Session did not take the best path

Problem statement

A session took one of the following paths:

The session took a path through the subarea network even though a better path existed through the APPN network, or the session took a path through the APPN network even though a better path existed through the subarea network.
After a rapid transport protocol (RTP) connection switches to a new path, a session takes a path that requires it to visit the same node twice. For example, an LU-LU session between HOSTA and HOSTC goes from HOSTA through HOSTC to HOSTB and back to HOSTC.

Probable cause

In the first situation described above, the SORDER operand or SSEARCH operand is coded with a value that indicates that the subarea network is to be searched before the APPN network is searched or that the APPN network is to be searched before the subarea network is searched.
In the second situation described, HOSTA and HOSTB support rapid-transport protocol (RTP), but HOSTC supports only automatic network routing (ANR). Because one of the LUs resides on an ANR node (which cannot be the endpoint of an RTP connection), at least one hop of the session is not using high performance routing (HPR). During an RTP path switch, the non-HPR hops cannot change, but the RTP hops can. In some configurations, it is possible that the new path for the RTP connection will traverse some of the same nodes as the non-HPR portion of the original session route.

User response

In the first situation, adjust the values on the SORDER and SSEARCH operands to suit your network.
In the second situation, the session should continue, so no user action is necessary. If a temporary loss of connectivity forced RTP to switch paths, after restoring the connectivity, you can use the MODIFY RTP command to force VTAM® to search for a better route for the RTP.