Subnet Masks And Octets; Determining Whether Devices Are On The Same Subnet - Extron electronics DXP DVI Pro User Manual

Subnet masks and octets

The subnet mask (figure 120) 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 indicates that this octet will be
compared between two IP addresses.
Typical Subnet Mask: 255.255.0.0
Figure 120.
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 121, below). 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
• 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
If the unmasked octets of the two IP addresses match (indicated by
figure below), the two addresses are on the same subnet.
If the two unmasked fields do not match (indicated by an unequal sign in the
figure below, examples 2 and 3), the addresses are not on the same subnet.
Example 1
Local IP Address: 192.168.254.254
Subnet Mask: 255.255.0.0 (?.?.X.X)
Remote IP Address: 192.168.2.25
= . = .X.X — Match
Match?:
(Same subnet)
Figure 121. Comparing the IP Addresses
DXP DVI Pro and DXP HDMI Series • Reference Information
0 indicates that this octet will not be
compared between two IP addresses.
Octets
in figure 121).
?
n
Example 2
192.168.254.254
255.255.0.0 (?.?.X.X)
190.190.2.25
≠ . ≠ .X.X — No match
(Different subnet)
in figure 121).
in example 1 of the
=
Example 3
192.168.254.254
255.255.0.0 (?.?.X.X)
192.190.2.25
= . ≠ .X.X — No match
(Different subnet)
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