Dynamic path update

Dynamic path update enables the VTAM® operator to add NCP path definitions dynamically without regenerating and reloading the NCP. Using the same operator facilities, you can also dynamically add VTAM path definitions. The explicit route definitions in VTAM and NCP can be replaced or deleted only if the explicit route is inoperative (a status of INOP).

Note: If you are not attempting to modify an ER mapping to a TG, the ER state is not checked and the ER can be either operative or inoperative.

Dynamic path update can also be used to change inactive (a status of INACT) or undefined VRs, path definition values for virtual route pacing window size on inoperative routes, and transmission group thresholds on operative routes.

To use dynamic path update, at least one route must be defined and operative to establish the necessary SSCP-PU session between VTAM and each NCP. The dynamic path update changes are transmitted to NCP on this session. Dynamic path update members are filed in the VTAM definition library. A dynamic path update member can contain path specifications that are added, replaced, or deleted from one or more NCP or VTAM subareas. A set of path update specifications that is targeted to a specific subarea node within a dynamic path update member is called a dynamic path specification set. A dynamic path update member can contain one or more dynamic path specification sets.

The dynamic path update member in the following sample can be used to add NCP3 to the network shown in Figure 1.

*  Dynamic Path Specification Set for VTAM 1 (subarea 1)
VTAM1    VPATH NETID=NETA
         PATH  DESTSA=3,
               ER0=(2,1),
               VR0=0
*  Dynamic Path Specification Set for NCP 2  (subarea 2)
NCP2     NCPPATH NETID=NETA
         PATH  DESTSA=3,
               ER0=(3,10)

Figure 1. Sample single-domain network

Note that the name on the NCPPATH definition statement identifies the NCP for which the PATH statements are to be processed.

A dynamic path update can be triggered by any of the following methods:

Activating a dynamic path update member using the VTAM configuration list or the VARY operator command. An active SSCP-PU session must exist between VTAM and the NCP whose routes are being dynamically updated, and the explicit routes being changed must be inoperative.
Specifying the NEWPATH operand when activating an NCP with an operator command. This causes VTAM to activate the dynamic path update member immediately following NCP activation.
Activating an NCP that has the NEWPATH operand specified on the PCCU definition statement for this host. This causes VTAM to activate the dynamic path update member immediately following NCP activation.

Note: Because dynamic path update changes do not alter VTAM or the NCP load module, you should use a method that ensures that these changes are reinstated if VTAM is restarted or if NCP is reloaded.

The dynamic path update member in the preceding example could be filed in the VTAM1 definition library. When the operator activates the dynamic path update member, VTAM1 identifies the dynamic path update member because the name in the VPATH definition statement matches its SSCPNAME (VTAM1). VTAM1 transmits the dynamic path update member to NCP2 using the active session path (SSCP-PU session).

Note: You should file the dynamic path update member for each subarea in separate dynamic path update members to avoid possible performance deterioration.

The following restrictions are placed on coding dynamic path update members and dynamic path specification sets:

A dynamic path update member can include path definitions for only one VTAM host. If an incorrect definition statement or VPATH or NCPPATH definition statement is encountered, VTAM discards all PATH definition statements that follow the definition statement that is not valid up to the next recognizable VPATH or NCPPATH definition statement and issues a warning message. PATH definition statements that were already processed are not affected.
When a dynamic path update member is activated using the VTAM configuration list or the VARY operator command, an NCPPATH definition statement is considered to be not valid if the NCP name on the NCPPATH definition statement does not match the resource name of an active NCP.
When a dynamic path update member is activated by specifying the NEWPATH operand, an NCPPATH definition statement is considered to be not valid if the NCP name on the NCPPATH definition statement does not match the resource name of the NCP being activated.
A dynamic path update member can include the DELETER operand if it applies to the host activating the dynamic path update member.

VTAM saves the name of the dynamic path update member in the NODELST data set (the VTAM configuration restart data set). The actual dynamic path specification sets are not saved in a VSAM configuration restart file.

Note: Extreme caution must be used when deleting or replacing a route for a node that is an intermediate routing node for other routes.

The NCPPATH definition statement identifies the NCP and the network to which the dynamic path update member applies in a dynamic path update member.