Why traffic cannot be transmitted at wire speed over a GRE tunnel

When a packet is forwarded through a tunnel, a label is added to the packet at the tunnel egress. That is, the packet length is increased. The GRE tunnel adds 24 or 32 bytes to the original packet, and the length of a label is 4 bytes on the VPN tunnel. In this case, the total traffic exceeds the wire speed. Packets are discarded during forwarding.

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