PIM SP Shared tree and SPT

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Mar 28th, 2007
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some time in multicasting PIM-SP use the Shared tree and SPT... shared tree include the RP and all multicast traffic flow through the RP to the multicast receiver... now my confusion is that what will csuse the SPT calculation in PIM-SM to find out the shortest path towards the source and make a root as source...?

and every time after source register to the RP in PIM-SM, every time source will send the Multicast traffice to the DR and DR encapsulate that traffic into the IP Packet and send that IP packet using unicast to the RP...so i want to just make sure that every time DR will follow the same procedure to forward the Multicast packet to RP using unicast method!!!


regards

Devang


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Harold Ritter Wed, 03/28/2007 - 12:54
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The change from the shared tree to the SPT is initiated right after the router, directly connected to a receiver, get the first packet from a guven multicast feed. At this point it has the source of the feed, which allows it to send PIM joins towards the source.


As for your second question, the DR sends the multicast messages encapsulated in a PIMv2 register message (unicast) to the RP until it received a PIMv2 register-stop message from the RP.


Hope this helps,

devang_etcom Wed, 03/28/2007 - 13:23
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For second question:

so DR will constantly send the Multicast packet encapsulated in PIMv2 message every time till the receivers are there to receive the multicast traffice... right!!!


Do you have any good artical which indicating the difference between various Multicast protocols (something like in table form)? ? ?

one more thing in (S,G)

S= Ip address of the Source and

G= Multicast address of that sources Group

right!!!

this (S,G) and (*,G) is put me in confusion state... do you have any good tricks?


regards

Devang


Harold Ritter Wed, 03/28/2007 - 13:51
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- DR send the mcast message in register message until it gets register-stop message.


- For good mcast documentation, please refer to the following URL:


http://www.cisco.com/go/multicast


- (S,G) stands for (source, multicast group) indeed.


- (*,G) is only used along the shared tree, whereas (S,G) is used along the SPT.


Hope this helps,

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