Amer Networks SS2R48G4i V2 - Manual (Page 89)

SS2R24G4i/SS2R48G4i
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Chapter 8 MAC Table Configuration
8.1 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.
8.1.1 Obtaining MAC Table
The MAC table can be built up staticly 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 SS2R24/48G4i switch switch, where PC1
and PC2 belongs to a same physical segment (same collision domain), the physical segment connects
to port 5 of SS2R24/48G4i switch switch; PC3 and PC4 belongs to the same physical segment that
connects to port 12 of SS2R24/48G4i switch 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 5 is added
to the switch MAC table.
2. At the same time, the switch learns the message is destined to 00-01-33-33-33-33, as the MAC
table contains only a mapping entry of MAC address 00-01-11-11-11-11 and port 5, and no port
mapping for 00-01-33-33-33-33 present, the switch broadcast this message to all the ports in the
switch (assuming all ports belong to the default VLAN1).
3. PC3 and PC4 on port 12 receive the message sent by PC1, but PC4 will not reply, as the
destination MAC address is 00-01-33-33-33-33, only PC3 will reply to PC1. When port 12 receives
the message sent by PC3, a mapping entry for MAC address 00-01-33-33-33-33 and port 12 is