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 Solaris 10 commands recognize the CIDR prefix designation of a network's subnet mask. However, the 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.

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

• For technical details on CIDR, refer to RFC 1519, Classless Inter-Domain Routing (CIDR): an Address Assignment and Aggregation Strategy.

• More general information about CIDR is available from Pacific Bell Internet at Classless Inter-Domain Routing (CIDR) Overview.

• Another CIDR overview can be found in the Wikipedia article,"Classless inter-domain routing".