APPN nodes use local form session identifiers (LFSIDs) instead of subarea addresses for external communication in an APPN network. VTAM® APPN nodes have subarea addresses that are completely internal to the nodes, used by the NCP in a composite network node to communicate with its owning VTAM. This subarea address is never used outside the composite network node.

When High-Performance Routing (HPR) is in use, LFSIDs are not used for the HPR portion of the sessions. Instead, automatic network routing (ANR) labels are used by each node to route the HPR network layer packets (NLPs). For further information about HPR, see High-Performance Routing (HPR).