An L2TP Dialup User on the AR2220 Can Get Online but Cannot Ping the LNS Address

Publication Date:  2015-04-01 Views:  280 Downloads:  0
Issue Description

Configuration of the AR2220 used as the LNS is as follows:

# l2tp enable # ip pool 1 network mask excluded-ip-address # l2tp-group 1 allow l2tp virtual-template 1 tunnel password cipher %$%$9]9>0T$B)K7'wdD$X=bP,QH~%$%$ tunnel name LNS # interface Virtual-Template1 ppp authentication-mode chap domain ydpt002.vpdn.ah remote address pool 1 ip address #

Fault Symptom:
A remote user dials up on the PC when the AR2220 functions as the gateway. The user can get online but cannot ping the gateway address.

Handling Process
1.  Run the gateway-list command in the view of IP pool on the LNS.

2.  Run the mandatory-lcp command in the view of L2TP group 1 on the LNS.
Root Cause
No configuration error is found on the LNS. The L2TP tunnel can be established successfully.

No error is found by running the display l2tp tunnel and display l2tp session commands. There must be an error in the process of receiving and sending packets.

Run the debugging l2tp all command. The command output shows that parameters in the packets received by the LNS are incorrect, so these packets are discarded.

Run the mandatory-lcp command on the LNS to enable the AR to renegotiate parameters in the packets. The fault is rectified.

When L2TP connections between dialup software on the network or non-Huawei LAC and the AR are established, several options (such as packet header compression) are not supported by the AR. The parameters involved in the negotiation do not affect the establishment of L2TP connections. Incorrect negotiations may cause incorrect packet encapsulation, leading to packet loss.

When the AR functions as the LNS, you are advised to enable LCP re-negotiation by running the mandatory-lcp command.

The mandatory-lcp command enables LCP renegotiation between the LNS and a remote user.