D-Link DWS-4026 [284/741] Configuring arp

ConfiguringARP

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

November2011 Page284

D‐LinkUWSUserManual

ConfiguringARP

TheARPprotocolassociatesalayer2MACaddresswithalayer3IPv4address.D‐LinkDWS‐4000Series

softwarefeaturesbothdynamicandmanualARPconfiguration.WithmanualARPconfiguration,youcan

staticallyaddentriesintotheARPtable.

ARPisanecessarypartoftheinternetprotocol(IP)andisuse

dtotranslateanIPaddresstoamedia(MAC)

address,definedbyalocalareanetwork(LAN)suchasEthernet.AstationneedingtosendanIPpacketmust

learntheMACaddressoftheIPdestination,orofthenexthoprouter,ifthedestinationisnotonthesame

bnet.ThisisachievedbybroadcastinganARPrequestpacket,towhichtheintendedrecipientrespondsby

unicastinganARPreplycontainingitsMACaddress.Oncelearned,theMACaddressisusedinthedestination

addressfieldofthelayer2headerprependedtotheIPpacket.

TheARPca

cheisatablemaintainedlocallyineachstationonanetwork.ARPcacheentriesarelearnedby

examiningthesourceinformationintheARPpacketpayloadfields,regardlessofwhetheritisanARPrequest

orresponse.Thus,whenanARPrequestisbroa dcasttoallstationsonaLANsegmen

torvirtualLAN(VLAN),

everyrecipienthastheopportunitytostorethesender’sIP andMACaddressintheirrespectiveARPcache.

TheARPresponse,beingunicast,isnormallyseenonlybytherequestor,whostoresthesenderinformationin

itsARPcache.Newerinformationalwaysreplacesexistingconte

ntintheARPcache.

ThenumberofsupportedARPentriesisplatform‐dependent2048fortheD‐LinkUnifiedSwitch.

Devicescanbemovedinanetwork,whichmeanstheIPaddressthatwasatonetimeassociatedwithacertain

MACaddressisnowfoundusingadifferentMAC,ormayha

vedisappearedfromthenetworkaltogether(i.e.,

ithasbeenreconfigured,disconnected,orpoweredoff).ThisleadstostaleinformationintheARPcacheunless

entriesareupdatedinreactiontonewinformationseenonthenetwork,periodicallyrefreshedtodetermine

ifanaddressstillexists,orremovedfromtheca

cheiftheentryhasnotbeenidentifiedasasenderofanARP

packetduringthecourseofanageoutinterval,usuallyspecifiedviaconfiguration.

UDPTTLExpiredPktsReceived SpecifiesthenumberofUDPpacketsreceivedwithexpiredTTL.

UDPPktsDiscarded SpecifiesthenumberofUDPpacketsdiscarded.

Table165:IPHelper–Help

erStatisticsFields(Cont.)

Field Description