diff --git a/cluster/aws/util.sh b/cluster/aws/util.sh
index eebd62cf66..382caf1a40 100644
--- a/cluster/aws/util.sh
+++ b/cluster/aws/util.sh
@@ -29,7 +29,9 @@ export AWS_DEFAULT_REGION=${AWS_REGION}
 AWS_CMD="aws --output json ec2"
 AWS_ELB_CMD="aws --output json elb"
 
-MASTER_INTERNAL_IP=172.20.0.9
+INTERNAL_IP_BASE=172.20.0
+MASTER_IP_SUFFIX=.9
+MASTER_INTERNAL_IP=${INTERNAL_IP_BASE}${MASTER_IP_SUFFIX}
 
 function json_val {
     python -c 'import json,sys;obj=json.load(sys.stdin);print obj'$1''
@@ -46,7 +48,11 @@ function get_vpc_id {
 }
 
 function get_subnet_id {
-  python -c "import json,sys; lst = [str(subnet['SubnetId']) for subnet in json.load(sys.stdin)['Subnets'] if subnet['VpcId'] == '$1']; print ''.join(lst)"
+  python -c "import json,sys; lst = [str(subnet['SubnetId']) for subnet in json.load(sys.stdin)['Subnets'] if subnet['VpcId'] == '$1' and subnet['AvailabilityZone'] == '$2']; print ''.join(lst)"
+}
+
+function get_cidr {
+  python -c "import json,sys; lst = [str(subnet['CidrBlock']) for subnet in json.load(sys.stdin)['Subnets'] if subnet['VpcId'] == '$1' and subnet['AvailabilityZone'] == '$2']; print ''.join(lst)"
 }
 
 function get_igw_id {
@@ -372,7 +378,7 @@ function kube-up {
 
   if [[ -z "$VPC_ID" ]]; then
 	  echo "Creating vpc."
-	  VPC_ID=$($AWS_CMD create-vpc --cidr-block 172.20.0.0/16 | json_val '["Vpc"]["VpcId"]')
+	  VPC_ID=$($AWS_CMD create-vpc --cidr-block $INTERNAL_IP_BASE.0/16 | json_val '["Vpc"]["VpcId"]')
 	  $AWS_CMD modify-vpc-attribute --vpc-id $VPC_ID --enable-dns-support '{"Value": true}' > $LOG
 	  $AWS_CMD modify-vpc-attribute --vpc-id $VPC_ID --enable-dns-hostnames '{"Value": true}' > $LOG
 	  add-tag $VPC_ID Name kubernetes-vpc
@@ -381,10 +387,15 @@ function kube-up {
 
   echo "Using VPC $VPC_ID"
 
-  SUBNET_ID=$($AWS_CMD describe-subnets | get_subnet_id $VPC_ID)
+  SUBNET_ID=$($AWS_CMD describe-subnets | get_subnet_id $VPC_ID $ZONE)
   if [[ -z "$SUBNET_ID" ]]; then
-	  echo "Creating subnet."
-	  SUBNET_ID=$($AWS_CMD create-subnet --cidr-block 172.20.0.0/24 --vpc-id $VPC_ID --availability-zone ${ZONE} | json_val '["Subnet"]["SubnetId"]')
+    echo "Creating subnet."
+    SUBNET_ID=$($AWS_CMD create-subnet --cidr-block $INTERNAL_IP_BASE.0/24 --vpc-id $VPC_ID --availability-zone ${ZONE} | json_val '["Subnet"]["SubnetId"]')
+  else
+    EXISTING_CIDR=$($AWS_CMD describe-subnets | get_cidr $VPC_ID $ZONE)
+    echo "Using existing CIDR $EXISTING_CIDR"
+    INTERNAL_IP_BASE=${EXISTING_CIDR%.*}
+    MASTER_INTERNAL_IP=${INTERNAL_IP_BASE}${MASTER_IP_SUFFIX}
   fi
 
   echo "Using subnet $SUBNET_ID"
@@ -458,7 +469,7 @@ function kube-up {
     --iam-instance-profile Name=$IAM_PROFILE_MASTER \
     --instance-type $MASTER_SIZE \
     --subnet-id $SUBNET_ID \
-    --private-ip-address 172.20.0.9 \
+    --private-ip-address $MASTER_INTERNAL_IP \
     --key-name kubernetes \
     --security-group-ids $SEC_GROUP_ID \
     --associate-public-ip-address \
@@ -539,7 +550,7 @@ function kube-up {
       --iam-instance-profile Name=$IAM_PROFILE_MINION \
       --instance-type $MINION_SIZE \
       --subnet-id $SUBNET_ID \
-      --private-ip-address 172.20.0.1${i} \
+      --private-ip-address $INTERNAL_IP_BASE.1${i} \
       --key-name kubernetes \
       --security-group-ids $SEC_GROUP_ID \
       --associate-public-ip-address \