diff --git a/tempest/api/compute/servers/test_attach_interfaces.py b/tempest/api/compute/servers/test_attach_interfaces.py
index 8201363..fdf55e5 100644
--- a/tempest/api/compute/servers/test_attach_interfaces.py
+++ b/tempest/api/compute/servers/test_attach_interfaces.py
@@ -13,10 +13,10 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
-import netaddr
 import time
 
 from tempest.api.compute import base
+from tempest.common.utils import net_utils
 from tempest import config
 from tempest import exceptions
 from tempest.lib import exceptions as lib_exc
@@ -125,18 +125,21 @@
 
     def _test_create_interface_by_fixed_ips(self, server, ifs):
         network_id = ifs[0]['net_id']
-        ip_list = [
-            ifs[n]['fixed_ips'][0]['ip_address'] for n in range(0, len(ifs))]
-        ip = str(netaddr.IPAddress(sorted(ip_list)[-1]) + 1)
+        subnet_id = ifs[0]['fixed_ips'][0]['subnet_id']
+        ip_list = net_utils.get_unused_ip_addresses(self.ports_client,
+                                                    self.subnets_client,
+                                                    network_id,
+                                                    subnet_id,
+                                                    1)
 
-        fixed_ips = [{'ip_address': ip}]
+        fixed_ips = [{'ip_address': ip_list[0]}]
         iface = self.client.create_interface(
             server['id'], net_id=network_id,
             fixed_ips=fixed_ips)['interfaceAttachment']
         self.addCleanup(self.ports_client.delete_port, iface['port_id'])
         iface = self.wait_for_interface_status(
             server['id'], iface['port_id'], 'ACTIVE')
-        self._check_interface(iface, fixed_ip=ip)
+        self._check_interface(iface, fixed_ip=ip_list[0])
         return iface
 
     def _test_show_interface(self, server, ifs):
diff --git a/tempest/api/network/test_floating_ips.py b/tempest/api/network/test_floating_ips.py
index 2156e64..2abbf93 100644
--- a/tempest/api/network/test_floating_ips.py
+++ b/tempest/api/network/test_floating_ips.py
@@ -13,10 +13,9 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
-import netaddr
-
 from tempest.api.network import base
 from tempest.common.utils import data_utils
+from tempest.common.utils import net_utils
 from tempest import config
 from tempest import test
 
@@ -192,8 +191,12 @@
     @test.idempotent_id('45c4c683-ea97-41ef-9c51-5e9802f2f3d7')
     def test_create_update_floatingip_with_port_multiple_ip_address(self):
         # Find out ips that can be used for tests
-        ips = list(netaddr.IPNetwork(self.subnet['cidr']))
-        list_ips = [str(ip) for ip in ips[-3:-1]]
+        list_ips = net_utils.get_unused_ip_addresses(
+            self.ports_client,
+            self.subnets_client,
+            self.subnet['network_id'],
+            self.subnet['id'],
+            2)
         fixed_ips = [{'ip_address': list_ips[0]}, {'ip_address': list_ips[1]}]
         # Create port
         body = self.ports_client.create_port(network_id=self.network['id'],
diff --git a/tempest/common/utils/net_utils.py b/tempest/common/utils/net_utils.py
new file mode 100644
index 0000000..d98fb32
--- /dev/null
+++ b/tempest/common/utils/net_utils.py
@@ -0,0 +1,48 @@
+# Copyright 2016 Hewlett Packard Enterprise Development Company
+#
+# Licensed under the Apache License, Version 2.0 (the "License"); you may
+# not use this file except in compliance with the License. You may obtain
+# a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+# License for the specific language governing permissions and limitations
+# under the License.
+
+import itertools
+import netaddr
+
+from tempest.lib import exceptions as lib_exc
+
+
+def get_unused_ip_addresses(ports_client, subnets_client,
+                            network_id, subnet_id, count):
+
+    """Return a list with the specified number of unused IP addresses
+
+    This method uses the given ports_client to find the specified number of
+    unused IP addresses on the given subnet using the supplied subnets_client
+    """
+
+    ports = ports_client.list_ports(network_id=network_id)['ports']
+    subnet = subnets_client.show_subnet(subnet_id)
+    ip_net = netaddr.IPNetwork(subnet['subnet']['cidr'])
+    subnet_set = netaddr.IPSet(ip_net.iter_hosts())
+    alloc_set = netaddr.IPSet()
+
+    # prune out any addresses already allocated to existing ports
+    for port in ports:
+        for fixed_ip in port.get('fixed_ips'):
+            alloc_set.add(fixed_ip['ip_address'])
+
+    av_set = subnet_set - alloc_set
+    ip_list = [str(ip) for ip in itertools.islice(av_set, count)]
+
+    if len(ip_list) != count:
+        msg = "Insufficient IP addresses available"
+        raise lib_exc.BadRequest(message=msg)
+
+    return ip_list