Subnet Masks And Octets; Determining Whether Devices Are On The Same Subnet - Extron electronics MPX 866 A User Manual

Subnet Masks and Octets

The subnet mask (see figure 74) 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
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.
Typical Subnet Mask:
Figure 74.

Determining Whether Devices Are on the Same Subnet

To determine the subnet, the IP address of the local device is compared to the IP address
of the remote device (see figure 75). 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
z z
the local device and the remote device are unmasked.
Unmasked octets are compared (indicated by
If the subnet mask octet contains the value 0, the related octets of the IP addresses of
z z
the local device and remote device are masked.
Masked octets are not compared (indicated by
If the unmasked octets of the two IP addresses match (indicated by
the two addresses are on the same subnet.
If the two unmasked fields do not match (indicated by
example 3), the addresses are not on the same subnet.
Local IP Address:
Subnet Mask:
Remote IP Address:
Figure 75.
0 indicates that this octet will not be
compared between two IP addresses.
255.255.0.0
Octets
Typical Subnet Mask
Example 1
192.168.254.254
255.255.0.0 (?.?.X.X)
192.168.2.25
Match?: =.=.X.X — Match
subnet)
(Same
Comparing the IP Addresses of the Local and Remote Devices
MPX 866 A Media Presentation Matrix Switcher • Ethernet Connection
? in figure 75).
X in figure 75).
= in figure 75, example 1),
≠
in figure 75, example 2 and
Example 2 Example 3
192.168.254.254 192.168.254.254
255.255.0.0 (?.?.X.X) 255.255.0.0 (?.?.X.X)
190.190.2.25 192.190.2.25
≠.≠.X.X
— No match =.≠.X.X
subnet)
(Different (Different
— No match
subnet)
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