3Com Switch 8800 Family IPsec Module Configuration and Command reference Guide

128 CHAPTER 8: CONFIGURATION OF L2TP
3 The types of Tunnel password authentication are inconsistent. The default
authentication type of VPN connection created by Windows 2000 is MSCHAP. If
the peer end does not support MSCHAP, CHAP is recommended for substitution.
Symptom 2: Data transmission fails. After the connection is established, no data
can be transmitted, e.g. the peer end cannot be pinged.
Troubleshooting: Possible causes are as follows:
■ The address set by the user is wrong: Generally, it is up to LNS to assign
addresses, but a user can also designate his own address. If the designated
address and the address assigned by LNS are not in the same network
segment, this problem occurs. It is recommended that LNS assign addresses
completely.
■ Network congestion: Congestion occurs to the Internet backbone and packet
loss is serious. L2TP uses User Datagram Protocol (UDP) for transmission.
Because UDP lacks in error control mechanism, applying L2TP on an unstable
line will result in ping failures.