Bridging versus LAN Switching

Layer-2 switches are really just bridges with more ports. However, there are
some important differences you should be aware of:

Bridges are software based, while switches are hardware based
because they use an ASICs chip to help make filtering decisions.

Bridges can only have one spanning-tree instance per bridge, while
switches can have many. (We cover spanning tree later in this chapter.)

Bridges can only have up to 16 ports, whereas a switch can have
hundreds.

There are three distinct functions of layer-2 switching:
Address learning
Layer-2 switches and bridges remember the source
hardware address of each frame received on an interface and enter this
information into a MAC database.
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.
Loop avoidance
If multiple connections between switches are created
for redundancy, network loops can occur. The Spanning-Tree Protocol
(STP) is used to stop network loops and allow redundancy.