diff --git a/ajax/networking/get_netcfg.php b/ajax/networking/get_netcfg.php
index 10d86ad7..cd36a8a3 100644
--- a/ajax/networking/get_netcfg.php
+++ b/ajax/networking/get_netcfg.php
@@ -46,7 +46,8 @@ if (isset($interface)) {
     preg_match('/static\sdomain_name_servers=(.*)/', $matched[0], $static_dns);
     preg_match('/fallback\sstatic_'.$interface.'/', $matched[0], $fallback);
     $dhcpdata['Metric'] = $metric[1];
-    $dhcpdata['StaticIP'] = $static_ip[1];
+    $dhcpdata['StaticIP'] = substr($static_ip[1], 0, strpos($static_ip[1],'/'));
+    $dhcpdata['SubnetMask'] = cidr2mask($static_ip[1]);
     $dhcpdata['StaticRouters'] = $static_routers[1];
     $dhcpdata['StaticDNS'] = $static_dns[1];
     $dhcpdata['FallbackEnabled'] = empty($fallback) ? false: true;
diff --git a/app/js/custom.js b/app/js/custom.js
index 25f121e5..a7eaa3cc 100644
--- a/app/js/custom.js
+++ b/app/js/custom.js
@@ -246,6 +246,7 @@ function loadInterfaceDHCPSelect() {
         jsonData = JSON.parse(data);
         $('#dhcp-iface')[0].checked = jsonData.DHCPEnabled;
         $('#txtipaddress').val(jsonData.StaticIP);
+        $('#txtsubnetmask').val(jsonData.SubnetMask);
         $('#txtgateway').val(jsonData.StaticRouters);
         $('#chkfallback')[0].checked = jsonData.FallbackEnabled;
         $('#txtrangestart').val(jsonData.RangeStart);
@@ -257,7 +258,7 @@ function loadInterfaceDHCPSelect() {
         $('#no-resolv')[0].checked = jsonData.upstreamServersEnabled;
         $('#cbxdhcpupstreamserver').val(jsonData.upstreamServers[0]);
         $('#txtmetric').val(jsonData.Metric);
-        if (jsonData.StaticIP !== null && jsonData.StaticIP !== '') {
+        if (jsonData.StaticIP !== null && jsonData.StaticIP !== '' && !jsonData.FallbackEnabled) {
             $('#chkstatic').closest('.btn').button('toggle');
             $('#chkstatic').closest('.btn').button('toggle').blur();
             $('#chkstatic').blur();
@@ -268,6 +269,9 @@ function loadInterfaceDHCPSelect() {
             $('#chkdhcp').blur();
             $('#chkfallback').prop('disabled', false);
         }
+        if (jsonData.FallbackEnabled) {
+            $('#dhcp-iface').prop('disabled', true);
+        }
     });
 }
 
diff --git a/templates/dhcp/general.php b/templates/dhcp/general.php
index 484c2690..49758696 100644
--- a/templates/dhcp/general.php
+++ b/templates/dhcp/general.php
@@ -41,6 +41,13 @@
     </div>
   </div>
 
+  <div class="row">
+    <div class="form-group col-md-6">
+      <label for="code"><?php echo _("Subnet Mask"); ?></label>
+      <input type="text" class="form-control" id="txtsubnetmask" name="SubnetMask" />
+    </div>
+  </div>
+
   <div class="row">
     <div class="form-group col-md-6">
       <label for="code"><?php echo _("Default gateway"); ?></label>