There are actually 5 classes of ips. Class a, b, and c are the ones used on the internet as a whole, and those ips have already been mentioned here. Class D has a 224.something range of ips that are considered private as well. However, this is hardly a consideration, since class D addresses are used strictly for multicasting purposes, and it's likely you'll never need one. Then, there's class E addresses. These start at 240, and there is one of these reserved for private use too, though again, I don't know what it is. Class E addresses are for experimental purposes, and are also generally multicast addresses. Again, you'll probably never see one of these ips on any network, and especially not on the internet. But, they are there, and are used occasionally, even if we don't encounter them.
