D-Link DI-304 User Manual - Subnet Mask

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: 

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 

192.168.255.255 

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.