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[Yang Li <yang.li@xxxxxxxxxxxx>]

Public bug reported:

In my environment, vlan and vxlan are both exist, and their mtu is 1500 and 1450.
I use vlan network to create a instance-A, and use vxlan network to create a instance-B, the instance-A and instance-B are in the same compute nodes.

Then I found the mtu of br-int is 1450, this will cause instance-A'iperf
result is 0 in , because instance-A's mtu 1500 is large than 1450.

I did some investigation, found that the ovs bridge's mtu is decided by
the minimum mtu tap device which belong to ovs bridge, for example, the
instance-A's tap mtu is 1500, the instance-B's mtu is 1450, then br-
int's mtu will be set to 1450 automatically.

Seems the neutron doesn't support this scenario which vlan and vxlan
both exist in ovs environment, I'm not sure if it's a bug.

I have a workaround to solve this problem, use command "ovs-vsctl set
int br-int mtu_request=1500", then the br-int will be always 1500, the
instance-A's iperf program worked fine.

** Affects: neutron
     Importance: Undecided
         Status: New

** Summary changed:

- multiple networks with different mtu cause network connectivity problem
+ multiple type networks with different mtu cause vm connectivity problem

** Description changed:

  In my environment, vlan and vxlan are both exist, and their mtu is 1500 and 1450.
- I use vxlan network to create a instance-A, and use vlan network to create a instance-B, the instance-A and instance-B are in the same compute nodes.
+ I use vlan network to create a instance-A, and use vxlan network to create a instance-B, the instance-A and instance-B are in the same compute nodes.
  
  Then I found the mtu of br-int is 1450, this will cause instance-A'iperf
  result is 0 in , because instance-A's mtu 1500 is large than 1450.
  
  I did some investigation, found that the ovs bridge's mtu is decided by
  the minimum mtu tap device which belong to ovs bridge, for example, the
  instance-A's tap mtu is 1500, the instance-B's mtu is 1450, then br-
  int's mtu will be set to 1450 automatically.
  
  Seems the neutron doesn't support this scenario which vlan and vxlan
  both exist, I'm not sure if it's a bug.
  
  I have a workaround to solve this problem, use command "ovs-vsctl set
  int br-int mtu_request=1500", then the br-int will be always 1500, the
  instance-A's iperf program worked fine.

** Description changed:

  In my environment, vlan and vxlan are both exist, and their mtu is 1500 and 1450.
  I use vlan network to create a instance-A, and use vxlan network to create a instance-B, the instance-A and instance-B are in the same compute nodes.
  
  Then I found the mtu of br-int is 1450, this will cause instance-A'iperf
  result is 0 in , because instance-A's mtu 1500 is large than 1450.
  
  I did some investigation, found that the ovs bridge's mtu is decided by
  the minimum mtu tap device which belong to ovs bridge, for example, the
  instance-A's tap mtu is 1500, the instance-B's mtu is 1450, then br-
  int's mtu will be set to 1450 automatically.
  
  Seems the neutron doesn't support this scenario which vlan and vxlan
- both exist, I'm not sure if it's a bug.
+ both exist in ovs environment, I'm not sure if it's a bug.
  
  I have a workaround to solve this problem, use command "ovs-vsctl set
  int br-int mtu_request=1500", then the br-int will be always 1500, the
  instance-A's iperf program worked fine.

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https://bugs.launchpad.net/bugs/1845603

Title:
  multiple type networks with different mtu cause vm connectivity
  problem

Status in neutron:
  New

Bug description:
  In my environment, vlan and vxlan are both exist, and their mtu is 1500 and 1450.
  I use vlan network to create a instance-A, and use vxlan network to create a instance-B, the instance-A and instance-B are in the same compute nodes.

  Then I found the mtu of br-int is 1450, this will cause
  instance-A'iperf result is 0 in , because instance-A's mtu 1500 is
  large than 1450.

  I did some investigation, found that the ovs bridge's mtu is decided
  by the minimum mtu tap device which belong to ovs bridge, for example,
  the instance-A's tap mtu is 1500, the instance-B's mtu is 1450, then
  br-int's mtu will be set to 1450 automatically.

  Seems the neutron doesn't support this scenario which vlan and vxlan
  both exist in ovs environment, I'm not sure if it's a bug.

  I have a workaround to solve this problem, use command "ovs-vsctl set
  int br-int mtu_request=1500", then the br-int will be always 1500, the
  instance-A's iperf program worked fine.

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