The problem that some people experience is that they try to convert the 6-bit subnet part from binary to decimal, and the 10-bit host part to decimal.
IP ADDRESS SUBNET MASK TABLE PLUS
For example, with 130.4.102.1, mask 255.255.252.0, the first 6 bits of the third octet comprise the subnet field, and the last 2 bits of the third octet, plus the entire fourth octet, comprise the host field. The confusing typically arises when the boundary between the subnet and host part of the address is in the middle of a byte, which occurs when the subnet mask has some value besidesĠ or 255 decimal. So, the conversion from binary back to decimal for the result of the Boolean AND-0000 1000 0000 0001 0000 0000 0000 0000-typically does not pose a problem. Because the mask has only 255s or 0s in decimal, the boundary between the subnet and host fields is on a byte boundary as well-between the second and third bytes, in this case. For instance, in the first example, the subnet mask is 255.255.0.0. The last step in this process, conversion of the binary number back to decimal, is the step that causes most of the problems for people new to subnetting. Step 4 Finally, the Boolean AND result must be converted back to decimal.
Step 3 Next, each bit is ANDed with the bit in the same position in the other number (in other words, a bitwise Boolean AND), giving the result of the Boolean AND. Step 2 Then you must convert the two numbers to binary, as seen in all five examples. Step 1 To begin, you start with a decimal address and mask stated in the question.
The steps taken to complete the tables are as follows: Table 12-14 Boolean AND Calculation for Subnet, Address 199.1.1.100, Mask 255.255.255.224Īlthough the tables show the answers, they do not show the process. The following tables (Tables 12-10 through 12-14) show the Boolean AND process for the five examples used in the previous section of this chapter: Table 12-10 Boolean AND Calculation for Subnet, Address 8.1.4.5, Mask 255.255.255.0 Finding the Subnet NumberĮarlier, you learned that computers perform a Boolean AND of the address and mask to find the subnet number. After deriving these two values, you easily can find the range of valid IP addresses in the subnet.
IP ADDRESS SUBNET MASK TABLE HOW TO
In the next several sections, you will learn how to derive the subnet number and the subnet broadcast address. The question might be straightforward, such as "What is the subnet number?", or it might be more subtle, such as "Which of the following IP addresses are in the same subnet as the stated address?" In either case, if you can dissect an IP address as described in this chapter, you can answer any variation of this type of question. One of the most common things you need to figure out is that after you know an IP address and subnet mask, you must answer questions about them.