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Knowledge Base

VPN Traffic Is Unavailable Because Parameters of the NE40 and the OSN 1500 Are Different

Publication Date:  2012-07-27  |   Views:  162  |   Downloads:  0  |   Author:  SU1001734784  |   Document ID:  EKB0000320011


Issue Description

The networking diagram where the problem occurs is as follows:

The NE40 uses the GE WAN board to connect the OSN. The NE40s at both ends function as PEs and are configured with MPLS L3VPN services. The OSN identifies services through VLAN tags on the WAN sub-interface to allocate the bandwidth for two E1 interfaces.

After the configuration is complete, NE40-1 and NE40-2 are connected to laptops. Then, use Bricks (a simple traffic testing software) to test the traffic. It is found that no traffic reaches the peer. 


Alarm Information


Handling Process

1. Check the physical connection, and you can find that all electrical and optical interfaces are Up.

2. Check the negotiation. The transmission negotiation of the router is Gigabit full duplex, but the transmission device is 100 B half duplex. This is because forcible negotiation is used on the GE interface of the NE40 by default, whereas auto-negotiation is used on the OSN 1500 by default. As a result, the problem occurs. After the negotiation is modified, the service is restored, but the peer still cannot receive the traffic.
3. Use commands to check the service configuration, and it is normal.
4. The version is V3R2C01B591. There is no precaution of related problems.

5. Check the traffic testing method. It is found that the length of the packet sent by Bricks is 32767, which exceeds the MTU of the transmission device. As a result, the traffic is discarded. Modify the length of the packet sent by Bricks to 1400, and the problem is solved. The peer receives traffic that is 4.1 Mbit/s, which accords with the design requirements. 


Root Cause

1. The physical connection fails.

2. The link negotiation fails.
3. The service configuration is incorrect.
4. The version is incorrect.

5. The traffic testing method is incorrect. 


1. When the NE40 uses the GE WAN board to connect the OSN, note the negotiation.

2. The OSN allocates bandwidths according to the VLAN tags on sub-interfaces, which is applicable to point-to-point connections.

3. A transmission device has its MTU on the link layer. A packet is not fragmented when the length of the packet exceeds the MTU. Instead, the packet is discarded. Such factor should be fully considered in the design.