Communications Server for z/OS V1R7 TCP/IP Implementation, Volume 1: Base Functions, Connectivity, and Routing

© Copyright IBM Corp. 2006. All rights reserved. 17

Chapter 2. The Resolver

TCP/IP protocols rely upon a strict system of addressing in order to reach a host in a network.

IPv4 addresses are represented in dotted-decimal format. The 32-bit address is divided along

8-bit boundaries. Each set of 8 bits is converted to its decimal equivalent and separated by

periods. In contrast, IPv6 addresses are 128 bits divided along 16-bit boundaries. Each 16-bit

block is converted to a 4-digit hexadecimal number and separated by colons. The resulting

representation is called colon-hexadecimal. The major drawback of this addressing system is

that, for most people, numbers are difficult to remember.

As a result, today's IP-based networks use a mapping of host names to host numbers or

addresses. The obvious advantage of this name-to-address mapping is that we can assign

easy-to-remember names to hosts in the network.

The Resolver is used to help applications establish a connection to a service that translates

host names and IP addresses.

This chapter discusses the following.

2

Section Topic

2.1, “Overview” on page 18 Discusses the basic concepts of the Resolver and

address space

2.2, “Why the Resolver address space is

important” on page 23

Discusses key characteristics of the Resolver address

space and why it may be important in your environment

2.3, “The common design scenarios for

the Resolver” on page 24

Presents commonly implemented Resolver design

scenarios, their dependencies, advantages,

considerations, and our recommendations

2.4, “How the Resolver address space is

implemented” on page 31

Presents selected implementation scenarios, tasks,

configuration examples, and problem determination

suggestions