Deciding on an IP Addressing Format for Your Network

When you plan your network addressing scheme, consider the following factors:

• The type of IP address that you want to use: IPv4 or IPv6

• The number of potential systems on your network

• The number of systems that are multihomed or routers, which require multiple network interface cards (NICs) with their own individual IP addresses

• Whether to use private addresses on your network

• Whether to have a DHCP server that manages pools of IPv4 addresses

Briefly, the type of IP addresses include the following:

IPv4 Addresses

These 32-bit addresses are the original IP addressing format for TCP/IP.

For an overview of class-based IPv4 addressing, refer to the following resources:

• Designing Your IPv4 Addressing Scheme in System Administration Guide: IP Services

• Internet Protocol DARPA Internet Program Protocol Specification

The IETF developed Classless Inter-Domain Routing (CIDR) addresses as a short to medium term remedy for the shortage of IPv4 addresses and the limited capacity of the global Internet routing tables.

For more information, refer to the following resources:

• Designing Your CIDR IPv4 Addressing Scheme in System Administration Guide: IP Services

• Classless Inter-domain Routing (CIDR): The Internet Address Assignment and Aggregation Plan

The following table provides the subnets in both CIDR notation and dotted decimal format.

Table 1-1 CIDR Prefixes and Their Decimal Equivalents

DHCP Addresses

The Dynamic Host Configuration Protocol (DHCP) protocol enables a system to receive configuration information from a DHCP server, including an IP address, as part of the booting process. DHCP servers maintain pools of IP address from which to assign addresses to DHCP clients. A site that uses DHCP can use a smaller pool of IP addresses than would be needed if all clients were assigned a permanent IP address. You can set up the DHCP service to manage your site's IP addresses, or a portion of the addresses. For more information, refer to Chapter 10, About DHCP (Overview).

IPv6 Addresses

The 128–bit IPv6 addresses provide greater address space than is available with IPv4. As with IPv4 addresses in CIDR format, IPv6 addresses are classless and use prefixes to designate the portion of the address that defines the site's network.

For more information about IPv6 addresses, refer to the following resources:

• IPv6 Addressing Overview in System Administration Guide: IP Services

• Internet Protocol, Version 6 (IPv6) Specification

Private Addresses and Documentation Prefixes

The IANA has reserved a block of IPv4 addresses and an IPv6 site prefix for use on private networks. These private addresses are used for network traffic within a private network. These addresses are also used in documentation.

The following table lists the private IPv4 address ranges and their corresponding netmasks.

For IPv6 addresses, the prefix 2001:db8::/32 is a special IPv6 prefix that is used specifically for documentation examples. The examples in this book use private IPv4 addresses and the reserved IPv6 documentation prefix.