Specifications

Understanding Multicast
April 16, 2009 Page 12 of 32
7. Aprunemessage(register‐stop)issentfromtheRPtothesource’sDR(number7infigure).
OncetrafficisflowingdowntheSPT,theRPTisprunedforthatgivenS,G.
Whenreceiversgoaway,prunesaresent(S,GprunemessagestowardsthesourceontheSPT,and

*,GprunemessagestowardstheRPontheRPT).Whennewreceiversappear,theprocessbegins
again.
PIM Support on Enterasys Devices
Enterasysdevicessupportversion2ofthePIMprotocolasdescribedinRFC2362anddraft‐ietf‐
pim‐sm‐v2‐new‐09.
ThePIMspecificationsdefineseveralmodesormethodsbywhichaPIMroutercanbuildthe
distributiontree.Enterasysdevicessupportsparsemode(PIM‐SM),whichusesonlythose
routers
thatneedtobeincludedinforwardingmulticastdata.PIM‐SMusesahost‐initiatedprocessto
buildandmaintainthemulticastdistributiontree.Sparsemoderoutersusebandwidthmore
efficientlythanothermodes,butcanrequiremoreprocessingtimewhenworkingwithlarge
numbersofstreams.
Key Features
KeyfeaturesofPIM‐SMarethefollowing:
•usesIGMPtopropagategroupmembershipinformation
•sendshellomessagestodetermineneighborpresenceand configuration
•sendsjoin/prunemessagestodeterminetheneedtoretainmulticastrouteinformationfora
particulargrouponaninterlace
•sendsassertmessagestoresolveconflictsthatoccurregardinginbound
interfaces
•usesroutesintheMulticastRoutingInformationBase(MRIB)toperformitsreversepath
forwardingcheck
Message Types
EnterasysPIM‐SM‐enableddevicesusethefollowingmessagetypes:
•Hello—Thesemessagesannouncethesender’spresencetootherPIM‐SMdevices.Thehello
packetincludesoptionssuchas:
–Holdtime—thelengthoftimetokeepthesenderreachable
–Designatedrouter(DR)priority—usedtodesignatewhichPIM‐
SMdevicewillacton
behalfofsourcesand receiversinthePIM‐SMdomain
•Register—Thesemessagesareusedbyasource’sDRtoencapsulate(register)multicastdata,
andsendittotherendezvouspoint(RP)—aPIM‐SMrouterdesignatedastherootofa
sharedtree.
Notes: PIM 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, PIM 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 PIM command set.
A minimum of 256 MB of memory is required on DFE modules in order to enable PIM. See the
SDRAM field of the show system hardware command to display the amount of memory installed
on a module. Module memory can be upgraded to 256 MB using the DFE-256MB-UGK memory kit.