Description of ML2 configuration options

Configuration option = Default value	Description
[ml2]
extension_drivers =	(ListOpt) An ordered list of extension driver entrypoints to be loaded from the neutron.ml2.extension_drivers namespace.
external_network_type = None	(StrOpt) Default network type for external networks when no provider attributes are specified. By default it is None, which means that if provider attributes are not specified while creating external networks then they will have the same type as tenant networks. Allowed values for external_network_type config option depend on the network type values configured in type_drivers config option.
mechanism_drivers =	(ListOpt) An ordered list of networking mechanism driver entrypoints to be loaded from the neutron.ml2.mechanism_drivers namespace.
path_mtu = 0	(IntOpt) The maximum permissible size of an unfragmented packet travelling from and to addresses where encapsulated Neutron traffic is sent. If <= 0, the path MTU is indeterminate.
physical_network_mtus =	(ListOpt) A list of mappings of physical networks to MTU values. The format of the mapping is <physnet>:<mtu val>. This mapping allows specifying a physical network MTU value that differs from the default segment_mtu value.
segment_mtu = 0	(IntOpt) The maximum permissible size of an unfragmented packet travelling a L2 network segment. If <= 0, the segment MTU is indeterminate.
tenant_network_types = local	(ListOpt) Ordered list of network_types to allocate as tenant networks.
type_drivers = local, flat, vlan, gre, vxlan, geneve	(ListOpt) List of network type driver entrypoints to be loaded from the neutron.ml2.type_drivers namespace.