Defining a multi-access SPOOL node (TCP/IP considerations)

For TCP/IP connections, an installation has a number of options when multiple MAS members connect to the network. An installation can define a unique IP address and port for each member of the MAS or for each NETSRV(nnn) in the MAS. In this way, connections into this node can be directed to a specific NETSRV(nnn) instance within the MAS. One advantage is that if you configure TCP/IP correctly, you can ensure there are multiple redundant connections between 2 nodes and lessen the impact of a failure (of a system or a piece of networking hardware) on your network; However, you might not be able to make a connection when there is a problem with the target NETSERV(nnn).

Another method uses SYSPLEX distributor to provide a single VIPA address for a SYSPLES. In this case, multiple NETSRV(nnn) address space (on multiple MVS™ images) will listen to the same IP address (VIPA). The connecting system only knows one address for the target system and Communication Server with the assistance of WLM determines which NETSRV handles the connection. An outage of a system or some network hardware does not impact the ability to establish an NJE connection; however, if there is a system outage, the active NJE connection that was assigned to that system will be terminated. New connections can then be established. Using this method, you cannot ensure that two parallel connections between two nodes will use different NETSRVs on different members, thus losing some redundancy. An advantage to this method is that it makes a simpler network setup and ensures that if at least one NETSRV is active, an NJE session can be established.