Campbell Scientific CR9000X Measurement and Control System - Manual (Page 19)

Quick Start
QS1.6.1.1 Subnet Mask and IP Settings
The SubNet Mask is a decimal equivalent of a 4-byte binary address. For
any bit set high in the computer's Mask, the corresponding bit in the IP
addresses, for devices that will be communicating with each other, must be
identical.
Example: A PC's SubNet Mask is set to 255.255.240 (binary representation:
is 11111111.11111111.11110000.00000000). For two devices to
communicate, the first two bytes of their IP addresses must be identical.
The first 4 bits of the third byte must also match. So if the third byte for the
PC's IP address is set to 192 (11000000), then any other device that is to
communicate with this PC would need to have the third byte set to
1100XXXX (first 4 bits identical). For this example, a third byte of
11000001 (193) or 11000011 (195) would work. Even 11000000 (192)
would work as long as the fourth byte is not identical for the two devices.
As the PC's Mask fourth byte is all zeros, none of its bits for the two
devices' IP addresses need to match.
It should be remembered that two devices on a network, or that will be
communicating with each other, should not have identical IP addresses. So
for the Subnet Mask of 255.255.240.0, one example of a good pair of IP
addresses is 128.255.192.1 and 128.255.192.2.
If the PC has a fixed IP address, set the CR9000X's Mask to the value of
the PC's SubNet mask, and use the above to determine the CR9000X's IP
address. Example, the PC mask is 255.255.255.0, and its IP address is
192.168.240.3. Valid IP address for the logger would be
192.168.240.XXXX, with XXXX ranging from 0 to 255 with the exception
of 3 (cannot be identical).
If you are using a computer that will be hooked up to a Network, then your
IT people should provide you information on what values you should use
for the SubNet mask and the IP address.
QS-11