SNR S2940-8G-v2 Switch Configuration Guide
MAC Table Configuration
Chapter 24
MAC Table Configuration
24.1 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.
24.1.1 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.
The topology of the figure above: 4 PCs connected to switch, where PC1 and PC2 belongs to
a same physical segment (same collision domain), the physical segment connects to port 1/5 of
switch; PC3 and PC4 belongs to the same physical segment that connects to port 1/12 of switch.
The initial MAC table contains no address mapping entries. Take the communication of PC1
and PC3 as an example, the MAC address learning process is as follow:
1. When PC1 sends message to PC3, the switch receives the source MAC address 00-01-11-
11-11-11 from this message, the mapping entry of 00-01-11-11-11-11 and port 1/5 is added
to the switch MAC table.
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