diff --git a/tempest/api/compute/admin/test_networks.py b/tempest/api/compute/admin/test_networks.py
index fb6376e..d7fb62d 100644
--- a/tempest/api/compute/admin/test_networks.py
+++ b/tempest/api/compute/admin/test_networks.py
@@ -64,5 +64,5 @@
             configured_network = CONF.compute.fixed_network_name
             self.assertIn(configured_network, [x['label'] for x in networks])
         else:
-            network_labels = [x['label'] for x in networks]
-            self.assertNotEmpty(network_labels)
+            raise self.skipException(
+                "Environment has no known-for-sure existing network.")
diff --git a/tox.ini b/tox.ini
index 47ef5eb..027442a 100644
--- a/tox.ini
+++ b/tox.ini
@@ -328,10 +328,15 @@
 setenv = {[tempestenv]setenv}
 deps = {[tempestenv]deps}
 # The regex below is used to select the slow tagged tests:
-regex = '\[.*\bslow\b.*\]'
+regex1 = '(.*\[.*\bslow\b.*\])'
+regex2 = 'test_port_security_macspoofing_port'
+# The regex below is used to run slow test in parallel except
+# test_port_security_macspoofing_port which fail many times
+# while running in parallel
 commands =
     find . -type f -name "*.pyc" -delete
-    tempest run --regex {[testenv:slow]regex} {posargs}
+    tempest run --regex {[testenv:slow]regex1} --exclude-regex {[testenv:slow]regex2} {posargs}
+    tempest run --combine --serial --regex {[testenv:slow]regex2} {posargs}
 
 [testenv:multinode]
 envdir = .tox/tempest