Involved Products and Versions
All products and versions
Networking
As shown in Figure 1-1, SwitchA is connected to DeviceA and DeviceB through Eth-Trunk5 and Eth-Trunk6 respectively. The member interfaces of Eth-Trunk5 are GE1/0/18 and GE2/0/18, and the member interfaces of Eth-Trunk6 are GE1/0/10 and GE2/0/10.
Figure 1-1 Networking diagram for the fault that some Eth-Trunk interfaces are Down and some Eth-Trunk interfaces are Up due to incorrect interface connections after LACP negotiation
Fault Symptom
When the Eth-Trunk link is adjusted, Eth-Trunk5 is Up and Eth-Trunk6 is Down. Before the adjustment, both Eth-Trunk5 and Eth-Trunk6 are Up.
Cause Analysis
When the four member interfaces are connected in the following sequence, the problem occurs:
1. In Eth-Trunk5, the member interface GE1/0/18 is connected to DeviceA, and the member interface GE2/0/18 is not connected. In this case, Eth-Trunk5 is Up.
In Eth-Trunk6, the member interface GE1/0/10 is connected to the peer DeviceB, and the member interface GE2/0/10 is not connected. In this case, Eth-Trunk6 is Up.
Both Eth-Trunk5 and Eth-Trunk6 are correctly connected. Therefore, both of them are Up.
2. When the member interface GE2/0/10 of Eth-Trunk6 is connected to DeviceA, a conflict occurs. In Eth-Trunk5 and Eth-Trunk6, the Eth-Trunk5 member interface with a smaller value of trunkid is selected. Therefore, the member interface GE2/0/10 is not selected. However, the other member interface GE1/0/10 is selected, which does not cause the entire Eth-Trunk6 to go Down.
When the member interface GE2/0/18 of Eth-Trunk5 is connected to DeviceB, Eth-Trunk6 is also connected to DeviceB. When this conflict occurs, the member interface of Eth-Trunk5 is selected in Eth-Trunk5 and Eth-Trunk6. The member interface GE2/0/10 of Eth-Trunk6 is not selected, and the entire Eth-Trunk6 goes Down.
The GE2/0/18 member interface of Eth-Trunk5 further compares information with the other member interface GE1/0/18 and finds that they are not connected to the same device. Therefore, the interface GE2/0/18 is not selected. However, a member interface of Eth-Trunk5 is already selected. Therefore, Eth-Trunk5 is not Down.
Troubleshooting Procedure
Step 1 Connect the cables correctly. The fault is rectified.
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