stackencapsulationEachrouteadd
routeadd 时间:2021-05-24 阅读:()
TCP/IPnetworkingTCP/IPAnetworkingprotocolsuiteUseseveralprotocols,mainonesaretcpandip.
IPstandsforInternetProtocolTCPstandsforTransmissionControlProtocol.
ThenativelanguageoftheInternetSupportedbymostOSs(Unix,MacOS,Windows,Netware,etc)DefinesauniformprogramminginterfacetodifferenttypesofnetworkhardwareTCP/IPandInternet1969ARPAnetExperimentalpacket-switchingnetworkStudyrobust,reliable,vendor-independentdatacommunicationVerysuccessful1975ARPAnetbecameoperationnetworkDevelopmentcontinuingTCP/IPwasdeveloped1983TCP/IPprotocolswereadoptedasMilitaryStandardsTCP/IPwasimplementedinBerkeleyUnix.
ARPAnetwasdividedintoMILNETandARPAnetTCP/IPandInternet1985NSFNetConnectedtothethenexistingInternet(MILNETplusARPAnet)LinkedtogetherthefiveNSFsupercomputercentersWantedtoextendthenetworktoeveryscientist1987newNSFNetbackboneFasterThree-tieredtopology:backbone,regionalnetworks,andlocalnetworks.
TCP/IPandInternet1990ARPAnetpassedoutofexistence1995NSFnetceaseditsroleasaprimaryInternetbackbonenetworkTodayInternetisbuildbycommercialproviders.
InfrastructureisbeingcreatedbyNationalnetworkprovider,callertier-oneprovidersRegionalnetworkproviderLocalaccessanduserservicesisprovidedbyInternetServiceProviders(ISPs)NetworkAccessPoints(NAPS):majorinterconnectionpointsTCP/IPandInternetHowtheinternetismanagedtodayCommercialforceSeveralorganizationInternetCorporationforAssignedNamesandNumbers(ICANN)www.
icann.
orgInternetEngineeringTaskForce(IETE)www.
ietf.
orgInternetSociety(ISOC)www.
isoc.
orgTCP/IPandInternetNetworkstandardsanddocumentationRequestforComments(RFC)Over4000hasbeencreatedFYSTDBCPDispatchcentralforRFC-relatedmatterswww.
rfc-editor.
orgNetworkingRoadMapTCP/IPcomponentsIP,theInternetProtocolroutesdatapacketsfromonemachinetoanotherICMP,theInternetControlMessageProtocolProvidesseveralkindsoflow-levelsupportforIPErrormessageRoutingassistanceDebugginghelpARP,theAddressResolutionProtocolTranslatesIPaddressestohardwareaddressesNetworkingRoadMapUDP,theUserDatagramProtocolDeliversdatatospecificapplicationsonthedestinationmachineProvides"unverified","besteffort"transportforindividualmessagesTCP,theTransmissionControlProtocolDeliversdatatospecificapplicationsonthedestinationmachineProvidesreliable,flowcontrolled,errorcorrectedconversationbetweenprocessesontwohosts.
TCP/IPnetworkmodelUTPcopper,fiber,radiawavesARP,DeviceDriversIPICMPTCPUDPARPSSH,FTP,WEBDNS,QuakeTraeroutePhysicallayerLinkLayerNetworkLayerTransportLayerApplicationLayerPacketsandencapsulationDatatravelsonanetworkintheformofpacketsEachpacketconsistsofAheader–whereitcamefromandwhereit'sgoing,protocolinfo,checksum,etc.
Apayload-dataAsapackettravelsdowntheprotocolstackencapsulationEachprotocoladdsitsownheaderinformationEachprotocol'sfinishedpacketbecomesthepayloadpartofthepacketgeneratedbythenextprotocol.
Onareceivingmachine,theencapsulationisreversedasthepackettravelsbackuptheprotocolstack.
PacketsandEncapsulationExample:AtypicalnetworkpacketEthernetheaderIPheaderUDPheaderApplicationdataEthernetCRCUDPpacket(108bytes)IPpacket(128bytes)Ethernetframe(146bytes)AddressingPacketsaddressingPacketsmustbeproperlyaddressedinordertoreachtheirdestinationAddressingschemesMAC(mediaaccesscontrol)addressesforhardwareIPaddressesforsoftwareHostnamesforpeoplePorts16bitnumberAddressparticularprocessesorservicesWell-knownportsaredefinedin/etc/servicesUnixsystemsrestrictaccessportunder1024toroot.
AddressingAddresstypesUnicast–addressesthatrefertoasinglehost(interface)Multicat–addressesthatidentifyagroupofhostsBroadcast–addressesthatincludeallhostsonthelocalnetworkIPaddressesFourbyteslongNetworkpartandhostpartWrittenasdecimalnumbers,oneforeachbyteseparatedbyperiodsWhen127isthefirstbyteofanaddress,itdenotesthe"loopbacknetwork"Lookbackaddress127.
0.
0.
1-localhostAddressingIPaddressclassesThetraditionalclassdeterminewhichbytesoftheaddresswereinthenetworkportionandwhichwereinthehostportionA1-126N.
H.
H.
HVeryearlynetworkB128-191N.
N.
H.
Hlargesites(65536)C192-223N.
N.
N.
H(256)D224-239MultipleaddressesE240-254ExperimentaladdressesAddressingSubnettingandnetmasksHostportionofanaddressis"borrowed"toextendthenetworkportionThisreassignmentisdonebyusingifconfigcommandtoassociateanexplicit"subnetmask"withanetworkinterface.
EachbitofthenetmaskthatcorrespondstothenetworkportionofanIPaddressissetto1,hostbitsaresetto0ThedivisionofnetworkpartandhostpartneednotfallonabyteboundaryNetworkbitsmustbecontiguousandmustappearatthehighorderendoftheaddressesAddressingNotationIpaddressnetmaskIpaddress/lengthofthenetworkpart128.
138.
243.
0/26Example128.
138.
243.
100/24NetmaskNetworkBroadcast128.
138.
243.
100/26100=01100100NetmaskNetworkBroadcastUseipcalctogetthevalues.
AddressingTheIPaddresscrisisFundamentalproblemswiththeoriginalclassallocatingschemeRunoutofBclassesRoutingtableweregrowingsolargeIPaddresswereallocatedonafirst-com,first-servedbasiswithnolocalityofreferencesolutionsShortterm:ClasslessInter-DomainRouting(CIDR)IPV6:extendtheaddressto16bytes665,570,793,348,866,943,898,599addressesAddressingAddressallocationRegionalIPaddressregistriesARINNorthandSouthAmericaAPNICAsia/PacificregionRIPEEuropeandsurroundingareasPrivateaddressesPacketsbearingprivateaddressescannotgetintointernetIPaddressreservedforprivateuse10.
0.
0.
0/8172.
16.
0.
0/12192.
168.
0.
0/16RoutingRoutingistheprocessofdirectingapacketthroughthemazeofnetworksthatstandbetweenitssourceanditsdestination.
Routinginfoisstoredinatableinthekernel.
Examineituse"netstat–r"ConfiguredynamicallyConfigurestatically#routeadd–net132.
236.
220.
64netmask255.
255.
255.
192132.
236.
212.
6#routeadddefault132.
236.
227.
1ARPTheaddressResolutionProtocoldiscoversthehardwareaddressassociatedwithaparticularIPaddress.
APRusesbroadcastpackets,cannotcrossnetworks"Doesanyoneknowthehardwareaddressfor128.
138.
116.
4"Checkthearpcachetablewitharpcommand#/usr/sbin/arp–aRARPReversetranslationQueryacentralservertodiscoveritsownaddressNeedconfigurationAdditionsofmachinestoanetworkBasicstepsareAssignaIPaddressandhostnameSetupthenewhosttoconfigureitsnetworkinterfacesatboottimeSetupadefaultrouteandperhapsfancierroutingPointtoaDNSnameserver,toallowaccesstotherestoftheInternet.
DebuggingAlwaystorebootifchangesaffectbootingAssigninghostnamesandIPaddressesMappinghostnamestoIPHostsfileNISorNIS+DNSOrCombinationaboveHostsfile/etc/hostsEachlinestartwithIP,continueswithvarioussymbolicnamesbywhichthataddressisknown.
EntriesLocalhost,gateway,specialhosts,…ReplicatesamehostsfileonmachinesConfigurehostnameCommandhostnamerunattheboottimeConfigurationfileAssigninghostnamesandIPaddressesConfigurenetworkinterfaces:ifconfigEnableordisablenetworkinterfaceSetIPaddressSetsubnetmaskSetotheroptionsRunattheboottime(usecommandwiththevaluefromconfigurefiles)Format$ifconfiginterfaceaddressoptions…up|downEx:#ifconfigeth0128.
138.
240.
7network255.
255.
255.
0upAssigninghostnamesandIPaddressesInterfacename:IdentifiesthehardwaretowhichthecommandappliesTwoorthreecharacterdevicenamefollowedbyanumber.
Theloopbackinterfaceisnamedlo0ThecommoninterfacenamesareIe0,le0,ln0,we0,hme0,eri0,lan0,…Displaytheinterfaces$netstat–iDisplaythesettingofinterfaces$ifconfig–aAssigninghostnamesandIPaddressesConfigurethenetworkinterfaceTheifconfigcommandssupportmanyoptionsSpecifyaddressSpecifynetmask,otherwiseitusesaddressclass(A,B,C)SpecifybroadcastDefaultcanbecalculatedfromIP+netmaskSomesitessetittoavoidcertaintypesofdenialofserviceattacks.
Notgood.
ActivateordeactivatethedevicedriverUsekeyworkup,down.
Ifconfigallowsyoutoconfigureainterfacecardbyhand,butthevalueisonlyinkernel.
Tomakeitsurvivethereboot,changetherightconfigurationfileConfigurestaticroutesCommandroutedefinesstaticroutesStaticroutewillstayintheroutingtableinmostcaseconfigurethedefaultroutingwhenaddingahosttolocalnetworkRoutingisperformedatwhatlayerThepackets'destinationIPiscomparedwiththeroute,ifitmatches,thepacketisforwardedtothe"nextgateway"IPaddressassociatedwiththatrouteRoutingaddedwhenconfiguretheinterface-PacketsdestinedforhostonadirectoryconnectednetworkDefaultrouteisinvokedwhenthereisnoroutethatmatchesthedestinationaddress.
ConfigurestaticroutesTheformat:#routeop[type]destinationgateway[hop-count]WhereOp:add,delete,get,change,flush,monitorDestination:hostaddress,networkaddress,orthekeyword"default"(0.
0.
0.
0)Gateway:amachinetowhichpacketsshouldbeforwardedMustbeonadirectlyconnectednetworkForwardingcanonlybeperformedonehopatatimeType:-net,-hostChecktheroutingtable:#netstat-nrConfigurestaticroutesdefaultroute#routeadddefaultgateway_ip_addressChangetheconfigurefileSolaris:/etc/defaultrouterHp-UX:/net/rc.
config.
d/netconfRedhat:/etc/sysconfig/networkConfiguringDNSToconfigureamachineasaDNSclientConfigure/etc/resolv.
confListDBSdomainsthatshouldbesearchedtoresolvenamethatareincompleteLinetheIPaddressesofthenameserverstocontactfornamelookupsExample:[ruihong@dafinn~]$more/etc/resolv.
confsearchcs.
mtu.
educsl.
mtu.
edumtu.
edunameserver141.
219.
152.
253nameserver141.
219.
152.
254ConfiguringDNSConfiguretheserviceswitchfileWhichonetakeeffect/etc/hosts,NIS,DNSSolaris,Hp-UX,Redhat:/etc/nsswitch.
confExample:hosts:filesnisdnsClause:[NOTFOUND=return]NetworkconfigurationfilesbysystemAll/etc/hosts/etc/recolv.
confSolaris/etc/hostname.
ifname/etc/nodename/etc/defaultrouter/etc/inet/netmasks/etc/inet/hostsHP-UX/etc/rc.
config.
d/netconfRedHat/etc/sysconfig/networkNetwork-scripts/ifcfg-ifnamePracticeCheckIPaddress/netmask/broadcastrouteArptableHostnameDNSModifyHostnameDnsresearchlistPingwoprDnsserversRemotedefaultroutePingwoprAddthedefaultroutebackagainRebootDHCPDynamicHostConfigurationProtocolDistributenetworkandadministrativeparameterstoDHCPclient,includeIPaddressandnetmasksGatewaysDNSnameserversSysloghostsWINsServers,Xfontservers,proxyservers,NTPserversTFTPservers(forloadingabootimage)Andmore…DHCPHowDHCPworksClientsends"WhoamI"DHCPDISCOVERmessageTobroadcast255.
255.
255.
255With0.
0.
0.
0asitsownaddressServerrespondswithOFFERmessagesClientsendsbackaREQUESTmessagesServerrespondswithACKorNAKClientrenewtheleasebysendinganotherREQUESTmessage
IPstandsforInternetProtocolTCPstandsforTransmissionControlProtocol.
ThenativelanguageoftheInternetSupportedbymostOSs(Unix,MacOS,Windows,Netware,etc)DefinesauniformprogramminginterfacetodifferenttypesofnetworkhardwareTCP/IPandInternet1969ARPAnetExperimentalpacket-switchingnetworkStudyrobust,reliable,vendor-independentdatacommunicationVerysuccessful1975ARPAnetbecameoperationnetworkDevelopmentcontinuingTCP/IPwasdeveloped1983TCP/IPprotocolswereadoptedasMilitaryStandardsTCP/IPwasimplementedinBerkeleyUnix.
ARPAnetwasdividedintoMILNETandARPAnetTCP/IPandInternet1985NSFNetConnectedtothethenexistingInternet(MILNETplusARPAnet)LinkedtogetherthefiveNSFsupercomputercentersWantedtoextendthenetworktoeveryscientist1987newNSFNetbackboneFasterThree-tieredtopology:backbone,regionalnetworks,andlocalnetworks.
TCP/IPandInternet1990ARPAnetpassedoutofexistence1995NSFnetceaseditsroleasaprimaryInternetbackbonenetworkTodayInternetisbuildbycommercialproviders.
InfrastructureisbeingcreatedbyNationalnetworkprovider,callertier-oneprovidersRegionalnetworkproviderLocalaccessanduserservicesisprovidedbyInternetServiceProviders(ISPs)NetworkAccessPoints(NAPS):majorinterconnectionpointsTCP/IPandInternetHowtheinternetismanagedtodayCommercialforceSeveralorganizationInternetCorporationforAssignedNamesandNumbers(ICANN)www.
icann.
orgInternetEngineeringTaskForce(IETE)www.
ietf.
orgInternetSociety(ISOC)www.
isoc.
orgTCP/IPandInternetNetworkstandardsanddocumentationRequestforComments(RFC)Over4000hasbeencreatedFYSTDBCPDispatchcentralforRFC-relatedmatterswww.
rfc-editor.
orgNetworkingRoadMapTCP/IPcomponentsIP,theInternetProtocolroutesdatapacketsfromonemachinetoanotherICMP,theInternetControlMessageProtocolProvidesseveralkindsoflow-levelsupportforIPErrormessageRoutingassistanceDebugginghelpARP,theAddressResolutionProtocolTranslatesIPaddressestohardwareaddressesNetworkingRoadMapUDP,theUserDatagramProtocolDeliversdatatospecificapplicationsonthedestinationmachineProvides"unverified","besteffort"transportforindividualmessagesTCP,theTransmissionControlProtocolDeliversdatatospecificapplicationsonthedestinationmachineProvidesreliable,flowcontrolled,errorcorrectedconversationbetweenprocessesontwohosts.
TCP/IPnetworkmodelUTPcopper,fiber,radiawavesARP,DeviceDriversIPICMPTCPUDPARPSSH,FTP,WEBDNS,QuakeTraeroutePhysicallayerLinkLayerNetworkLayerTransportLayerApplicationLayerPacketsandencapsulationDatatravelsonanetworkintheformofpacketsEachpacketconsistsofAheader–whereitcamefromandwhereit'sgoing,protocolinfo,checksum,etc.
Apayload-dataAsapackettravelsdowntheprotocolstackencapsulationEachprotocoladdsitsownheaderinformationEachprotocol'sfinishedpacketbecomesthepayloadpartofthepacketgeneratedbythenextprotocol.
Onareceivingmachine,theencapsulationisreversedasthepackettravelsbackuptheprotocolstack.
PacketsandEncapsulationExample:AtypicalnetworkpacketEthernetheaderIPheaderUDPheaderApplicationdataEthernetCRCUDPpacket(108bytes)IPpacket(128bytes)Ethernetframe(146bytes)AddressingPacketsaddressingPacketsmustbeproperlyaddressedinordertoreachtheirdestinationAddressingschemesMAC(mediaaccesscontrol)addressesforhardwareIPaddressesforsoftwareHostnamesforpeoplePorts16bitnumberAddressparticularprocessesorservicesWell-knownportsaredefinedin/etc/servicesUnixsystemsrestrictaccessportunder1024toroot.
AddressingAddresstypesUnicast–addressesthatrefertoasinglehost(interface)Multicat–addressesthatidentifyagroupofhostsBroadcast–addressesthatincludeallhostsonthelocalnetworkIPaddressesFourbyteslongNetworkpartandhostpartWrittenasdecimalnumbers,oneforeachbyteseparatedbyperiodsWhen127isthefirstbyteofanaddress,itdenotesthe"loopbacknetwork"Lookbackaddress127.
0.
0.
1-localhostAddressingIPaddressclassesThetraditionalclassdeterminewhichbytesoftheaddresswereinthenetworkportionandwhichwereinthehostportionA1-126N.
H.
H.
HVeryearlynetworkB128-191N.
N.
H.
Hlargesites(65536)C192-223N.
N.
N.
H(256)D224-239MultipleaddressesE240-254ExperimentaladdressesAddressingSubnettingandnetmasksHostportionofanaddressis"borrowed"toextendthenetworkportionThisreassignmentisdonebyusingifconfigcommandtoassociateanexplicit"subnetmask"withanetworkinterface.
EachbitofthenetmaskthatcorrespondstothenetworkportionofanIPaddressissetto1,hostbitsaresetto0ThedivisionofnetworkpartandhostpartneednotfallonabyteboundaryNetworkbitsmustbecontiguousandmustappearatthehighorderendoftheaddressesAddressingNotationIpaddressnetmaskIpaddress/lengthofthenetworkpart128.
138.
243.
0/26Example128.
138.
243.
100/24NetmaskNetworkBroadcast128.
138.
243.
100/26100=01100100NetmaskNetworkBroadcastUseipcalctogetthevalues.
AddressingTheIPaddresscrisisFundamentalproblemswiththeoriginalclassallocatingschemeRunoutofBclassesRoutingtableweregrowingsolargeIPaddresswereallocatedonafirst-com,first-servedbasiswithnolocalityofreferencesolutionsShortterm:ClasslessInter-DomainRouting(CIDR)IPV6:extendtheaddressto16bytes665,570,793,348,866,943,898,599addressesAddressingAddressallocationRegionalIPaddressregistriesARINNorthandSouthAmericaAPNICAsia/PacificregionRIPEEuropeandsurroundingareasPrivateaddressesPacketsbearingprivateaddressescannotgetintointernetIPaddressreservedforprivateuse10.
0.
0.
0/8172.
16.
0.
0/12192.
168.
0.
0/16RoutingRoutingistheprocessofdirectingapacketthroughthemazeofnetworksthatstandbetweenitssourceanditsdestination.
Routinginfoisstoredinatableinthekernel.
Examineituse"netstat–r"ConfiguredynamicallyConfigurestatically#routeadd–net132.
236.
220.
64netmask255.
255.
255.
192132.
236.
212.
6#routeadddefault132.
236.
227.
1ARPTheaddressResolutionProtocoldiscoversthehardwareaddressassociatedwithaparticularIPaddress.
APRusesbroadcastpackets,cannotcrossnetworks"Doesanyoneknowthehardwareaddressfor128.
138.
116.
4"Checkthearpcachetablewitharpcommand#/usr/sbin/arp–aRARPReversetranslationQueryacentralservertodiscoveritsownaddressNeedconfigurationAdditionsofmachinestoanetworkBasicstepsareAssignaIPaddressandhostnameSetupthenewhosttoconfigureitsnetworkinterfacesatboottimeSetupadefaultrouteandperhapsfancierroutingPointtoaDNSnameserver,toallowaccesstotherestoftheInternet.
DebuggingAlwaystorebootifchangesaffectbootingAssigninghostnamesandIPaddressesMappinghostnamestoIPHostsfileNISorNIS+DNSOrCombinationaboveHostsfile/etc/hostsEachlinestartwithIP,continueswithvarioussymbolicnamesbywhichthataddressisknown.
EntriesLocalhost,gateway,specialhosts,…ReplicatesamehostsfileonmachinesConfigurehostnameCommandhostnamerunattheboottimeConfigurationfileAssigninghostnamesandIPaddressesConfigurenetworkinterfaces:ifconfigEnableordisablenetworkinterfaceSetIPaddressSetsubnetmaskSetotheroptionsRunattheboottime(usecommandwiththevaluefromconfigurefiles)Format$ifconfiginterfaceaddressoptions…up|downEx:#ifconfigeth0128.
138.
240.
7network255.
255.
255.
0upAssigninghostnamesandIPaddressesInterfacename:IdentifiesthehardwaretowhichthecommandappliesTwoorthreecharacterdevicenamefollowedbyanumber.
Theloopbackinterfaceisnamedlo0ThecommoninterfacenamesareIe0,le0,ln0,we0,hme0,eri0,lan0,…Displaytheinterfaces$netstat–iDisplaythesettingofinterfaces$ifconfig–aAssigninghostnamesandIPaddressesConfigurethenetworkinterfaceTheifconfigcommandssupportmanyoptionsSpecifyaddressSpecifynetmask,otherwiseitusesaddressclass(A,B,C)SpecifybroadcastDefaultcanbecalculatedfromIP+netmaskSomesitessetittoavoidcertaintypesofdenialofserviceattacks.
Notgood.
ActivateordeactivatethedevicedriverUsekeyworkup,down.
Ifconfigallowsyoutoconfigureainterfacecardbyhand,butthevalueisonlyinkernel.
Tomakeitsurvivethereboot,changetherightconfigurationfileConfigurestaticroutesCommandroutedefinesstaticroutesStaticroutewillstayintheroutingtableinmostcaseconfigurethedefaultroutingwhenaddingahosttolocalnetworkRoutingisperformedatwhatlayerThepackets'destinationIPiscomparedwiththeroute,ifitmatches,thepacketisforwardedtothe"nextgateway"IPaddressassociatedwiththatrouteRoutingaddedwhenconfiguretheinterface-PacketsdestinedforhostonadirectoryconnectednetworkDefaultrouteisinvokedwhenthereisnoroutethatmatchesthedestinationaddress.
ConfigurestaticroutesTheformat:#routeop[type]destinationgateway[hop-count]WhereOp:add,delete,get,change,flush,monitorDestination:hostaddress,networkaddress,orthekeyword"default"(0.
0.
0.
0)Gateway:amachinetowhichpacketsshouldbeforwardedMustbeonadirectlyconnectednetworkForwardingcanonlybeperformedonehopatatimeType:-net,-hostChecktheroutingtable:#netstat-nrConfigurestaticroutesdefaultroute#routeadddefaultgateway_ip_addressChangetheconfigurefileSolaris:/etc/defaultrouterHp-UX:/net/rc.
config.
d/netconfRedhat:/etc/sysconfig/networkConfiguringDNSToconfigureamachineasaDNSclientConfigure/etc/resolv.
confListDBSdomainsthatshouldbesearchedtoresolvenamethatareincompleteLinetheIPaddressesofthenameserverstocontactfornamelookupsExample:[ruihong@dafinn~]$more/etc/resolv.
confsearchcs.
mtu.
educsl.
mtu.
edumtu.
edunameserver141.
219.
152.
253nameserver141.
219.
152.
254ConfiguringDNSConfiguretheserviceswitchfileWhichonetakeeffect/etc/hosts,NIS,DNSSolaris,Hp-UX,Redhat:/etc/nsswitch.
confExample:hosts:filesnisdnsClause:[NOTFOUND=return]NetworkconfigurationfilesbysystemAll/etc/hosts/etc/recolv.
confSolaris/etc/hostname.
ifname/etc/nodename/etc/defaultrouter/etc/inet/netmasks/etc/inet/hostsHP-UX/etc/rc.
config.
d/netconfRedHat/etc/sysconfig/networkNetwork-scripts/ifcfg-ifnamePracticeCheckIPaddress/netmask/broadcastrouteArptableHostnameDNSModifyHostnameDnsresearchlistPingwoprDnsserversRemotedefaultroutePingwoprAddthedefaultroutebackagainRebootDHCPDynamicHostConfigurationProtocolDistributenetworkandadministrativeparameterstoDHCPclient,includeIPaddressandnetmasksGatewaysDNSnameserversSysloghostsWINsServers,Xfontservers,proxyservers,NTPserversTFTPservers(forloadingabootimage)Andmore…DHCPHowDHCPworksClientsends"WhoamI"DHCPDISCOVERmessageTobroadcast255.
255.
255.
255With0.
0.
0.
0asitsownaddressServerrespondswithOFFERmessagesClientsendsbackaREQUESTmessagesServerrespondswithACKorNAKClientrenewtheleasebysendinganotherREQUESTmessage
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