Specifications

SecureStack B2 Configuration Guide 14-1

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).

About Multicasting

Multicastingisusedtosupportreal‐timeapplicationssuchasvideoconferencesorstreaming

audio.Amulticastserverdoesnothavetoestablishaseparateconnectionwitheachclient.It

merelybroadcastsitsservicetothenetwork,andanyhoststhatwanttoreceivethemulticast

switch/router.Althoughthisapproachreducesthenetwork

overheadrequiredbyamulticastserver,thebroadcasttrafficmustbecarefullyprunedatevery

For information about... Refer to page...

IGMP Overview 14-1

Configuring IGMP at Layer 2 14-2