User Guide

PMP 450 Planning Guide
Data network planning
This section describes factors to be considered when planning PMP 450 data networks.
Understanding addresses
A basic understanding of Internet Protocol (IP) address and subnet mask concepts is required for engineering
your IP network.
IP address
The IP address is a 32-bit binary number that has four parts (octets). This set of four octets has two segments,
depending on the class of IP address. The first segment identifies the network. The second identifies the hosts
or devices on the network. The subnet mask marks a boundary between these two sub-addresses.
Dynamic or static addressing
For any computer to communicate with a module, the computer must be configured to either
• use DHCP (Dynamic Host Configuration Protocol). In this case, when not connected to the network, the
computer derives an IP address on the 169.254 network within two minutes.
• have an assigned static IP address (for example, 169.254.1.5) on the 169.254 network.
If an IP address that is set in the module is not the 169.254.x.x network address, then the network operator
must assign the computer a static IP address in the same subnet.
When a DHCP server is not found
To operate on a network, a computer requires an IP address, a subnet mask, and possibly a gateway address.
Either a DHCP server automatically assigns this configuration information to a computer on a network or an
operator must input these items.
When a computer is brought on line and a DHCP server is not accessible (such as when the server is down or
the computer is not plugged into the network), Microsoft and Apple operating systems default to an IP address
of 169.254.x.x and a subnet mask of 255.255.0.0 (169.254/16, where /16 indicates that the first 16 bits of the
address range are identical among all members of the subnet).
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pmp-0047 (March 2014)