From dac8138fc83af658cb7ec735f8f45c348ada8de4 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Christian=20K=C3=B6nig?= <ckoenig@posteo.de>
Date: Sat, 4 Jun 2022 23:17:43 +0200
Subject: [PATCH] Base DHCP settings on default gateway address and not on
 IPV4_ADDRESS from setupVars.conf
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Signed-off-by: Christian König <ckoenig@posteo.de>
---
 settings.php | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/settings.php b/settings.php
index 3cf7f423..26d6c2b5 100644
--- a/settings.php
+++ b/settings.php
@@ -76,10 +76,16 @@ if (isset($setupVars["PIHOLE_INTERFACE"])) {
 } else {
     $piHoleInterface = "unknown";
 }
-if (isset($setupVars["IPV4_ADDRESS"])) {
-    $piHoleIPv4 = $setupVars["IPV4_ADDRESS"];
+
+// get the gateway address for the default route on the Pi-hole interface
+if ($piHoleInterface !== "unknown") {
+$IPv4GW=shell_exec("ip -4 route | grep default | grep '${piHoleInterface}' | cut -d ' ' -f 3");
 } else {
-    $piHoleIPv4 = "unknown";
+    $IPv4GW = "unknown";
+}
+// if the route did not return anything
+if (empty($IPv4GW)) {
+    $IPv4GW = "unknown";
 }
 
 // DNS settings
@@ -432,8 +438,8 @@ if (isset($_GET['tab']) && in_array($_GET['tab'], array("sysadmin", "dns", "piho
                     } else {
                         $DHCP = false;
                         // Try to guess initial settings
-                        if ($piHoleIPv4 !== "unknown") {
-                            $DHCPdomain = explode(".", $piHoleIPv4);
+                        if ($IPv4GW !== "unknown") {
+                            $DHCPdomain = explode(".", $IPv4GW);
                             $DHCPstart = $DHCPdomain[0] . "." . $DHCPdomain[1] . "." . $DHCPdomain[2] . ".201";
                             $DHCPend = $DHCPdomain[0] . "." . $DHCPdomain[1] . "." . $DHCPdomain[2] . ".251";
                             $DHCProuter = $DHCPdomain[0] . "." . $DHCPdomain[1] . "." . $DHCPdomain[2] . ".1";