Missing trailing bytes (gprs-llc)

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Hi,

Captures I have show four trailing bytes (in vlan.trailer field but also in the Packet Bytes section). These bytes are required by the endpoint. Whenever I try to transport these raw packets via an L2GRE tunnel, the trailing bytes seem to get lost. Could it be that the switching equipment in between don't know where the frame ends?

When transporting directly on the wire, the frames remain intact, when transporting them on an IP layer, the trailing bytes get lost.

Any idea how to troubleshoot this?

Any help is appreciated, joozju