Problem Description

Networking situation:

SE800 -- OSN3500 -- 2500+ -- 2016 Ethernet switch - - PC

Configuring EVPL Services on Transport

The SE800 adopts the QinQ technology, which in essence encapsulates Layer 2 tags on the service VLANs; and the Huawei OSN 3500- N2EGS2, which supports MPLS services. The 2500+ device is configured with an EFT0 pure pass-through network board.

Failure phenomenon: PC dial-up error code: 721 (verify user name and password, and then this code appears)

Warning message

None

Processing

1、Self-ring to exclude SE800, Ethernet switch problem.

2、Suspecting that there is a problem with EVPL service configuration, recheck and confirm that the fault remains the same.

3, query the rmon count of the transmission device, confirmed that the transmission device has send and receive counts, proving that the transmission device is not a packet loss.

4, on-site packet capture test. It is found that the packet sent by SE800 will be stripped of the 4-byte outer label after being processed by OSN3500 's EGS2, and then when it is transmitted to the downstream switch from the 2500+EFT board, the length of the message is only 60 bytes. After on-site testing and consulting with DigitalComm 800 to confirm, the 2016 switch used on-site cannot handle messages smaller than 64 bytes (most switches cannot handle packets smaller than 64 bytes). All 60-byte packets sent to the switch by the transmission device are discarded by the switch. As a result, the PC never receives the response message from the SE800, causing the PC dialing to be unsuccessful.

After using EMS4 board to replace EGS2 board on OSN3500, the service is normal.

Root cause

1. Problems with SE800 or Ethernet switches

2、Problems with EVPL service configuration

3、Transmission equipment packet loss

4、Panel docking mismatch problem

Recommendations and Summary

Suggestion: Add EGS2 single board short packet mending function

Summarize: If the customer requires to support QinQ function in the opened Ethernet service, pay attention to avoid this kind of problem in the board configuration.