Fieldbus
Communication
•
107
ETHERNET
WAGO-I/O-SYSTEM 750
ETHERNET TCP/IP
If a network is to be directly connected to the Internet, only registered,
internationally unique IP addresses allocated by a central registration service
may be used. These are available from Inter
NIC
(International Network
Information Center).
Attention
Direct connection to the Internet should only be performed by an authorized
network administrator and is therefore not described in this manual.
Subnets
To allow routing within large networks a convention was introduced in the
specification
RFC 950
. Part of the Internet address, the subscriber ID is
divided up again into a subnetwork number and the station number of the
node. With the aid of the network number it is possible to branch into internal
subnetworks within the partial network, but the entire network is physically
connected together. The size and position of the subnetwork ID are not
defined; however, the size is dependent upon the number of subnets to be
addressed and the number of subscribers per subnet.
1
8
16
24
32
1 0
Net-ID
Subnet-ID
Host-ID
Fig. 4-10: Class B address with Field for Subnet ID
Subnet mask
A subnet mask was introduced to encode the subnets in the Internet. This
involves a bit mask, which is used to mask out or select specific bits of the IP
address. The mask defines the subscriber ID bits used for subnet coding,
which denote the ID of the subscriber. The entire IP address range
theoretically lies between 0.0.0.0 and 255.255.255.255. Each 0 and 255 from
the IP address range are reserved for the subnet mask.
The standard masks depending upon the respective network class are as
follows:
•
Class A Subnet mask:
255
.
0
.
0
.
0
•
Class B Subnet mask:
255 .255 .0 .0
•
Class C Subnet mask:
255
.
255
.
255
.
0
Depending on the subnet division the subnet masks may, however, contain
other values beyond 0 and 255, such as 255.255.255.128 or 255.255.255.248.
Your network administrator allocates the subnet mask number to you.
