User`s guide

XStack Storage User’s Guide 177

Appendix E Understanding IP Addresses and Subnet Masking

When you configure the TCP/IP settings on the XStack Storage unit, an IP address, subnet mask,

and default gateway are required. To configure these settings correctly, it is necessary to

understand how TCP/IP networks are addressed and divided into networks and subnetworks. This

appendix provides a brief tutorial about IP addresses and subnetworks.

E.1 Understanding IP Addresses

An IP address is a way to identify a computer or device on a TCP/IP network. Networks using the

TCP/IP protocol route messages based on the IP address of the destination. IP addresses are

expressed as four decimal numbers to make Internet addresses easy for human users to read and

write. These four numbers are called “octets,” because they each have eight positions when

viewed in binary form. Each octet is separated from the next octet by a period (or “dot”). For

this reason, this format is called “dotted-decimal notation.”

If you add all the octet positions (8 positions x 4 octets), you get 32. This is why IP addresses are

considered 32-bit numbers. Since each of the eight positions can have two different states (1 or

0), the total number of possible combinations per octet is 28 or 256. As a result, each octet can

contain any value from 0 to 255. Combine the four octets and you get 232, equivalent to

4,294,967,296 unique values. Out of the almost 4.3 billion possible combinations, certain values

are restricted from use as typical IP addresses. For example, the IP address 0.0.0.0 is reserved

for the default network and the address 255.255.255.255 is reserved for broadcasts.

An example of an IP address is:

192.168.1.1

The binary value that corresponds to the decimal format of this IP address is:

11000000.10101000.00000001.00000001

To calculate the binary octets in an IP address, convert the decimal values as follows:

1. The rightmost (or least-significant bit) of an octet will hold a value of 2

2. The bit just to the left of that will hold a value of 2

3. This continues until the leftmost (most-significant) bit, which will hold a value of 27.

Therefore, if all binary bits are a one, the decimal equivalent would be 255 as shown below:

1 1 1 1 1 1 1 1

128 64 32 16 8 4 2 1

(128+64+32+16+8+4+2+1=255)