When configuring MTU on a tunnel, consider the following: - At least one mpls label will be present when passing through the tunnel. Accounting should include all labels in the stack, for example, explicit null or entropy label;
- vlan and q-in-q headers must be taken into account (if they present);
- If MTU of the outgoing interface is exceeded, the packet will be dropped (if GRE traffic match fragment is disabled);
- Control world is not supported;
- DF bit will be set to 1.
Approximate packet structure is given in figure below:
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