When you use the IP multicast software forwarding feature you can avoid initial data loss experienced by multicast applications; this is suitable for low bandwidth conditions.
When you configure the IP multicast software forwarding feature the system forwards the initial packets of an IP multicast data stream it receives and creates a corresponding hardware record for subsequent packets.
By default, multicast software forwarding is disabled.
Note
This procedure is supported only on a DvR Controller. It is not supported on a DvR Leaf node.
IP multicast software forwarding is a global system configuration feature that is only applicable to traditional PIM protocol and IGMP Snooping protocols, not SPB-PIM Gateway or Layer 3 VSN SPB Multicast. If you enable IP multicast software forwarding, the hardware continues to forward IP multicast traffic. The software only forwards initial data traffic.
After a new data stream arrives, the first data packet is sent to the CPU, which programs the multicast route in hardware, and all packets that arrive subsequent to this programming are forwarded by hardware only.
If you enable software forwarding, all initial packets received before hardware programming is complete are sent to the CPU for forwarding and packet suppression by the hardware is disabled.
If you do not enable software forwarding, only the first data packet is sent to the CPU and subsequent packets are suppressed by the hardware so that the CPU is not overwhelmed with traffic. During this time, packets suppressed by the hardware are dropped.
Important
To avoid overloading the CPU, ensure that you do not use the IP multicast software forwarding feature for video multicast applications.
Switch:1#show multicast software-forwarding
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Mcast Software Forwarding - GlobalRouter
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McastSoftwareForwarding :enabled