Networking on z/OS
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TCP/IP on z/OS

Networking on z/OS

TCP/IP on z/OS supports all of the well-known server and client applications.

The TCP/IP started task is the engine that drives all IP-based activity on z/OS. The TCP/IP profile data set controls the configuration of the TCP/IP environment.

The FTP server implements the FTP standard and can communicate with any FTP clients on the network. The telnet server implements a standard line mode telnet daemon.

Even though z/OS is an EBCDIC host, communication with ASCII-based IP applications is seamless.

IP applications running on z/OS use a resolver configuration file for environmental values. Locating a resolver configuration file is somewhat complicated by the dual operating system nature of z/OS (UNIX and MVS).

IPv4 versus IPv6: As of the time of writing, IPv6 continues to be the coming standard for IP addresses. However, it has not been widely implemented yet. Therefore, although this information uses examples and scenarios in an IPv4 context only, you should be aware that IPv6 is fully supported on z/OS.
  • The TCP/IP daemon
    The single entity that handles, and is required for, all IP-based communications in a z/OS environment is the TCP/IP daemon itself. The TCP/IP daemon implements the IP protocol stack and runs a huge number of IP applications to the same specifications as any other operating system might do. That's the beauty of TCP/IP.
  • The TCP/IP profile
    The TCP/IP profile is read by TCP/IP when it is started. If a change needs to be made to the TCP/IP configuration after it has been started, TCP/IP can be made to re-read the profile dynamically (or read a new profile altogether).
  • The FTP server
    FTP, like some other IP applications, is actually a z/OS UNIX System Services application. It can be started within an MVS environment, but it does not remain there very long. It immediately forks itself into the z/OS UNIX environment and tells the parent task to kill itself.
  • The telnet daemon
    There are two telnet servers available in the z/OS operating environment. One is the TN3270 server, which supports line mode telnet, but it is seldom used for just that. Instead, it is primarily used to support the TN3270 Enhanced protocol. The other telnet server is a line mode server only, referred to as the z/OS UNIX Telnet server, or otelnetd. This section describes the otelnetd server only.
  • A good resolver is hard to find
    The resolver configuration file defines the operating characteristics of IP applications.
  • TCP/IP clients
    z/OS supports all the well-known servers. In addition z/OS supports all of the well-known IP client applications.
Parent topic: TCP/IP implementation on the mainframe

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