To address the issue, Huawei performed the following operations and observed the following information:
1. Checked L2TP-group configurations. Configurations of L2TP-groups for users test1 and test2 on the LAC were the same and the tunnel for user test1 had been successfully set up. Therefore, L2TP-group configurations were correct.
2. Changed two interfaces on the LAC to work in ETH-trunk or loopback mode, or make user test1 to go online from the loopback interface and user tests 2 from the Eth-trunk. The problem persisted. Therefore, this issue was not caused by inconsistent interface modes.
3. Tested whether a tunnel could be set up for user test2 if user test2 went online first. A tunnel could be successfully set up for user test2. The later online user test1 was carried on the tunnel set for user test1. If user test2 went offline and then user test1 went online a few minutes later, a tunnel could be set up for user test1.
4. According to the preceding analysis, concluded that the LNS set up a tunnel based on the tunnel name rather than interface information carried in a tunnel request sent from the LAC. Because the two L2TP-groups on the LAC had the same tunnel name, the LNS considered that user test2 which was supposed to go online on another tunnel belonged to user test1 and carried user test2 on the tunnel for user test1.5. Changed the tunnel name of L2TP-groups on the LAC to different values, created two L2TP-groups on the LNS, and specified different remote tunnel names. The problem was result.