This setting configures the unit for VNIP topology support on a per-interface basis. Establishing a VNIP topology is a fundamental prerequisite to applying the VNIP feature set which includes PVC-based delay measurement, diagnostics, and congestion monitoring. With VNIP enabled on an interface the unit will attempt to locate VNIP peers out that port. As peers are discovered and logged the unit will report the topology it has learned on its opposite interface. If VNIP is inactive on one interface it will not engage in any VNIP dialog; however it will continue to listen for topology messages on the inactive interface and will reflect these messages out the opposite interface if VNIP is enabled. With VNIP inactive on both interfaces the unit will transparently pass all VNIP messages. The topology database includes ip addresses, DLCI values, and the number of VNIP hops in between. (1) Topology Inactive: VNIP messages pass through unit (2) Topology Enabled on DTE only: unit logs VNIP peers seen out the DTE interface. Unit listens for topology reports from the WAN but doesn't generate any towards the WAN. Will report learned WAN topology towards the DTE. (3) Topology Enabled on WAN only: unit logs VNIP peers seen out the WAN interface. Unit listens for topology reports from the DTE but doesn't generate any towards the DTE. Will report learned DTE topology towards the WAN. (4) Topolgy Enabled on Both DTE and WAN: Unit logs VNIP peers seen out both interfaces and generates DTE topolgy reports towards the WAN and vice versa.