Specifications

Understanding Multicast

April 16, 2009 Page 4 of 32

IGMP Support on Enterasys Devices

EnterasysdevicesimplementIGMPversion2(RFC2236),whichincludesinteroperabilitywith

version1hosts.IGMPversion1isdefinedinRFC1112.

DependingonyourEnterasysdevice,IGMPcanbeconfiguredindependentlyattheswitchlevel

(Layer2)andattherouterlevel(Layer3).

EnterasysdevicessupportIGMPasfollows:

• PassivelysnoopingontheIGMPqueryandIGMPreportpacketstransferredbetweenIP

multicastswitchesandIPmulticasthostgroupstolearnIPmulticastgroupmembers.Each

Layer2devicerecordswhichportsIGMPpacketsarereceivedon,dependingonthekindof

IGMPmessage,somulticastdatatrafficisnot

floodedacrosseveryportontheVLANwhenit

isreceivedbytheswitch.

IGMPsnoopingisdisabledbydefaultonEnterasysdevices.Youcanautomaticallyenableit

usingthesetigmpenablecommandonEnterasysMatrixN‐Seriesdevicesortheset

igmpsnoopingadminmodecommandforSecureStackandD‐Series,

G‐Series,andI‐Series

devicesasdescribedin“ConfiguringIGMP”onpage 15.

•ActivelysendingIGMPquerymessagestolearnlocationsofmulticastswitchesandmember

hostsinmulticastgroupswithineachVLAN.

Example: Sending a Multicast Stream

Figure 2 Sending a Multicast Stream with No Directly Attached Hosts

Figure 2providesanexampleofIGMPprocessingonEnterasy sdeviceswhentherearenodirectly

attachedhosts.

1. AsingleIPmulticastserver,withnodirectlyattachedhosts,sendsamulticaststreamintothe

networkviaSwitch1.

2. BecauseIGMPsnoopingisdisabled,Switch1floodsthemulticaststreamtoall

portswhich

arelinkedtoRouter1andRouter2.

Router 1

Host 1

Solicited Join

Network A

Unsolicited Join

& IGMP Leave

Host 2

Multicast Server

Switch 1

Router 2