Field Controls 10 manual IP configuration, Addressing basics

IP configuration

IP configuration

Your CER controller uses the common TCP/IP protocols to provide the connection to the client machine over Ethernet. Like any server or device, it needs a 'unique' IP number to be addressed. This chapter shows the basic concepts necessary to install and operate the controller, it does not intend to be a TCP/IP networking guide.

Addressing basics

Unique address

Every device attached to a TCP/IP network is identified by a unique IP address which is a 32-bit number. To make it easier to memorize such addresses, they are usually expressed as four 8-bit numbers between 0 and 255, seperated by dots, e.g.: 192.168.4.1. There are restrictions on using 0 and 255 so avoid those in an address.

Although an IP address is a single value, it consists of two parts: the network ID and the host ID of your computer. The network ID identifies the systems located on the same physical network. The host ID identifies a workstation, server, router, or other TCP/IP device within the network.

Even if a network is not connected to the Internet, it has become custom to choose an address in a range reserved for private networks. That makes it possible to connect your private network to the Internet later without having to reconfigure. The following ranges are reserved for local use (taken from RFC 1597):

10.0.0.0to 10.255.255.255

172.16.0.0to 172.31.255.255 192.168.0.0 to 192.168.255.255

Classes and subnets

After receiving a network ID from your system administrator, you must pick a unique ID for your CER controller. Three classes are defined to accommodate networks of varying sizes. The address class can be identified by the first octet of the address or network ID. The examples in the table below use w.x.y.z to designate the bytes of the IP address.

Class	w values	Network ID	Host ID	Subnet mask
A	1-126	w	x.y.z	255.0.0.0
B	128-191	w.x	y.z	255.255.0.0
C	192-223	w.x.y	z	255.255.255.0

Subnet masks are 32-bit values that allow the recipient of IP packets to distinguish the network ID portion from the host ID. Subnet masks are created by assigning 1's to network ID bits and 0's to host ID bits. The 32-bit value is then converted to dotted-decimal notation, as shown in the table. For example, when the IP address is 192.168.4.1 and the subnet mask is 255.255.0.0, the network ID is 192.168 and the host ID is 4.1.

To prevent addressing and routing problems, all computers on a logical network must use the same subnet mask and network ID.

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