diff --git a/tempest/api/network/common.py b/tempest/api/network/common.py
index c3fb821..43e7f68 100644
--- a/tempest/api/network/common.py
+++ b/tempest/api/network/common.py
@@ -56,7 +56,9 @@
 
 class DeletableSubnet(DeletableResource):
 
-    _router_ids = set()
+    def __init__(self, *args, **kwargs):
+        super(DeletableSubnet, self).__init__(*args, **kwargs)
+        self._router_ids = set()
 
     def add_to_router(self, router_id):
         self._router_ids.add(router_id)