#SUBNET MASK TABLE 4 BITS HOW TO#

Table 12-7 Two Examples Using More Challenging Masks Consider the following addresses and masks, along with the binary version of the masks, as shown in Table 12-7. Examining the subnet masks in binary helps overcome the challenge. However, when the mask uses other decimal values besides 0 and 255, deciphering the number of host bits is more difficult. So, for every decimal 0 in the mask, there are 8 host bits. Most of us can calculate the number of host bits easily if the mask uses only decimal 255s and 0s because it is easy to remember that decimal 255 represents 8 binary 1s, and decimal 0 represents 8 binary 0s. In fact, if you remembered that the default mask for Class C networks is 255.255.255.0, you might have realized already that no subnetting was being used in this example. The mask has eight binary 0s, yielding 8 host bits, with no bits remaining for the subnet part of the address. 199.1.1.100 is in a Class C network, which means that there are 24 network bits. In fact, this example does not even use subnetting.

A subnet mask of 255.255.255.0 has only eight binary 0s, implying 8 host bits, which leaves 8 subnet bits in this case.įor another example, consider 199.1.1.100, with mask 255.255.255.0. First, 130.4.102.1 is in a Class B network, so there are 16 network bits. Two other examples with easy-to-convert masks might help your understanding. 255 decimal is eight binary 1s, and 0 decimal is eight binary 0s.) The size of the subnet part of the address is what's left over, or 8 bits. (If you do not believe me, look at Appendix B, in the binary-to-decimal conversion chart. There are 16 host bits because, when you convert 255.255.0.0 to binary, there are 16 binary 0s-the last 16 bits in the mask. In this example, there are 8 network bits because the address is in a Class A network, 8.0.0.0. Table 12-6 First Example, with Rules for Learning Network, Subnet, and Host Part SizesĪlways defined as number of binary 0s in mask If you have forgotten the ranges of values in the first octet for addresses in Class A, B, and C networks, refer to Table 12-2 earlier in the chapter. Table 12-6 lists these three key facts along with the first example. ■ The subnet part of the address is what's left over in the 32-bit address. ■ The host part of the address always is defined by the mask binary 0s in the mask mean that the corresponding address bits are part of the host field.

■ The network part of the address always is defined by class rules.

#SUBNET MASK TABLE 4 BITS HOW TO#

The following facts tell you how to find the sizes of the network, subnet, and host parts of an IP address: The rest of the answers follow from those two facts. So, the key to answering these types of questions is to figure out how many host bits remain after applying subnetting, which then can tell you the size of the subnet field. With subnetting, the network part of the address does not shrink or change, but the host field shrinks to make room for the subnet field. You also already have read that, without subnetting, Class A, B, and C addresses have 24, 16, or 8 bits in their host fields, respectively. You already have learned that Class A, B, and C networks have either 8, 16, or 24 bits in their network fields, respectively. From those facts, you easily can figure out how many hosts exist in the subnet and how many subnets you can create in that network using that subnet mask. You also should know how to figure out how many network, subnet, and host bits are used with that subnetting scheme.

Subnet mask table 4 bits