An engineer is troubleshooting why a MAC address was not listed in the MAC table and discovers that the VLAN was enabled only on the interface that data is coming in on. Which change fixes this…

For a switch to properly learn a MAC address and forward frames within a specific VLAN, that VLAN must be enabled and allowed on all interfaces (both ingress and egress) that frames for that VLAN are expected to traverse. If the VLAN is only enabled on the incoming interface, the switch cannot forward frames out other ports, preventing MAC address learning for destinations on those ports.

Disabling sticky MAC, a port security feature, does not resolve the underlying problem of a VLAN not being enabled on all necessary interfaces for proper frame forwarding and MAC learning.

Removing loop detection mechanisms like STP would create network loops, which would severely disrupt network operation and MAC address table stability, rather than fixing a VLAN configuration issue.

Flushing the MAC address table only clears existing entries and does not address the root cause, which is the incorrect VLAN configuration preventing future MAC address learning and forwarding.