When Layer 3 multicast forwarding fails on an S series switch, how can I determine whether the reason is that the TTL value of multicast data packet is 1

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All S series switches that support Layer 3 multicast can generate multicast forwarding entries for multicast data packets with the TTL value of 1, but cannot forward such multicast data packets.
Use either of the following methods to check whether the TTL value of multicast data packets is 1:
- Obtain packet headers by capturing incoming multicast packets on the uplink interface. Check whether the TTL value of multicast data packets is 1.
- Run the debugging mfib packet command in the user view to enable debugging of Layer 3 multicast packets, and then run the reset multicast forwarding-table group-address command to delete all multicast forwarding entries. Check whether "TTL=1" is displayed in the debugging information.

Other related questions:
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 a Layer 3 multicast forwarding entry contain a loopback inbound interface
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.

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.

Why does an S series switch fail to generate Layer 3 multicast forwarding entries when receiving multicast data packets with destination IP addresses in the SSM group address range
An S series switch generates Layer 3 multicast forwarding entries for the group addresses in the SSM group address range only when receiving multicast protocol packets. Multicast data packets cannot trigger generation of Layer 3 multicast forwarding entries for such group addresses. Use either of the following methods to solve this problem: - Configure IGMPv3 or SSM mapping on user-side interfaces. When users order multicast programs, they can send IGMP messages with source-group information to trigger generation of Layer 3 multicast forwarding entries. - Configure PIM-SM on downstream devices. When users need to join a specified source-group, they can send PIM messages with source-group information to trigger generation of Layer 3 multicast forwarding entries.

Do S series switches support the Layer 3 multicast function
To achieve multicast forwarding of video services on Layer 3 networks, you need to configure the Layer 3 multicast function on switches. The Layer 3 multicast function requires two multicast protocols as follows: - Internet Group Management Protocol (IGMP): It is used to establish and maintain multicast group memberships between receiver hosts and directly connected multicast routers. - Protocol Independent Multicast (PIM): It is used to obtain multicast requirements of receiver hosts, generate multicast routing entries, and set up multicast forwarding paths. IGMP and PIM are supported by Huawei S series modular switches, and Sx7 series fixed switches including the S3700EI, S3700HI, S5700EI, S5710EI, S5720EI, S5700HI, S5710HI, S5720SI, S5720S-SI, S5720HI, S6700EI, S6720EI and S6720S-EI.

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