Cause why an AR cannot learn correct MAC address entries

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The possible causes are as follows:
- The AR does not receive packets because the link is Down, the interface does not join the VLAN, the interface participates in spanning tree calculation and is blocked, or MAC address flapping detection is configured and the interface or MAC address is blocked.
- Loops cause MAC address flapping.
- The AR is disabled from learning MAC address entries or the sticky MAC function is enabled on the interface.
- The number of learned MAC address entries has reached the maximum.
- The static or blackhole route is configured.

Other related questions:
Why cannot the switch learn an MAC address
The possible causes are: The mac-limit command is used on an interface and the VLAN that the interface belongs to and the number of dynamic MAC address entries learned by the interface reaches the limit. MAC address learning is disabled on the Ethernet interface and the VLAN that the interface belongs to by using the mac-address learning disable command. A blackhole MAC entry or static MAC entry is created or the sticky MAC function is enabled.

Why cannot a switch port learn MAC addresses
Failure of MAC address learning may be caused by configuration. If the switch port is in Up state, check whether the port, VLAN, and traffic policy is configured to allow MAC address learning and all VLANs, and check the status of the spanning tree.

Is MAC address of virtual machine learned by S series switch correct?
It is normal that S series switches (except S1700 switches) can learn MAC addresses of VMs. MAC address learning is the prerequisite for communication.

Why are source MAC addresses not learned
The causes are as follows: -The device does not receive packets because the link is Down, the interface does not join the VLAN, the interface participates in spanning tree calculation and is blocked, and so on. -Loops cause MAC address flapping. -MAC address learning is disabled or corresponding Sticky MAC address entries already exist. -The number of learned MAC address entries has reached the maximum. -The static or blackhole route is configured.

Possible causes for a failure to learn ND entries
In V100R002 and later versions, a switch fails to learn ND entries due to the following possible causes: - The physical state or protocol state of the interface is Down. You can run the display ipv6 interface interface-type interface-number command in any view to check the physical state and protocol state of an interface. - The STP state of the interface is Discarding. You can run the display stp brief command in any view to check the STP state of an interface. - The number of ND entries or IPv6 routes exceeds the limit. - You can run the display ipv6 neighbors command in any view to check information about ND entries. - You can run the display ipv6 routing-table statistics command in any view to check statistics on IPv6 routes.

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