Network topology: 7750 from A-Huawei PTN 3900-Huawei PTN 3900-WDM from F-WDM from F-Huawei NE5000E.
E-Line services were configured on PTN 3900s in exclusive mode.
Symptom: Symptom: Ping tests between 7750 and NE5000E failed, and IS-IS negotiation failed.
Possible causes included:
1. Service configurations on PTNs were incorrect.
2. Port negotiation modes were different.
3. Port TAG attributes were incorrect.
4. MTU values were incorrect.
5. Configurations on 7750 and/or NE5000E were incorrect.
6. WDM equipment was faulty.
To address the issue, Huawei performed the following operations and observed the following information:
1. Checked service configurations on PTNs and performed ping tests between PTNs. The configurations were correct and ping tests succeeded.
2. Checked alarms and link status. No alarms were found. Port negotiation modes of interconnected equipment were the same.
3. Consulted the engineers of company A and found that the TAG attribute of 7750 was Access, different from that of NE5000E. After NE5000E's TAG attribute was changed to Access. Ping tests between 7750 and NE5000E succeeded, but IS-IS negotiation still failed.
4. Consulted the engineers of company A and found that the MTU on 7750 was 1600. After the PTN MTU was changed to 1600. IS-IS negotiation succeeded.
When encountering a fault in an interconnection scenario, check Huawei equipment first and then third-party equipment. If Huawei service configurations are correct, check whether they are consistent with those on the interconnected equipment.