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Two L2TP-Groups Failed to Set up Different Tunnels to the LNS Because They Had the Same Tunnel Name

Publication Date:  2013-10-24 Views:  19 Downloads:  0
Issue Description
Two ME60s running V100R006C05SPC600 served as an LAC and an LNS, respectively. Two L2TP-groups having the same tunnel name were configured on the LAC. One was bound with Eth-trunk1 and the other was bound with loopback20. One L2TP-group was configured on the LNS. When user test1 went online from Eth-trunk1, the L2TP tunnel from Eth-trunk1 to the LNS was successfully set up. The output of the display l2tp tunnel command showed that the tunnel was normal. User test1 kept online and user test2 went online from loopback20. The output of the display l2tp tunnel command showed that no tunnel had been set up from loopback20 to the LNS, and user test2 was carried by the tunnel for user test1.
Handling Process

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.
Root Cause
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.
Solution
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.
Suggestions
None

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