NE20 enables L2TP services, and the version is upgraded to VRP3.30-0521.04 from VRP3.30-0330.20. After successful upgrade, L2TP dial-up users cannot pass authentication.
Change the default interface for RADIUS packets at NE20 to LOOPBACK interface of new version. However, VRP3.30-0521.04 does not support the change to interface for RADIUS packets, so it needs to upgrade to another version of VRP5.10-1243.01; at this point, change the interface to LOOPBACK, solving the problem.
After upgrade for version, the difference in configurations between VRP3.30-0521.04 and VRP3.30-0330.20 lies in that the old version uses physical interface for RADIUS authentication, and the new version uses LOOPBACK interface in RADIUS authentication. Through checkup on debugging information, only the packets to RADIUS are found, and no echoes from RADIUS are found. So the problem is caused by that NE20 does not receive the echo packets from RADIUS because the interface for NE20 to transmit packets to RADIUS is defaulted to the physical interface.
It is suggested to upgrade the version of NE20 without changing the configurations of RADIUS. Transfer the address of physical itnerface to LOOPBACK interface, and the version should be upgraded to VRP5.10-1243.01 or later version.