RADVision L2W-323, Руководство пользователя

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Appendix C
C-3
A subnet mask is used to divide the suffix of the network IP address into two – the first part
identifies the subnet and the second part identifies the hosts on the subnet. The subnet mask
uses “1” bits to identify the network address and 0 bits to identify the host portion of the
address.
The following figure illustrates a Class C network mask and an example subnet mask. When
applied to a Class C network address, this subnet mask divides the network into four unique
sub-network addresses.
0 8 16 24 31
Class C Network Mask
Class C Subnet Mask
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0
prefix
suffix
prefix
suffix
Figure 63 - Class C subnet mask
If we apply the subnet mask of 255.255.255.192 reserving two higher bits for the subnet
address, the following sub-network addresses are created: 192.36.20.0, 192.36.20.64,
192.36.20.128 and 192.36.20.192. This leaves six bits in the suffix for host addressing, and
62 valid host addresses can be assigned per subnet.
Hexadecimal Notation
The terminal session may ask you to enter the IP subnet mask in hexadecimal (hex) format.
Hexadecimal is a base-16 number system, in which there are 16 numerals (including 0–15)
for each numeric position (instead of 10 numerals, as in the decimal system). In the decimal
system, when we add a “1” to the last digit “9,” we add a column to the left. Similarly, in
hex, when we add a “1” to the last digit “15” (in decimal notation), we add a column to the
left. Thus “10” in hex is “16” in decimal. The problem is how to represent the double-digit
numbers 10-15 (decimal) as a single digit in hex.