Specifications

AP Overview
9-4 Configuring Access Points
TheDNSentryallowstheAPtocommunicatewithaRoamAboutSwitchthatisnotonthe
AP’ssu bnet.IftheAPisunabletolocateaRoamAboutSwitchonthesubnetitisconnectedto,
theAPsendsDNSrequeststowlan‐switch,wheretheDNSsuffixformynetwork.com
islearned
throughDHCP.
Distributed APs and STP
IfSpanningTreeProtocol(STP)isenabledontheportthatisdirectlyconnectedtoaDistributed
AP,youmightneedtochangetheSTPconfigurationontheport,toallowtheAPtoboot.
Aspartofthebootprocess,anAPdisablesandreenablesthelinkonthe port
overwhichtheAPis
attemptingtoboot.IfSTPisenabledonthedevicethatisdirectlyconnectedtotheport,thelink
statechangecancausetheportontheotherdevicetoleavetheforwarding stateandstop
forwardingtraffic.Theportremainsunabletoforwardtraffic
forthedurationoftheSTP
forwardingdelay.
AnAPwaits30secondstoreceiveareplytoitsDHCPDiscovermessage,thentriestobootusing
theotherAPport.Ifthebootattemptfailsontheotherportalso,theAPthenreattemptstobooton
thefirstport.
Theprocesscontinuesuntilabootattemptissuccessful.IfSTPpreventstheother
device’sportfromforwardingtrafficduringeachbootattempt,theAPrepeatedlydisablesand
reenablesthelink,causingSTPtorepeatedlystoptheotherdevice’sportfromforwardingtraffic.
Asaresult,thebootattemptis
neversuccessful.
ToallowanAPtobootoveralinkthathasSTPenabled,dooneofthefoll owingontheother
device:
•DisableSTPontheotherdevice’sport.
•Enabletheportfastconvergencefeature,ifsupported,ontheotherdevice’sport.(Onsome
vendors’devices,thisfeatureiscalled
PortFast.)
•IftheotherdeviceisrunningRapidSpanningTreeorMultipleSpanningTree,settheportinto
edgeportmode.
Distributed APs and DHCP Option 43
TheDHCPoption43fieldinaDHCPOffermessagecanprovidesasimpleandeffectivewayfor
APstofindRoamAboutSwitchesacrossanintermediateLayer3network,andisespeciallyuseful
innetworksthataregeographicallydistributedorhaveaflatdomainnamespace.Youcanusethe
DHCP
option43fieldtoprovidealistofRoamAboutSwitchIPaddresses,withouttheneedto
configureDNSservers.
TouseDHCPoption43,configuretheoptiontocontainacomma‐separatedlistofRoamAbout
SwitchIPaddressesorhostnames,inthefollowingformat:
ip:ip-addr1,ip-addr2,...
or
host:hostname1,hostname2,...
YoucanuseanIPaddresslistorahostnamelist,butnotboth.Ifthelistcontainsbothtypesof
values,theAPdoesnotattempttousethelist.
Note: STP on a port directly connected to a Distributed AP can prevent the AP from booting.