diff --git a/tempest/api/network/base.py b/tempest/api/network/base.py
index 6bec0d7..8308e34 100644
--- a/tempest/api/network/base.py
+++ b/tempest/api/network/base.py
@@ -96,6 +96,12 @@
         cls.metering_labels = []
         cls.metering_label_rules = []
         cls.ethertype = "IPv" + str(cls._ip_version)
+        if cls._ip_version == 4:
+            cls.cidr = netaddr.IPNetwork(CONF.network.project_network_cidr)
+            cls.mask_bits = CONF.network.project_network_mask_bits
+        elif cls._ip_version == 6:
+            cls.cidr = netaddr.IPNetwork(CONF.network.project_network_v6_cidr)
+            cls.mask_bits = CONF.network.project_network_v6_mask_bits
 
     @classmethod
     def resource_cleanup(cls):
diff --git a/tempest/api/network/test_networks.py b/tempest/api/network/test_networks.py
index 206d1a8..26199fc 100644
--- a/tempest/api/network/test_networks.py
+++ b/tempest/api/network/test_networks.py
@@ -34,8 +34,7 @@
     def resource_setup(cls):
         super(BaseNetworkTestResources, cls).resource_setup()
         cls.network = cls.create_network()
-        cls.subnet = cls._create_subnet_with_last_subnet_block(cls.network,
-                                                               cls._ip_version)
+        cls.subnet = cls._create_subnet_with_last_subnet_block(cls.network)
         cls._subnet_data = {6: {'gateway':
                                 str(cls._get_gateway_from_tempest_conf(6)),
                                 'allocation_pools':
@@ -64,20 +63,13 @@
                                 'new_dns_nameservers': ['7.8.8.8', '7.8.4.4']}}
 
     @classmethod
-    def _create_subnet_with_last_subnet_block(cls, network, ip_version):
+    def _create_subnet_with_last_subnet_block(cls, network):
         # Derive last subnet CIDR block from project CIDR and
         # create the subnet with that derived CIDR
-        if ip_version == 4:
-            cidr = netaddr.IPNetwork(CONF.network.project_network_cidr)
-            mask_bits = CONF.network.project_network_mask_bits
-        elif ip_version == 6:
-            cidr = netaddr.IPNetwork(CONF.network.project_network_v6_cidr)
-            mask_bits = CONF.network.project_network_v6_mask_bits
-
-        subnet_cidr = list(cidr.subnet(mask_bits))[-1]
+        subnet_cidr = list(cls.cidr.subnet(cls.mask_bits))[-1]
         gateway_ip = str(netaddr.IPAddress(subnet_cidr) + 1)
         return cls.create_subnet(network, gateway=gateway_ip,
-                                 cidr=subnet_cidr, mask_bits=mask_bits)
+                                 cidr=subnet_cidr, mask_bits=cls.mask_bits)
 
     @classmethod
     def _get_gateway_from_tempest_conf(cls, ip_version):
@@ -473,14 +465,8 @@
     def test_bulk_create_delete_subnet(self):
         networks = [self.create_network(), self.create_network()]
         # Creates 2 subnets in one request
-        if self._ip_version == 4:
-            cidr = netaddr.IPNetwork(CONF.network.project_network_cidr)
-            mask_bits = CONF.network.project_network_mask_bits
-        else:
-            cidr = netaddr.IPNetwork(CONF.network.project_network_v6_cidr)
-            mask_bits = CONF.network.project_network_v6_mask_bits
-
-        cidrs = [subnet_cidr for subnet_cidr in cidr.subnet(mask_bits)]
+        cidrs = [subnet_cidr
+                 for subnet_cidr in self.cidr.subnet(self.mask_bits)]
 
         names = [data_utils.rand_name('subnet-') for i in range(len(networks))]
         subnets_list = []
diff --git a/tempest/api/network/test_ports.py b/tempest/api/network/test_ports.py
index 5c36747..eb53fbb 100644
--- a/tempest/api/network/test_ports.py
+++ b/tempest/api/network/test_ports.py
@@ -84,25 +84,13 @@
         self.assertTrue(port1['admin_state_up'])
         self.assertTrue(port2['admin_state_up'])
 
-    @classmethod
-    def _get_ipaddress_from_tempest_conf(cls):
-        """Return subnet with mask bits for configured CIDR """
-        if cls._ip_version == 4:
-            cidr = netaddr.IPNetwork(CONF.network.project_network_cidr)
-            cidr.prefixlen = CONF.network.project_network_mask_bits
-
-        elif cls._ip_version == 6:
-            cidr = netaddr.IPNetwork(CONF.network.project_network_v6_cidr)
-            cidr.prefixlen = CONF.network.project_network_v6_mask_bits
-
-        return cidr
-
     @decorators.attr(type='smoke')
     @decorators.idempotent_id('0435f278-40ae-48cb-a404-b8a087bc09b1')
     def test_create_port_in_allowed_allocation_pools(self):
         network = self.create_network()
         net_id = network['id']
-        address = self._get_ipaddress_from_tempest_conf()
+        address = self.cidr
+        address.prefixlen = self.mask_bits
         if ((address.version == 4 and address.prefixlen >= 30) or
            (address.version == 6 and address.prefixlen >= 126)):
             msg = ("Subnet %s isn't large enough for the test" % address.cidr)
diff --git a/tempest/api/network/test_routers.py b/tempest/api/network/test_routers.py
index 3883cc2..981f29c 100644
--- a/tempest/api/network/test_routers.py
+++ b/tempest/api/network/test_routers.py
@@ -59,13 +59,6 @@
             msg = "router extension not enabled."
             raise cls.skipException(msg)
 
-    @classmethod
-    def resource_setup(cls):
-        super(RoutersTest, cls).resource_setup()
-        cls.tenant_cidr = (CONF.network.project_network_cidr
-                           if cls._ip_version == 4 else
-                           CONF.network.project_network_v6_cidr)
-
     @decorators.attr(type='smoke')
     @decorators.idempotent_id('f64403e2-8483-4b34-8ccd-b09a87bcc68c')
     @testtools.skipUnless(CONF.network.public_network_id,
@@ -202,7 +195,7 @@
     def test_update_delete_extra_route(self):
         # Create different cidr for each subnet to avoid cidr duplicate
         # The cidr starts from project_cidr
-        next_cidr = netaddr.IPNetwork(self.tenant_cidr)
+        next_cidr = netaddr.IPNetwork(self.cidr)
         # Prepare to build several routes
         test_routes = []
         routes_num = 4
@@ -278,7 +271,7 @@
         network02 = self.create_network(
             network_name=data_utils.rand_name('router-network02-'))
         subnet01 = self.create_subnet(network01)
-        sub02_cidr = netaddr.IPNetwork(self.tenant_cidr).next()
+        sub02_cidr = netaddr.IPNetwork(self.cidr).next()
         subnet02 = self.create_subnet(network02, cidr=sub02_cidr)
         router = self._create_router()
         interface01 = self._add_router_interface_with_subnet_id(router['id'],
diff --git a/tempest/api/network/test_routers_negative.py b/tempest/api/network/test_routers_negative.py
index 60b9de7..27bda3a 100644
--- a/tempest/api/network/test_routers_negative.py
+++ b/tempest/api/network/test_routers_negative.py
@@ -40,9 +40,6 @@
         cls.router = cls.create_router()
         cls.network = cls.create_network()
         cls.subnet = cls.create_subnet(cls.network)
-        cls.tenant_cidr = (CONF.network.project_network_cidr
-                           if cls._ip_version == 4 else
-                           CONF.network.project_network_v6_cidr)
 
     @decorators.attr(type=['negative'])
     @decorators.idempotent_id('37a94fc0-a834-45b9-bd23-9a81d2fd1e22')
@@ -57,7 +54,7 @@
     @decorators.idempotent_id('11836a18-0b15-4327-a50b-f0d9dc66bddd')
     def test_router_add_gateway_net_not_external_returns_400(self):
         alt_network = self.create_network()
-        sub_cidr = netaddr.IPNetwork(self.tenant_cidr).next()
+        sub_cidr = netaddr.IPNetwork(self.cidr).next()
         self.create_subnet(alt_network, cidr=sub_cidr)
         self.assertRaises(lib_exc.BadRequest,
                           self.routers_client.update_router,