System Administration Guide: IP Services

Creating the IPv6 Numbering Scheme

Unless your proposed IPv6 network is entirely new, use your existing IPv4 topology as the basis for the IPv6 numbering scheme.

Creating a Numbering Scheme for Subnets

Begin your numbering scheme by mapping your existing IPv4 subnets into equivalent IPv6 subnets. For example, consider the subnets illustrated in Figure 4–1. Subnets 1–4 use the RFC 1918 IPv4 private address designation for the first 16 bits of their addresses, in addition to the digits 1–4 to indicate the subnet. For illustrative purposes, assume that the IPv6 prefix 2001:db8:3c4d/48 has been assigned to the site.

The following table shows how the private IPv4 prefixes map into IPv6 prefixes.

IPv4 Subnet Prefix 

Equivalent IPv6 Subnet Prefix





Creating an IPv6 Addressing Plan for Nodes

For most hosts, stateless autoconfiguration of IPv6 addresses for their interfaces is an appropriate, time saving strategy. When the host receives the site prefix from the nearest router, Neighbor Discovery automatically generates IPv6 addresses for each interface on the host.

Servers need to have stable IPv6 addresses. If you do not manually configure a server's IPv6 addresses, a new IPv6 address is autoconfigured whenever a NIC card is replaced on the server. Keep the following tips in mind when you create addresses for servers:

Due to the limited number of IPv4 addresses, in the past a network designer had to consider where to use global, registered addresses and private, RFC 1918 addresses. However, the notion of global and private IPv4 addresses does not apply to IPv6 addresses. You can use global unicast addresses, which include the site prefix, on all links of the network, including the public DMZ.