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

Chapter 3. Base functions 77

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Configuring the SITE table (HOSTS.LOCAL)

You can set up the local hosts file to support local host name resolution. If you use only the

local hosts file for this purpose, your sockets applications will only be able to resolve names

and IP addresses that appear in your local hosts file.

If you need to resolve host names outside your local area, you can configure the Resolver to

use a domain name server (see the NSINTERADDR statement in the TCPIP.DATA

configuration file). If you use a domain name server, you do not need to set up any host

definitions in your Resolver configuration, but you may still do so. If you have configured your

Resolver to use a name server, it will always try to do so, unless your applications were

written with a RESOLVE_VIA_LOOKUP symbol in the source code.

In our environment we decided to use the Resolver for all our network resolution requests and

therefore chose to implement IPNODES rather than the HOST.LOCAL file.

Refer to Chapter 2, “The Resolver” on page 17, and the z/OS Communications Server: IP

Configuration Guide, Version 1 Release 7, SC31-8775-07; and z/OS Communications

Server: IP Configuration Reference, Version 1 Release 7, SC31-8776-08, for further

explanation and details.

3.7 Steps for configuring stack

The following steps apply to configuring the TCP/IP stack data sets to support base functions:

1. Decide on a stack name and an associated stack DATASETPREFIX. For example, we

chose TCPIPE as the stack name and TCPIPA as the DATASETPREFIX.

2. Decide on network connections for the stack. We configured two OSA-EXPRESS

features, each card having two ports. We configured four connections across the two

features. For redundancy we assigned two pairs of interfaces, each pair using one port

per feature and each pair attached to the same VLAN. This facilitates ARP Takeover,

which is recommended in a flat network (no routing daemon such as OMPROUTE).

Example 3-6 Link assignments

DEVICE OSA2080 MPCIPA

LINK OSA2080LNK IPAQENET OSA2080 VLANID 10

DEVICE OSA20A0 MPCIPA

LINK OSA20A0LNK IPAQENET OSA20A0 VLANID 11

DEVICE OSA20C0 MPCIPA

LINK OSA20C0LNK IPAQENET OSA20C0 VLANID 10

DEVICE OSA20E0 MPCIPA

LINK OSA20E0LNK IPAQENET OSA20E0 VLANID 11

HOME

10.10.10.210 STAVIPA1LNK

10.10.2.212 OSA2080LNK

10.10.3.213 OSA20A0LNK

10.10.2.214 OSA20C0LNK

10.10.3.215 OSA20E0LNK

Figure 3-9 on page 78 illustrates the OSA2080LNK and OSA20C0 pair connecting to the

same VLAN via two different OSA-Express cards. The same logic applies to the OSA20A0

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

and OSA20E0 pair. OSA2080LNK and OSA20A0 share one 2-port feature and OSA20C0

and OSA20E0 share the other 2-port feature.

Figure 3-9 Network diagram

3. Assign static routing paths (see Example 3-7) for traffic to the network using the

OSA-Express ports and IP address based on the network diagram.

Example 3-7 Defined static routes

BEGINRoutes

; Direct Routes - Routes that are directly connected to my interfaces

; Destination Subnet Mask First Hop Link Name Packet Size ;

ROUTE 10.10.3.0 255.255.255.0 = OSA20A0LNK mtu defaultsize

ROUTE 10.10.2.0 255.255.255.0 = OSA20C0LNK mtu defaultsize

ROUTE 10.10.3.0 255.255.255.0 = OSA20E0LNK mtu defaultsize

; Default Route - All packets to an unknown destination are routed

;through this route.

; Destination First Hop Link Name Packet Size

ROUTE DEFAULT 10.10.3.1 OSA20A0LNK mtu defaultsize

ROUTE DEFAULT 10.10.2.1 OSA20C0LNK mtu defaultsize

ROUTE DEFAULT 10.10.3.1 OSA20E0LNK mtu defaultsize

ENDRoutes

We used multiple ROUTE DEFAULT statements for OSA-Express port redundancy.

4. Allocate the TCPPARMS library to be used for explicitly allocated configuration data sets

for the stack, or create a new member in your existing TCPPARMS library. For example,

we allocated TCPIPE.TCPPARMS(DATAE30).

5. Alter your SYS1.PARMLIB(BPXPRMxx). We modified our member as shown in

Example 3-8 on page 79.