0 and 254 can t be assigned to hosts). (Business web site)
0 and 254 can t be assigned to hosts). Here is an example of a Class C network number: 194.122.56 When IP addresses were created, nobody expected that, even though this numbering scheme represented millions of potential addresses, there wouldn t be enough to go around. Now, if you get an official pool of addresses assigned to you for the Internet, you will get either a Class C address or part of a Class A or Class B address. The question becomes: How can a network number be divided among several networks? The answer is: by using a netmask. Understanding netmasks Let s say that you are assigned the Class B address 135.84, but you are only given the pool of numbers available to the address 135.84.118. How do you tell your network that every address beginning with 135.84.118 represents a host on your network, but that other addresses beginning with 135.84 should be routed to another network? The answer is with the netmask. The netmask essentially identifies the network number for a network. When you assign the IP address that is associated with your computer’s interface to the LAN (eth0), you are asked for a netmask. By default, your computer will fill in a number that masks the part of your IP address that represents the Class of your network. For example, the default netmasks for Class A, B, and C networks are the following: Class A netmask: 255.0.0.0 Class B netmask: 255.255.0.0 Class C netmask: 255.255.255.0 Now, if your network was assigned the network number 135.84.118, to tell your computer that 135.84.118 is the network number and not 135.84 (as it normally would be for a Class B address), add a netmask of 255.255.255.0. Thus, your network has available host numbers of 1 to 254 (which would go into the fourth part of the number). To further confuse the issue, you could mask only one or more bits that are part of the IP address. Instead of using the number 255, you could use any other number from 1 to 254 to mask only part of the numbers in that part of the address. (The numbers that you can use for each network get rather strange when you do this.) Classless Inter-Domain Routing The class method of allocating IP addresses had several major drawbacks. First, few organizations fell neatly into one class or another. For most organizations, a Class C address (up to 256 IP addresses) was too small, and a Class B address (up to 65,534 IP addresses) was too big. The result was a lot of wasted numbers in a world where IP addresses were running short. Second, IP classes resulted in too many routing table entries. As a result, routers were becoming overloaded with information. The Classless Inter-Domain Routing addressing scheme set out to deal with these problems. The scheme is similar to IP address classes, but offers much more flexibility in assigning how much of the 32-bit IP address is the network identifer. Instead of the first 8, 16, or 32 bits identifying the network, 13 to 27 bits could identify the network. As a result, groups of assigned IP addresses could contain from 32 to about 524,000 host addresses.
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