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Why Cannot Multicast Entries Be Created?

Latest reply: May 15, 2017 00:27:07 1582 1 0 0 0
Why Cannot Multicast Entries Be Created?
  • x
  • convention:

Created May 15, 2017 00:27:07

If multicast entries cannot be created, you can perform checks from the following two aspects:

Check whether protocol processing on the control plane is successful, including whether IGMP messages are received and whether a multicast forwarding table is generated based on IGMP and PIM.
Check whether the forwarding entries generated on the forwarding plane are correct.
Basic Configuration Check
Different from unicast, multicast can implement source-address-based forwarding. After a deview receives multicast (S, G) data through an interface, it searches for the unicast route to S. If finding a downstream interface to S and that this downstream interface is just the interface through which the multicast data is received, the deview forwards the multicast data; otherwise, it discards the data. Such a mechanism is called reverse path forwarding (RPF). RPF is a basis of multicast forwarding for different multicast protocols. Therefore, you need to first check whether unicast routes to the RP and multicast source are normal:

Run the display pim rp-info command to check whether an RP exists and can be pinged successfully, and whether the upstream interface is enabled with PIM.
If the multicast source can be pinged successfully, run the display ip routing-table command to check whether routes to the multicast source are available. If there are multiple routes to the multicast source, you need to ensure that PIM is enabled on the outbound interface of each route; otherwise, the RPF check fails.
Run the display pim neighbor command to check whether the PIM neighbor relationship is established. Check the value of the Uptime field in the command output. If the value is at the second level, it indicates that the neighbor relationship alternates between Up and Down. This may be caused by a link fault.
<HUAWEI> display pim neighbor
Neighbor's Address Interface Name Uptime Expires Gigabitethernet1/0/0 24:49:42 00:01:34 Gigabitethernet1/0/0 96:16:10 00:01:38Check that the TTL value of the multicast data sent by the multicast source is sufficient to reach the destination.
Whether the device Has Received IGMP Packets
To confirm if IGMP host messages are received, view the statistics about IGMP Join messages or IGMP messages.

Run the display igmp group command to view information about IGMP groups. If no group information is displayed in the command output, run the display igmp control-message counters command to check if IGMP host messages are received.

Static join to a group

PIM-SM must be enabled on the interface to be added to a group statically. The configurations are as follows:

interface Gigabitethernet1/0/0
undo shutdown
igmp enable
igmp host-join
pim sm
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