IP Addressing: DHCP Configuration Guide, Cisco IOS XE Fuji 16.8.x

152 Pages·2017·3.32 MB·English

IP Addressing: DHCP Configuration Guide, Cisco IOS XE Fuji 16.8.x
(NCS 4200 Series)
First Published: 2018-03-16
Americas Headquarters
Cisco Systems, Inc.
170 West Tasman Drive
San Jose, CA 95134-1706
USA
http://www.cisco.com
Tel: [phone]
800 553-NETS (6387)
Fax: [phone]
©2018CiscoSystems,Inc.Allrightsreserved.
CONTENTS
CHAPTER 1 DHCPOverview 1
InformationAboutDHCP 1
DHCPOverview 1
LimitationsandRestrictionsforDHCP 2
BenefitsofUsingDHCP 2
DHCPServerRelayAgentandClientOperation 3
DHCPDatabase 4
DHCPAttributeInheritance 4
DHCPOptionsandSuboptions 4
AdditionalReferencesforDHCPOverview 6
Glossary 7
CHAPTER 2 ConfiguringtheCiscoIOSXEDHCPServer 9
PrerequisitesforConfiguringtheDHCPServer 9
InformationAbouttheCiscoIOSXEDHCPServer 10
OverviewoftheDHCPServer 10
DatabaseAgents 10
AddressConflicts 10
DHCPAddressPoolConventions 10
DHCPAddressPoolSelection 10
AddressBindings 11
PingPacketSettings 11
DHCPAttributeInheritance 12
DHCPServerAddressAllocationUsingOption82 12
DHCPAddressAllocationUsingOption82FeatureDesign 13
UsageScenarioforDHCPAddressAllocationUsingOption82 14
DHCPClassCapability 14
HowtoConfiguretheCiscoIOSXEDHCPServer 15
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ConfiguringaDHCPDatabaseAgentorDisablingConflictLogging 15
ExcludingIPAddresses 16
ConfiguringDHCPAddressPools 17
ConfiguringaDHCPAddressPool 17
ConfiguringaDHCPAddressPoolwithSecondarySubnets 22
TroubleshootingTips 27
VerifyingtheDHCPAddressPoolConfiguration 27
ConfiguringManualBindings 29
TroubleshootingTips 31
ConfiguringDHCPStaticMapping 31
ConfiguringtheDHCPServertoReadaStaticMappingTextFile 33
CustomizingDHCPServerOperation 35
ConfiguringaRemoteDevicetoImportDHCPServerOptionsfromaCentralDHCP
Server 37
ConfiguringtheCentralDHCPServertoUpdateDHCPOptions 37
ConfiguringtheRemoteDevicetoImportDHCPOptions 39
ConfiguringDHCPAddressAllocationUsingOption82 41
RestrictionsforDHCPAddressAllocationUsingOption82 41
EnablingOption82forDHCPAddressAllocation 41
TroubleshootingTips 42
DefiningtheDHCPClassandRelayAgentInformationPatterns 42
TroubleshootingTips 43
DefiningtheDHCPAddressPool 43
ConfiguringaStaticRoutewiththeNext-HopDynamicallyObtainedThroughDHCP 45
ClearingDHCPServerVariables 47
ConfigurationExamplesfortheCiscoIOSXEDHCPServer 48
Example:ConfiguringtheDHCPDatabaseAgent 48
Example:ExcludingIPAddresses 48
Example:ConfiguringDHCPAddressPools 48
Example:ConfiguringaDHCPAddressPoolwithMultipleDisjointSubnets 49
ConfiguringManualBindingsExample 51
Example:ConfiguringStaticMapping 51
ImportingDHCPOptionsExample 51
ConfiguringDHCPAddressAllocationUsingOption82Example 52
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ConfiguringaStaticRoutewiththeNext-HopDynamicallyObtainedThroughDHCP
Example 53
AdditionalReferences 54
CHAPTER 3 ConfiguringtheCiscoIOSXEDHCPClient 57
InformationAbouttheDHCPClient 57
DHCPClientOperation 57
DHCPClientOverview 58
HowtoConfiguretheDHCPClient 59
ConfiguringtheDHCPClient 59
TroubleshootingTips 60
ConfigurationExamplesfortheDHCPClient 60
ConfiguringtheDHCPClientExample 60
CustomizingtheDHCPClientConfigurationExample 61
AdditionalReferences 61
TechnicalAssistance 62
CHAPTER 4 ISSUandSSO--DHCPHighAvailabilityFeatures 63
FindingFeatureInformation 64
PrerequisitesforDHCPHighAvailability 64
RestrictionsforDHCPHighAvailability 64
InformationAboutDHCPHighAvailability 64
ISSU 64
SSO 64
ISSUandSSO--DHCPServer 65
ISSUandSSO--DHCPRelayonUnnumberedInterface 65
ISSUandSSO--DHCPProxyClient 66
ISSUandSSO--DHCPODAPClientandServer 67
HowtoConfigureDHCPHighAvailability 68
ConfigurationExamplesforDHCPHighAvailability 68
AdditionalReferences 68
FeatureInformationforDHCPHighAvailabilityFeatures 70
Glossary 71
CHAPTER 5 ImplementingDHCPforIPv6 73
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DHCPv6PrefixDelegation 73
ConfiguringNodesWithoutPrefixDelegation 73
ClientandServerIdentification 74
RapidCommit 74
DHCPv6ClientandRelayFunctions 74
ClientFunction 74
DHCPv6RelayAgent 75
DHCPv6RelaySSOandISSU 76
HowtoImplementDHCPforIPv6 78
ConfiguringtheDHCPv6ServerFunction 78
ConfiguringtheDHCPv6ConfigurationPool 78
ConfiguringaBindingDatabaseAgentfortheServerFunction 80
ConfiguringtheDHCPv6ClientFunction 81
ConfiguringtheDHCPv6RelayAgent 83
ConfiguringRouteAdditionforRelayandServer 84
DefiningaGeneralPrefixwiththeDHCPv6PrefixDelegationClientFunction 84
ConfiguringaVRF-AwareRelayforMPLSVPNSupport 85
ConfiguringaVRF-AwareRelay 85
RestartingtheDHCPv6ClientonanInterface 87
DeletingAutomaticClientBindingsfromtheDHCPv6BindingTable 87
TroubleshootingDHCPv6 88
VerifyingtheDHCPv6Configuration 89
ExampleVerifyingtheDHCPv6Configuration 90
ConfigurationExamplesforImplementingDHCPv6 92
Example:ConfiguringtheDHCPv6ClientFunction 92
CHAPTER 6 IPv6AccessServices:DHCPv6RelayAgent 95
InformationAboutIPv6AccessServices:DHCPv6RelayAgent 95
DHCPv6RelayAgent 95
DHCPv6RelayAgentNotificationforPrefixDelegation 97
DHCPv6RelayOptions:RemoteIDforEthernetInterfaces 97
DHCPv6RelayOptions:ReloadPersistentInterfaceIDOption 98
DHCPv6RelayChaining 98
HowtoConfigureIPv6AccessServices:DHCPv6RelayAgent 98
ConfiguringtheDHCPv6RelayAgent 98
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ConfigurationExamplesforIPv6AccessServices:DHCPv6RelayAgent 100
Example:ConfiguringtheDHCPv6RelayAgent 100
AdditionalReferences 100
CHAPTER 7 DHCPFeaturesConfiguration 103
LimitationsandRestrictions 103
DHCPFeatures 103
DHCPServer 104
DHCPRelayAgent 104
DHCPSnooping 104
Option-82DataInsertion 105
CiscoIOSDHCPServerDatabase 108
DHCPSnoopingBindingDatabase 108
ConfiguringDHCPFeatures 110
DefaultDHCPConfiguration 110
DHCPSnoopingConfigurationGuidelines 111
ConfiguringtheDHCPServer 112
ConfiguringtheDHCPRelayAgent 112
SpecifyingthePacketForwardingAddress 113
EnablingDHCPSnoopingandOption82 114
EnablingtheCiscoIOSDHCPServerDatabase 116
EnablingtheDHCPSnoopingBindingDatabaseAgent 116
StoppingtheDatabaseAgentandBindingfiles 117
ClearingtheStatisticsoftheDHCPSnoopingBindingDatabaseAgent 117
DeletingBindingEntriesfromtheDHCPSnoopingBindingDatabase 118
DisablingDHCPSnooping 118
DisplayingDHCPSnoopingInformation 118
Pre-assignedAddressReservedintheDHCPPool 118
AutomaticGenerationofSubscriberIdentifier 119
DHCPServerPort-BasedAddressAllocation 119
DHCPServerPort-BasedAddressAllocation 120
ConfiguringDHCPServerPort-BasedAddressAllocation 120
DefaultPort-BasedAddressAllocationConfiguration 120
Port-BasedAddressAllocationConfigurationGuidelines 120
EnablingDHCPServerPort-BasedAddressAllocation 121
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Pre-assigningIPAddresses 122
RemovinganIPAddressReservationfromaDHCPPool 123
AutomaticGenerationofSubscriberIdentifier 123
DisablingDHCPPort-BasedAddressAllocation 124
DisplayingDHCPServerPort-BasedAddressAllocation 124
AdditionalReferences 124
CHAPTER 8 ConfigurationofDynamicARPInspection 127
DynamicARPInspection 127
InterfaceTrustStatesandNetworkSecurity 129
RateLimitingofARPPackets 130
LoggingofDroppedPackets 130
ConfiguringDynamicARPInspection 131
DefaultDynamicARPInspectionConfiguration 131
DynamicARPInspectionConfigurationGuidelines 131
ConfiguringDynamicARPInspectioninDHCPEnvironments 132
ExampleforConfiguringDynamicARPInspection 134
DisablingDynamicARPInspection 134
ConfiguringARPACLsforNon-DHCPEnvironments 134
ExampleforConfiguringanARPACL 136
RemovingtheARPACL 137
LimitingtheRateofIncomingARPPackets(optional) 137
PerformingValidationChecks(optional) 138
ConfiguringtheLogBuffer(optional) 140
ReturningtotheDefaultLogBufferSettings 141
DisplayingDynamicARPInspectionInformation 142
ClearingorDisplayingDynamicARPInspectionStatistics 142
ClearingorDisplayingDynamicARPInspectionLoggingInformation 143
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CHAPTER
DHCP Overview
TheDynamicHostConfigurationProtocol(DHCP)isbasedontheBootstrapProtocol(BOOTP),which
providestheframeworkforpassingconfigurationinformationtohostsonaTCP/IPnetwork.DHCPadds
thecapabilitytoautomaticallyallocatereusablenetworkaddressesandconfigurationoptionstoInternet
hosts.DHCPconsistsoftwocomponents:aprotocolfordeliveringhost-specificconfigurationparameters
fromaDHCPservertoahostandamechanismforallocatingnetworkaddressestohosts.DHCPisbuilton
aclient/servermodel,wheredesignatedDHCPserverhostsallocatenetworkaddressesanddeliver
configurationparameterstodynamicallyconfiguredhosts.
ThismoduledescribestheconceptsneededtounderstandCiscoIOSXEDHCP.
• InformationAboutDHCP, page 1
• AdditionalReferencesforDHCPOverview, page 6
• Glossary, page 7
Information About DHCP
DHCP Overview
CiscoroutersrunningCiscoIOSXEsoftwareincludeDynamicHostControlProtocol(DHCP)serverand
relayagentsoftware.TheCiscoIOSXEDHCPserverisafullDHCPserverimplementationthatassignsand
managesIPaddressesfromspecifiedaddresspoolswithintheroutertoDHCPclients.Theseaddresspools
canalsobeconfiguredtosupplyadditionalinformationtotherequestingclientsuchastheIPaddressofthe
DNSserver,thedefaultrouter,andotherconfigurationparameters.IftheCiscoIOSXEDHCPservercannot
satisfyaDHCPrequestfromitsowndatabase,itcanforwardtherequesttooneormoresecondaryDHCP
serversdefinedbythenetworkadministrator.
DHCPsupportsthreemechanismsforIPaddressallocation:
•Automaticallocation—DHCPassignsapermanentIPaddresstoaclient.
•Dynamicallocation—DHCPassignsanIPaddresstoaclientforalimitedperiodoftime,whichiscalled
alease(oruntiltheclientexplicitlyrelinquishestheaddress).DHCPalsosupportson-demandaddress
pools(ODAPs),whichisafeatureinwhichpoolsofIPaddressescanbedynamicallyincreasedor
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DHCP Overview
Limitations and Restrictions for DHCP
reducedinsizedependingontheaddressutilizationlevel.ODAPssupportaddressassignmentfor
customersusingprivateaddresses.
•Manualallocation—ThenetworkadministratorassignsanIPaddresstoaclientandDHCPisused
simplytoconveytheassignedaddresstotheclient.
TheformatofDHCPmessagesisbasedontheformatofBOOTPmessages,whichensuressupportforBOOTP
relayagentfunctionalityandinteroperabilitybetweenBOOTPclientsandDHCPservers.BOOTPrelayagents
eliminatetheneedfordeployingaDHCPserveroneachphysicalnetworksegment.BOOTPisexplainedin
RFC951,BootstrapProtocol(BOOTP),andRFC1542,ClarificationsandExtensionsfortheBootstrap
Protocol.
ThemainadvantageofDHCPcomparedtoBOOTPisthatDHCPdoesnotrequirethattheDHCPserverbe
configuredwithallMACaddressesofallclients.DHCPdefinesaprocessbywhichtheDHCPserverknows
theIPsubnetinwhichtheDHCPclientresides,anditcanassignanIPaddressfromapoolofvalidIPaddresses
inthatsubnet.MostoftheotherinformationthatDHCPmightsupply,suchasthedefaultrouterIPaddress,
isthesameforallhostsinthesubnetsoDHCPserverscanusuallyconfigureinformationpersubnetrather
thanperhost.ThisfunctionalityreducesnetworkadministrationtaskscomparedtoBOOTP.
Limitations and Restrictions for DHCP
ThefollowinglimitationsandrestrictionsapplywhenconfiguringDHCPfeatures:
•Thedhcpsnoopingfeatureisnotsupported.
•Option82isnotsupported.
•TheroutercannotbeusedasaDHCPv6server.
•Forbulkleasequerysupport,useanexternalDHCPv6server.
Benefits of Using DHCP
TheDHCPimplementationoffersthefollowingbenefits:
•ReducedInternetaccesscosts
UsingautomaticIPaddressassignmentateachremotesitesubstantiallyreducesInternetaccesscosts.
StaticIPaddressesareconsiderablymoreexpensivetopurchasethanareautomaticallyallocatedIP
addresses.
•Reducedserverconfigurationtasksandcosts
BecauseDHCPiseasytoconfigure,itminimizesoperationaloverheadandcostsassociatedwithdevice
configurationtasksandeasesdeploymentbynontechnicalusers.
•Centralizedmanagement
BecausetheDHCPservermaintainsconfigurationsforseveralsubnets,anadministratoronlyneedsto
updateasingle,centralserverwhenconfigurationparameterschange.
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