func (net UbuntuNetManager) writeResolvConf(networks boshsettings.Networks) error {
	buffer := bytes.NewBuffer([]byte{})

	const ubuntuResolvConfTemplate = `# Generated by bosh-agent
{{ range .DNSServers }}nameserver {{ . }}
{{ end }}`

	t := template.Must(template.New("resolv-conf").Parse(ubuntuResolvConfTemplate))

	// Keep DNS servers in the order specified by the network
	dnsNetwork, _ := networks.DefaultNetworkFor("dns")

	type dnsConfigArg struct {
		DNSServers []string
	}
	dnsServersArg := dnsConfigArg{dnsNetwork.DNS}
	err := t.Execute(buffer, dnsServersArg)
	if err != nil {
		return bosherr.WrapError(err, "Generating config from template")
	}

	err = net.fs.WriteFile("/etc/resolvconf/resolv.conf.d/head", buffer.Bytes())
	if err != nil {
		return bosherr.WrapError(err, "Writing to /etc/resolvconf/resolv.conf.d/head")
	}

	_, _, _, err = net.cmdRunner.RunCommand("resolvconf", "-u")
	if err != nil {
		return bosherr.WrapError(err, "Updating resolvconf")
	}

	return nil
}

func (creator interfaceConfigurationCreator) createMultipleInterfaceConfigurations(networks boshsettings.Networks, interfacesByMAC map[string]string) ([]StaticInterfaceConfiguration, []DHCPInterfaceConfiguration, error) {
	if len(interfacesByMAC) < len(networks) {
		return nil, nil, bosherr.Errorf("Number of network settings '%d' is greater than the number of network devices '%d'", len(networks), len(interfacesByMAC))
	}

	for name := range networks {
		if mac := networks[name].Mac; mac != "" {
			if _, ok := interfacesByMAC[mac]; !ok {
				return nil, nil, bosherr.Errorf("No device found for network '%s' with MAC address '%s'", name, mac)
			}
		}
	}

	// Configure interfaces with network settings matching MAC address.
	// If we cannot find a network setting with a matching MAC address, configure that interface as DHCP
	var networkSettings boshsettings.Network
	var err error
	staticConfigs := []StaticInterfaceConfiguration{}
	dhcpConfigs := []DHCPInterfaceConfiguration{}

	for mac, ifaceName := range interfacesByMAC {
		networkSettings, _ = networks.NetworkForMac(mac)
		staticConfigs, dhcpConfigs, err = creator.createInterfaceConfiguration(staticConfigs, dhcpConfigs, ifaceName, networkSettings)
		if err != nil {
			return nil, nil, bosherr.WrapError(err, "Creating interface configuration")
		}
	}

	return staticConfigs, dhcpConfigs, nil
}

func (net UbuntuNetManager) writeResolvConf(networks boshsettings.Networks) error {
	buffer := bytes.NewBuffer([]byte{})

	const resolvConfTemplate = `# Generated by bosh-agent
{{ range .DNSServers }}nameserver {{ . }}
{{ end }}`

	t := template.Must(template.New("resolv-conf").Parse(resolvConfTemplate))

	// Keep DNS servers in the order specified by the network
	dnsNetwork, _ := networks.DefaultNetworkFor("dns")

	type dnsConfigArg struct {
		DNSServers []string
	}

	dnsServersArg := dnsConfigArg{dnsNetwork.DNS}

	err := t.Execute(buffer, dnsServersArg)
	if err != nil {
		return bosherr.WrapError(err, "Generating DNS config from template")
	}

	if len(dnsNetwork.DNS) > 0 {
		// Write out base so that releases may overwrite head
		err = net.fs.WriteFile("/etc/resolvconf/resolv.conf.d/base", buffer.Bytes())
		if err != nil {
			return bosherr.WrapError(err, "Writing to /etc/resolvconf/resolv.conf.d/base")
		}
	} else {
		// For the first time before resolv.conf is symlinked to /run/...
		// inherit possibly configured resolv.conf

		targetPath, err := net.fs.ReadLink("/etc/resolv.conf")
		if err != nil {
			return bosherr.WrapError(err, "Reading /etc/resolv.conf symlink")
		}

		if targetPath == "/etc/resolv.conf" {
			err := net.fs.CopyFile("/etc/resolv.conf", "/etc/resolvconf/resolv.conf.d/base")
			if err != nil {
				return bosherr.WrapError(err, "Copying /etc/resolv.conf for backwards compat")
			}
		}
	}

	err = net.fs.Symlink("/run/resolvconf/resolv.conf", "/etc/resolv.conf")
	if err != nil {
		return bosherr.WrapError(err, "Setting up /etc/resolv.conf symlink")
	}

	_, _, _, err = net.cmdRunner.RunCommand("resolvconf", "-u")
	if err != nil {
		return bosherr.WrapError(err, "Updating resolvconf")
	}

	return nil
}

func (net ubuntuNetManager) SetupDhcp(networks boshsettings.Networks, errCh chan error) error {
	net.logger.Debug(ubuntuNetManagerLogTag, "Configuring DHCP networking")

	buffer := bytes.NewBuffer([]byte{})
	t := template.Must(template.New("dhcp-config").Parse(ubuntuDHCPConfigTemplate))

	// Keep DNS servers in the order specified by the network
	// because they are added by a *single* DHCP's prepend command
	dnsNetwork, _ := networks.DefaultNetworkFor("dns")
	dnsServersList := strings.Join(dnsNetwork.DNS, ", ")
	err := t.Execute(buffer, dnsServersList)
	if err != nil {
		return bosherr.WrapError(err, "Generating config from template")
	}

	dhclientConfigFile := net.dhclientConfigFile()
	written, err := net.fs.ConvergeFileContents(dhclientConfigFile, buffer.Bytes())
	if err != nil {
		return bosherr.WrapError(err, "Writing to %s", dhclientConfigFile)
	}

	if written {
		args := net.restartNetworkArguments()

		net.logger.Debug(ubuntuNetManagerLogTag, "Restarting network interfaces")

		_, _, _, err := net.cmdRunner.RunCommand("ifdown", args...)
		if err != nil {
			net.logger.Error(ubuntuNetManagerLogTag, "Ignoring ifdown failure: %s", err)
		}

		_, _, _, err = net.cmdRunner.RunCommand("ifup", args...)
		if err != nil {
			net.logger.Error(ubuntuNetManagerLogTag, "Ignoring ifup failure: %s", err)
		}
	}

	addresses := []boship.InterfaceAddress{
		// eth0 is hard coded in AWS and OpenStack stemcells.
		// TODO: abstract hardcoded network interface name to the NetManager
		boship.NewResolvingInterfaceAddress("eth0", net.ipResolver),
	}

	go func() {
		net.addressBroadcaster.BroadcastMACAddresses(addresses)
		if errCh != nil {
			errCh <- nil
		}
	}()

	return nil
}

func (net centosNetManager) SetupNetworking(networks boshsettings.Networks, errCh chan error) error {
	nonVipNetworks := boshsettings.Networks{}
	for networkName, networkSettings := range networks {
		if networkSettings.IsVIP() {
			continue
		}
		nonVipNetworks[networkName] = networkSettings
	}

	staticInterfaceConfigurations, dhcpInterfaceConfigurations, err := net.buildInterfaces(nonVipNetworks)
	if err != nil {
		return err
	}

	dnsNetwork, _ := nonVipNetworks.DefaultNetworkFor("dns")
	dnsServers := dnsNetwork.DNS

	interfacesChanged, err := net.writeNetworkInterfaces(dhcpInterfaceConfigurations, staticInterfaceConfigurations, dnsServers)
	if err != nil {
		return bosherr.WrapError(err, "Writing network configuration")
	}

	dhcpChanged := false
	if len(dhcpInterfaceConfigurations) > 0 {
		dhcpChanged, err = net.writeDHCPConfiguration(dnsServers, dhcpInterfaceConfigurations)
		if err != nil {
			return err
		}
	}

	if interfacesChanged || dhcpChanged {
		net.restartNetworkingInterfaces()
	}

	staticAddresses, dynamicAddresses := net.ifaceAddresses(staticInterfaceConfigurations, dhcpInterfaceConfigurations)

	err = net.interfaceAddressesValidator.Validate(staticAddresses)
	if err != nil {
		return bosherr.WrapError(err, "Validating static network configuration")
	}

	err = net.dnsValidator.Validate(dnsServers)
	if err != nil {
		return bosherr.WrapError(err, "Validating dns configuration")
	}

	net.broadcastIps(append(staticAddresses, dynamicAddresses...), errCh)

	return nil
}

func (net UbuntuNetManager) SetupNetworking(networks boshsettings.Networks, errCh chan error) error {
	if networks.IsPreconfigured() {
		// Note in this case IPs are not broadcasted
		return net.writeResolvConf(networks)
	}

	staticConfigs, dhcpConfigs, dnsServers, err := net.ComputeNetworkConfig(networks)
	if err != nil {
		return bosherr.WrapError(err, "Computing network configuration")
	}

	interfacesChanged, err := net.writeNetworkInterfaces(dhcpConfigs, staticConfigs, dnsServers)
	if err != nil {
		return bosherr.WrapError(err, "Writing network configuration")
	}

	dhcpChanged := false
	if len(dhcpConfigs) > 0 {
		dhcpChanged, err = net.writeDHCPConfiguration(dnsServers)
		if err != nil {
			return err
		}
	}

	if interfacesChanged || dhcpChanged {
		err = net.removeDhcpDNSConfiguration()
		if err != nil {
			return err
		}

		net.restartNetworkingInterfaces(net.ifaceNames(dhcpConfigs, staticConfigs))
	}

	staticAddresses, dynamicAddresses := net.ifaceAddresses(staticConfigs, dhcpConfigs)

	err = net.interfaceAddressesValidator.Validate(staticAddresses)
	if err != nil {
		return bosherr.WrapError(err, "Validating static network configuration")
	}

	err = net.dnsValidator.Validate(dnsServers)
	if err != nil {
		return bosherr.WrapError(err, "Validating dns configuration")
	}

	net.broadcastIps(append(staticAddresses, dynamicAddresses...), errCh)

	return nil
}

func (net UbuntuNetManager) ComputeNetworkConfig(networks boshsettings.Networks) ([]StaticInterfaceConfiguration, []DHCPInterfaceConfiguration, []string, error) {
	nonVipNetworks := boshsettings.Networks{}
	for networkName, networkSettings := range networks {
		if networkSettings.IsVIP() {
			continue
		}
		nonVipNetworks[networkName] = networkSettings
	}

	staticConfigs, dhcpConfigs, err := net.buildInterfaces(nonVipNetworks)
	if err != nil {
		return nil, nil, nil, err
	}

	dnsNetwork, _ := nonVipNetworks.DefaultNetworkFor("dns")
	dnsServers := dnsNetwork.DNS
	return staticConfigs, dhcpConfigs, dnsServers, nil
}

func (net centosNetManager) writeResolvConf(networks boshsettings.Networks) error {
	buffer := bytes.NewBuffer([]byte{})
	t := template.Must(template.New("resolv-conf").Parse(centosResolvConfTemplate))

	// Keep DNS servers in the order specified by the network
	dnsNetwork, _ := networks.DefaultNetworkFor("dns")
	dnsServersArg := dnsConfigArg{dnsNetwork.DNS}

	err := t.Execute(buffer, dnsServersArg)
	if err != nil {
		return bosherr.WrapError(err, "Generating config from template")
	}

	err = net.fs.WriteFile("/etc/resolv.conf", buffer.Bytes())
	if err != nil {
		return bosherr.WrapError(err, "Writing to /etc/resolv.conf")
	}

	return nil
}

func (net WindowsNetManager) SetupNetworking(networks boshsettings.Networks, errCh chan error) error {

	nonVipNetworks := boshsettings.Networks{}

	for networkName, networkSettings := range networks {
		if networkSettings.IsVIP() {
			continue
		}
		nonVipNetworks[networkName] = networkSettings
	}

	err := net.setupInterfaces(nonVipNetworks)
	if err != nil {
		return err
	}

	dnsNetwork, _ := nonVipNetworks.DefaultNetworkFor("dns")
	dns := net.setupDNS(dnsNetwork)
	time.Sleep(5 * time.Second)
	return dns
}

func (net centosNetManager) SetupDhcp(networks boshsettings.Networks, errCh chan error) error {
	net.logger.Debug(centosNetManagerLogTag, "Configuring DHCP networking")

	buffer := bytes.NewBuffer([]byte{})
	t := template.Must(template.New("dhcp-config").Parse(centosDHCPConfigTemplate))

	// Keep DNS servers in the order specified by the network
	// because they are added by a *single* DHCP's prepend command
	dnsNetwork, _ := networks.DefaultNetworkFor("dns")
	dnsServersList := strings.Join(dnsNetwork.DNS, ", ")
	err := t.Execute(buffer, dnsServersList)
	if err != nil {
		return bosherr.WrapError(err, "Generating config from template")
	}

	written, err := net.fs.ConvergeFileContents("/etc/dhcp/dhclient.conf", buffer.Bytes())
	if err != nil {
		return bosherr.WrapError(err, "Writing to /etc/dhcp/dhclient.conf")
	}

	if written {
		net.restartNetwork()
	}

	addresses := []boship.InterfaceAddress{
		// eth0 is hard coded in AWS and OpenStack stemcells.
		// TODO: abstract hardcoded network interface name to the NetManager
		boship.NewResolvingInterfaceAddress("eth0", net.ipResolver),
	}

	go func() {
		net.addressBroadcaster.BroadcastMACAddresses(addresses)
		if errCh != nil {
			errCh <- nil
		}
	}()

	return err
}

func describeUbuntuNetManager() {
	var (
		fs                            *fakesys.FakeFileSystem
		cmdRunner                     *fakesys.FakeCmdRunner
		ipResolver                    *fakeip.FakeResolver
		addressBroadcaster            *fakearp.FakeAddressBroadcaster
		interfaceAddrsProvider        *fakeip.FakeInterfaceAddressesProvider
		netManager                    UbuntuNetManager
		interfaceConfigurationCreator InterfaceConfigurationCreator
	)

	writeNetworkDevice := func(iface string, macAddress string, isPhysical bool) string {
		interfacePath := fmt.Sprintf("/sys/class/net/%s", iface)
		fs.WriteFile(interfacePath, []byte{})
		if isPhysical {
			fs.WriteFile(fmt.Sprintf("/sys/class/net/%s/device", iface), []byte{})
		}
		fs.WriteFileString(fmt.Sprintf("/sys/class/net/%s/address", iface), fmt.Sprintf("%s\n", macAddress))

		return interfacePath
	}

	stubInterfacesWithVirtual := func(physicalInterfaces map[string]boshsettings.Network, virtualInterfaces []string) {
		interfacePaths := []string{}

		for iface, networkSettings := range physicalInterfaces {
			interfacePaths = append(interfacePaths, writeNetworkDevice(iface, networkSettings.Mac, true))
		}

		for _, iface := range virtualInterfaces {
			interfacePaths = append(interfacePaths, writeNetworkDevice(iface, "virtual", false))
		}

		fs.SetGlob("/sys/class/net/*", interfacePaths)
	}

	stubInterfaces := func(physicalInterfaces map[string]boshsettings.Network) {
		stubInterfacesWithVirtual(physicalInterfaces, nil)
	}

	BeforeEach(func() {
		fs = fakesys.NewFakeFileSystem()
		cmdRunner = fakesys.NewFakeCmdRunner()
		ipResolver = &fakeip.FakeResolver{}
		logger := boshlog.NewLogger(boshlog.LevelNone)
		interfaceConfigurationCreator = NewInterfaceConfigurationCreator(logger)
		addressBroadcaster = &fakearp.FakeAddressBroadcaster{}
		interfaceAddrsProvider = &fakeip.FakeInterfaceAddressesProvider{}
		interfaceAddrsValidator := boship.NewInterfaceAddressesValidator(interfaceAddrsProvider)
		dnsValidator := NewDNSValidator(fs)
		netManager = NewUbuntuNetManager(
			fs,
			cmdRunner,
			ipResolver,
			interfaceConfigurationCreator,
			interfaceAddrsValidator,
			dnsValidator,
			addressBroadcaster,
			logger,
		).(UbuntuNetManager)
	})

	Describe("ComputeNetworkConfig", func() {
		Context("when there is one manual network and neither is marked as default for DNS", func() {
			It("should use the manual network for DNS", func() {
				networks := boshsettings.Networks{
					"manual": factory.Network{DNS: &[]string{"8.8.8.8"}}.Build(),
				}
				stubInterfaces(networks)
				_, _, dnsServers, err := netManager.ComputeNetworkConfig(networks)
				Expect(err).ToNot(HaveOccurred())
				Expect(dnsServers).To(Equal([]string{"8.8.8.8"}))
			})
		})

		Context("when there is a vip network and a manual network and neither is marked as default for DNS", func() {
			It("should use the manual network for DNS", func() {
				networks := boshsettings.Networks{
					"vip":    boshsettings.Network{Type: "vip"},
					"manual": factory.Network{Type: "manual", DNS: &[]string{"8.8.8.8"}}.Build(),
				}
				stubInterfaces(networks)
				_, _, dnsServers, err := netManager.ComputeNetworkConfig(networks)
				Expect(err).ToNot(HaveOccurred())
				Expect(dnsServers).To(Equal([]string{"8.8.8.8"}))
			})
		})
		Context("when there is a vip network and a manual network and the manual network is marked as default for DNS", func() {
			It("should use the manual network for DNS", func() {
				networks := boshsettings.Networks{
					"vip":    boshsettings.Network{Type: "vip"},
					"manual": factory.Network{Type: "manual", DNS: &[]string{"8.8.8.8"}, Default: []string{"dns"}}.Build(),
				}
				stubInterfaces(networks)
				_, _, dnsServers, err := netManager.ComputeNetworkConfig(networks)
				Expect(err).ToNot(HaveOccurred())
				Expect(dnsServers).To(Equal([]string{"8.8.8.8"}))
			})
		})

//.........这里部分代码省略.........