L2TP dials in successfully, but it aborts automatically after one minute

Publication Date:  2012-07-27 Views:  79 Downloads:  0
Issue Description

  L2TP dials in successfully, but it aborts automatically after one minute


PC―8850 (LAC)-- AR2831 (LNS) 



Alarm Information

No



Handling Process
From the information above, once the user established PPP connection with virtual template, PPP needs to transmit regularly negotiating packets of EchoRequest/EchoReply to make sure if the link is normal. If no echo packet is received from the peer within the negotiation time duration (3 seconds by default), PPP will re-transmit the previous packet. If EchoReply is not received for five times, the peer will be regarded as dropping offline, and then the PPP link will be disconnected. If network delay is very large or the quality is not good, EchoReply will be replied slowly or discarded. After changing the timeout interval to 10 seconds (ppp timer egotiate 10), adding the negotiation timeout interval could avoid dropping offline. Ten-second is not required; if the delay duration is not very big in actual network, the timeout interval could smaller.

Root Cause

1. L2TP dials in successfully, and the address of virtual template could be pinged through, indicating that the configuration of L2TP is normal. The network delay may be too large or the quality is not good, causing the PPP link to be blocked.



2. In case L2TP dials in successfully, turn on the switch for debug ppp interface Virtual-Template1, the information as follows appears: 



      Virtual-Template1:0 : Echo Timer Expired ,Retransmit = 4                 


................



      Virtual-Template1:0 : Echo Timer Expired ,Retransmit = 1                 


...............



%Jul 22 17:32:35:114 2005 sanjin-route IFNET/5/UPDOWN:Line protocol on the inter


face Virtual-Template1:0 is DOWN                                               



%Jul 22 17:32:35:114 2005 sanjin-route IFNET/5/UPDOWN:PPP IPCP protocol on the i


nterface Virtual-Template1:0 is DOWN                                           


 *0.85497116 sanjin-route PPP/8/debug2:                                         



  PPP Event:                                                                   



      Virtual-Template1:0 : Echo Timer Expired ,Retransmit = 0                 



*0.85497116 sanjin-route PPP/8/debug2:                                         



  PPP Event:                                                                   



      Virtual-Template1:0 LCP Close  Event                                     



      state opened                                                              



*0.85497117 sanjin-route PPP/8/debug2:                                         



  PPP State Change:                                                            



      Virtual-Template1:0 LCP : opened --> closing 

According to the above information, when the Virtual-Template1 of LNS transmits EchoRequest packet to PC, it receives no EchoReply from the peer, causing Virtual-Template1 to DOWN. By default, if no reply is received for five times of EchoRequest, the link will be disconnected.

END