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Inline NAC Design Procedures

Enterasys NAC Design Guide 5-29

However,theclosertheNACControllerisplacedtotheedgeofthenetwork,themoreNAC

Controllersarerequiredonthenetwork,increasingNACdeploymentcostandcomplexity.

Conversely,whenmovingtheNACControllertowardsthecoreofthenetwork,fewerNAC

Controllersarerequired,decreasingNACdeploymentcostand

complexity, butalsodecreasing

thelevelofsecurity.

ForimplementingNAConwiredandwirelessLANs,itisrecommendedthattheLayer2NAC

Controllerispositionedbetweentheaccesslay eranddistributionlayerbeforethefirstroutedhop

inthenetwork.Asanalternative,theNACControllermaybepositioned

deeperintothenetwork

afterthefirstroutedhopusingtheLayer3configuration.TheLayer3NACControllercanalsobe

positionedafteraVPNconcentratororWANconnectiontoimplementNACforremoteusers.

Unliketheout‐of‐bandNACdesign,theimplementationofremediationand/orMAC(network)

registrationdoesnotaffectthelocationoftheNACController.TheNACControllerwill

appropriatelyinterceptwebtrafficforthepurposeofremediationandregistration.

Lastly,itshouldbeunderstoodthatsomeadva ntagesexistwiththedeploymentofaLayer2NAC

ControlleroveraLayer3NACController,whichmay

affectthedecisionofhowNACControllers

arepositioned.WhileaLayer2NACControlleralwaysknowstheMACaddressofthe

downstreamconnectedend‐system,theLayer3NACControllermaynotbeabletodeterminethe

MACaddressofadownstreamend‐system(denotedas“Unknown”inNACManager.)



TechniquessuchasNetBIOSlookupsandDHCPsnoopingareimplementedtoattempttoresolve

theIPaddressofthedownstreamconnectedend‐systems;however,scenariosexistwheretheIP

addressofthedownstreamend‐systemmaynotbedetermined.

TheMACaddressofadownstreamend‐systemwillbedetermined

bytheNACControllerinthe

followingscenarios:

•End‐systemssupportNetBIOSandahostfirewalldoesnotdropinboundNetBIOS requests 

fortheLANconnection.

•DHCPisimplementedandtheDHCPserverexistsupstreamfromtheNACController.

SincetheLayer3NACControllermaynotbeabletodeterminethe

MACaddressofa

downstreamend‐system,“LockMAC”andMACoverridesarenotapplicabletoLayer3NAC

Controllers.Furthermore,MAC(network)registrationmaynotbeimplementedwhentheMAC

addressofadownstreamconnectedend‐systemisunknown.Inthiscase,theend‐systemis

assignedtheSecurityDomain’s

defaultNACconfiguration.

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Enterasys-networks 9034385 Manual de usuario Pagina 93