Distributed Dynamic VIPA

Distributed DVIPA (Dynamic Virtual IP Addressing) allows you to concurrently run identical z/OS® Explorer setups on different systems in your sysplex, and have TCP/IP, optionally with the help of WLM, distribute the client connections among these systems.

There are several ways you can configure a distributed DVIPA, but z/OS Explorer does impose some restrictions on these options.
  • RSE daemon owns the port that is defined for distributed DVIPA, but the actual work happens in the RSE server, which is active as a thread in another address space. Therefore, you cannot use the SERVERWLM distribution method to do load balancing across your systems, because WLM will give advice based on statistics for RSE daemon, not RSE server.
  • When using a sysplex with an even number of systems, you should not use ROUNDROBIN as distribution method to do load balancing across your systems, unless you enable encrypted communication.

    z/OS Explorer clients first attempt to use encryption while setting up communication, and try again without encryption if this fails. This behavior for non-encrypted communication combined with ROUNDROBIN on a sysplex with an even number of systems will result in all uneven numbered systems (first, third, ...) being skipped, and all connections will go to the even numbered systems (second, fourth, ...).

  • The client only knows the DVIPA address used by the Sysplex Distributor for RSE daemon. The Sysplex Distributor will pass the connection request to one of the available RSE daemons, which in turn will start an RSE server thread that will bind to a port on that system. When the client connects to this port, it will use the DVIPA address again, not the actual system address, so you must ensure that the Sysplex Distributor redirects the new connection to the correct system.

    Therefore, z/OS Explorer requires the definition of SYSPLEXPORTS in the VIPADISTRIBUTE statement to ensure that the ports used by the RSE server threads are unique within the sysplex.

    Note:
    • The usage of SYSPLEXPORTS implies that the EZBEPORT structure must be defined in your coupling facility.
    • The usage of SYSPLEXPORTS implies that TCP/IP will select an ephemeral port for the secondary connection. This implies that you cannot reserve ports for these connections in your TCP/IP profile with the PORT and PORTRANGE directives. You also cannot use _RSE_PORTRANGE in rse.env to limit the ports used by z/OS Explorer. z/OS Explorer does provide a workaround for this restriction, because this complicates firewall setup.
There are also some restrictions within z/OS Explorer when using distributed DVIPA:
  • The enable.dDVIPA directive in rse.env must be enabled.
  • To ensure that the z/OS Explorer client will not interfere with the correct port selection by TCP/IP, you should enable the deny.nonzero.port directive in rse.env.
  • All participating z/OS Explorer servers must have an identical setup. You should share /usr/lpp/IBM/zexpl and /etc/zexpl among all participating systems. You should also share /var/zexpl/pushtoclient, if these directories are used. Note that /var/zexpl/WORKAREA and /var/zexpl/logs must be unique for each system.
  • See Running multiple instances to learn which z/OS Explorer components must be shared, and which ones must be unique per system.

JES Job Monitor and other z/OS Explorer servers only interact with the local RSE, and thus do not require a DVIPA setup.

Distributed DVIPAs are defined by the VIPADEFine and VIPABackup keywords of the VIPADynamic block in your TCP/IP profile. The VIPADISTribute keyword adds the required Sysplex Distributor definitions. Distributed DVIPA requires that all participating stacks are sysplex-aware, which is done via the SYSPLEXRouting and DYNAMICXCF keywords of the IPCONFIG block in your TCP/IP profile. See Communications Server: IP Configuration Reference (SC31-8776) for more details on these directives.

See MVS Setting Up a Sysplex (SA22-7625) and Communication Server: SNA Network Implementation Guide (SC31-8777) for more information about setting up the EZBEPORTS structure in your coupling facility.