Ip Addressing

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Part II ✦ Protocols and Standards

Figure 4-1: The WINIPCFG command displays the IP configuration on a Windows 98 system.

Figure 4-2: IPCONFIG displays the IP configuration of a Windows 2000 system.

IP Addressing
The native addressing scheme on a TCP/IP network is a 32-bit binary-based address (commonly called an IP address) divided into 4 eight-bit sections called octets. Octetsare usually represented in decimal notation (for easier use by humans), and can represent a value range from 0 to 255. If you ever see an IP address with a number higher than 255, you are either in the middle of a test, or you are watching The Net.

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Understanding IP addressing requires a solid knowledge of the binary system. many books that detail IPaddressing and subnetting; at first glance, IP addressing and subnetting can be intimidating. Remember that all IP addressing and subnetting centers around two numbers, one and zero. When a numbering system only has two numbers, how hard can it possibly be? Binary notation is a base-2 numbering system. In effect, every number used in an IP address can be calculated by using some combination of thepowers of 2. The first step in learning IP addressing and subnetting is to understand the powers of 2; a chart is an efficient way to represent them (see Table 4-4). Exponent notation is nothing more than taking a number and multiplying it by itself a number of times equal to the exponent (for example, 25=2*2*2*2*2=32) . Table 4-4 lists the values of 2 raised to the power of x for the values 0 to10.

Table 4-4 Powers of 2
Value of X 0 1 2 3 4 5 6 7 8 9 10 2X 1 2 4 8 16 32 64 128 256 512 1024

Generally, knowing the powers of 2 through 210 is sufficient for just about anything you’ll do with IP addresses. In an IP address, the highest power of 2 that can be represented is 27. 8 bits per octet in an IP address: 27 26 25 24 23 22 21 20. Placing a one in one of the eight value positions,effectively turns on (or adds into the value being represented) the power of two for that position. If the value of the bit is needed to make an IP address, that bit is considered turned on. Each of the eight positions in an octet represents a different value — ascending from 20 to 27, left to right, as follows:
27 26 128 25 64 24 32 23 16 22 7 21 4 20 2 1

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Part II ✦ Protocols andStandards

Converting decimal to binary
Given that computers depend on binary notation to do their work, knowing how to convert values from other notations (in particular, decimal) to binary is useful. Fortunately, the computer itself provides a helpful hint: 1 means on, 0 means off. To convert from decimal to binary in the range of 0 – 255, you can use this hint (along with Table 4-4) to repeating atwo-step operation: Find the highest bit value used in the number, and then “turn on” that bit value by placing a one in its place. Continue this process until you get a remainder of 0. The decimal number 27, for example, can be converted to binary in the following manner: 1. Because the highest bit used in 27 is 16 (which is 24), place a 1 in the 24 position. 2. Because the value of 24 is 16,that 16 has to be subtracted from 27. This leaves a remainder of 11. 3. Apply the process of finding the highest bit value in 11. That value is 23, which is 8. 4. Subtract 8 from 11, which gives you a remainder of 3. 5. Find the highest bit value in 3. That value is 21, which is 2. 6. Subtract 2 from 3 and (again) apply the process to the remainder of 1. The only bit value that can have the value of1 is 20. When you reach a remainder of 0, binary conversion is complete. A compact summary of these steps: 27 16 11 8 3 2 1 The highest bit value used is 24, which is 16. Subtract 16 from 27. Remainder =11 The highest bit value used is 23, which is 8. Subtract 8 from 11. Remainder = 3. The highest bit value used is 21, which is 2. Subtract 2 from 3. Remainder =1 The only bit value that can be...