Specifications

AP Overview
RoamAbout Mobility System Software Configuration Guide 9-7
•ThefullyqualifieddomainnameofaRoamAboutSwitchtouseasabootdevice,andtheIP
addressofaDNSserverusedtoresolvetheRoamAboutSwitch’sname.
Theseitemsarereferredtoby letterinthedescriptionofhowtheAPcontactsaRoamAbout
Switchin“Howa
DistributedAPContactsanRBTSwitch(Sta ticallyConfiguredAddress)”on
page 9‐8.IftheAPdoesnothavestaticIPaddressinformationconfigured,oritsstaticIP
configurationisdisabled ,thentheAPobtainsitsIPaddressthroughDHCP.
Contacting a RoamAbout Switch
AftertheAPhasanIPaddress,itattemptstocontactaRoamAboutSwitchonthenetwork.The
methodusedforcontactingaRoamAboutSwitchdependsonwhethertheAP’sIPaddresswas
obtainedthroughDHCPorwasconfiguredstatically.
How an AP Contacts a RoamAbout Switch (DHCP-Obtained Address)
1. IftheDHCPOffermessagecontainsRoamAboutSwitchIPaddressesorhostnamesinthe
Option43field,theAPproceedsasfollows:
•IftheDHCPOffermessagecontainedoneormoreIPaddresses intheOption43field,the
APsendsaunicastFindRASmessagetoeachaddress.Theprocess
skipstoStep 6on
page 9‐8.
•IftheDHCPOffer messagecontainedoneormorehostnamesintheOption43field,theAP
sendsDNSRequeststotheDNSserverfortheIPaddressesofthehosts,thensendsa
unicastFindRASmessagetoeachaddress.Theprocessskipsto
Step 6onpage 9‐8.
•IfnoRoamAboutSwitchesreply,theAPrepeatedlyresendstheFindRASmessages.Ifno
RoamAboutSwitchesreply,theprocesscontinueswithStep 3onpage 9‐8.
2. IfnoIPaddressesorhostnameswerespecifiedintheOption43fieldoftheDHCPOffer
message,theAPsendsa
FindRASmessagetoUDPport5000onthesubnetbroadcastaddress
.
•RoamAboutSwitchesinthesameIPsubnetastheAPreceivethemessageandrespond
withaFindRASReplymessage.
•IftheAPisconfiguredasaDistributedAPonaswitchandtheconnectionbiasis
high,theRoamAboutSwitchimmediatelysendsaFindRASReplymessage.
•Ifthe
APisconfiguredasaDistributedAPonaswit chbuttheconnectionbiasislow,
thatRoamAboutSwitchwaitsonesecond,thensendsaFindRASReplymessage.The
delayallowsswitcheswithhighbias fortheAPtorespondfirst.
•IfanRoamAboutSwitchthatreceivestheFind
RASmessagedoesnothavethe
DistributedAPinitsconfigurationbutanotherRoamAboutSwitchinthesame
MobilityDomaindoes,theswitchwaitstwoseconds,thensendsaFindRASReply
messagewiththeIPaddressofthebestswitchtouse.Thedeterminationofbest
switchisbasedon
thebiassettingsfortheAPoneachswitchandonthecapacityof
eachswitchtoaddnewactiveAPconnections.
Note: This method requires DNS address records on the DNS server that map the hostnames
to the RoamAbout Switch IP addresses.