Dynamic definition of VTAM-to-VTAM connections

Dynamic definition of VTAM-to-VTAM connections depends on the functions of XCF in a sysplex. The MVS™ system programmer must establish the XCF environment. VTAM® requires that a value for the MVS symbol &SYSCLONE be provided during MVS initialization. VTAM joins the XCF group named ISTXCF. No action is required to specify this group.

VTAM uses the XCF facilities only if they exist. If XCF facilities are not available or if subarea routing is used exclusively, VTAM-VTAM communication within a sysplex requires explicit definition.

Whether VTAM attempts to establish connectivity through XCF with other nodes in the sysplex during VTAM initialization is determined by the value specified for the start option XCFINIT.

If XCFINIT=YES is specified (for an APPN node), VTAM joins the ISTXCF group at VTAM initialization. As it becomes aware of each other member node of the Sysplex, VTAM builds a TRLE and APPN PU definition for that node and begins the activation of the APPN PU. XCFINIT=YES is the default for APPN nodes. XCFINIT=YES is not allowed for pure subarea nodes.
If XCFINIT=DEFINE is specified, VTAM joins the ISTXCF group at VTAM initialization. If the node is a pure subarea node, as it becomes aware of each other member node of the Sysplex, VTAM builds a TRLE definition for that node, but does not activate it. While this option does not enable SNA communications over XCF for pure subarea nodes, it does allow TCP/IP communications through XCF to be enabled. If the node supports APPN, as it becomes aware of each other member node of the sysplex, VTAM builds a TRLE and APPN PU definition for that node, but does not activate the APPN PU. This option is useful in APPN configurations where XCF connectivity is desirable for TCP/IP communications but not for APPN communications.
If XCFINIT=NO is specified, VTAM does not join the ISTXCF group at VTAM initialization. The operator can cause VTAM to join the ISTXCF group at a later time by activating the ISTLSXCF major node (using the V ACT,ID=ISTLSXCF command).

Activation of the APPN PU for VTAM connectivity through XCF requires that HPR support in the node be specified as (or defaulted to) HPR=RTP. [If HPR=(RTP,ANR) is specified, VTAM will still treat XCF links as having RTP-level HPR support, not just ANR-level support.]

When VTAM builds a dynamic APPN PU definition to support XCF connectivity to another VTAM node in the sysplex, it adds dynamic PU definitions to the ISTLSXCF major node as each VTAM joins the XCF group. The first four characters of the names of the PUs defined in this manner default to ISTP. The next two characters are the &SYSCLONE value of this VTAM. The last two characters are the &SYSCLONE value of the partner VTAM.

When VTAM builds a dynamic TRLE entry to describe the connectivity characteristics used for XCF connections, it adds the entry to the ISTTRL major node. The first four characters of the names of the TRLEs defined in the TRL major node default to ISTT. The next two characters are the &SYSCLONE value of this VTAM. The last two characters are the &SYSCLONE value of the partner VTAM.

Requirement: The XCF major node (ISTLSXCF) and the PU representing the XCF connection to the VTAM on the other side of the XCF connection must each be active for SNA connectivity between the two nodes to be established.

Example: As an example, consider a sysplex with two nodes, Node A and Node B. Each can be started as a pure subarea node or as an APPN node. The APPN node can have XCFINIT=YES, XCFINIT=NO, or XCFINIT=DEFINE. The pure subarea node can have XCFINIT=DEFINE or XCFINIT=NO. Each can be started at the z/OS® V1R7 level or above or with a prior level of z/OS code (prior levels cannot have XCFINIT=DEFINE). Table 1 shows the XCF connectivity between the two nodes for each of these combinations. To make the table more readable, the following points apply:

If either node (or both nodes) specify XCFINIT=NO, no XCF connectivity is established. The node with XCFINIT=NO will not join the ISTXCF group and other VTAM nodes in the group will not be aware of that node's presence in the Sysplex and will not build support for XCF connectivity to that node.
Nodes that specify XCFINIT=NO when started can subsequently be allowed to participate in the Sysplex group by activating the ISTLSXCF major node. At that point, pure subarea nodes behave as if XCFINIT=DEFINE had been specified, and APPN nodes behave as if XCFINIT=YES had been specified.
Pure subarea nodes at the pre-V1R7 level default to XCFINIT=NO. No other XCFINIT value can be specified.

Therefore, in Table 1, each node can be one of the following types:

A V1R7 or later pure subarea node specifying XCFINIT=DEFINE (or defaulted to DEFINE)
A V1R7 or later APPN node specifying XCFINIT=DEFINE
A V1R7 or later APPN node specifying XCFINIT=YES (or defaulted to YES)
A pre-V1R7 APPN node specifying XCFINIT=YES (or defaulted to YES)

Table 1. VTAM to VTAM connection example
		Node B
		V1R7 pure subarea XCFINIT= DEFINE	V1R7 APPN XCFINIT= DEFINE	V1R7 APPN XCFINIT= YES	Pre-V1R7 APPN XCFINIT= YES
Node A	V1R7 pure subarea XCFINIT= DEFINE	Result 1	Result 1	Result 1	Result 2
	V1R7 APPN XCFINIT= DEFINE	Result 1	Result 6	Result 6	Result 5
	V1R7 APPN XCFINIT= YES	Result 1	Result 6	Result 3	Result 3
	Pre-V1R7 APPN XCFINIT= YES	Result 7	Result 4	Result 3	Result 3

Results:

Node A and Node B have XCF TRLEs defined, but no XCF APPN PUs are defined. SNA connectivity is not available. TCP/IP stacks on the two nodes can establish connectivity.
Node A and Node B have XCF TRLEs defined. Node B has the XCF APPN PU defined and activated. The PU remains in Pending Request Contacted (PREQC) state until manually deactivated by the operator. SNA connectivity is not available. TCP/IP stacks on the two nodes can establish connectivity.
Node A and Node B have XCF TRLEs and XCF APPN PUs defined and activated. Each PU activation will complete. SNA connectivity will be established. TCP/IP stacks on the two nodes can establish connectivity.
Node A and Node B have XCF TRLEs and XCF APPN PUs defined. Node A has activated the XCF PU. The PU remains in Pending Request Contacted (PREQC) state until the operator either manually deactivates the PU on Node A or manually activates the PU on Node B. TCP/IP stacks on the two nodes can establish connectivity. If the PU on Node B is activated, SNA connectivity is established.
Node A and Node B have XCF TRLEs and XCF APPN PUs defined. Node B has activated the XCF PU. The PU remains in Pending Request Contacted (PREQC) state until the operator either manually deactivates the PU on Node B or manually activates the PU on Node A. TCP/IP stacks on the two nodes can establish connectivity. If the PU on Node A is activated, SNA connectivity is established.
Node A and Node B have XCF TRLEs and XCF APPN PUs defined, but the PU is not activated by either node. TCP/IP stacks on the two nodes can establish connectivity. If the XCF PU is activated on either Node A or Node B, SNA connectivity is established.
Node A and Node B have XCF TRLEs defined. Node A has the XCF APPN PU defined and activated. The PU remains in Pending Request Contacted (PREQC) state until manually deactivated by the operator. SNA connectivity is not available. TCP/IP stacks on the two nodes can establish connectivity.

You can define a model for dynamic XCF local SNA PUs in a model major node to override the XCF default values for the operands of the PU definition statement (for example, CPCP or TGP). Coding a TRLE operand signifies that the model is for XCF connections. Do not specify CONNTYPE=LEN on the XCF model definition. Only one model definition is in effect at a time. The first model activated is the one used for the dynamic PUs. DYNTYPE=XCF can be coded in a model major node definition.

You can change the default values for the first four characters of the dynamic PU names added to ISTLSXCF by specifying up to four characters as the name of the model PU. The default values for the first four characters of the dynamic TRLE names added to the ISTTRL major node can be changed by specifying up to four characters on the TRLE operand of the model PU.