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Docker lowers interface MTU with 50 less then connected network, why?

It seems that docker lowers the MTU on a network interface by itself with 50 less then set on the network you connect.

So:

  • If the network has an MTU of 1500, eth0 becomes 1450.
  • If you set it on 1450 (because your underlying network is encapsulated) eth0 gets an MTU of 1400

Why does this happen ? Is it because Docker encapsulates it’s own networks ?