Unreachable partner information about a path through an Enterprise Extender connection network is sent to an end node's network node server when the failure is detected in an end node, or broadcast to all adjacent network nodes when the failure is detected in a network node, using control vectors X'44', X'46', X'47', and X'4C' on topology database updates (TDUs). Therefore, it is possible for the unreachable partner information displayed in one node to have an expiration time that is slightly different from the expiration time for the same unreachable path in another node, because of delays in network traffic.

When a CP-CP session is established between two network nodes, there is an exchange of topology information. The unreachable partner information, including the unreachable time value, is sent in the control vector X'4C'. However, it is possible that a significant amount of time has expired between the time that the failure was detected and the time this topology information is sent. To make sure the time the unreachable partner information expires is consistent, the unreachable time value is modified in the control vector X'4C'. When this occurs, the unreachable value will not be displayed in the node that receives the modified unreachable time value. Instead, five asterisks (*****) will be displayed in the UNRCHTIM column on a DISPLAY NET,TOPO,LIST=UNRCHTIM command. However, the expiration times in the node detecting the failure and the node receiving the modified unreachable time value should be consistent.

Unreachable partner information that is detected by an end node and reported to the end node's NNS is not maintained by the end node. If the end node switches to a new NNS, a CP-CP session is established between the end node and its new NNS and the end node's topology information is sent to the NNS. However, because the end node is not maintaining unreachable partner information, any unreachable paths that had been detected by the end node and reported to the old NNS are not included in this topology information sent to the new NNS. Therefore, some failures will be necessary when attempting to establish new sessions, or when HPR path switches occur, until the new NNS learns about the unreachable paths.

Unreachable partner information is not copied to the topology data set when a MODIFY CHKPT command is issued with TYPE=ALL or TYPE=TOPO specified, or when a HALT or HALT,QUICK command is issued to end VTAM®. Therefore, some failures are necessary when attempting to establish new sessions, or when HPR path switches occur, in order to refresh the unreachable partner information after restarting VTAM.