D-Link DWS-4026 [252/741] Dhcp snooping vlan configuration

ConfiguringDHCPSnooping

D-Link UnifiedWiredandWirelessAccessSystem

November2011 Page252

D‐LinkUWSUserManual

DHCPSnoopingVLANConfiguration

TheDHCPsnoopingapplicationdoesnotforwardservermessagesbecausetheyareforwardedinhardware.

DHCPsnoopingforwardsvalidDHCPclientmessagesreceivedonnon‐routingVLANs.Themessageis

forwardedonalltrustedinterfacesintheVLAN.

DHCPsnoopingcanbeconfiguredonswitchingVLANsandroutingVLANs.WhenaDHCPpac

ketisreceivedon

aroutingVLAN,theDHCPsnoopingapplicationappliesitsfilteringrulesandupdatesthebindingsdatabase.If

aclientmessagepassesfilteringrules,themessageisplacedintothesoftwareforwardingpath,whereitmay

beprocessedbytheDHCPrelayagent,thelocalDHCPserver,orfo

rwardedasanIPpacket.

DHCPsnoopingisdisabledgloballyandonallVLANsbydefault.Portsareuntrustedbydefault.

ToaccesstheDHCPSnoopingVLANConfigurationpage,clickLAN>L2Features >DHCPSnooping>VLAN

Configurationinthenavigationtree.

Figure157:DHCPSnoopingVLANConfiguration

•ClickSubmittoapplythenewc

onfigurationandcausethechangetotakeeffect.Thesechangeswillnot

beretainedacrossapowercycleunlessaSaveconfigurationisperformed.

DHCPSnoopingInterfaceConfiguration

ThehardwareratelimitsDHCPpacketssenttotheCPUfromuntrustedinterfacesto15packetspersecond.

Thereisnohardwareratelimitingontrustedinterfaces.

TopreventDHCPpacketsfrombeingusedasaDoSattackwhenDHCPsnoopingisenabled,thesnooping

applicationenforcesaratelimit forDHCPpa

cketsreceivedonuntrustedinterfaces.DHCPsnoopingmonitors

thereceiverateoneachinterfaceseparately.Ifthereceiverateexceedstheconfigurationlimit,DHCPsnooping

bringsdowntheinterface.Youmustdo“noshutdown”onthisinterfacetofurtherworkwiththatport.Youcan

configureboththerateandthebur

stinterval.

Table138:DHCPSnoopingVLANConfiguration

Field Description

VLANID SelecttheVLANforwhichinformationtobedisplayedorconfiguredforthe

DHCPsnoopingapplication.

DHCPSnoopingMode EnablesordisablestheDHCPsnoopingfeatureontheselectedVLAN.The

defaultisDisable.