Chapter 10: MAC Address Table
Overview
The
Dynamic MAC addresses are addresses that the switch learns automatically by examining the source MAC addresses of the frames received by the ports. This type of MAC address is not stored indefinitely in the MAC address table. The switch deletes a dynamic MAC address from the table if it does not receive any frames from the node after a specified period of time. The switch assumes that the node is no longer active and that its MAC address can be purged from the table. This prevents the MAC address table from becoming filled with addresses of nodes that are no longer active.
The MAC address table can also store a static MAC address which is a MAC address of an end node that you assign to a switch port manually. A static MAC address remains in the table indefinitely and is never deleted by the switch, even when the end node is inactive. You can only delete a static MAC address by manually configuring the switch with the
There are two reasons to enter static MAC addresses. You may want to enter end nodes the switch does not learn in its normal dynamic learning process. Or, you want a MAC address to remain permanently in the table, even when the end node is inactive.
Static multicast addresses are a subset of the static MAC addresses. With the Static Multicast Address feature, you can add static multicast addresses to the MAC address table. You can then assign the static MAC address to a port or ports which are called Group Members in the
In some network environments that are confined to one LAN (such as an industrial application with a server, a switch and many controllers), there may be various multicast streams that need to be distributed to some network nodes, but not others. If the data sent in these streams is time- sensitive and cannot be delayed because of the configuration time associated with the IGMP Snooping feature, then static multicast addresses may be the solution.
If a multicast address and its associated ports of the switch are predefined within the network design and they will not change over time, then they can be manually entered as static entries into the MAC address table. This allows the multicast stream to be forwarded immediately to those
