Independent LUs attaching to VTAM® through a type 2.1 PU can be dynamically defined as cross-domain resources. No system definition of the independent LU is required.

If the independent LU initiates the session, the adjacent link station (ALS), through which the independent LU contacts the network, does not have to be predefined to VTAM. For example, if the independent LU is attached through a token-ring network, the adjacent link station would be specified in the form of the medium access control address (MACADDR) of the host. VTAM discovers the resource during session startup and dynamically creates a CDRSC to represent the LU.

If the independent LU is the destination LU unit rather than the originating LU. and the destination LU is located on a LEN node, then you can dynamically define the independent LU using the adjacent link station (ALS) selection function of the session management exit routine. (An independent logical unit that is the destination LU on an APPN node has no such restriction.) Using this exit routine, you can provide VTAM with a method of contacting the independent LU. For information about the ALS selection function, see Dynamic selection of session connections. For information about writing a session management exit routine, see z/OS Communications Server: SNA Customization.

To have your independent LUs dynamically defined, perform the following steps:

1. Code DYNLU=YES in the start list, or use it on the START command when starting VTAM; code DYNLU=YES on the adjacent CP (ADJCP) definition statement for the adjacent APPN node; or code DYNLU=YES on all PU definition statements that represent links to the adjacent node. Coding DYNLU=YES enables VTAM to learn about the independent LU during session activation and dynamically define representations of the LU. If you code DYNLU=YES when starting VTAM (either in the start list or on the START command), you can restrict dynamically defined LUs from being used to connect to an adjacent node by coding DYNLU=NO on the ADJCP statement for the adjacent node or by coding DYNLU=NO on all PU definition statements that represent links to the adjacent node.
   Results: The DYNLU value is associated with an adjacent node when the first link to that adjacent node is activated. When the DYNLU value is associated with the adjacent node, that value will be propagated to all other links when they are activated. See z/OS Communications Server: SNA Resource Definition Reference for further information about determining the source of the DYNLU value assigned to an adjacent CP and attached resources.
2. For virtual route transmission groups (VRTGs), the default for the CDRDYN start option is YES, enabling dynamic CDRSC definition for the host node. The CDRDYN operand can also be specified on the host CDRM definition statement, but it will be overridden by the CDRDYN start option. You must also code CDRSC=OPT on the CDRM definition statement for an adjacent node to allow dynamically defined CDRSCs for sessions with that node. If you code CDRDYN=YES on the host CDRM definition statement, or allow the CDRDYN start option to default to YES, you can restrict dynamically defined CDRSCs from being used for sessions with an adjacent node by coding CDRSC=REQ (or allow it to default) on the CDRM definition statement for the adjacent node.
   Results: The DYNLU value is set for an adjacent APPN node from the CDRSC keyword associated with the CDRM for that node when the first link that is activated to the adjacent node represents a virtual route transmission group (VRTG).
3. Set the CDRSCTI start option if you want to change the amount of time that the dynamic definitions of independent LUs are retained after session termination (default is 8 minutes).
4. Code the CPCDRSC=YES start option in a host that is connected to a LEN CP to allow dynamic definition of the LEN CP independent LU when it is the destination LU. DYNLU still controls dynamic definition of all independent LUs (including LEN CPs) when they are the originating LU.

The PACING and VPACING operands specified on the PU definition statement associated with the session are sifted down to the CDRSC. The default logon mode table for dynamic CDRSCs is specified using the DYNMODTB start option or the DYNMODTB operand on the MODIFY VTAMOPTS command. You can also replace the existing table that is being used by dynamic CDRSCs by using the MODIFY TABLE,OPTION=LOAD command. If a default logon mode table for dynamic CDRSCs is not specified, ISTINCLM is used. The logon mode for each session is extracted from the BIND request that is passed to VTAM.

If the adjacent link station that the independent LU is using is being dynamically defined using dynamic switched definitions, you need to ensure that you have an entry for the mode you want to use in the logon mode table for the resource. If the mode entry is not found in the logon mode table for the resource or in the default logon mode table, the session fails. You can specify a default logon mode entry for dynamic CDRSCs using the DYNDLGMD start option or the DYNDLGMD operand on the MODIFY VTAMOPTS command. You can also override this value for a specific dynamic CDRSC using the MODIFY DEFAULTS or MODIFY RESOURCE commands.

Dynamic CDRSCs are created and maintained in the ISTCDRDY major node. ISTCDRDY is activated automatically during VTAM initialization, and deactivated automatically during VTAM termination. The operator can deactivate ISTCDRDY with the VARY INACT command, in which case all dynamically defined CDRSCs are also deactivated and the dynamic CDRSC function is disabled. In addition, all sessions involving dynamically created CDRSCs (including CP-CP sessions with this host, if the partner CP was dynamically defined) are terminated.

For information about how VTAM handles multiple definitions of one independent LU resource, see the z/OS Communications Server: SNA Resource Definition Reference.

You can use dynamic definition of independent LU with other functions, such as multiple connections to a subarea, casual connection, or APPN.