diff --git a/etc/tempest.conf.sample b/etc/tempest.conf.sample
index 9a9952d..d5311a9 100644
--- a/etc/tempest.conf.sample
+++ b/etc/tempest.conf.sample
@@ -758,8 +758,10 @@
 # value)
 #public_network_id =
 
-# Id of the public router that provides external connectivity (string
-# value)
+# Id of the public router that provides external connectivity. This
+# should only be used when Neutron's 'allow_overlapping_ips' is set to
+# 'False' in neutron.conf. usually not needed past 'Grizzly' release
+# (string value)
 #public_router_id =
 
 # The network region name to use. If empty, the value of
diff --git a/tempest/config.py b/tempest/config.py
index 6e8238a..163817c 100644
--- a/tempest/config.py
+++ b/tempest/config.py
@@ -449,7 +449,9 @@
     cfg.StrOpt('public_router_id',
                default="",
                help="Id of the public router that provides external "
-                    "connectivity"),
+                    "connectivity. This should only be used when Neutron's "
+                    "'allow_overlapping_ips' is set to 'False' in "
+                    "neutron.conf. usually not needed past 'Grizzly' release"),
     cfg.IntOpt('build_timeout',
                default=300,
                help="Timeout in seconds to wait for network operation to "