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Subnet Masks and Octets
The subnet mask (see figure 106) is used to determine whether the analog 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 zeroes, 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.
0 indicates that this octet will not be
compared between two IP addresses.
Typical Subnet Mask: 255.255.0.0
Octets
Figure 106. Typical Subnet Mask
Determining Whether Devices Are on the Same Subnet
To determine the subnet, the IP address of the analog device is compared to the IP address
of the remote device (see figure 107). The octets of each address are compared or not
compared, depending on the value in the related subnet mask octet.
•
If a subnet mask octet contains the value 255, the related octets of the IP addresses of
the analog device and the remote device are unmasked.
Unmasked octets are compared (indicated by ? in figure 107).
•
If the subnet mask octet contains the value 0, the related octets of the IP addresses of
the analog device and remote device are masked.
Masked octets are not compared (indicated by X in figure 107).
If the unmasked octets of the two IP addresses match (indicated by = in figure 107, example 1),
the two addresses are on the same subnet.
If the two unmasked fields do not match (indicated by ≠ in figure 107, example 2 and
example 3), the addresses are not on the same subnet.
Local IP Address:
Subnet Mask:
Remote IP Address:
Match?:
Example 1
192.168.254.254
255.255.0.0 (?.?.X.X)
192.168.2.25
=.=.X.X — Match
(Same subnet)
Example 2
192.168.254.254
255.255.0.0 (?.?.X.X)
190.190.2.25
≠.≠.X.X — No match
(Different subnet)
Example 3
192.168.254.254
255.255.0.0 (?.?.X.X)
192.190.2.25
=.≠.X.X — No match
(Different subnet)
Figure 107. Comparing the IP Addresses of the Analog and Remote Devices
CrossPoint and MAV Series Matrix Switchers • Ethernet Connection
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