Subnet masks and octets, Determining whether devices are on the same subnet, On the same subnet – Extron Electronics SMX System User Guide User Manual

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SMX System MultiMatrix Switcher • Ethernet Control 112

Subnet Masks and Octets

The subnet mask (see figure 69) is used to determine whether the local and remote devices
are on the same or different subnet. The subnet mask consists of four numeric octets
separated by dots. Each octet can be numbered from 000 through 255, up to 3 digits total
per octet. Leading zeros are optional. 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 69.

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 70). 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 octects of the local device
address and the remote device IP address are unmasked.
Unmasked octets are compared (indicated by

in figure 70).

•

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

in figure 70).

If the unmasked octets of the two IP addresses match (indicated by

in figure 70,

example 1), the two addresses are on the same subnet.
If the two unmasked fields do not match (indicated by ≠ in figure 70, example 2 and

example 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)

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 70.

Comparing the IP Addresses