Why is multicast forwarding interrupted on an interface after the interface receives Hello messages

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After static IGMP groups are configured on an interface, the device uses the PIM protocol to set up multicast forwarding entries. Multicast data can be forwarded through the interface as long as the interface is included in the downstream interface list in the corresponding multicast forwarding entry.

If the source address of a received PIM Hello message is larger than the interface address, or the DR priority of the PIM Hello message is larger than the priority of the interface, the switch can no longer function as the DR. All data packets on a shared network segment are forwarded by the DR is no Assert election occurs. Therefore, the device considers that multicast data packets will be forwarded by the new DR and then prunes the downstream interface.

Other related questions:
Can the NAT interface of the AR router be configured with multicast
Multicast can be configured on the interface where NAT is configured. NAT is only valid for unicast packets.

Why are statistics on received and sent Hello messages both 0
Run the display mpls ldp interface command to check the interface status. The command output is displayed as follows: display mpls ldp interface LDP Interface Information in Public Network Codes:LAM(Label Advertisement Mode), IFName(Interface name) A '*' before an interface means the entity is being deleted. ------------------------------------------------------------------------------ IFName Status LAM TransportAddress HelloSent/Rcv ------------------------------------------------------------------------------ Vlanif10 Active DU 1.1.1.1 29574/29539 ------------------------------------------------------------------------------ In normal cases, the interface status is Active. If the interface status is Inactive, the interface cannot receive or send Hello messages. In most cases, the interface status is Inactive because the interface is shut down or no IP address is configured for the interface.

How to check the statistics on received and sent Hello messages
Run the display mpls ldp interface command to check the statistics on received and sent Hello messages on an interface. The command output is displayed as follows: display mpls ldp interface LDP Interface Information in Public Network Codes:LAM(Label Advertisement Mode), IFName(Interface name) A '*' before an interface means the entity is being deleted. ------------------------------------------------------------------------------ IFName Status LAM TransportAddress HelloSent/Rcv ------------------------------------------------------------------------------ Vlanif10 Active DU 1.1.1.1 29574/29539 ------------------------------------------------------------------------------ The value of the field HelloSent/Rcv indicates the statistics on received and sent Hello messages

Why does the number of received and sent Hello messages remain unchanged in a short period
Run the display mpls ldp interface verbose command to check the interval of the Hello Hold timer after negotiation. The interval of the Hello Hold timer after negotiation is the smaller value between the configurations on the two ends of the LDP session. By default, the interval of the Remote Hello Hold timer is 45s, and the interval of the Link Hello Send timer is one third of that of the Remote Hello Hold timer. An LSR sends a Hello message at the interval of the Hello Hold timer. The statistics about received and sent Hello messages increase only after an LSR sends or receives a Hello message. Therefore, the statistics on received and sent Hello messages may not increase in a short period.

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.

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