50 Ethernet module User’s Manual
Chapter 4 Preparing for Operation (Software)
4
(b) IP address acquisition
Taking future uses into account, we strongly recommend acquiring an official IP
address.
(c) Notes on IP addresses
The following IP addresses cannot be used with the EN311, both for the local
station and for remote station addresses.
• Addresses starting with 127 (7FH).
• Addresses in which the network address is all zeros or all ones.
• Addresses in which the host address is all zeros or all ones.
(d) Broadcast addresses
The only broadcast address that can be used with the EN311 is 255.255.255.255
(FF.FF.FF.FF).
The broadcast address 0.0.0.0 used on some UNIX systems (4.2 BSD) cannot
be used.
UNIX is an operating system used on engineering workstations (EWS) and other
computers. There are several versions of UNIX, including ones developed by
AT&T Bell Laboratories Inc., and ones developed by the University of California
at Berkeley. In particular, 4.2 BSD is a version developed at Berkeley.
(2) Subnets and the subnet mask
One technique for managing a network with a large number of nodes (stations) is to
divide that network into multiple subnets. A subnet operates by taking some number
of bits in the host address of the IP address for each class, and using those bits as a
subnetwork address. This allows the installation to operate the network internally as
multiple subnetworks, while the network is recognized externally as a single network.
The subnet mask is used to determine how many bits of the host address to allocate
as the subnet address. In the subnet mask, the network address field and the
subnetwork address field are set to 1 and the remaining field (the subnet host
address field) is set to 0.
Example:When a subnetwork address field of 12 bits is used in a class A IP address.
1111 1111 1111 1111 1111 0000 0000 0000 (Hexadecimal notation: FFFFF000)
When a subnet mask is used, all nodes (stations) on the subnetwork must use the same
subnet mask. In the EN311, the user cannot set the subnet mask. The subnet masks
(with the network address field filled with ones) for each class are generated
automatically as shown in Table 4-4 from the specified IP address.
Table 4-4 Relationship between the Local IP Address and the Generated Subnet
Mask on the EN311
Local IP Address Subnet mask
Class A 255.0.0.0 (FF000000)
Class B 255.255.0.0 (FFFF0000)
Class C 255.255.255.0 (FFFFFF00)
Subnetwork
address field
Host
address field
Network
address
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