H3C Technologies H3C S12500 Series Switches - Manual (Page 86)

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Layer 2 port information for all IGMP multicast groups in the VLAN and use the reset igmp group
command clear all IGMP multicast group information on the corresponding VLAN interface.
Otherwise this configuration cannot take effect.
• For more information about the reset igmp group port-info and reset igmp group commands, see
IP Multicast Command Reference.
• If the VLAN enabled with the multicast programs-on-demand function is not a multicast VLAN but
has IGMP snooping enabled, this configuration cannot take effect.
• If you configure the multicast programs-on-demand function in a VLAN that has been enabled with
BIDIR-PIM, you must use the reset multicast forwarding-table command to clear all the forwarding
entries in the multicast forwarding table. Otherwise, the configuration cannot take effect.
After you enable delivering the multicast packets that failed RPF check to the CPU, use the reset multicast
forwarding-table command to clear all the forwarding entries in the multicast forwarding table.
Otherwise this configuration cannot take effect.
Forwarding the packets in the VLAN
A multicast packet that failed RPF check on a VLAN interface might be expected by some receivers in the
VLAN. You can enable forwarding such multicast packets through multicast or broadcast in the VLAN so
that the receivers can receive them.
With this feature enabled, the router searches its multicast forwarding table after receiving a packet that
failed RPF check. If a match is found, it multicasts the packet according to the matching entry. Otherwise,
the router broadcasts the packet in the VLAN.
To enable this feature, you also need to enable the multicast programs-on-demand function.
To enable forwarding multicast packets in case of RPF check failure:
Step Command Remarks
1. Enter system view. system-view N/A
2. Enable forwarding multicast
packets in case of RPF check
failure on VLAN interfaces.
multicast rpf-fail-pkt bridging Disabled by default.
3. Enter VLAN view. vlan vlan-id N/A
4. Enable the multicast
programs-on-demand function
in the VLAN. multicast forwarding on-demand Disabled by default.
Delivering the packet to the CPU
In the following cases, a multicast packet that failed RPF check needs to be delivered to the CPU:
• When a multicast packet arrives on an outgoing interface of the corresponding multicast
forwarding entry, the packet will fail RPF check and needs to be sent to the CPU in order to trigger
the assert mechanism to prune the unwanted branch.
• If the SPT and RPT have different incoming interfaces on the receiver-side DR (the last-hop router),
the multicast traffic will fail RPF check on the SPT incoming interface during an RPT-to-SPT switchover
before the RPF information is refreshed. If the RPT is pruned at this moment, the multicast service will
be instantaneously interrupted. By delivering packets that failed RPF check on a non-outgoing
interface to the CPU, the router can determine whether the packets that have failed RPF check on the
SPT interface are expected. If they are, the router initiates an RPT prune.
For more information about the assert mechanism, DR and RPT-to-SPT switchover, see "Configuring PIM."