GFK-2224Q January 2017 241Chapter 13 Network AdministrationThis chapter discusses how devices are identified on the network and how data is routed among devices. Themain topics covered are:▪ IP Addressing▪ Gateways▪ Subnets and Supernets13.1 IP AddressingEach TCP/IP node on a network must have a unique IP address. The TCP/IP Ethernet Interface is such a node, asis a PC running TCP/IP. There may be other nodes on the network that are not involved with communications tothe PLCs, but no matter what their function, each TCP/IP node must have its own IP address. It is the IP addressthat identifies each node on the IP network (or system of connected networks). The term “host” is often used toidentify a node on a network.IP Address Format for Network Classes A, B, CThe IP address is 32 bits long and has a netid part and a hostid part. Each network is a Class A, Class B or ClassC network. The class of a network determines how an IP address is formatted and is based on the number ofbits in the netid part of the IP address.0 1Class A 0 netid hostid8 16 24 310 1Class B 1 netid hostid08 16 24 310 1 2Class C 1 netid hostid1 08 16 24 31Figure 97: IP Address Format for Network Classes A, B, CIn general, the netid part is assigned by the Internet authorities and the hostid part is assigned by your localnetwork administrator. The class of network determines the number of hosts that can be supported. A Class Anetwork can support 2 24 -2 (16,777,214) hosts, Class B, 2 16 -2 (65,534) hosts, and Class C, 28 -2 (254) hosts. Theminus 2 refers to host numbers reserved for the network itself and the local broadcast.Each node on the same physical network must have an IP address of the same class and must have the samenetid. Each node on the same physical network must have a different hostid thus giving it a unique IP address.IP addresses are written in “dotted-decimal” format as four decimal integers (0-255) separated by periodswhere each integer gives the value of one byte of the IP address. For example, the 32-bit IP address:00001010 00000000 00000000 00000001is written as10.0.0.1
