IP Address Format
An IP address is a 32-bit number that can be represented in many formats. Routers and computers are designed to operate efficiently on binary numbers, so a binary representation is a natural way for them to store and manipulate IP addresses. A typical 32-bit IP address to a router would look something like this:
10011100000110100001111000111100
This may be a fine representation for routers, but for us it is not the most appealing method. So let’s take a look at the binary representation and see if we can find a way to represent these numbers using a method that may be a bit more palatable. One way is to simply represent the IP address as a decimal number. The binary number used in the example above has a decimal value of
2,618,957,372
This may be easier to read, but the size of the number makes it cumbersome to work with. Another representation scheme is to break up the binary number into pieces and represent each piece as a decimal number. A natural size for binary pieces is 8 bits, which is the familiar “byte” or not-as-familiar “octet” (octet is the telecommunication term, but the two words can be used interchangeably). So let’s take our binary number, write it using groups of 8 bits (four octets) and then represent each group as a decimal number.
10011100
00011010
00011110
00111100
156
26
30
60
Table 2-1: Range of IP Addresses
Low
High
Binary
0000000000000000000
0000000000000
11111111111111111111111111111111
Decimal
0
4,294,967,295
Dotted Decimal
0.0.0.0
255.255.255.255
We don’t need all that space between the numbers, so let’s use a period, or dot, as a separator. Now our IP address has the form
156.26.30.60
which is referred to as dotted decimal notation. How many IP addresses are there? The range of IP addresses in all our representation schemes is shown in Table 2-1.
Theoretically, there are 4,294,967,296 possible IP addresses, although we will discover in this chapter that the actual usable number of IP addresses is much smaller.