diff --git a/config.yaml b/config.yaml
index 36ff290b..7e757614 100644
--- a/config.yaml
+++ b/config.yaml
@@ -153,8 +153,10 @@ options:
     type: string
     default: "physnet1:1000:2000"
     description: |
-      Space-delimited list of Neutron network-provider & vlan-id-ranges using
-      format "<provider>:<start>:<end> ...".
+      Space-delimited list of <physical_network>:<vlan_min>:<vlan_max> or
+      <physical_network> specifying physical_network names usable for VLAN
+      provider and tenant networks, as well as ranges of VLAN tags on each
+      available for allocation to tenant networks.
   # Network configuration options
   # by default all access is over 'private-address'
   os-data-network:
diff --git a/hooks/charmhelpers/contrib/openstack/neutron.py b/hooks/charmhelpers/contrib/openstack/neutron.py
index 02c92e9c..b3f4e2b7 100644
--- a/hooks/charmhelpers/contrib/openstack/neutron.py
+++ b/hooks/charmhelpers/contrib/openstack/neutron.py
@@ -256,11 +256,14 @@ def network_manager():
 def parse_mappings(mappings):
     parsed = {}
     if mappings:
-        mappings = mappings.split(' ')
+        mappings = mappings.split()
         for m in mappings:
             p = m.partition(':')
-            if p[1] == ':':
-                parsed[p[0].strip()] = p[2].strip()
+            key = p[0].strip()
+            if p[1]:
+                parsed[key] = p[2].strip()
+            else:
+                parsed[key] = ''
 
     return parsed
 
@@ -283,13 +286,13 @@ def parse_data_port_mappings(mappings, default_bridge='br-data'):
     Returns dict of the form {bridge:port}.
     """
     _mappings = parse_mappings(mappings)
-    if not _mappings:
+    if not _mappings or _mappings.values() == ['']:
         if not mappings:
             return {}
 
         # For backwards-compatibility we need to support port-only provided in
         # config.
-        _mappings = {default_bridge: mappings.split(' ')[0]}
+        _mappings = {default_bridge: mappings.split()[0]}
 
     bridges = _mappings.keys()
     ports = _mappings.values()
@@ -309,6 +312,8 @@ def parse_vlan_range_mappings(mappings):
 
     Mappings must be a space-delimited list of provider:start:end mappings.
 
+    The start:end range is optional and may be omitted.
+
     Returns dict of the form {provider: (start, end)}.
     """
     _mappings = parse_mappings(mappings)
diff --git a/unit_tests/test_neutron_utils.py b/unit_tests/test_neutron_utils.py
index befa9eb3..96254bcd 100644
--- a/unit_tests/test_neutron_utils.py
+++ b/unit_tests/test_neutron_utils.py
@@ -930,7 +930,8 @@ class TestQuantumAgentReallocation(CharmTestCase):
             'process_name': 'neutron-nvsd-agent',
             'executable_name': '/usr/local/bin/neutron-nvsd-agent',
             'config_files': ['/etc/neutron/neutron.conf',
-                         '/etc/neutron/plugins/oneconvergence/nvsdplugin.ini'],
+                             '/etc/neutron/plugins/oneconvergence/'
+                             'nvsdplugin.ini'],
             'log_file': '/var/log/neutron/nvsd-agent.log',
         }
         neutron_plugin_openflow_context = {