Understanding the network.pdf - Back to Home

Figure 1.12. A collection of nodes attached to a
bridged network and the BAT.
The BAT lists the transmission protocol address of each node on the network and
associates it with the respective bridge port the node is adjacent to (refer to Figure
1.10). This table is constantly updated as nodes are added and removed from the
network.
The bridge must relay all transmission protocol broadcast packets. Broadcast
packets are destined for all nodes on the network (regardless of which side of the
bridge they are on). Although a network can have multiple collision domains, it has
only one broadcast domain. Broadcast packets are used to send information that all
nodes on the network either require or must respond to (this situation arises more
often than you might think). If the number of nodes on the network increases,
broadcast packets can be a source of significant network performance loss. The only
way to reduce the size of a broadcast domain is to reduce the number of nodes that
participate in it. This is accomplished by creating a second network segment and
moving nodes over to it. For the nodes on the separate networks to communicate,
a network protocol and a device called a router must be used.
In the same way that a hub is a collection of repeaters, a device known as a switch
functionally behaves as a collection of bridges. Switches have become more
common in recent years due to reductions in price, and they represent a significant
shift in the way data networks are designed. Bridging and switching will be
addressed and explained thoroughly in Chapter 6, "Network Switches."