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

Chapter 2. The Resolver 31

Advantages

When using a multiple stack environment, setting up a global environment with a minimum

set of common statements has the advantage of preserving the entire image from being

changed inadvertently. It has also the advantage of creating a default environment that could

be used for those who are not planning to create their own Resolver definitions.

Considerations

In a multiple stack environment, it is important to review how the applications will be

implemented. Some of these applications might be implemented to open their socket with a

specific bind and to do this they will need to code TCPIPJOBNAME to direct them to the

different stacks. Therefore, when designing the global definitions in the Resolver address

space, do not code a TCPIPJOBNAME in GLOBALTCPIPDATA, but allow it to be coded in

local TCPIP.DATA.

2.3.3 Recommendations

To implement the Resolver address space, it is important to first determine whether your

environment will require a single TCP/IP stack or multiple TCP/IP stacks.

In both cases the Resolver is an independent address space and has to be up and running

before the TCP/IP stack is started. However, when implementing for a multiple stack

environment, you must determine how the global files will be defined and which global

statements will be used. This will depend on how independent each stack will be within the

z/OS LPAR. The recommendation is to create a global TCPIP.DATA data set for a single

stack environment, and a default TCPIP.DATA data set if a multiple stack environment is

required.

In the next session we will configure the Resolver address space to create the global and

default definitions to provide the same environment for all applications, which do not have

specific needs. This will allow specific local statements to be defined at the stack level or

application level. To be able to do that, each stack (if more than one is desired) or each

application that needs to have its own resolver statements, has to define to its own

TCPIP.DATA data set for local statements.

It is also recommended to start the Resolver address space during the initialization of the

UNIX System Services via the RESOLVER_PROC() statement within BPXPRMxx, as we will

show in the next section.

2.4 How the Resolver address space is implemented

Based upon our recommendations, we will show the implementation details for the Resolver

address space.

2.4.1 Implementing the Resolver address space

In this section we are going to show the necessary tasks to implement and configure the

Resolver address space in our test environment. Figure 2-10 on page 32 shows the data sets

that are need to configure the Resolver address space.

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

Figure 2-10 Resolver data sets

Implementation tasks

To implement the Resolver address space in our test environment we followed these steps:

1. Set up the Resolver procedure.

2. Configure the setup data set.

3. Configure the global TCPIP.DATA data set statements.

4. Configure the default TCPIP.DATA data set statements.

5. Create the ETC.IPNODES data set.

Set up the Resolver procedure

In this step, we prepare the resolver procedure to be started during the UNIX System

Services initialization as recommended. To do so, we used the BPXPRMxx statement,

RESOLVER_PROC, to specify the procedure name we want to use to start the Resolver

address space. Figure 2-11 on page 33 show the partial contents of BPXPRMxx (member of

SYS1.PARMLIB).

System Resolver

TCPIPA

Stack

LPAR32

TCPIPA.TCPPARMS(DATAA32):

Hostname SC32A

TCPIPJobname TCPIPA

...

//RESOLVER PROC PARMS='CTRACE(CTIRES00)'

//EZBREINI EXEC PGM=EZBREINI,REGION=0M,TIME=1440,PARM=&PARMS

//SETUP DD DSN=USER1.TCPCS.TCPPARMS(RSSETUP),DISP=SHR,FREE=CLOSE

RSSETUP

GLOBALTCPIPDATA('TCPIPA.TCPPARMS(GLOBAL)')

DEFAULTTCPIPDATA('TCPIPA.TCPPARMS(DEFAULT)')

GLOBALIPNODES (’TCPIPA.TCPPARMS(IPNODES)’)

COMMONSEARCH

TCPIPA.TCPPARMS(GLOBAL):

Nameserver=9.1.1.1

Domain=itso.ibm.com

Resolvevia=UDP

...

TCPIPA.TCPPARMS(IPNODES):

9.12.6.7 OURDNS

10.10.1.230 WTSC30A

10.10.1.221 WTSC32A

10.10.1.241 WTSC31A...

TCPIPA.TCPPARMS(DEFAULT):

Hostname SC32

TCPIPJobname TCPIPA