Since we think of layer-2 switching as the same as a bridged network, we
must also think it has the same problems as a bridged network.
Recall that bridges are good if we design the network correctly, meaning we break
up the collision domains correctly.
The right way to create bridged networks
is to make sure that users spend 80 percent of their time on the local segment.
Bridged networks break up collision domains, but the network is still one
large broadcast domain. Layer-2 switches (bridges) cannot break up broadcast
domains, which can cause performance issues and limit the size of your
Broadcasts and multicasts, along with the slow convergence of
spanning tree, can cause major problems as the network grows. Because of
these problems, layer-2 switches cannot completely replace routers (layer-3
devices) in the internetwork.