Running GETHOSTC

RSCSDNS has access to a copy of the GETHOSTC MODULE file on the RSCS production disk (RSCS 403). GETHOSTC runs on RSCSDNS and performs DNS searches on behalf of RSCS. GETHOSTC listens on a TCP/IP port for a connect request from the RSCS server. When a connect request is received, GETHOSTC reads the fully qualified host name sent by RSCS (up to 255 characters), issues the DNS search, and returns the 4-byte dotted decimal IP address to RSCS.

You need to define the port on which GETHOSTC will listen. This port is identified on the DNSPORT operand on the PARM statement for LPR-type, TCPASCII-type, TCPNJE-type, and UFT-type links. The default for GETHOSTC and for these PARM statements is port 900.

Using TCP/IP Well-Known Ports
By default, TCP/IP restricts the use of well-known ports (1–1023). To use port 900 or any other well-known port when usage is restricted, the RSCSDNS server must be authorized on a PORT statement in the TCP/IP configuration file (PROFILE TCPIP). For more information, see z/VM: TCP/IP Planning and Customization.

Before invoking GETHOSTC, the RSCSDNS virtual machine must be set up as follows:

Link and access the C/C++ runtime library (supplied with z/VM as part of Language Environment®).
Global the SCEERUN LOADLIB:
```
GLOBAL LOADLIB SCEERUN
```
SCEERUN is part of the C/C++ runtime library.
Link and access the following minidisks:
- TCPMAINT 592, or equivalent
- RSCS 403
Note: The links are predefined in the sample definition for the RSCSDNS virtual machine.

To start GETHOSTC, issue the GETHOSTC command. The syntax is:

port: is the TCP/IP port on which GETHOSTC will listen for connect requests. The default is 900.

Multiple virtual machines can run GETHOSTC, all listening on the same port. If a well-known port is used, each of the user IDs running GETHOSTC must be authorized on a PORT statement in the TCP/IP configuration file (PROFILE TCPIP).