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Chapter 4 MAC Table Configuration
4.1 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.
4.1.1 Obtaining MAC Table
The MAC table can be built up by static configuration and dynamic learning. 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.