Specifications

Appendix C Operating Environment Installation and Operation Manual
C-8 IP Environment FCD-E1LC Ver. 1.0
Host Portion
In general, the host portion is used to identify an individual host connected to an
IP network. For exceptions, see
Subnetting section below.
After obtaining an IP network address, the using organization is free to assign
host identifiers in accordance with its specific needs.
The following host identifiers have special meanings, and must not be assigned
to an actual host:
• The “all-zeros“ host identifier is interpreted as a network identifier.
• The “all-ones“ host identifier is interpreted as a broadcast address. Therefore,
a message with an “all-ones“ host identifier is accepted by all the hosts in the
network.
Global vs. Private IP Addresses
Given the current number of users already having access to the Internet, and the
rapid increase in this number, the 32-bit IP space address available in Version 4 of
the IP protocol is rather limited.
On the other hand, an IP address must permit unambiguous identification of any
host in the Internet. That is the reason the allocation of IP addresses to networks
is globally controlled by a universally-accepted IP registry organization (IANA).
Although any address used on the Internet must be unique, there are many IP
networks, called private networks, which are not connected to the Internet. A
private network is also created when the access of hosts to the Internet is
controlled by protocols and procedures that do not permit an outsider to find
and use directly the actual address of the hosts connected to that network. A
typical example of a private network is the internal IP network of an enterprise
(such networks are often called
intranets ).
In recognition of this fact, IANA permits using two types of addresses:
• Global addresses, i.e., addresses that and are unique in the whole Internet
• Private addresses, i.e., addresses allocated for internal use only and
therefore cannot be used on the Internet.
Although no restrictions need to be imposed on private addresses except for
conforming to the structure specified in the
Network Portion section above,
the following address spaces have been specifically put aside by IANA for use
as private addresses:
 The Class A addresses in the range of 10.0.0.0 to 10.255.255.255 (this
group of addresses is formally referred to as 10/8). This address space is
actually one Class A network number.
 The Class B addresses in the range of 172.16.0.0 to 172.31.255.255 (this
group of addresses is formally referred to as 172.16/12). This address
space defines 16 contiguous Class B network numbers.
 The Class C addresses in the range of 192.168.0.0 to 192.168.255.255
(this group of addresses is formally referred to as 192.168/16). This
address space defines 256 contiguous Class C network numbers.
Note