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Chapter 21 MAC Table Configuration
21.1 Introduction to MAC Table
MAC table is a table identifies the mapping relationship between destination MAC addresses
and switch ports. MAC addresses can be categorized as static MAC addresses and dynamic
MAC addresses. Static MAC addresses are manually configured by the user, have the highest
priority and are permanently effective (will not be overwritten by dynamic MAC addresses);
dynamic MAC addresses are entries learnt by the switch in data frame forwarding, and is
effective for a limited period. When the switch receives a data frame to be forwarded, it stores
the source MAC address of the data frame and creates a mapping to the destination port.
Then the MAC table is queried for the destination MAC address, if hit, the data frame is
forwarded in the associated port, otherwise, the switch forwards the data frame to its
broadcast domain. If a dynamic MAC address is not learnt from the data frames to be
forwarded for a long time, the entry will be deleted from the switch MAC table.
There are two MAC table operations:
1. Obtain a MAC address.
2. Forward or filter data frame according to the MAC table.
21.1.1 Obtaining MAC Table
The MAC table can be built up statically and dynamically. Static configuration is to set up a
mapping between the MAC addresses and the ports; dynamic learning is the process in which
the switch learns the mapping between MAC addresses and ports, and updates the MAC table
regularly. In this section, we will focus on the dynamic learning process of MAC table.
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