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 Modular Layer 2 (ml2) configuration options

The Modular Layer 2 (ml2) plug-in has two components: network types and mechanisms. You can configure these components separately. This section describes these configuration options.

[Note]MTU bug with VXLAN tunnelling

Due to a bug in Linux Bridge software maximum transmission unit (MTU) handling, using VXLAN tunnels does not work by default.

  • A simple workaround is to increase the MTU value of the physical interface and physical switch fabric by at least 50 bytes. For example, increase the MTU value to 1550. This value enables an automatic 50-byte MTU difference between the physical interface (1500) and the VXLAN interface (automatically 1500-50 = 1450). An MTU value of 1450 causes issues when virtual machine taps are configured at an MTU value of 1500.

  • Another workaround is to decrease the virtual ethernet devices' MTU. Set the network_device_mtu option to 1450 in the neutron.conf file, and set all guest virtual machines' MTU to the same value by using a DHCP option. For information about how to use this option, see Configure OVS plug-in.

Table 7.11. Description of configuration options for ml2
Configuration option = Default value Description
mechanism_drivers = (ListOpt) An ordered list of networking mechanism driver entrypoints to be loaded from the neutron.ml2.mechanism_drivers namespace.
tenant_network_types = local (ListOpt) Ordered list of network_types to allocate as tenant networks.
type_drivers = local, flat, vlan, gre, vxlan (ListOpt) List of network type driver entrypoints to be loaded from the neutron.ml2.type_drivers namespace.

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