Enterasys SecureStack B3 User Manual

SecureStack B3 Configuration Guide 12-1
12
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group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
registerwiththeirlocal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 12-1
Configuring IGMP at Layer 2 12-2

Enterasys SecureStack B3 Specifications

General

Brand	Enterasys
Model	SecureStack B3
Category	Switch
Language	English