Why does a Layer 3 multicast forwarding entry contain a loopback inbound interface

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When the source IP address of multicast data packets is the same as the IP address of the VLANIF interface on the source DR, the corresponding Layer 3 multicast forwarding entry contains a loopback inbound interface. To solve this problem, change the source IP address of multicast data packets. Ensure that the source IP address is on the same network segment as the IP address of VLANIF interface, but is different from the IP address of VLANIF interface.

Other related questions:
Why is no Layer 3 multicast forwarding entry generated on S series switches after users order multicast programs
The possible causes are as follows: - No RP is configured on the PIM-SM network. In this case, configure static or dynamic RP. - The route to the multicast source or RP is unreachable. In this case, configure a unicast routing protocol to enable the switch to learn the routes to the multicast source or RP.

How does an S series switch age Layer 3 multicast entries
PIM deletes a Layer 3 multicast entry when the following conditions are met: - No traffic matches the entry. The multicast FIB management module counts packets matching each Layer 3 multicast entry. If no packet matches an entry within 210 seconds, the multicast FIB management module sends an entry inactive message to the PIM module. - The outbound interface list of the entry does not contain any outbound interface learned from PIM Join messages or PIM Prune messages. The outbound interfaces learned from IGMP on the designated router (DR) do not affect aging of Layer 3 multicast entries. If all the preceding conditions are met, PIM considers the entry invalid and deletes it.

Can an S series switch accurately forward multicast data packets if only Layer 3 multicast is configured
For S series switches, Layer 3 multicast protocols can identify only Layer 3 VLANIF interfaces. If only Layer 3 multicast is configured and Layer 2 multicast is not enabled, multicast data is replicated on a VLANIF interface and broadcast in the corresponding VLAN, but cannot be forwarded to an accurate physical interface. When Layer 2 multicast is enabled in the VLAN corresponding to the VLANIF interface, multicast data can be accurately forwarded through a Layer 2 interface.

Why does an S series switch generates Layer 2 multicast forwarding entries in only one VLAN
After an S series switch receives Report messages from the same multicast group in different VLANs, Layer 2 multicast entries are generated in only the VLAN where Report messages are generated first. The causes are as follows: An S5700SI switch running a version earlier than V200R005 or an S5710-C-LI does not generate the same multicast forwarding entry for a multicast group in multiple VLANs. That is, a multicast group can have a forwarding entry only in one VLAN. To solve this problem, configure a multicast VLAN so that multicast data can be distributed to user VLANs through the multicast VLAN. - The preceding restriction does not apply to the S5700SI, S5710-X-LI, S5700S-28X-LI-AC, S5700S-52X-LI-AC, S5720S-SI, S5720SI, and E600 running V200R005 and later versions. These switches, however, cannot generate the same multicast forwarding entry for a multicast group in multiple multicast VLANs. That is, a multicast group can have a forwarding entry only in one multicast VLAN. - The S2700 does not allow an interface to function as the outbound interface of the same multicast forwarding entry in multiple VLAN. That is, one interface can function as the outbound interface of a multicast group in only one VLAN. To solve this problem, add each interface to only one VLAN so that a multicast group has different outbound interfaces in different VLANs.

Why cannot an S series switches learn ARP entries after Layer 3 forwarding is enabled on the switch's sub-interfaces
Q: Why cannot a switch learn ARP entries when connected to other devices after Layer 3 forwarding is enabled on the switch's sub-interfaces? A: In V100R002 and later versions, sub-interfaces of S series switches do not respond to ARP requests by default when Layer 3 forwarding is enabled on the sub-interfaces. The sub-interfaces respond to ARP requests only after the arp-proxy enable command is executed.

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