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Understanding Multicast

April 16, 2009 Page 6 of 32

KeyfeaturesofDVMRParethefollowing:

•usesthewell‐knownmulticastIPaddress224.0.0.4

•usesIGMPtoexchangeroutingdatagrams

•doesnotrequireanunderlyingLayer3routingprotocoltoprovideapathtoremotemulticast

destinations

• combinesmanyofthefeaturesofthe RoutingInformationProtocol(RIP)withtheTruncated

ReversePathBroadcasting(TRPB)algorithmtoroutemulticastpacketsbetweensourcesand

receivers

DVMRP Support on Enterasys Devices

DVMRProutingisimplementedonEnterasysdevicesasspecifiedinRFC1075anddraft‐ietf‐idmr‐

dvmrp‐v3‐10.txt.

EnterasysdevicessupportthefollowingDVMRPcomponents:

• ProbeMessagesforneighbordiscovery

• RouteTableformaintainingroutestoallDVRMP networks

• RouteReportsforrouteexchangewithadjacentdevices

• MrouteTablefor

maintainingper‐source‐groupmulticasttrees

• PruneMessagesforterminatingmu lticastdeliverytrees

• GraftMessagesforre‐addingprunedmulticastdeliverytrees

Probe Messages

EachDVMRP‐enabledinterfacetransmitsmulticastprobepacketstoinformotherDVMRP

routersthatitisoperational.Probemessagesaresentevery10secondsoneveryinterfacerunning

DVMRP.Thesemessagesprovide:

• AmechanismforDVMRPdevicestolocateeachother.Probemessagescontainalistofthe

neighborsdetected

foreachenabledinterface.Ifnoneighborsarefound,thenetworkis

consideredtobealeafnetwork.

• AmechanismforDVMRPdevicestodeterminethecapabilitiesofneighboringdevices.

Probemessagescontainflagsaboutneighbors’DVMRPcapabilitiesandversioncompliance.

• Akeep‐alivefunctionforquicklydetectingneighborloss.

Ifaprobemessagefroman

adjacentneighborisnotseenwithin35seconds,theneighboristimedout.

Notes: DVMRP is supported on Enterasys Matrix N-Series, SecureStack C2 and C3, and G-Series

platforms on which routing has been enabled.

On SecureStack C2 and C3 devices and G-Series devices, DVMRP is an advanced routing feature

that must be enabled with a license key. If you have purchased an advanced license key, and have

enabled routing on the device, you must activate your license to enable the DVMRP command set.