionsinLinux2.0.0andHigher...............................................34
3.2.ATourofLinuxNetworkDevices............................................................................................37
3.3.EthernetInstallation..................................................................................................................38
3.3.1.EthernetAutoprobing...................................................................................................39
3.4.ThePLIPDriver........................................................................................................................41
3.5.ThePPPandSLIPDrivers........................................................................................................43
3.6.OtherNetworkTypes................................................................................................................43
4.ConfiguringtheSerialHardware.......................................................................................................45
4.1.CommunicationsSoftwareforModemLinks...........................................................................45
4.2.IntroductiontoSerialDevices...................................................................................................46
4.3.AccessingSerialDevices..........................................................................................................46
4.3.1.TheSerialDeviceSpecialFiles....................................................................................48
4.4.SerialHardware.........................................................................................................................49
4.5.UsingtheConfigurationUtilities..............................................................................................50
4.5.1.ThesetserialCommand................................................................................................50
4.5.2.ThesttyCommand.......................................................................................................61
4.6.SerialDevicesandthelogin:Prompt........................................................................................69
4.6.1.ConfiguringthemgettyDaemon..................................................................................70
5.ConfiguringTCP/IPNetworking.......................................................................................................73
5.1.Mountingthe/procFilesystem.................................................................................................73
5.2.InstallingtheBinaries...............................................................................................................74
5.3.SettingtheHostname................................................................................................................74
5.4.AssigningIPAddresses............................................................................................................75
5.5.CreatingSubnets.......................................................................................................................76
5.6.WritinghostsandnetworksFiles..............................................................................................76
5.7.InterfaceConfigurationforIP...................................................................................................78
5.7.1.TheLoopbackInterface................................................................................................78
5.7.2.EthernetInterfaces........................................................................................................80
5.7.3.RoutingThroughaGateway.........................................................................................82
5.7.4.ConfiguringaGateway.................................................................................................83
5.7.5.ThePLIPInterface.......................................................................................................84
5.7.6.TheSLIPandPPPInterfaces.......................................................................................85
5.7.7.TheDummyInterface...................................................................................................85
5.7.8.IPAlias.........................................................................................................................86
5.8.AllAboutifconfig.....................................................................................................................86
5.9.ThenetstatCommand...............................................................................................................89
5.9.1.DisplayingtheRoutingTable.......................................................................................89
5.9.2.DisplayingInterfaceStatistics......................................................................................91
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5.9.3.DisplayingConnections................................................................................................92
5.10.CheckingtheARPTables.......................................................................................................92
6.NameServiceandResolverConfiguration........................................................................................96
6.1.TheResolverLibrary................................................................................................................96
6.1.1.Thehost.confFile.........................................................................................................96
6.1.2.Thensswitch.confFile..................................................................................................98
6.1.3.ConfiguringNameServerLookupsUsingresolv.conf...............................................101
6.1.4.ResolverRobustness...................................................................................................103
6.2.HowDNSWorks.....................................................................................................................103
6.2.1.NameLookupswithDNS..........................................................................................109
6.2.2.TypesofNameServers...............................................................................................110
6.2.3.TheDNSDatabase.....................................................................................................111
6.2.4.ReverseLookups........................................................................................................113
6.3.Runningnamed.......................................................................................................................114
6.3.1.Thenamed.bootFile...................................................................................................115
6.3.2.TheBIND8host.confFile.........................................................................................117
6.3.3.TheDNSDatabaseFiles............................................................................................118
6.3.4.Caching-onlynamedConfiguration...........................................................................122
6.3.5.WritingtheMasterFiles.............................................................................................123
6.3.6.VerifyingtheNameServerSetup...............................................................................125
6.3.7.OtherUsefulTools......................................................................................................128
7.SerialLineIP......................................................................................................................................130
7.1.GeneralRequirements.............................................................................................................130
7.2.SLIPOperation.......................................................................................................................130
7.3.DealingwithPrivateIPNetworks...........................................................................................137
7.4.Usingdip.................................................................................................................................137
7.4.1.ASampleScript..........................................................................................................138
7.4.2.AdipReference..........................................................................................................139
7.5.RunninginServerMode.........................................................................................................143
8.ThePoint-to-PointProtocol..............................................................................................................154
8.1.PPPonLinux..........................................................................................................................154
8.2.Runningpppd..........................................................................................................................155
8.3.UsingOptionsFiles.................................................................................................................156
8.4.UsingchattoAutomateDialing..............................................................................................157
8.5.IPConfigurationOptions........................................................................................................160
8.5.1.ChoosingIPAddresses...............................................................................................160
8.5.2.RoutingThroughaPPPLink.....................................................................................161
8.6.LinkControlOptions..............................................................................................................165
8.7.GeneralSecurityConsiderations.............................................................................................167
8.8.AuthenticationwithPPP.........................................................................................................167
8.8.1.PAPVersusCHAP......................................................................................................168
8.8.2.TheCHAPSecretsFile..............................................................................................169
8.8.3.ThePAPSecretsFile..................................................................................................170
8.9.DebuggingYourPPPSetup....................................................................................................171
8.10.MoreAdvancedPPPConfigurations....................................................................................172
8.10.1.PPPServer................................................................................................................172
8.10.2.DemandDialing........................................................................................................173
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8.10.3.PersistentDialing......................................................................................................179
9.TCP/IPFirewall.................................................................................................................................181
9.1.MethodsofAttack...................................................................................................................181
9.2.WhatIsaFirewall?.................................................................................................................183
9.3.WhatIsIPFiltering?...............................................................................................................184
9.4.SettingUpLinuxforFirewalling............................................................................................185
9.4.1.KernelConfiguredwithIPFirewall...........................................................................185
9.4.2.TheipfwadmUtility...................................................................................................186
9.4.3.TheipchainsUtility....................................................................................................186
9.4.4.TheiptablesUtility.....................................................................................................187
9.5.ThreeWaysWeCanDoFiltering...........................................................................................187
9.6.OriginalIPFirewall(2.0Kernels)...........................................................................................189
9.6.1.Usingipfwadm...........................................................................................................189
9.6.2.AMoreComplexExample.........................................................................................192
9.6.3.SummaryofipfwadmArguments..............................................................................193
9.7.IPFirewallChains(2.2Kernels).............................................................................................197
9.7.1.Usingipchains............................................................................................................198
9.7.2.ipchainsCommandSyntax.........................................................................................198
9.7.3.OurNaïveExampleRevisited....................................................................................202
9.7.4.ListingOurRuleswithipchains.................................................................................203
9.7.5.MakingGoodUseofChains......................................................................................203
9.8.NetfilterandIPTables(2.4Kernels).......................................................................................208
9.8.1.BackwardCompatabilitywithipfwadmandipchains.................................................211
9.8.2.Usingiptables.............................................................................................................211
9.8.3.OurNaïveExampleRevisited,YetAgain..................................................................216
9.9.TOSBitManipulation.............................................................................................................217
9.9.1.SettingtheTOSBitsUsingipfwadmoripchains.......................................................218
9.9.2.SettingtheTOSBitsUsingiptables...........................................................................219
9.10.TestingaFirewallConfiguration...........................................................................................220
9.11.ASampleFirewallConfiguration.........................................................................................222
10.IPAccounting...................................................................................................................................229
10.1.ConfiguringtheKernelforIPAccounting............................................................................229
10.2.ConfiguringIPAccounting...................................................................................................229
10.2.1.AccountingbyAddress............................................................................................230
10.2.2.AccountingbyServicePort......................................................................................232
10.2.3.AccountingofICMPDatagrams..............................................................................235
10.2.4.AccountingbyProtocol............................................................................................236
10.3.UsingIPAccountingResults................................................................................................236
10.3.1.ListingAccountingDatawithipfwadm...................................................................237
10.3.2.ListingAccountingDatawithipchains....................................................................237
10.3.3.ListingAccountingDatawithiptables.....................................................................238
10.4.ResettingtheCounters..........................................................................................................238
10.5.FlushingtheRuleset..............................................................................................................239
10.6.PassiveCollectionofAccountingData.................................................................................239
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11.IPMasqueradeandNetworkAddressTranslation......................................................................241
11.1.SideEffectsandFringeBenefits...........................................................................................242
11.2.ConfiguringtheKernelforIPMasquerade...........................................................................243
11.3.ConfiguringIPMasquerade..................................................................................................244
11.3.1.SettingTimingParametersforIPMasquerade.........................................................246
11.4.HandlingNameServerLookups...........................................................................................249
11.5.MoreAboutNetworkAddressTranslation...........................................................................250
12.ImportantNetworkFeatures...........................................................................................................251
12.1.TheinetdSuperServer..........................................................................................................251
12.2.ThetcpdAccessControlFacility..........................................................................................253
12.3.TheServicesandProtocolsFiles..........................................................................................255
12.4.RemoteProcedureCall.........................................................................................................257
12.5.ConfiguringRemoteLoginandExecution............................................................................258
12.5.1.Disablingther;Commands......................................................................................259
12.5.2.InstallingandConfiguringssh..................................................................................259
13.TheNetworkInformationSystem..................................................................................................267
13.1.GettingAcquaintedwithNIS................................................................................................268
13.2.NISVersusNIS+...................................................................................................................270
13.3.TheClientSideofNIS..........................................................................................................270
13.4.RunninganNISServer.........................................................................................................271
13.5.NISServerSecurity...............................................................................................................272
13.6.SettingUpanNISClientwithGNUlibc..............................................................................273
13.7.ChoosingtheRightMaps......................................................................................................275
13.8.UsingthepasswdandgroupMaps.......................................................................................277
13.9.UsingNISwithShadowSupport..........................................................................................279
14.TheNetworkFileSystem.................................................................................................................282
14.1.PreparingNFS.......................................................................................................................283
14.2.MountinganNFSVolume....................................................................................................283
14.3.TheNFSDaemons................................................................................................................286
14.4.TheexportsFile.....................................................................................................................287
14.5.Kernel-BasedNFSv2ServerSupport...................................................................................289
14.6.Kernel-BasedNFSv3ServerSupport...................................................................................289
15.IPXandtheNCPFilesystem..........................................................................................................291
15.1.Xerox,Novell,andHistory...................................................................................................291
15.2.IPXandLinux.......................................................................................................................292
15.2.1.CalderaSupport........................................................................................................292
15.2.2.MoreonNDSSupport..............................................................................................293
15.3.ConfiguringtheKernelforIPXandNCPFS..........................................................................293
15.4.ConfiguringIPXInterfaces...................................................................................................294
15.4.1.NetworkDevicesSupportingIPX............................................................................294
15.4.2.IPXInterfaceConfigurationTools...........................................................................294
15.4.3.Theipx_configureCommand...................................................................................294
15.4.4.Theipx_interfaceCommand....................................................................................296
15.5.ConfiguringanIPXRouter...................................................................................................297
15.5.1.StaticIPXRoutingUsingtheipx_routeCommand.................................................298
15.5.2.InternalIPXNetworksandRouting.........................................................................298
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15.6.MountingaRemoteNetWareVolume..................................................................................300
15.6.1.ASimplencpmountExample...................................................................................301
15.6.2.ThencpmountCommandinDetail..........................................................................301
15.6.3.HidingYourNetWareLoginPassword....................................................................313
15.6.4.AMoreComplexncpmountExample......................................................................313
15.7.ExploringSomeoftheOtherIPXTools...............................................................................314
15.7.1.ServerList................................................................................................................314
15.7.2.SendMessagestoNetWareUsers............................................................................314
15.7.3.BrowsingandManipulatingBinderyData...............................................................315
15.8.PrintingtoaNetWarePrintQueue........................................................................................319
15.8.1.UsingnprintwiththeLinePrinterDaemon.............................................................323
15.8.2.ManagingPrintQueues............................................................................................325
15.9.NetWareServerEmulation....................................................................................................326
16.ManagingTaylorUUCP...................................................................................................................327
16.1.UUCPTransfersandRemoteExecution...............................................................................328
16.1.1.TheInnerWorkingsofuucico..................................................................................329
16.1.2.uucicoCommand-lineOptions.................................................................................330
16.2.UUCPConfigurationFiles....................................................................................................331
16.2.1.AGentleIntroductiontoTaylorUUCP....................................................................331
16.2.2.WhatUUCPNeedstoKnow....................................................................................334
16.2.3.SiteNaming..............................................................................................................335
16.2.4.TaylorConfigurationFiles........................................................................................335
16.2.5.GeneralConfigurationOptionsUsingtheconfigFile..............................................336
16.2.6.HowtoTellUUCPAboutOtherSystemsUsingthesysFile..................................337
16.2.7.IdentifyingAvailableDevicesThroughtheportFile...............................................342
16.2.8.HowtoDialaNumberUsingthedialFile...............................................................343
16.2.9.UUCPOverTCP......................................................................................................344
16.2.10.UsingaDirectConnection.....................................................................................345
16.3.ControllingAccesstoUUCPFeatures..................................................................................346
16.3.1.CommandExecution................................................................................................346
16.3.2.FileTransfers............................................................................................................346
16.3.3.Forwarding................................................................................................................347
16.4.SettingUpYourSystemforDialingIn.................................................................................348
16.4.1.ProvidingUUCPAccounts.......................................................................................348
16.4.2.ProtectingYourselfAgainstSwindlers.....................................................................349
16.4.3.BeParanoid:CallSequenceChecks.........................................................................350
16.4.4.AnonymousUUCP...................................................................................................351
16.5.UUCPLow-LevelProtocols.................................................................................................351
16.5.1.ProtocolOverview....................................................................................................352
16.5.2.TuningtheTransmissionProtocol............................................................................353
16.5.3.SelectingSpecificProtocols.....................................................................................354
16.6.Troubleshooting....................................................................................................................354
16.6.1.uucicoKeepsSaying“WrongTimetoCall”............................................................355
16.6.2.uucicoComplainsThattheSiteIsAlreadyLocked.................................................355
16.6.3.YouCanConnecttotheRemoteSite,buttheChatScriptFails..............................355
16.6.4.YourModemDoesNotDial.....................................................................................355
16.6.5.YourModemTriestoDialbutDoesn’tGetOut......................................................355
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16.6.6.LoginSucceeds,buttheHandshakeFails................................................................356
16.7.LogFilesandDebugging......................................................................................................356
17.ElectronicMail.................................................................................................................................359
17.1.WhatIsaMailMessage?......................................................................................................360
17.2.HowIsMailDelivered?........................................................................................................362
17.3.EmailAddresses....................................................................................................................363
17.3.1.RFC-822...................................................................................................................363
17.3.2.ObsoleteMailFormats.............................................................................................363
17.3.3.MixingDifferentMailFormats................................................................................364
17.4.HowDoesMailRoutingWork?............................................................................................365
17.4.1.MailRoutingontheInternet....................................................................................365
17.4.2.MailRoutingintheUUCPWorld............................................................................366
17.4.3.MixingUUCPandRFC-822....................................................................................367
17.5.Configuringelm....................................................................................................................370
17.5.1.GlobalelmOptions...................................................................................................371
17.5.2.NationalCharacterSets............................................................................................371
18.Sendmail...........................................................................................................................................374
18.1.Introductiontosendmail.......................................................................................................374
18.2.Installingsendmail................................................................................................................374
18.3.OverviewofConfigurationFiles...........................................................................................375
18.4.Thesendmail.cfandsendmail.mcFiles................................................................................375
18.4.1.TwoExamplesendmail.mcFiles..............................................................................376
18.4.2.TypicallyUsedsendmail.mcParameters..................................................................377
18.5.Generatingthesendmail.cfFile............................................................................................381
18.6.InterpretingandWritingRewriteRules................................................................................381
18.6.1.sendmail.cfRandSCommands...............................................................................382
18.6.2.SomeUsefulMacroDefinitions...............................................................................382
18.6.3.TheLefthandSide....................................................................................................382
18.6.4.TheRighthandSide..................................................................................................383
18.6.5.ASimpleRulePatternExample...............................................................................384
18.6.6.RulesetSemantics.....................................................................................................385
18.7.ConfiguringsendmailOptions..............................................................................................387
18.8.SomeUsefulsendmailConfigurations..................................................................................389
18.8.1.TrustingUserstoSettheFrom:Field......................................................................389
18.8.2.ManagingMailAliases.............................................................................................389
18.8.3.UsingaSmartHost...................................................................................................390
18.8.4.ManagingUnwantedorUnsolicitedMail(Spam)...................................................392
18.8.5.ConfiguringVirtualEmailHosting..........................................................................395
18.9.TestingYourConfiguration...................................................................................................397
18.10.Runningsendmail...............................................................................................................401
18.11.TipsandTricks....................................................................................................................402
18.11.1.ManagingtheMailSpool.......................................................................................402
18.11.2.ForcingaRemoteHosttoProcessitsMailQueue.................................................403
18.11.3.AnalyzingMailStatistics.......................................................................................403
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19.GettingEximUpandRunning........................................................................................................406
19.1.RunningExim.......................................................................................................................407
19.2.IfYourMailDoesn’tGetThrough........................................................................................408
19.3.CompilingExim....................................................................................................................409
19.4.MailDeliveryModes............................................................................................................410
19.5.MiscellaneousconfigOptions...............................................................................................411
19.6.MessageRoutingandDelivery.............................................................................................412
19.6.1.RoutingMessages.....................................................................................................412
19.6.2.DeliveringMessagestoLocalAddresses.................................................................413
19.6.3.AliasFiles.................................................................................................................414
19.6.4.MailingLists.............................................................................................................415
19.7.ProtectingAgainstMailSpam..............................................................................................416
19.8.UUCPSetup..........................................................................................................................417
20.Netnews.............................................................................................................................................419
20.1.UsenetHistory.......................................................................................................................419
20.2.WhatIsUsenet,Anyway?.....................................................................................................420
20.3.HowDoesUsenetHandleNews?.........................................................................................421
21.CNews..............................................................................................................................................424
21.1.DeliveringNews....................................................................................................................424
21.2.Installation.............................................................................................................................425
21.3.ThesysFile...........................................................................................................................427
21.4.TheactiveFile.......................................................................................................................431
21.5.ArticleBatching....................................................................................................................432
21.6.ExpiringNews.......................................................................................................................435
21.7.MiscellaneousFiles...............................................................................................................437
21.8.ControlMessages..................................................................................................................438
21.8.1.ThecancelMessage..................................................................................................439
21.8.2.newgroupandrmgroup.............................................................................................439
21.8.3.ThecheckgroupsMessage........................................................................................439
21.8.4.sendsys,version,andsenduuname...........................................................................441
21.9.CNewsinanNFSEnvironment...........................................................................................441
21.10.MaintenanceToolsandTasks.............................................................................................442
22.NNTPandthenntpdDaemon.........................................................................................................445
22.1.TheNNTPProtocol..............................................................................................................446
22.1.1.ConnectingtotheNewsServer................................................................................446
22.1.2.PushingaNewsArticleontoaServer......................................................................447
22.1.3.ChangingtoNNRPReaderMode............................................................................448
22.1.4.ListingAvailableGroups..........................................................................................449
22.1.5.ListingActiveGroups..............................................................................................449
22.1.6.PostinganArticle.....................................................................................................449
22.1.7.ListingNewArticles.................................................................................................450
22.1.8.SelectingaGrouponWhichtoOperate...................................................................450
22.1.9.ListingArticlesinaGroup.......................................................................................451
22.1.10.RetrievinganArticleHeaderOnly.........................................................................451
22.1.11.RetrievinganArticleBodyOnly............................................................................452
22.1.12.ReadinganArticlefromaGroup...........................................................................452
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