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Appendix
G
AdvancedInformation About IP and MAC
Addresses
This appendix gives an overview of IP addresses, gateways, subnet masks and MAC addresses.
IP Addresses
EachTCP/IPhost on a network must have a unique IP Address. The TCP/IP Ethernet Interface is such a host, as is a PC runningTCP/IP. There may be other hosts on the network that are not involved with communications to the PLCs, but no matter what their function, each TCP/IP host must have its own IP Address. It is the IP Address that identifies the host on the IP network (or system of connected networks).
The IP Address is 32 bits long and has a netid part and a hostid part. Each network is a Class A, Class B or Class C network. The class of a network determines how an IP address is formatted:
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| a45404 |
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Class A | 0 |
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Class B | 1 | 0 |
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| 0 1 | 2 | 8 | 16 | 24 | 31 | ||||
Class C | 1 | 1 | 0 |
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Figure G-1. IP Address Format for Network Classes A, B, C
Each host on the same physical network must have an IP Address of the same class and must have the same netid. Each host on the same network must have a different hostid thus giving it a unique IP Address.
IP addresses are written as four decimal integers separated by periods where each integer gives the value of one byte of the IP address. For example, the
00000011 | 00010000 | 00010010 | 00101111 |
is written as
3.16.18.47