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DES-7200 Configuration Guide Chapter 10 PIM-Snooping Configuration
10-1
10 PIM-Snooping
Configuration
10.1 PIM Snooping Overview
Within the network that the L2 switches connect with several routers, the
multicast frames are forwarded in the broadcast form, which easily leads to the
multicast flow storm and a waste of network bandwidth.
IGMP Snooping deals with the problem occurs when the connected receiving
devices in the VLAN are all hosts and enables the multicast flow to be forwarded
only to the port where the registered users are, not influencing other users.
However, when the receiving devices in the VLAN in the downstream direction
are the routers with PIM protocol enabled, IGMP Snooping fails to regulate the
Layer 2 forwarding of the multicast flow. And PIM Snooping deals with the
problem of Layer 2 forwarding of the multicast flow for the connected routers in
the VLAN with PIM protocol enabled. PIM Snooping must be combined with IGMP
Snooping to manage the Layer 2 forwarding of the multicast flow in the VLAN.
The figure below shows the flooding of multicast frames before the PIM snooping
is enabled and the restriciton of multicast frames after the PIM snooping is
enabled.
As shown in Figure-1, multicast frames is flooded to all the ports of the switch
when the PIM snooping is not enabled.
Figure-1 Multicast flow When the PIM Snooping is not enabled
As shown in the Figure-2, multicst frames flow only to the ports that connect with
the multicast routers B and C, but not to the router D.
Figure-2 Multicast flow after the PIM Snooping is enabled