From 42e9d86d68e353d396ced83ac20c06689812ff7c Mon Sep 17 00:00:00 2001
From: Franco Fichtner <franco@opnsense.org>
Date: Wed, 13 May 2020 09:36:15 +0200
Subject: [PATCH] radvd: use default value "0" on unknown mtu

---
 src/etc/inc/plugins.inc.d/dhcpd.inc | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/src/etc/inc/plugins.inc.d/dhcpd.inc b/src/etc/inc/plugins.inc.d/dhcpd.inc
index 002f56974..d7a20daf7 100644
--- a/src/etc/inc/plugins.inc.d/dhcpd.inc
+++ b/src/etc/inc/plugins.inc.d/dhcpd.inc
@@ -253,18 +253,18 @@ function dhcpd_radvd_configure($verbose = false, $blacklist = array())
             $realtrackif = get_real_interface($config['interfaces'][$dhcpv6if]['track6-interface'], 'inet6');
 
             $trackmtu = legacy_interface_stats($realtrackif)['mtu'];
-            if (!empty($trackmtu)) {
+            if (!empty($trackmtu) && !empty($mtu)) {
                 if ($trackmtu < $mtu) {
                     $mtu = $trackmtu;
                 }
             }
         }
 
-        if (!empty($dhcpv6ifconf['AdvLinkMTU'])) {
+        if (!empty($dhcpv6ifconf['AdvLinkMTU']) && !empty($mtu)) {
             if ($dhcpv6ifconf['AdvLinkMTU'] < $mtu) {
                 $mtu = $dhcpv6ifconf['AdvLinkMTU'];
             } else {
-                log_error("Warning! AdvLinkMTU set in config is not lower than the interface MTU, therefore can't be applied.");
+                log_error('Warning! Skipping AdvLinkMTU configuration since it cannot be applied.');
             }
         }
 
@@ -276,7 +276,7 @@ function dhcpd_radvd_configure($verbose = false, $blacklist = array())
         if (!empty($dhcpv6ifconf['AdvDefaultLifetime'])) {
             $radvdconf .= sprintf("\tAdvDefaultLifetime %s;\n", $dhcpv6ifconf['AdvDefaultLifetime']);
         }
-        $radvdconf .= sprintf("\tAdvLinkMTU %s;\n", !empty($mtu) ? $mtu : 1280);
+        $radvdconf .= sprintf("\tAdvLinkMTU %s;\n", !empty($mtu) ? $mtu : 0);
 
         switch ($dhcpv6ifconf['rapriority']) {
             case "low":
@@ -454,7 +454,7 @@ function dhcpd_radvd_configure($verbose = false, $blacklist = array())
 
         $mtu = legacy_interface_stats($realif)['mtu'];
         $trackmtu = legacy_interface_stats($realtrackif)['mtu'];
-        if (!empty($trackmtu)) {
+        if (!empty($trackmtu) && !empty($mtu)) {
             if ($trackmtu < $mtu) {
                 $mtu = $trackmtu;
             }
@@ -488,7 +488,7 @@ function dhcpd_radvd_configure($verbose = false, $blacklist = array())
         $radvdconf .= "# Generated config for {$autotype} delegation from {$trackif} on {$if}\n";
         $radvdconf .= "interface {$realif} {\n";
         $radvdconf .= "\tAdvSendAdvert on;\n";
-        $radvdconf .= sprintf("\tAdvLinkMTU %s;\n", !empty($mtu) ? $mtu : 1280);
+        $radvdconf .= sprintf("\tAdvLinkMTU %s;\n", !empty($mtu) ? $mtu : 0);
         $radvdconf .= "\tAdvManagedFlag on;\n";
         $radvdconf .= "\tAdvOtherConfigFlag on;\n";