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AR Router Troubleshooting Guide

This Product Documentation provides guidance for maintaining AR Enterprise Router, covering common information collection and fault diagnostic commands, typical fault troubleshooting guide, and troubleshooting.
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An L2TP Dialup User on the AR2220 Can Get Online but Cannot Ping the LNS Gateway Address

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

This section provides a case that an L2TP dialup user on the AR2220 can get online but cannot ping the LNS gateway address.

Networking

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

#
l2tp enable
#
ip pool 1  
 network 192.168.1.0 mask 255.255.255.0  
 excluded-ip-address 192.168.1.254
#
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 192.168.1.254 255.255.255.0
#

Fault Symptom

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

Fault Analysis

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 anddisplay 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.

Procedure

  1. Run the gateway-list 192.168.1.254 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.

Suggestion

  • 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.
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Updated: 2019-08-09

Document ID: EDOC1000079719

Views: 494800

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