private vs. public IP addresses

[Travis Siegel]

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.