diff --git a/etc/inc/openvpn.inc b/etc/inc/openvpn.inc
index 2c078b236e..57e0469c8c 100644
--- a/etc/inc/openvpn.inc
+++ b/etc/inc/openvpn.inc
@@ -670,6 +670,10 @@ function openvpn_reconfigure($mode, $settings) {
 		$conf .= "float\n";
 	}
 
+	if ($settings['topology_subnet']) {
+		$conf .= "topology subnet\n";
+	}
+
 	openvpn_add_custom($settings, $conf);
 
 	openvpn_create_dirs();
diff --git a/usr/local/www/vpn_openvpn_server.php b/usr/local/www/vpn_openvpn_server.php
index 654cd5fa19..91c14c5022 100644
--- a/usr/local/www/vpn_openvpn_server.php
+++ b/usr/local/www/vpn_openvpn_server.php
@@ -150,6 +150,7 @@ if($_GET['act']=="edit"){
 
 		$pconfig['dynamic_ip'] = $a_server[$id]['dynamic_ip'];
 		$pconfig['pool_enable'] = $a_server[$id]['pool_enable'];
+		$pconfig['topology_subnet'] = $a_server[$id]['topology_subnet'];
 
 		$pconfig['serverbridge_dhcp'] = $a_server[$id]['serverbridge_dhcp'];
 		$pconfig['serverbridge_interface'] = $a_server[$id]['serverbridge_interface'];
@@ -378,6 +379,7 @@ if ($_POST) {
 
 		$server['dynamic_ip'] = $pconfig['dynamic_ip'];
 		$server['pool_enable'] = $pconfig['pool_enable'];
+		$server['topology_subnet'] = $pconfig['topology_subnet'];
 
 		$server['serverbridge_dhcp'] = $pconfig['serverbridge_dhcp'];
 		$server['serverbridge_interface'] = $pconfig['serverbridge_interface'];
@@ -639,6 +641,7 @@ function tuntap_change() {
 			document.getElementById("serverbridge_interface").style.display="none";
 			document.getElementById("serverbridge_dhcp_start").style.display="none";
 			document.getElementById("serverbridge_dhcp_end").style.display="none";
+			document.getElementById("topology_subnet_opt").style.display="";
 			break;
 		case "tap":
 			document.getElementById("ipv4_tunnel_network").className="vncell";
@@ -647,6 +650,7 @@ function tuntap_change() {
 				document.getElementById("serverbridge_interface").style.display="";
 				document.getElementById("serverbridge_dhcp_start").style.display="";
 				document.getElementById("serverbridge_dhcp_end").style.display="";
+				document.getElementById("topology_subnet_opt").style.display="none";
 				if (document.iform.serverbridge_dhcp.checked) {
 					document.iform.serverbridge_interface.disabled = false;
 					document.iform.serverbridge_dhcp_start.disabled = false;
@@ -657,6 +661,7 @@ function tuntap_change() {
 					document.iform.serverbridge_dhcp_end.disabled = true;
 				}
 			} else {
+				document.getElementById("topology_subnet_opt").style.display="none";
 				document.iform.serverbridge_dhcp.disabled = true;
 				document.iform.serverbridge_interface.disabled = true;
 				document.iform.serverbridge_dhcp_start.disabled = true;
@@ -1386,6 +1391,31 @@ if ($savemsg)
 							</table>
 						</td>
 					</tr>
+					<tr id="topology_subnet_opt">
+						<td width="22%" valign="top" class="vncell"><?=gettext("Topology"); ?></td>
+						<td width="78%" class="vtable">
+							<table border="0" cellpadding="2" cellspacing="0">
+								<tr>
+									<td>
+										<?php set_checked($pconfig['topology_subnet'],$chk); ?>
+										<input name="topology_subnet" type="checkbox" id="topology_subnet" value="yes" <?=$chk;?>/>
+									</td>
+									<td>
+										<span class="vexpl">
+											<?=gettext("Allocate only one IP per client (topology subnet), rather than an isolated subnet per client (topology net30)."); ?><br/>
+										</span>
+									</td>
+								</tr>
+								<tr>
+									<td>&nbsp;</td>
+									<td>
+										<?=gettext("Relevant when supplying a virtual adapter IP address to clients when using tun mode on IPv4."); ?><br/>
+										<?=gettext("Some clients may require this even for IPv6, such as OpenVPN Connect on iOS. Others may break if it is present, such as older versions of OpenVPN or clients such as Yealink phones."); ?><br>
+									</td>
+								</tr>
+							</table>
+						</td>
+					</tr>
 					<tr>
 						<td width="22%" valign="top" class="vncell"><?=gettext("DNS Default Domain"); ?></td>
 						<td width="78%" class="vtable">