Qtech QSW-3900-48-SFP-DC [199/313] Working theory of pim sm

Qtech QSW-3900-24-SFP-DC [199/313] Working theory of pim sm
QTECH Software Configuration Manual
12-198
Picture for Assert Mechanism
12.9.1.4 Graft
When the pruned downlink node needs to restore to transmission state, this node uses graft packet to inform
uplink node. Enable multicast route before configuring IGMP protocol.
12.9.1.5 SRM
To avoid repeat forwarding –pruning, new protocol standard adds this mechanism. Router connected to
multicast source timely sends SRM, and PIM will refresh pruning state after receiving it.
12.9.2 Working theory of PIM-SM
The working process of PIM-SM are: Neighbor Discovering, RP sharing tree generating, multicast source
register and SPT shift. Neighbor Discovering is the same as that of PIM-DM.
12.9.2.1 RP sharing tree (RPT) generating
When host adding to a multicast group G, leave router connected with this host know there is receiver of
multicast group G through IGMP packet, it will calculate the corresponded convergent point RP and send join packet
to the upper node. Passing each router from leave router to RP, (*, G) item will be generated in transmission table.
No matter where it sending from, it was sent to multicast group G. When RP received the packet to multicast group G,
packet will arrive leave router along the established path to host. Above forms RPT with the root of RP.
12.9.2.2 Multicast source register
When multicast source S sends a multicast packet to multicast group G, PIM-SM multicast router will
encapsulate received multicast packet to register packet and send it to corresponded RP in the form of unicast. If there
are many PIM-SM multicast router in a network interface, DR (Designated Router) will send this multicast packet.

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