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C
Appendix
C-1GFK-1084B
Advanced Information About IP and MAC
Addresses
This appendix gives an overview of IP addresses, gateways, subnet masks and MAC
addresses.
IP Addresses
Each TCP/IP node on a network must have a unique IP address. The TCP/IP Ethernet
Interface is such a node, as is a PC running TCP/IP. There may be other nodes on the
network that are not involved with communications to the PLCs, but no matter what
their function, each TCP/IP node must have its own IP address. It is the unique IP address
that identifies each node on the IP network (or system of connected networks). (Note
that Internet terminology often uses the term “host” to identify a node on a network.)
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 the IP
Address bits are aportioned between the netid and hostid parts:
01
a45404
Class A 0 netid hostid
8162431
01
Class B 1 netid hostid0
8162431
012
Class C 1 netid hostid10
8162431
Figure C-1. IP Address Format for Network Classes A, B, C
Each node on the same local network must have an IP address of the same class and must
have the same netid. Each node on the same network must have a different hostid thus
giving it a unique IP address.