You may remember that in binary, the right most digit represents ones, the next digit to the left represents twos, the next digit to the left represents fours, and so on. But what is magic about 255? It turns out that this is an easy number to represent in binary. Why in the world does /29 mean that there are eight addresses available? IP addresses run from 0.0.0.0 through 255.255.255.255. This would tell these computers that the only valid IP addresses on this network are from 66.235.22.8 to 66.235.22.15. Note that you would set the subnet mask on these computers to 255.255.255.248.
#What is 255 255 255 255 used for on a network free#
Given the CIDR of 66.235.22.8/29, you would be free to assign the addresses 66.235.22.9 through 66.235.22.14 to host computers you want to connect directly to the Internet. Why is it that Table 1 shows that you were issued eight addresses, but the ISP told you that you only have six? The reason is that the first and last addresses are reserved. As Table 1 shows, the number after the “/” indicates the total number of IP addresses available. The /29 specifies that there are a total of eight IP addresses in this block. It means that there are eight IP addresses in this network.īy giving you the CIDR address of 66.235.22.8, the ISP is telling you that your network-addressing block starts at this address. As you look over the information from the ISP, you may wonder what the /29 stands for. CIDR resolved a problem with a shortage in Internet addresses, but more on CIDR next month. First, you should know that CIDR stands for Classless Inter-Domain Routing. If you are not familiar with CIDR, you may be a little confused. Your Internet Service Provider (ISP) tells you that you have six public IP addresses and that your CIDR address is 66.235.22.8/29. Let's say that you are an engineer at a television station that has a T1 connection to the Internet. It may be easier to understand subnet masks if we look at an example. In binary numbers, the right-most digit represents ones, the next digit to the left represents twos, the next digit to the left represents fours, and so on.