Information Technology Reference
In-Depth Information
Forwarding
Blocking
Forwarding
Blocking
Figure 3-3
Spanning Tree Protocol
Collision Domain
Collision Domain
Broadcast Domain
(IP Subnet)
Figure 3-4
Switches Control Collision Domains
Switches have characteristics similar to bridges; however, they have more ports and run
faster. Switches keep a table of MAC addresses per port, and they implement STP.
Switches are data link layer devices. They are transparent to protocols operating at the
network layer and above. Each port on a switch is a separate collision domain but is part
of the same broadcast domain. Switches do not control broadcasts on the network.
The use of LAN switches instead of bridges or hubs is nearly universal. Switches are pre-
fer red over shared technolo g y bec au s e they prov ide full bandw idth in each direc t ion
when configured in duplex mode. All the devices on a hub share the bandwidth in a single
collision domain. Switches can also use VLANs to provide more segmentation. The “LAN
Design Types and Models” section discusses VLANs.
Routers
Routers make forwarding decisions based on network layer addresses. When an Ethernet
