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Layer 2 Learning and Forwarding for VLANs Acting as a Switch for a Layer 2 Trunk Port
Layer 2 learning is enabled by default. A set of VLANs, configured to function as a switch with a Layer 2 trunk port, learns unicast media access control (MAC) addresses to avoid flooding packets to the trunk port.
 | Note: Traffic is not flooded back onto the interface on which it was received. However, because this “split horizon” occurs at a late stage, the packet statistics displayed by commands such as show interfaces queue will include flood traffic. |
You can optionally disable Layer 2 learning for the entire set of VLANs as well as modify the following Layer 2 learning and forwarding properties:
- Limit the number of MAC addresses learned from the Layer 2 trunk port associated with the set of VLANs
- Modify the size of the MAC address table for the set of VLANs
- Enable MAC accounting for the set of VLANs
