cat 0001-Find-if-the-IP-is-already-used.patch

From c4e29cd30fb6b23e5589a7e08dcf2fe3f7041c61 Mon Sep 17 00:00:00 2001
From: Marek Goldmann <marek.goldmann@gmail.com>
Date: Sat, 18 Jan 2014 18:48:53 +0100
Subject: [PATCH] Find if the IP is already used

---
 network.go | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

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
+				}
 			}
 		}
 
-- 
1.8.4.2