Enterasys b5

Enterasys B5 CLI Reference 13-1
13
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anIP
network.
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
EnterasysB5canalso
activelysendL3IGMPquerymessagestolearnlocationsofmulticastdevicesandmemberhosts
inmulticastgroupswithineachVLAN.
However,notethatIGMPneitheraltersnorroutesanyIPmulticastpackets.SinceIGMPisnot
concernedwiththedeliveryofIPmulticastpacketsacrosssubnetworks,
multicastroutingis
neededifIPmulticastpacketshavetoberoutedacrossdifferentsubnetworks.
For information about... Refer to page...
IGMP Overview 13-1
Configuring IGMP at Layer 2 13-2
Configuring IGMP on Routing Interfaces 13-10