news/ipv4-free-pool-depleted. There are a finite number of IP addresses, and they were horribly mismanaged when the Internet was young. Network Address Translation (NAT), Classless Internet Do- main Routing (CIDR), and Variable Length Subnet Masks (VLSM) changed all that, and we got some breathing room. That was about 10 years ago, and the news is once again reporting that we're about to run out of IP addresses. While everyone panics, I try to remind nervous CEOs that this is only an issue with publicly routable IP ad- dresses. Still, given that there are a finite number of these addresses, we'll hit the wall sooner or later. IPv4 (the currently well-known standard) uses 32-bit addresses. This translates to 4,294,967,296 (4.2 X 109) IP addresses, though large blocks of them are considered either reserved or unroutable. For example, 16 million of them are contained within the 10.0.0.0/8 private address space. Let's say, for the sake of argument, that there are four billion public IP addresses. Are we really running out of them? Where have they gone? If you're not familiar with scientific notation, allow me to explain it, since I use it a lot in this chapter. Scientific notation allows us to repre- sent ridiculously large numbers in an easy-to-read format. Simply put, take any number, and then move the decimal until the number is a single digit with one decimal. The number of places you moved the decimal point is a power of 10. The number 1,000 would be written 1.010³. Another way to think of it (though technically inaccurate) is "one with three zeros." Here are some other examples to help you wrap your head around scientific notation. As you can see, scientific notation is easier to read and process in print than listing a pile of zeros: 1.0x106 = 1,000,000 (one million) 1.0x109 = 1,000,000,000 (one billion) 1.0x1012 = 1,000,000,000,000 (one trillion) 1.0x1015 = 1,000,000,000,000,000 (one quadrillion) For more information on the naming of large numbers, check out the nerd-friendly Wikipedia entry titled "Names of 