DXP HD 4K Series • Reference Information
107
Subnet masks and octets
The subnet mask (see figure 108) is used to determine whether the local and remote
devices are on the same subnet or different subnets. The subnet mask consists of four
numeric octets separated by dots. Each octet can be numbered from 000 through 255.
Leading zeros, up to three digits total per octet, are optional. Each octet typically contains
either 255 or 0. The octets determine whether or not the same octets of two IP addresses
will be compared when determining if two devices are on the same subnet.
255.255.0.0
Typical Subnet Mask:
Octets
255 indicates that this octet will be
compared between two IP addresses.
0 indicates that this octet will not be
compared between two IP addresses.
Figure 108.
Subnet Mask and Octets
Determining whether devices are on the same subnet
To determine the subnet, the local device IP address is compared to the remote device IP
address (see figure 109. The octets of each address are compared or not, depending on the
value in the related subnet mask octet.
•
If a subnet mask octet contains the value 255, the related octets of the local device
address and the remote device IP address are unmasked.
Unmasked octets are compared
(indicated by
?
in figure 109).
•
If the subnet mask octet contains the value 0, the related octets of the local device and
remote device IP addresses are masked.
Masked octets are not compared
(indicated by
n
in figure 109).
If the unmasked octets of the two IP addresses
match
(indicated by
=
in example 1 of
figure 109), the two addresses
are
on the same subnet
.
If the two unmasked fields
do not match
(indicated by an unequal sign
in figure 109,
examples 2 and 3), the addresses
are not on the same subnet
.
192.168.254.254
255.255.0.0 (?.?.X.X)
192.168.2.25
= . = .X.X — Match
(Same subnet)
(Different subnet)
(Different subnet)
Local IP Address:
Subnet Mask:
Remote IP Address:
Match?:
Example 1
Example 2
192.168.254.254
255.255.0.0 (?.?.X.X)
190.190.2.25
≠
.
≠
.X.X — No match
Example 3
192.168.254.254
255.255.0.0 (?.?.X.X)
192.190.2.25
=
.
≠
.X.X — No match
Figure 109.
Comparing the IP Addresses