Accton Technology ES4626 - Manual (Page 684)

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the multicast-forwarding item (S, G). Through this process, a SPT (Shortest Path Tree) is
established with source S as root. Prune process is started by a sub-router.
The process above is called Flooding-Prune process. Each pruned node also
provides overtime mechanism at the same time. In case of overtime of prune, the router
will restart flooding-prune process. Flooding-prune of PIM-DM is conducted periodically
3. RPF examination
Adopting RPF examination, PIM-DM establishes a multicast forwarding tree initiating
from data source, using existing unicast routing table. When a multicast packet arrives,
the router will determine the correctness of its coming path 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
will 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 two multicast router A and B in the same LAN segment have their own receiving
paths to multicast source S, they will respectively forward multicast data packet to LAN
after receiving the packet from multicast source S. Then downstream nodes multicast
router C will receive two multicast packets that are exactly the same. Once router detects
such circumstance, a unique forwarder will be selected through “assert” mechanism. The
optimized forwarding path is selected through “assert” packet. If the priority and costs of
two or more than two paths are same, the node with a larger IP address will be selected
as the upstream neighbor of item (S, G), which will be responsible for forwarding the (S,
G) multicast packet.
5. Graft
When the pruned downstream node needs to recover to forwarding status, this node
uses Graft Message to notify upstream nodes to resume multicast data forwarding.
17.1.2 PIM-DM Configuration Task List
1、 Start PIM-DM (Required)
2、 Configure PIM-DM auxiliary parameters (Optional)
Configure PIM-DM interface parameters
Configure PIM-DM hello message interval time
3、 Shut down PIM-DM protocol
1. Start PIM-DM Protocol
It’s easy to make basic configuration of the PIM-DM routing protocol in EdgeCore
layer 3 switch, only need to turn on PIM multicast switch in Global Mode and turn on