Manual – Controllers DHE/DHF/DHR21B (standard) and DHE/DHF/DHR41B (advanced)
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Installing the DHR21B/41B option
Assembly and Installation Notes
Subnet mask
A subnet mask is used to divide the network classes into even finer sections. Like the
IP address, the subnet mask is represented by 4 decimal numbers separated by decimal
points.
Example: 255.255.255.128
Each decimal number stands for one byte (= 8 bits) of the subnet mask and can also be
represented using binary code (see following table).
If you compare the IP addresses with the subnet masks, you see that in the binary
representation of the subnet mask all ones determine the network address and all the
zeros determine the station address (see following table).
The class C network with the address 192.168.10. is further subdivided into
255.255.255.128 using the subnet mask. Two networks are created with the address
192.168.10.0 and 192.168.10.128.
The following station addresses are permitted in the two networks:
•
192.168.10.1 ... 192.168.10.126
•
192.168.10.129 ... 192.168.10.254
The network stations use a logical AND operation for the IP address and the subnet
mask to determine whether there is a communication partner in the same network or in
a different network. If the communication partner is in a different network, the standard
gateway is addressed for passing on the data.
Standard gateway
The standard gateway is also addressed via a 32-bit address. The 32-bit address is
represented by 4 decimal numbers separated by decimal points.
Example: 192.168.10.1
The standard gateway establishes a connection to other networks. In this way, a
network station that wants to address another station can use a logical AND operation
with the IP address and the subnet mask to determine whether the required station is
located in the same network. If this is not the case, the station addresses the standard
gateway (router), which must be part of the actual network. The standard gateway then
takes on the job of transmitting the data packages.
DHCP (Dynamic
Host Configuration
Protocol)
Instead of setting the 3 parameters IP address, subnet mask and standard gateway
manually, they can be assigned automatically by a DHCP server in the Ethernet
network.
This means the IP address is assigned from a table, which contains the allocation of
MAC address to IP address.
Parameter P785 indicates whether the DHR21B/41B option expects the IP parameters
to be assigned manually or via DHCP.
Byte 1
Byte 2
Byte 3
Byte 4
11111111
.
11111111
.
11111111
.
10000000
Byte 1
Byte 2
Byte 3
Byte 4
IP address
decimal
192
.
168
.
10
.
129
binary
11000000
.
10101000
.
00001010
.
10000001
Subnet mask
decimal
255
.
255
.
255
.
128
binary
11111111
.
11111111
.
11111111
.
10000000
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