Hierarchical Addressing and Routing Infrastructure

As important as the expanded address space is the use of hierarchical address formats. The IPv4 addressing hierarchy includes network, subnet, and host components in an IPv4 address. IPv6, with its 128-bit addresses, provides globally unique and hierarchical addressing based on prefixes rather than address classes, which keeps routing tables small and backbone routing efficient.

The general format is as follows:

Table 1. IPv6 Address Format
global routing prefix subnet ID interface ID
n bits m bits 128-(n+m) bits

The global routing prefix is a value (typically hierarchically structured) assigned to a site; the subnet ID is an identifier of a link within the site; and the interface ID is a unique identifier for a network device on a given link (usually automatically assigned).

When configured for unicast routing, the TCP/IP for z/VM stack may also be configured to provide autoconfiguration information for other hosts-prefixes, parameters, and default routes, as specified in the RFC 2461, Neighbor Discovery for IP Version 6 (IPv6).