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Low Internet Access Speed Because ME60 Serving as an LNS Used the Tunnel-based Rate Limit Policy

Publication Date:  2013-09-30 Views:  25 Downloads:  0
Issue Description
L2TP services were configured between an ME60 running V600R002C02SPC700 and an E320. The ME60 served as an LNS and the E320 served as an LAC. After the service cutover, users had low Internet access speed.
Handling Process

Huawei performed the following operations to address the problem:

1. Tested other types of services between the ME60 and the E320 and switched interfaces and optical lines.

No packet loss occurred in the test. The problem persisted after interfaces and optical lines were switched.

2. Confirmed that the same L2TP services between the E320 and an MA5200G that served as the LNS were normal.

3. Adjusted the MTU and MSS in the VT profile based on experience.

The problem persisted.

4. Performed repeated tests and found that the Internet access speed of the test PC was high immediately after an L2TP tunnel was reset or was configured on another interface, and then decreased gradually.

According to the traffic statistics on interfaces between the LNS and the LAC, the traffic was always not more than 10 Mbit/s regardless of the number of online users (the rate limit for a user account was 10 Mbit/s). Therefore, it was suspected that a rate limit policy caused the problem. According to R&D explanations, if ME60 running V600R002C02SPC700 functions as an LNS, it applies the tunnel-based QoS scheduling scheme to L2TP users by default. This means that the account rate limit is directly applied to L2TP tunnels. After the rate limit policy for L2TP tunnels was changed to the session-based scheme, the problem was resolved.

l2tp-group default-lns
 qos scheduling-mode session
Root Cause
When ME60 running V600R002C02SPC700 functions as an LNS, it applies the tunnel-based QoS scheme to L2TP users by default. This means that the account rate limit is directly applied to L2TP tunnels.
Solution

Changed rate limit policy for L2TP groups to be the session-based scheme.

l2tp-group default-lns
 qos scheduling-mode session
Suggestions
When ME60 running V600R002C02SPC700 functions as an LNS, it applies the tunnel-based QoS scheme to L2TP users by default. This means that the account rate limit is directly applied to L2TP tunnels. As a result, multiple users share one tunnel, resulting in low Internet access speed. In the scenario in which an ME60 functions as an LNS to interconnect with an LAC, modify the QoS scheme for L2TP groups to prevent services from being affected.

END