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["Dr. Jens Rosenboom" <j.rosenboom@xxxxxxxx>]

Public bug reported:

My goal is to achieve an MTU of 1500 for both Vlan and Vxlan based
tenant networks.

So I set the path_mtu to 1550, while leaving global_physnet_mtu at the
default value of 1500.

However, the MTU for my Vxlan networks is still calculated as 1450,
because the underlying MTU is calculated as min(1500,1550)=1500 and then
the encapsulation overhead is subtracted from that.

IMHO the correct calculation would be to subtract the encapsulation
overhead only from the path_mtu if it is specified and possibly take the
minimum of that and global_physnet_mtu.

** Affects: neutron
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/1592017

Title:
  ML2 uses global MTU for encapsulation calculation

Status in neutron:
  New

Bug description:
  My goal is to achieve an MTU of 1500 for both Vlan and Vxlan based
  tenant networks.

  So I set the path_mtu to 1550, while leaving global_physnet_mtu at the
  default value of 1500.

  However, the MTU for my Vxlan networks is still calculated as 1450,
  because the underlying MTU is calculated as min(1500,1550)=1500 and
  then the encapsulation overhead is subtracted from that.

  IMHO the correct calculation would be to subtract the encapsulation
  overhead only from the path_mtu if it is specified and possibly take
  the minimum of that and global_physnet_mtu.

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