Enterasys Matrix DFE-Gold Series Configuration Guide 9-1
9

IGMP Configuration

ThischapterdescribestheIGMPConfigurationsetofcommandsandhowtousethem.

About IP Multicast Group Management

TheInternetGroupManagementProtocol(IGMP)runsbetweenhostsandtheirimmediately
neighboringmulticastswitchdevice.Theprotocol’smechanismsallowahosttoinformitslocal
switchdevicethatitwantstoreceivetransmissionsaddressedtoaspecificmulticastgroup.
Amulticastenabledswitchdevicecanperiodicallyaskitshostsiftheywanttoreceivemulticast
traffic.IfthereismorethanoneswitchdeviceontheLANperformingIPmulticasting,oneof
thesedevicesiselected“querierandassumestheresponsibilityofqueryingtheLANforgroup
members.
BasedonthegroupmembershipinformationlearnedfromIGMP,aswitchdevicecandetermine
which(ifany)multicasttrafficneedstobeforwardedtoeachofitsports.AtLayer3,multicast
switchdevicesusethisinformation,alongwithamulticastroutingprotocol,tosupportIP
multicastingacrosstheInternet.
IGMPprovidesthefinalstepinanIPmulticastpacketdeliveryservicesinceitisonlyconcerned
withforwardingmulticasttrafficfromthelocalswitchdevicetogroupmembersonadirectly
attachedsubnetworkorLANsegment.
ThisswitchdevicesupportsIPmulticastgroupmanagementby
• passivelysnoopingontheIGMPqueryandIGMPreportpacketstransferredbetweenIP
multicastswitchesandIPmulticasthostgroupstolearnIPmulticastgroupmembers,and
•activelysendingIGMPquerymessagestosolicitIPmulticastgroupmembers.
ThepurposeofIPmulticastgroupmanagementistooptimizeaswitchednetwork’sperformance
somulticastpacketswillonlybeforwardedtothoseportscontainingmulticastgrouphostsor
multicastswitchdevicesinsteadoffloodingtoallportsinthesubnet(VLAN).
InadditiontopassivelymonitoringIGMPqueryandreportmessages,theEnterasysMatrixSeries
devicecanalsoactivelysendIGMPquerymessagestolearnlocationsofmulticastswitchesand
memberhostsinmulticastgroupswithineachVLAN.
For information about... Refer to page...
About IP Multicast Group Management 9-1
IGMP Configuration Summary 9-2
Enabling / Disabling IGMP 9-2
Configuring IGMP 9-5