The term network layout refers to the way that network computers, network components, and other physical parts of a network, such as cabling, are deployed. Three fundamental types exist: linear, star, and ring. The branching tree is also addressed, although this layout is actually two stars that have been connected.
In a linear layout, all computers are connected to the network on one network cable or segment. The linear layout was extremely common in the past but is rapidly being replaced by the star layout. It is now mostly used in networks to which relatively fewer machines (30) are connected. Figure 3.2 illustrates a linear layout.
In a star layout, all computers are directly connected to a hub or a switch, which is a device that allows multiple cables to connect all at one point. Note here that if the interconnecting device in a star network is a hub, the network functions logically, just like a bus network, such that all clients receive all communications. Therefore, a star with a hub is also vulnerable to packet-sniffing attacks. Figure 3.3 shows an example of a star layout.
In this layout, two or more star layouts are connected to each other (see Figure 3.4).
A cable can connect to itself, thus forming what amounts to a self-enclosed circuit. In a ring layout, all hosts are connected to this circuit (see Figure 3.5).
Although other, more sophisticated manifestations of these layouts exist, all can in one form or another be characterized as one of these fundamental types. Modern Ethernets usually use the star and bus layouts together; the star connects systems to a bus together. Layout is also an important consideration in network security because some types of layouts are more vulnerable to certain kinds of attacks than are others. In the bus layout, for example, all computers listen to all packets sent over the network segment to which they are attached. This makes these networks particularly vulnerable to eavesdropping attacks in which one host has a program installed to copy every packet that reaches that host's NIC.