System Administration Guide: IP Services

Designing Your CIDR IPv4 Addressing Scheme

The network classes that originally constituted IPv4 are no longer in use on the global Internet. Today, the IANA distributes classless CIDR format addresses to its registries around the world. Any IPv4 address that you obtain from an ISP is in CIDR format, as shown in Figure 2–2.

The network prefix of the CIDR address indicates how many IPv4 addresses are available for hosts on your network. Note that these host addresses are assigned to interfaces on a host. If a host has more than one physical interface, you need to assign a host address for every physical interface that is in use.

The network prefix of a CIDR address also defines the length of the subnet mask. Most Oracle Solaris 10 commands recognize the CIDR prefix designation of a network's subnet mask. However, the Oracle Solaris installation program and /etc/netmask file require you to set the subnet mask by using dotted decimal representation. In these two cases, use the dotted decimal representation of the CIDR network prefix, as shown in the next table.

Table 2–3 CIDR Prefixes and Their Decimal Equivalent

CIDR Network Prefix 

Available IP Addresses 

Dotted Decimal Subnet Equivalent 



















For more information on CIDR addresses, refer to the following sources: