Ip addresses and octets, Subnet masks and octets, Determining whether devices are on the same subnet – Extron Electronics Annotator User Guide User Manual
Page 107
IP addresses and octets
Valid IP addresses consist of four 1-, 2-, or 3-digit numeric subfields, properly called octets,
which are separated by dots (periods) (figure 61). Each octet can be numbered from 000
through 255. Leading zeros, up to 3 digits total per octet, are optional. Values of 256 and
above are invalid.
192.168.254.254
Typical IP Address:
Octets
Figure 61.
IP Address and Octets
Subnet masks and octets
The subnet mask (figure 62) 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 3 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 62.
Subnet Mask and Octets
Determining whether devices are on the same subnet
To determine the subnet, the local device’s IP address is compared to the remote device’s
IP address (figure 63 below). Each address’s octets 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’s
address and the remote device’s IP address are unmasked.
Unmasked octets are compared (indicated by
?
in the figure below).
•
If the subnet mask octet contains the value 0, the related octets of the local device’s
and remote device’s IP addresses are masked.
Masked octets are not compared (indicated by
X
in the figure below).
If the unmasked octets of the two IP addresses match (indicated by
=
in the figure below,
example 1), 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, 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)
(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 63.
Comparing the IP Addresses
Annotator • Ethernet Connection
101