User`s guide

XStack Storage User’s Guide 181
E.2.3 Class C Network Addresses
Class C network addresses are used for small to mid-size businesses. IP addresses with a first
octet from 192 to 223 are part of this class. Every Class C network address has a 24-bit network
prefix, with the three highest order bits set to 1-1-0, followed by a 21-bit network number and
an 8-bit host-number that identifies each host. This means there are 2,097,152 (221) Class C
networks, each with 254 (2
8
-2) possible hosts, for a total of 536,870,912 (2
29
) unique IP
addresses. Class C networks make up 12.5% (or 1/8th) of the total available IP addresses. Class C
networks are also referred to as “/24s” since they have a 24-bit network prefix.
In a Class C address, the first three octets are the network portion. The Class C example in Figure
E-1 has a major network address of 193.18.9. Eight bits (octet 4) are for local subnets and hosts,
ideal for networks with no more than 254 hosts.
Class C Address Example:
Network Host
195.24.54 106
E.3 Network Masks
A network mask helps you know which portion of the address identifies the network and which
portion of the address identifies the node. Subnet masks are usually represented in the same
representation used for addresses themselves; in IPv4, dotted decimal notation - four numbers
from zero to 255 separated by periods (for example, 255.128.0.0).
Class A, B, and C networks have the following default masks:
 Class A: 255.0.0.0
 Class B: 255.255.0.0
 Class C: 255.255.255.0
An IP address on a Class A network that has not been subnetted has an address/mask pair similar
to:
8.20.15.1 255.0.0.0
To see how the mask helps to identify the network and node parts of the address, convert the
address and mask to binary numbers.
8.20.15.1 = 00001000.00010100.00001111.00000001
255.0.0.0 = 11111111.00000000.00000000.00000000
Once the address and mask are represented in binary, identifying the network and host addresses
is easy:
 Any address bits with a corresponding mask bits set to 1 represent the network address.
 Any address bits that have corresponding mask bits set to 0 represent the node address.