Key Point

Broadcast and multicast frames are, by default, flooded to all ports of a Layer 2 switch, other than the incoming port. The same is true for unicast frames that are destined to any device that is not in the MAC address table.

MAC addresses can also be statically configured in the MAC address table, and you can specify a maximum number of addresses allowed per port.

One advantage of static addresses is that less flooding occurs, both when the switch first comes up and because of not aging out the addresses. However, this also means that if a device is moved, the switch configuration must be changed. A related feature available in some switches is the ability to sticky-leam addressesthe address is dynamically learned, as described earlier, but is then automatically entered as a static command in the switch configuration. Limiting the number of addresses per port to one and statically configuring those addresses can ensure that only specific devices are permitted access to the network; this feature is particularly useful when addresses are sticky-learned.

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