Now that we know the range of addresses that are available, does it matter which one we use? Well, that depends upon how the systems are connected, as we hinted at earlier. The reason is that every system directly connected to a public network (such as the Internet) must have an individual IP address that doesn't conflict with any other. Some companies simply pick a range at random; others may use one they know belongs to someone else, safe in the knowledge that the two will never clash (always a dangerous practice!).
Both these methods are fine in theory, but problems can occur if, for example, someone connects the system and forgets to alter its address. Another method is to use a “reserved” address.