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DSL-504 ADSL Router User’s Guide
59
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:
Class Beginning
Address
Ending
Address
A 10.0.0.0 10.255.255.255
B 172.16.0.0 172.31.255.255
C 192.168.0.0 192.168.255.25
5
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.
IP Class Subnet Mask
Class A 255.0.0.0
Class B 255.255.0.0
Class C 255.255.255.0
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.