Specifications

LSNAT Overview
September 8, 2010 Page 6 of 28
configuredwiththedefaultweight,eachrealserveristreatedequallyasdescribedinthesimple
roundrobin.Whenanon‐defaultweightisappliedtoanyrealserversintheserverfarm,the
algorithmtakesthatweightintoaccountwhenassigningsessionstotherealservers.
Considerthefollowingexample.
Aserverfarmcontainsthreerealserverswiththefollowing
weights:serverAhasaweightof1,serverBhasaweightof2,andserverChasaweightof3.For
eachsix(thesumofthethreeweights)activesessions,serverAwillbeassigned
1session,serverB
willbeassigned2sessions,andserverCwillbeassigned3sessionsinaroundrobinfashion.For
thisexample,theweightratiobetweenthethreeserverswouldbe1:2:3.
Least Connections
Theleastconnectionsalgorithmalwaysassignsthenextsessiontotheserverwiththeleast
numberofactivesessionscurrentlyassigned.
Stickiness
StickinessreferstotheabilityofavirtualservertoassociatetheclientsourceIPaddress(and
optionally,destinationIPanddestinationUDP/TCPportnumber)IPnetworktupleinformationto
arealserver.
Avirtualserverusingstickinesswillcreateastickyentrywhenitcreatesabinding.Thesticky
entry
containsamappingoftheIPnetworktupleinformationandtherealserverthatwas
selected.Thebindingscancomeandgobutthestickyentriespersistusingaseparateidletimer.
Whenanewrequestisprocessedbyavirtualserver,thestickytableischeckedforanentry
matching
thevirtualserverʹsstickytype.Ifanentryisfound,thentheloadbalancingalgorithmis
skippedandtherequestismappedtothestickyentry’sindica ted real server.
Inthiswayavirtualserverassociatesparticularclientstoarealserverforaslongasthesticky
entryremains
inthetable.
Astickyentrywillonlystartagingwhenithasnoassociatedbindings.
The Real Server
Arealserverisanactualphysicalserverthatisamemberofaserverfarm.Oncearealserver
becomesamemberofaserverfarm,youmustenableitforservice.Allotherrealserver
configurationsareoptional.
Realserversmaybelongtomultipleserverfarms.Eachserverfarm
isaccessedbyauniquevirtual
server.TheLSNATrouterwillapplytheloadbalancingalgorithmfortheserverfarmassociated
withthissession.Thevirtualserverconfigurationcontainstheoptionalstickypersistence
configurationforthissession.
Eachrealservercanbeoptionallyconfiguredforfailuredetection,maximumnumberofactive
connections,andrealserverweightusedbytheweightedroundrobinloadbalancing algorithm.
Failure Detection
ItisimportantforLSNATtoknowwhetheraserverisdownsoitcanberemovedfromtheserver
selectionprocess.Thereareanumberofmethodstodeterminewhetherarealserverisupor
downbeforebeingselectedforapotentialLSNATsession:
• Ping‐Therealserver
ispinged.
•TCP/UDPPortServiceVerification‐Theapplicationserviceportisverified.
• ApplicationContentVerification(ACV)‐Thecontentofanapplicationisverified.