Three Switch Functions at Layer 2
Table 5.1 describes the three distinct functions of layer-2 switching (you need to remember
these!).
Now I’ll show the output of a
show mac address-table
command. The MAC table, as
it is often called, will display the hardware addresses that the switch has learned. From this
table the forwarding decisions are also made.
The following command in Table 5.2 is used to display the forward/filter table on a switch:
TABLE 5 . 1
Functions of Layer-2 Switching
Functions of Layer-2 Switching
Function Meaning
Address learning Layer-2 switches and bridges remember the source hardware
address of each frame received on an interface, and they enter
this information into a MAC database called a
forward/filter table
.
Forward/filter decisions When a frame is received on an interface, the switch looks at
the destination hardware address and finds the exit interface
in the MAC database. The frame is forwarded out the specified
destination port only.
Loop avoidance If multiple connections between switches are created for
redundancy purposes, network loops can occur. Spanning-Tree
Protocol is used to stop network loops while still permitting
redundancy.