active to send a prune message to upstream without waiting for timeout of upstream pruning
state so as to enable pruning to forwarding state.
As long as Source S can still send messages to Group G, the first hop switch will periodically
send (S,G) a state refresh message to initial broadcast tree to finish the refreshing. With
PIM-DM state refresh mechanism, you can refresh the state of downstream so that pruning
of broadcast tree branches will not time out.
Except for DR election in multi-path access network, PIM-DM also introduces the following
mechanism: use assertion to select a single forwarder in case that multicast packets are
forwarded repeatedly to the same segment; use join/prune suppression to reduce redundant
join/prune messages; use pruning deny to deny these illegal pruning.
In PIM-DM domain, PIM-DM switches periodically send Hello message to find adjacent PIM
switches and make judgment of leaf network and leaf routers and is also responsible for DR
election in multi-path access network.
To be suitable for IGMP v1, PIM-DM is responsible for DR selection. Choose the highest
Priority to be DR when all the PIM neighbors support DR Priority on the interface. If the
priority is identical, choose the switch with the largest interface IP to be DR. If many switches
do not announce their priorities in hello messages, switches with the highest interface IP
value is selected to be DR.
PIM-DM v2 of our switches supports neighbor filtering list, CIDR, VLSM and IGMP v1, v2,
v3.
35.2 PIM-SM Overview
The PIM-SM (Protocol Independent Multicast Sparse Mode) is a protocol independent
multicast sparse mode. In the PIM-SM domain, the device which runs the PIM-SM protocol
periodically sends the Hello messages, to detect the neighboring PIM-SM device, and be
responsible for dispatching the selection of the device DR in the multiple access networks.
Where, the DR is responsible for sending the join/prune message in the root node of the
multicast distribution tree direction for the direct connection group member, or sending the
data of the direct connection multicast source to the multicast distribution tree.
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