gistfile1.diff

diff --git a/network.go b/network.go
index 22ea8ba..d4cbabd 100644
--- a/network.go
+++ b/network.go
@@ -10,6 +10,7 @@ import (
        "github.com/dotcloud/docker/utils"
        "log"
        "net"
+       "os/exec"
        "strconv"
        "sync"
        "syscall"
@@ -466,8 +467,14 @@ func (alloc *IPAllocator) run() {
                        }
 
                        if _, inUse = alloc.inUse[newNum]; !inUse {
-                               // We found an unused IP
-                               break
+                               _, err := exec.Command("arping", "-f", "-c", "1", "-q", "-I", "docker0", intToIP(newNum).String()).Output()
+                               if err != nil {
+                                       // We found an unused IP
+                                       break
+                               } else {
+                                       // Address is already used by some other host on network
+                                       continue
+                               }
                        }
                }