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acket Loss Occurred When Eth-trunk Worked in Manual Load Balancing Mode

Publication Date:  2013-09-22 Views:  36 Downloads:  0
Issue Description

1. The customer reported that some services for users connected to an access device were interrupted. The live network topology was as shown in Figure 1. That is, Eth-trunk was deployed between R1 and R2. Because no GE optical ports were available, O/E converters were deployed between R1 and R2.

 

2. Some services were interrupted between two devices configured with Eth-trunk. The two devices were directly connected by optical fibers.
Handling Process

To address issue 2, Huawei performed the following operations and observed the following information:

1. Checked the links.
A link between R1 and an O/E converter failed, and all upstream traffic flowed to R2 over the other link. It was suspected that service interruption was caused by downlink traffic-related fault.

2. Logged in to R2 and found that R2 transmitted data to both links.

Because R1 and R2 were connected in manual mode and O/E converters were deployed between them, R2 could not detect that a port on R1 became down. In manual mode, a port is a member of the Eth-trunk as long as it is up. Therefore, R2 transmitted data to both links. By default, packets are forwarded in per destination mode, and therefore some services for some users were unavailable. (In per packet mode, severe packet loss would occur in services for all users.)

To address issue 2, Huawei performed the following operations and observed the following information:

1. Checked the physical links and found that one fiber was broken.
2. Checked the configurations and found that Eth-trunk worked in manual mode. Because one fiber transmitted data and one fiber received data, one device failed to receive data when one fiber was broken, and the related port entered the down state. All traffic switched to the other fiber. The other device could receive data from the peer end and the related port was still in the up state and was a member of the Eth-trunkAfter the fiber fault was rectified, services recovered.
Root Cause
Eth-trunk in manual load balancing mode could not detect port or link exception, resulting in packet loss.
Solution
Eth-trunk was changed to work in static LACP mode.
Suggestions

If O/E converters are used, bind links in LACP mode.

If devices are connected by fibers and do not support detection of single-point fiber faults, bind links in static LACP mode.

END