Pim-Dm Configuration Task List - Edge-Core ES3628EA User Manual

packet to all downstream PIM-DM nodes on the network (Flooding). If the RPF check
fails, i.e. the Multicast packet is input from the incorrect interface, and then the message
is discarded. After this procedure, in the PIM-DM Multicast domain, every node will
create a (S, G) table entry. If there is no Multicast group member in the downstream
nodes, then a Prune message is sent to upstream nodes to notify them not to transmit
data of this Multicast group any more. After receiving Prune message, the upstream
nodes will delete the corresponding interface from the output interface list to which their
Multicast transmission table entry (S, G) corresponds. Thus a SPT（Shortest Path Tree,
SPT） tree with source S as root is created. The Prune process is initiated by leaf router
first.
The process above is called Flooding&Prune process. Each pruned node also
provides time-out mechanics at the same time. When Prune is timed-out, the router will
restart Flooding&Prune process. The PIM-DM Flooding&Prune is periodically processed.
3. RPF Check
With RPF Check, PIM-DM makes use of existing Unicast routing table to establish a
Multicast transmission tree initiating from data source. When a Multicast packet arrives,
the router will determine whether the coming path is correct first. If the arrival interface is
the interface connected to Multicast source indicated by Unicast routing, then this
Multicast packet is considered to be from the correct path. Otherwise the Multicast packet
is to be discarded as redundant message. The Unicast routing message used as path
judgment can root in any Unicast Routing Protocol, such as messages found by RIP,
OSPF, etc. It doesn't rely on any specific Unicast Routing Protocol.
4. Assert Mechanism
If each of two Multicast routers A and B on the same LAN segment has a receiving
route respectively and both will transmit the Multicast packet to the LAN after receiving
the Multicast data packet sent by the Multicast Source S, then the downstream node
Multicast router C will receive two exactly same Multicast packets. The router needs to
choose a unique transmitter through Assert mechanism after it detects this situation. An
optimal transmission path is selected through sending out Assert packet. If the priority
and cost of two or more path are same, then the node with larger IP address is taken as
the upstream neighbor of the (S, G) entry and in charge of the transmission of the (S, G)
Multicast packet.
5. Graft
When the pruned downstream node needs to recover to transmission status, this
node uses Graft Packet to notify upstream nodes to restore multicast data transmission.

16.2.2 PIM-DM Configuration Task List

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