D-Link DSL-504T User Manual page 91

DSL-504T User's Manual
App. B: IP Concepts
IP Concepts (continued)
Note: All network addresses outside of these ranges (Class D and E) are either
reserved or set aside for experimental networks or multicasting.
When an IP address's host portion contains only zero(s), the address identifies a network
and not a host. No physical device may be given such an address.
The network portion must start with a value from 1 to 126 or from 128 to 223. Any
other value(s) in the network portion may be from 0 to 255, except that in class B the
network addresses 128.0.0.0 and 191.255.0.0 are reserved, and in class C the network
addresses 192.0.0.0 and 223.255.255.0 are reserved.
The value(s) in the host portion of a physical device's IP address can be in the range of
0 through 255 as long as this portion is not all0 or all255. Values outside the range of
0 to 255 can never appear in an IP address (0 to 255 is the full range of integer values
that can be expressed with eight bits).
The network portion must be the same for all the IP devices on a discrete physical
network (a single Ethernet LAN, for example, or a WAN link). The host portion must be
different for each IP device — or, to be more precise, each IP-capable port or interface
— connected directly to that network.
The network portion of an IP address will be referred to in this manual as a network
number; the host portion will be referred to as a host number.
To connect to the Internet or to any private IP network that uses an Internet-assigned
network number, you must obtain a registered IP network number from an
Internet-authorized network information center. In many countries you must apply
through a government agency, however they can usually be obtained from your Internet
Service Provider (ISP).
If your organization's networks are, and will always remain, a closed system with no
connection to the Internet or to any other IP network, you can choose your own network
numbers as long as they conform to the above rules.
If your networks are isolated from the Internet, e.g. only between your two branch
offices, you can assign any IP Addresses to hosts without problems. However, the
Internet Assigned Numbers Authority (IANA) has reserved the following three blocks
of IP Addresses specifically for private (stub) networks:
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