The topology of a network in a city is as follows after reconstruction (MA5200F functions as BAS connecting to NE40):
Provincial NE40 ← NE40 ← S2403H ← PC
MA5200F is at MA2.10-7127; NE40 is at VRP3.10-0420. Individual users use PPPOE dial-up instead of using static IP address to access network. In test after cutover, a user uses PPPOE dialing software to access network; if it does not go offline normally, it cannot access network through dial-up again in a short time; however, it could dial well after a long interval. After many times test, the problem persists.
Check the configuration of MA5200F for delay, and it is as follows: ppp keepalive interval 120 retransmit 5, which means that MA5200F detects the handshaking with users every 120 seconds, and the times of handshaking detected are 5. Consequently, M5200F will release the user after is drops offline 600 seconds (10 minutes) later, and then the user could come online again.
Change the setting for handshaking detection of MA5200F to 20 seconds, and the times of detection to 3 which is the default value of system. Therefore, one minute delay is acceptable for users. PPPOE dialing recovers to normal.
Use Sinffer software to capture packets; after analysis on PPPOE packets, it is found that if the user gets offline abruptly, the PADI packets sent by PC at user side do not get response, viz.: that BAS equipment (MA5200F) does not use PADO packet to echo to PC at user side, so the PC and MA5200F are disconnected at PPPOE discovery stage. If dial after a long interval, MA5200F echoes PC at user side with PADO packet, setting up PPPOE connection; the user could access network normally.
After the analysis above, the user may drop offline or get offline abruptly, but MA5200F regards it is still online because of delay, so when the user dials for access to network again, it cannot come online normally.