Start option list with border node support

A VTAM® border node (BN=YES) is an extension to VTAM network node capabilities which allows APPN connectivity between APPN networks and allows partitioning of APPN networks into smaller subnetworks to reduce topology and search activity.

Requirement: NCP V7R1 or later is required for border node function through an NCP.

Figure 1. APPN subnetworks through APPN multiple network connectivity support

A diagram that shows four APPN subnetworks are connected, demonstrating what a border node is.

VTAM border node implements extended border node function, which allows two types of subnetwork boundaries. An extended subnetwork boundary interconnects two extended border nodes. A peripheral subnetwork boundary interconnects a border node with a network node which does not have the extended border node function. While the peripheral boundary allows more flexibility concerning the capabilities of the partner node across the boundary, it is limited to supporting searches and sessions where either the origin or destination of the search resides in the subnetwork of the non-native partner node. See the z/OS Communications Server: SNA Network Implementation Guide for more information about border nodes.

In Figure 1, the subnetwork boundary between HOSTA and HOSTB is an extended boundary, if both VTAMs were started with BN=YES. The boundary between HOSTB and the AS/400® in subnetwork D is a peripheral boundary because the AS/400 does not have extended border node capabilities.

Following is a start list for an APPN interchange node implementing the border node function.

The BNDYN start option controls the level of dynamics that VTAM uses when routing a request across APPN subnetwork boundaries. BNDYN=NONE defeats dynamics and requires that adjacent cluster routing lists be defined for all cross-subnetwork routing. BNDYN=LIMITED allows cross-subnetwork routing targets which match the destination resource's network identifier to be included dynamically, in addition to any cross-subnetwork routing targets through which this node has learned the destination resource's network identifier. BNDYN=FULL will exhaustively search all active cross-subnetwork targets in its search for the destination resource. The BNDYN start option is valid only when BN=YES for this node.

The BNORD start option is used to control the search order when searching across subnetwork boundaries. BNORD=PRIORITY (the default value) tells VTAM that in performing cross-subnetwork searches VTAM should give preference to nodes for which the most recent search was successful and to nodes whose NETID matches the DLU's NETID. BNORD=DEFINED specifies that searches are performed in the order that you define border nodes and nonnative network nodes. The BNORD start option is valid only when BN=YES for this node.

The SNVC (subnetwork visit count) start option is a number between 1-255 that specifies the maximum number of subnetworks that the border node will search when looking for a resource. SNVC=1 restricts the search to the current network. Thus, SNVC=4 restricts the search to networks three hops away. This start option is valid only when BN=YES for this node.

*  =====> BEGINNING OF DATA SET ATCSTR01
**********************************************************************
*   ATCSTR01 - VTAM START LIST FOR AN ICN NODE - A01                 *
**********************************************************************
         BN=YES,                ** BORDER NODE                       **X
         BNDYN=FULL,            ** DYNAMIC ADJCLUST TABLE            **X
         BNORD=PRIORITY,        ** TABLE SEARCH ORDER                **X
         CONFIG=01,             ** MAJOR NODE ACTIVATION CONFIG LIST **X
         CPCP=YES,              ** CP-CP SESSION CAPABLE             **X
         DYNLU=YES,             ** DYNAMIC LU                        **X
         HOSTPU=A01NPU,         ** HOST SUBAREA PU NETWORK NAME      **X
         HOSTSA=01,             ** UNIQUE SUBAREA ADDRESS            **X
         NETID=NETA,            ** HOST NETWORK IDENTIFIER           **X
         NODETYPE=NN,           ** NETWORK NODE                      **X
         SNVC=4,                ** SUBNETWORK VISIT COUNT            **X
         SSCPID=01,             ** UNIQUE SSCP IDENTIFIER            **X
         SSCPNAME=A01N          ** GATEWAY SSCP NAME                 **
*  =====> END OF DATA SET ATCSTR01

To customize routing for a VTAM border node to match the requirements of your installation, VTAM offers the ability to define adjacent cluster routing lists. For more information about these lists, see Adjacent cluster routing list.

An APPN network boundary is automatically established when two APPN network nodes have differing network identifiers. In addition, you can also create a subnetwork boundary by coding the NATIVE operand on the ADJCP statement or PU statement representing a partner APPN network node. For an example of a subnetwork boundary for a local SNA PU (using APPN host-to-host channel), see Defining subnetwork boundaries.