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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 all-0 or all-255. 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:
It is recommended that you choose private network IP Addresses from the above list. For more information on address
assignment, refer to RFC 1597, Address Allocation for Private Internets and RFC 1466, Guidelines for Management of IP
Address Space.
Subnet Mask
In the absence of subnetworks, standard TCP/IP addressing may be used by specifying subnet masks as shown below.
Subnet mask settings other than those listed above add significance to the interpretation of bits in the IP address. The bits of
the subnet mask correspond directly to the bits of the IP address. Any bit an a subnet mask that is to correspond to a net ID bit
in the IP address must be set to 1.
Class
Beginning Address
A
10.0.0.0
B
172.16.0.0
C
192.168.0.0
IP Class
Class A
Class B
Class C
97
DI-206 ISDN Remote Router
Ending Address
10.255.255.255
172.31.255.255
192.168.255.255
Subnet Mask
255.0.0.0
255.255.0.0
255.255.255.0
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