Preventing ISG Session Storms: L2TP Congestion Control and Call Admission
When running Cisco ASR1000 with ISG (Internet Services Gateway) or BNG (Broadband Network Gateway) functionality, bulk session state changes — particularly when many subscriber sessions drop and reconnect simultaneously — can cause session setup failures and CPU overload. Proper tuning of L2TP window sizing and call admission control prevents cascading failures. L2TP Congestion Avoidance When PPPoEoL2TP tunnels experience flaps (rapid up/down cycles), user sessions often fail to establish properly during the recovery phase. This is typically related to the L2TP window size (WS) parameter negotiated during tunnel setup. ...