diff --git a/lib/neutron_plugins/services/l3 b/lib/neutron_plugins/services/l3
index 2180099..61b8402 100644
--- a/lib/neutron_plugins/services/l3
+++ b/lib/neutron_plugins/services/l3
@@ -102,10 +102,20 @@
 
     neutron_plugin_configure_l3_agent $Q_L3_CONF_FILE
 
-    _move_neutron_addresses_route "$PUBLIC_INTERFACE" "$OVS_PHYSICAL_BRIDGE" True False "inet"
+    # If we've given a PUBLIC_INTERFACE to take over, then we assume
+    # that we can own the whole thing, and privot it into the OVS
+    # bridge. If we are not, we're probably on a single interface
+    # machine, and we just setup NAT so that fixed guests can get out.
+    if [[ -n "$PUBLIC_INTERFACE" ]]; then
+        _move_neutron_addresses_route "$PUBLIC_INTERFACE" "$OVS_PHYSICAL_BRIDGE" True False "inet"
 
-    if [[ $(ip -f inet6 a s dev "$PUBLIC_INTERFACE" | grep -c 'global') != 0 ]]; then
-        _move_neutron_addresses_route "$PUBLIC_INTERFACE" "$OVS_PHYSICAL_BRIDGE" False False "inet6"
+        if [[ $(ip -f inet6 a s dev "$PUBLIC_INTERFACE" | grep -c 'global') != 0 ]]; then
+            _move_neutron_addresses_route "$PUBLIC_INTERFACE" "$OVS_PHYSICAL_BRIDGE" False False "inet6"
+        fi
+    else
+        local default_dev=""
+        default_dev=$(ip route | grep ^default | awk '{print $5}')
+        sudo iptables -t nat -A POSTROUTING -o $default_dev -s $FLOATING_RANGE -j MASQUERADE
     fi
 }
 
diff --git a/lib/nova b/lib/nova
index 16f6e9b..1369c40 100644
--- a/lib/nova
+++ b/lib/nova
@@ -128,7 +128,7 @@
 # --------------------------
 
 NETWORK_MANAGER=${NETWORK_MANAGER:-${NET_MAN:-FlatDHCPManager}}
-PUBLIC_INTERFACE=${PUBLIC_INTERFACE:-$PUBLIC_INTERFACE_DEFAULT}
+
 VLAN_INTERFACE=${VLAN_INTERFACE:-$GUEST_INTERFACE_DEFAULT}
 FLAT_NETWORK_BRIDGE=${FLAT_NETWORK_BRIDGE:-$FLAT_NETWORK_BRIDGE_DEFAULT}
 
@@ -659,8 +659,9 @@
 }
 
 function create_nova_conf_nova_network {
+    local public_interface=${PUBLIC_INTERFACE:-$PUBLIC_INTERFACE_DEFAULT}
     iniset $NOVA_CONF DEFAULT network_manager "nova.network.manager.$NETWORK_MANAGER"
-    iniset $NOVA_CONF DEFAULT public_interface "$PUBLIC_INTERFACE"
+    iniset $NOVA_CONF DEFAULT public_interface "$public_interface"
     iniset $NOVA_CONF DEFAULT vlan_interface "$VLAN_INTERFACE"
     iniset $NOVA_CONF DEFAULT flat_network_bridge "$FLAT_NETWORK_BRIDGE"
     if [ -n "$FLAT_INTERFACE" ]; then