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[All About Switch] 1 SSH Packets Fail to Be Forwarded Through the GRE Tunnel Established Between the S5720EI and S7706

Latest reply: Mar 16, 2018 09:48:27 1545 1 0 0 0

Involved Products and Versions

S series switches running all versions



Fault Symptom

The model of Switch_1 is S5720EI and the model of Switch_2 is S7706. When a GRE tunnel is established between the two switches, SSH packets fail to be forwarded.

Cause Analysis

The onsite test shows that small-sized packets can be normally forwarded. When the size of packets exceeds 1400 bytes, the packets fail to be forwarded.

It is confirmed that there is a transmission device on the intermediate link, and the size of forwarded packets exceeds the MTU value of the transmission device.

The (non-X series) cards of the S5720EI and S7706 do not support GRE packet fragmentation. When the size of forwarded packets exceeds the MTU value of the transmission device, the transmission device discards the packets.

Troubleshooting Procedure

Adjust the size of the packets sent at the source of the packets sending, and do not exceed the MTU value of the transmission device.

Conclusions and Suggestions

In the GRE tunnel scenario:

l   The S5720HI and X series cards support packet fragmentation on the forwarding plane by default.

Other models and cards do not support packet fragmentation on the forwarding plane.

This post was last edited by All_About_Switch at 2018-03-29 08:53.
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Created Mar 16, 2018 09:48:27

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