R2631E router and partner's device set up L2TP tunnel and it fails.
R2631E version information: VRP (tm) Software Version 1.63 8040-002.
Turn on DEBGGING of R2631 and capture DEBGGING information, find the following information:
L2TP : Receive control message, value: INCOMING_CALL_CONNECTED
L2TP : Tx Connect speed, value: 0
L2TP: Tx connect speed error.
L2TP:L2TP_Phy_Down -- l2tp lcp down (IF_NET:(null pointer))
According to the analysis, opposite device is defaulted to negotiate from 0 when negotiating L2TP connection speed, but R2631E is not from 0. When R2631 receives opposite negotiated SPEED, it regards that illegal data results in negotiation failure. Upgrade R2631E to VRP1.74-0115. R2631E negotiates L2TP from default 0. Both sides can connect successfully. The problem is solved.
1. The configuration of relevant parameters of both sides of L2TP is different.
2. When L2TP negotiates, default negotiation parameter of both sides of the device is different.