@@ -522,6 +522,11 @@ func postContainersCreate(srv *Server, version float64, w http.ResponseWriter, r

 		out.Warnings = append(out.Warnings, "Your kernel does not support memory swap capabilities. Limitation discarded.")

 	}

+	if srv.runtime.capabilities.IPv4Forwarding {

+		log.Println("Warning: IPv4 forwarding is disabled.")

+		out.Warnings = append(out.Warnings, "IPv4 forwarding is disabled.")

+	}

+

 	b, err := json.Marshal(out)

 	if err != nil {

 		return err

@@ -24,6 +24,7 @@ type APIInfo struct {

 	NGoroutines        int    `json:",omitempty"`

 	MemoryLimit        bool   `json:",omitempty"`

 	SwapLimit          bool   `json:",omitempty"`

+	IPv4Forwarding     bool   `json:",omitempty"`

 	LXCVersion         string `json:",omitempty"`

 	NEventsListener    int    `json:",omitempty"`

 	KernelVersion      string `json:",omitempty"`

@@ -510,6 +510,9 @@ func (cli *DockerCli) CmdInfo(args ...string) error {

 	if !out.SwapLimit {

 		fmt.Fprintf(cli.err, "WARNING: No swap limit support\n")

 	}

+	if !out.IPv4Forwarding {

+		fmt.Fprintf(cli.err, "WARNING: IPv4 forwarding is disabled.\n")

+	}

 	return nil

 }

@@ -534,6 +534,10 @@ func (container *Container) Start(hostConfig *HostConfig) error {

 		container.Config.MemorySwap = -1

 	}

+	if !container.runtime.capabilities.IPv4Forwarding {

+		log.Printf("WARNING: IPv4 forwarding is disabled. Networking will not work")

+	}

+

 	// Create the requested bind mounts

 	binds := make(map[string]BindMap)

 	// Define illegal container destinations

@@ -1025,7 +1025,8 @@ Display system-wide information

 		"NFd": 11,

 		"NGoroutines":21,

 		"MemoryLimit":true,

-		"SwapLimit":false

+		"SwapLimit":false,

+		"IPv4Forwarding":true

 	   }

         :statuscode 200: no error

@@ -15,8 +15,9 @@ import (

 )

 type Capabilities struct {

-	MemoryLimit bool

-	SwapLimit   bool

+	MemoryLimit    bool

+	SwapLimit      bool

+	IPv4Forwarding bool

 }

 type Runtime struct {

@@ -240,6 +241,12 @@ func (runtime *Runtime) UpdateCapabilities(quiet bool) {

 		if !runtime.capabilities.SwapLimit && !quiet {

 			log.Printf("WARNING: Your kernel does not support cgroup swap limit.")

 		}

+

+		content, err3 := ioutil.ReadFile("/proc/sys/net/ipv4/ip_forward")

+		runtime.capabilities.IPv4Forwarding = err3 == nil && len(content) > 0 && content[0] == '1'

+		if !runtime.capabilities.IPv4Forwarding && !quiet {

+			log.Printf("WARNING: IPv4 forwarding is disabled.")

+		}

 	}

 }

@@ -269,6 +269,7 @@ func (srv *Server) DockerInfo() *APIInfo {

 		Images:             imgcount,

 		MemoryLimit:        srv.runtime.capabilities.MemoryLimit,

 		SwapLimit:          srv.runtime.capabilities.SwapLimit,

+		IPv4Forwarding:     srv.runtime.capabilities.IPv4Forwarding,

 		Debug:              os.Getenv("DEBUG") != "",

 		NFd:                utils.GetTotalUsedFds(),

 		NGoroutines:        runtime.NumGoroutine(),