DVS 510 Series • Reference Information 121
Local and remote devices
The local and remote devices are defined from the point of view of the function being
described. In this guide, subnetting is an issue when you are using the controlling computer
to set TCP/IP and e-mail values in the DVS (see “Establishing an Ethernet Connection
Using TCP” on page 48. When you are setting up the variables for e-mail notification, the
scaler is the local device and the e-mail server is the remote device.
IP addresses and octets
Valid IP addresses consist of four 1-, 2-, or 3-digit numeric
sub-fields, called “octets,” which are separated by dots
(periods) (see the figure at right). Each octet can be
numbered from 000 through 255. Leading zeros, up to three digits total per octet, are
optional. Values of 256 and above are invalid.
Subnet masks and octets
The subnet mask (figure 58) 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.
255.255.0.0Typical 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 58. 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 59). 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 ? in figure 59).
• 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 X in figure 59).
If the unmasked octets of the two IP addresses match (indicated by = in example 1 of the
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.
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 59. Comparing the IP Addresses
192.168.254.254Typical IP Address:
Octets