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D-Link DWS-4026 [93/741] Configuring sntp settings

ConfiguringSNTPSettings

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

November2011 Page93

D‐LinkUWSUserManual

ConfiguringSNTPSet tings

D‐LinkDWS‐4000SeriesDWS‐4000SeriesswitchsoftwaresupportstheSimpleNetworkTimeProtocol(SNTP).

SNTPassuresaccuratenetworkdeviceclocktimesynchronizationuptothemillisecond.Timesynchronization

isperformedbyanetworkSNTPserver.D‐LinkDWS‐4000SeriessoftwareoperatesonlyasanSNTPclientand

can

notprovidetimeservicestoothersystems.

TimesourcesareestablishedbyStratums.Stratumsdefinetheaccuracyoftheref erenceclock.Thehigherthe

stratum(wherezeroisthehighest),themoreaccuratetheclock.Thedevicereceivestimefromstratum1and

abovesinceitisitselfastratum2de

vice.

Thefollowingisanexampleofstratums:

• Stratum0:Arealtimeclockisusedasthetimesource,forexample,aGPSsystem.

• Stratum1:AserverthatisdirectlylinkedtoaStratum0timesourceisused.Stratum1timeservers

provideprimarynetworktimestandards.

• St

ratum2:ThetimesourceisdistancedfromtheStratum1serveroveranetworkpath.Forexample,a

Stratum2serverreceivesthetimeoveranetworklink,viaNTP,fromaStratum1server.

InformationreceivedfromSNTPserversisev aluate dbasedonthetimelevelandservertype

SNTPtimedefinitionsareassessedanddeterminedbythefollowingtimelevels:

• T1:Timeatwhichtheoriginalrequestwassentbytheclient.

• T2:Timeatwhichtheoriginalrequestwasreceivedbytheserver.

• T3:Timeatwhichtheserversentareply.

• T4:Timeatwhichtheclien

treceivedtheserver'sreply.

ThedevicecanpollUnicastandBroadcastservertypesfortheservertime.

PollingforUnicastinformationisusedforpollingaserverforwhichtheIPaddressisknown.SNTPserversthat

havebeenconfiguredonthedevicearetheonlyonesthatar

epolledforsynchronizationinformation.T1

throughT4areusedtodetermineservertime.Thisisthepreferredmethodforsynchronizingdevicetime

becauseitisthemostsecuremethod.Ifthismethodisselected,SNTPinformationisacceptedonlyfromSN TP

serversdefinedonthedeviceusingtheSNTPSer

verConfigurationpage.

Broadca stinformationisusedwhentheserverIPaddressisunknown.WhenaBroadcastmessageissentfrom

anSNTPserver,theSNTPclientlistenstothemessage.IfBroadca stpollingisenabled,anysynchronization

informationisaccepted,evenifithasnotbeenrequestedbythedevice.Thi

sistheleastsecuremethod.

Thedeviceretrievessynchronizationinformation,eitherbyactivelyrequestinginformationorateverypoll

interval.IfUnicastandBroadcastpollingareenabled,theinformationisretrievedinthisorder:

•Informationfromserversdefinedonthedeviceispreferred.IfUnicastpollingisnotenabledorifno

rversaredefinedonthedevice,thedeviceacceptstimeinformationfromanySNTPserverthat

responds.

•IfmorethanoneUnicastdeviceresponds,synchronizationinformationispreferredfromthedevicewith

theloweststratum.

•Iftheservershavethesamestratum,synchronizationinformationisacceptedfromtheSNTPser

verthat

respondedfirst.

D-Link DWS-4026 [93/741] Configuring sntp settings

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