Filter
Top Products
6-2 TCP/IP Ethernet Communications for the Series 90™ PLC User's Manual
–
May 2002 GFK-1541B
6
IP Addressing
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
IP address
that identifies each node on the IP network (or
system of connected networks). The term “host” is often used to identify a node on a network.
IP Address Format for Network Classes A, B, C
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
and is based on the number of bits in the
netid
part of the IP address.
01
Class A 0 netid hostid
8162431
01
Class B 1 netid hostid0
8162431
01 2
Class C 1 netid hostid10
8162431
In general, the
netid
part is assigned by the Internet authorities and the
hostid
part is assigned by
your local network administrator. The class of network determines the number of hosts that can
be supported. A Class A network can support 2
24
-2 (16,777,214) hosts, Class B, 2
16
-2 (65,534)
hosts, and Class C, 2
8
-2 (254) hosts. The minus 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 same netid. 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
periods where each integer gives the value of one byte of the IP address. For example, the 32-bit
IP address
00001010 00000000 00000000 00000001
is written as
10.0.0.1
One can determine the class of an IP address by examining the first integer in its dotted-decimal
IP address and comparing with the range of values in the following table.
Range of first integer Class
0 - 127 A
128 - 191 B
192 - 223 C
224-239 D (Reserved for Multicast Use)
240 - 255 E (Reserved for Experimental Use)