Neutron - Automatic network mtu

1、neutron.conf
network_device_mtu=1450 
 
# 生效的设备：neutron 网络节点上的 qdhcp 和 qrouter network namespace
的 qr，qg 和 ns 接口以及对应的 veth tap 设备
/usr/lib/python2.7/site-packages/neutron/agent/linux/interface.py  
if self.conf.network_device_mtu:
            ns_dev.link.set_mtu(self.conf.network_device_mtu)
            if self.conf.ovs_use_veth:
                root_dev.link.set_mtu(self.conf.network_device_mtu)

2、ml2_conf.ini
path_mtu = 9000
segment_mtu = 1500

flat网络类型如何获取MTU: 
/usr/lib/python2.7/site-packages/neutron/plugins/ml2/drivers/type_flat.py
class FlatTypeDriver(helpers.BaseTypeDriver):    # 父类BaseTypeDriver
    """Manage state for flat networks with ML2.
    The FlatTypeDriver implements the 'flat' network_type. Flat
    network segments provide connectivity between VMs and other
    devices using any connected IEEE 802.1D conformant
    physical_network, without the use of VLAN tags, tunneling, or
    other segmentation mechanisms. Therefore at most one flat network
    segment can exist on each available physical_network.
    """
    def __init__(self):
        super(FlatTypeDriver, self).__init__()
        self._parse_networks(cfg.CONF.ml2_type_flat.flat_networks)
        
# 如果定义了flat provider的physet_mtus，取physical_network_mtus和segment_mtu的最小值
    def get_mtu(self, physical_network):
        seg_mtu = super(FlatTypeDriver, self).get_mtu()
        mtu = []
        if seg_mtu > 0:
            mtu.append(seg_mtu)
        if physical_network in self.physnet_mtus:
            mtu.append(int(self.physnet_mtus[physical_network]))
        return min(mtu) if mtu else 0
        
/usr/lib/python2.7/site-packages/neutron/plugins/ml2/drivers/helpers.py
class BaseTypeDriver(api.TypeDriver):
    """BaseTypeDriver for functions common to Segment and flat."""
    def __init__(self):
        try:
            self.physnet_mtus = utils.parse_mappings(
                cfg.CONF.ml2.physical_network_mtus
            )
        except Exception:
            self.physnet_mtus = []
    def get_mtu(self, physical_network=None):
        return cfg.CONF.ml2.segment_mtu

vlan网络类型如何获取MTU: 
class VlanTypeDriver(helpers.SegmentTypeDriver):   # 父类SegmentTypeDriver
    """Manage state for VLAN networks with ML2.
    The VlanTypeDriver implements the 'vlan' network_type. VLAN
    network segments provide connectivity between VMs and other
    devices using any connected IEEE 802.1Q conformant
    physical_network segmented into virtual networks via IEEE 802.1Q
    headers. Up to 4094 VLAN network segments can exist on each
    available physical_network.
    """
    def __init__(self):
        super(VlanTypeDriver, self).__init__(VlanAllocation)
        self._parse_network_vlan_ranges()
        
# vlan的获取mtu方式和flat一样
    def get_mtu(self, physical_network):
        seg_mtu = super(VlanTypeDriver, self).get_mtu()
        mtu = []
        if seg_mtu > 0:
            mtu.append(seg_mtu)
        if physical_network in self.physnet_mtus:
            mtu.append(int(self.physnet_mtus[physical_network]))
        return min(mtu) if mtu else 0
        
/usr/lib/python2.7/site-packages/neutron/plugins/ml2/drivers/helpers.py
class BaseTypeDriver(api.TypeDriver):
    """BaseTypeDriver for functions common to Segment and flat."""
    def __init__(self):
        try:
            self.physnet_mtus = utils.parse_mappings(
                cfg.CONF.ml2.physical_network_mtus
            )
        except Exception:
            self.physnet_mtus = []
    def get_mtu(self, physical_network=None):
        return cfg.CONF.ml2.segment_mtu
        
class SegmentTypeDriver(BaseTypeDriver):
    """SegmentTypeDriver for segment allocation.
    Provide methods helping to perform segment allocation fully or partially
    specified.
    """
    def __init__(self, model):
        super(SegmentTypeDriver, self).__init__()
        self.model = model
        self.primary_keys = set(dict(model.__table__.columns))
        self.primary_keys.remove("allocated")

vxlan网络类型如何获取MTU:
class VxlanTypeDriver(type_tunnel.EndpointTunnelTypeDriver):   # 父类EndpointTunnelTypeDriver
    def __init__(self):
        super(VxlanTypeDriver, self).__init__(
            VxlanAllocation, VxlanEndpoints)
    def get_type(self):
        return p_const.TYPE_VXLAN
    def initialize(self):
        try:
            self._initialize(cfg.CONF.ml2_type_vxlan.vni_ranges)
        except n_exc.NetworkTunnelRangeError:
            LOG.exception(_LE("Failed to parse vni_ranges. "
                              "Service terminated!"))
            raise SystemExit()            
    def get_endpoints(self):
        """Get every vxlan endpoints from database."""
        vxlan_endpoints = self._get_endpoints()
        return [{'ip_address': vxlan_endpoint.ip_address,
                 'udp_port': vxlan_endpoint.udp_port,
                 'host': vxlan_endpoint.host}
                for vxlan_endpoint in vxlan_endpoints]
    def add_endpoint(self, ip, host, udp_port=p_const.VXLAN_UDP_PORT):
        return self._add_endpoint(ip, host, udp_port=udp_port)
    def get_mtu(self, physical_network=None):
        mtu = super(VxlanTypeDriver, self).get_mtu()
        return mtu - p_const.VXLAN_ENCAP_OVERHEAD if mtu else 0  # mtu - vxlan开销，自动减去vxlan overhead
        
from neutron.plugins.common import constants as p_const
/usr/lib/python2.7/site-packages/neutron/plugins/common/constants.py
# Network Type MTU overhead
GENEVE_ENCAP_MIN_OVERHEAD = 50
GRE_ENCAP_OVERHEAD = 42
VXLAN_ENCAP_OVERHEAD = 50  # vxlan开销

class EndpointTunnelTypeDriver(TunnelTypeDriver):
class TunnelTypeDriver(helpers.SegmentTypeDriver):
    """Define stable abstract interface for ML2 type drivers.
    tunnel type networks rely on tunnel endpoints. This class defines abstract
    methods to manage these endpoints.
    """
    def get_mtu(self, physical_network=None):
        seg_mtu = super(TunnelTypeDriver, self).get_mtu()
        mtu = []
        if seg_mtu > 0:
            mtu.append(seg_mtu)
        if cfg.CONF.ml2.path_mtu > 0:
            mtu.append(cfg.CONF.ml2.path_mtu)
        return min(mtu) if mtu else 0

gre网络类型如何获取MTU:
class GreTypeDriver(type_tunnel.EndpointTunnelTypeDriver):    # 父类也是EndpointTunnelTypeDriver
    def __init__(self):
        super(GreTypeDriver, self).__init__(
            GreAllocation, GreEndpoints)
    def get_type(self):
        return p_const.TYPE_GRE
    def initialize(self):
        try:
            self._initialize(cfg.CONF.ml2_type_gre.tunnel_id_ranges)
        except n_exc.NetworkTunnelRangeError:
            LOG.exception(_LE("Failed to parse tunnel_id_ranges. "
                              "Service terminated!"))
            raise SystemExit()
    def get_endpoints(self):
        """Get every gre endpoints from database."""
        gre_endpoints = self._get_endpoints()
        return [{'ip_address': gre_endpoint.ip_address,
                 'host': gre_endpoint.host}
                for gre_endpoint in gre_endpoints]
    def add_endpoint(self, ip, host):
        return self._add_endpoint(ip, host)
    def get_mtu(self, physical_network=None):
        mtu = super(GreTypeDriver, self).get_mtu(physical_network)
        return mtu - p_const.GRE_ENCAP_OVERHEAD if mtu else 0     # mtu - gre开销,自动减去gre overhead
        
from neutron.plugins.common import constants as p_const
/usr/lib/python2.7/site-packages/neutron/plugins/common/constants.py
# Network Type MTU overhead
GENEVE_ENCAP_MIN_OVERHEAD = 50
GRE_ENCAP_OVERHEAD = 42    # gre开销，为什么是42，还不清楚
VXLAN_ENCAP_OVERHEAD = 50  # vxlan开销

L版发现neutron多了种网络类型geneve，Geneve简介，暂时还不知道怎么玩的
http://blog.csdn.net/yeasy/article/details/39928153

3、neutron.conf
advertise_mtu = true

以前的做法：
[root@controller2 ~(keystone_admin)]# cat /etc/neutron/dnsmasq-neutron.conf  # 对所有network都生效
dhcp-option-force=26,1450    # 现在可以把这个去掉
log-facility=/var/log/neutron/neutron-dnsmasq.log

/usr/lib/python2.7/site-packages/neutron/agent/linux/dhcp.py
class Dnsmasq(DhcpLocalProcess):
    # The ports that need to be opened when security policies are active
    # on the Neutron port used for DHCP.  These are provided as a convenience
    # for users of this class.
        if cfg.CONF.advertise_mtu:
            mtu = self.network.mtu
            # Do not advertise unknown mtu
            if mtu > 0:
                cmd.append('--dhcp-option-force=option:mtu,%d' % mtu)   # 看这里
        # Cap the limit because creating lots of subnets can inflate
        # this possible lease cap.
        cmd.append('--dhcp-lease-max=%d' %
                   min(possible_leases, self.conf.dnsmasq_lease_max))
        cmd.append('--conf-file=%s' % self.conf.dnsmasq_config_file)
        if self.conf.dnsmasq_dns_servers:
            cmd.extend(
                '--server=%s' % server
                for server in self.conf.dnsmasq_dns_servers)