Specifications

SecureStack C3 Configuration Guide 10-1
10
IGMP Configuration
ThischapterdescribestheIGMPConfigurationsetofcommandsandhowtousethem.
IGMP Overview
About IP Multicast Group Management
TheInternetGroupManagementProtocol(IGMP)runsbetweenhostsandtheirimmediately
neighboringmulticastdevice.Theprotocol’smechanismsallowahosttoinformitslocaldevice
thatitwantstoreceivetransmissionsaddressedtoaspecificmulticastgroup.
Amulticast‐enableddevicecanperiodicallyaskitshostsiftheywantto
receivemulticasttraffic.If
thereismorethanonedeviceontheLANperformingIPmulticasting,oneofthesedevicesis
elected“querier”andassumestheresponsibilityofqueryingtheLANforgroupmembers.
BasedonthegroupmembershipinformationlearnedfromIGMP,adevicecandeterminewhich(if
any)multicast
trafficneedstobeforwardedtoeachofitsports.AtLayer‐3,multicastdevicesuse
thisinformation,alongwithamulticastroutingprotocol,tosupportIPmulticastingacrossthe
Internet.
IGMPprovidesthefinalstepinanIPmulticastpacketdeliveryservice,sinceitisonlyconcerned
withforwardingmulticast
trafficfromthelocaldevicetogroupmembersonadirectlyattached
subnetworkorLANsegment.
ThisdevicesupportsIPmulticastgroupmanagementbypassivelysnoopingontheIGMPquery
andIGMPreportpacketstransferredbetweenIPmulticastdevicesandIP multicasthostgroupsto
learnIPmulticastgrou pmembers.
Thepurpose
ofIPmulticastgroupmanagementistooptimizeaswitchednetwork’sperformance
somulticastpacketswillonlybeforwardedtothoseportscontainingmulticastgrouphostsor
multicastdevicesinsteadoffloodingtoallportsinthesubnet(VLAN).
InadditiontopassivelymonitoringIGMPqueryandreportmessages,theSecureStack
C3canalso
activelysendIGMPquerymessagestolearnlocationsofmulticastdevicesandmemberhostsin
multicastgroupswithineachVLAN.
However,notethatIGM P neitheraltersnorroutesanyIPmulticastpackets.SinceIGMPisnot
concernedwiththedeliveryofIPmulticastpacketsacrosssubnetworks,anexternal
IPmulticast
deviceisneededifIPmulticastpacketshavetoberoutedacrossdifferentsubnetworks.
For information about... Refer to page...
IGMP Overview 10-1
Configuring IGMP at Layer 2 10-2
Configuring IGMP on Routing Interfaces 10-11