2021-06-11 0

CE8860 has CRC error increase on mutilple port

Issue Description

As shown in the following figure, CE8860 is connected to NE and Juniper. The CE8860 has a CRC increase on the port 25GE 1/2/3,、25GE1/2/11 and the peer port in J device. The other CE8860 ports receive no CRC, but the ports of devices which connected to CE8860 receive the CRC.
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Alarm Information

CRC error lkeep increasing very quickly on  those port .

Handling Process

1.For the issue that CRC increase on the port 25GE 1/2/3,、25GE1/2/11 and the peer port in Juniper，we judged that the physical link is abnormal. The repair of the 25GE1/2/11 is performed on site. After the repair, the CRC growth of the CE side port disappears. The result verifies that the CRC increase of 25GE1/2/11 is caused by the abnormality of the physical link between the peer Juniper port.
2.For the issue that CE8860 ports receive no CRC but the peer devices receive the CRC, We read the packet count inside the chip, and notice that there is TFCS in the port packet count. This means that there is a CRC in the packet sent by the CE8860, this is the reason why port of the devices which connected with CE8860 received the CRC. It is important to confirm how TFCS is generated.
3.Check current-configuration, we noticed that the packet forwarding mode is configured to cut-through, it means that CRC error packets are also forwarded but not discarded.
4.The usage scenario and precautions of cut-through is described in the product documentation. When low packet delay is required, run the assign forward mode command to set the packet forwarding mode to cut-through to speed up packet forwarding. We must pay attention that in cut-through mode CRC error packets are also forwarded but not discarded.

Root Cause

CE8860 received CRC error packets caused by the abnormality of the physical link, and CRC error packets are forwarded but not discarded due to the configuration of the cut-through mode.

Solution

  1. Repair the abnormality of the physical link
  2. Confirm whether the device packet forwarding mode needs to be in the cut-through mode based on the current network service scenario.

 

Suggestions

Suggest remove “cut-through mode” on normal scenario. otherwise one fiber have CRC error, it it will impact all the ports.