Fixed #5771

EXCEPT that the link in the help text does not point to the correct place (yet)

1 files changed, 20 insertions, 7 deletions

diff --git a/src/usr/local/www/interfaces.php b/src/usr/local/www/interfaces.php
index 0d82dd5..6615b7a 100644
--- a/src/usr/local/www/interfaces.php
+++ b/src/usr/local/www/interfaces.php
@@ -1755,13 +1755,26 @@ $group->setHelp('This field can be used to modify ("spoof") the MAC address of t
 				'Enter a MAC address in the following format: xx:xx:xx:xx:xx:xx or leave blank');
 $section->add($group);
 
-$section->addInput(new Form_Input(
-	'mtu',
-	'MTU',
-	'number',
-	$pconfig['mtu']
-))->setHelp('If you leave this field blank, the adapter\'s default MTU will be used. ' .
-			'This is typically 1500 bytes but can vary in some circumstances.');
+// If the interface is a VLAN and has a LAGG as a parent, the MTU cannot be set here.
+// We can determine that by parsing the interface name (begins with "lagg", contains "_vlan")
+if(  (strrpos($wancfg['if'], "lagg", -strlen($wancfg['if'])) !== FALSE)  && (strpos($wancfg['if'], "_vlan") !== false)) {
+	$section->addInput(new Form_Input(
+		'mtu',
+		'MTU',
+		'number',
+		$pconfig['mtu']
+	))->setHelp('<span class="text-danger">' . 'You may not set the MTU of a VLAN interface that has a LAGG parent here. ' . '<br />' . 
+				'<a href="interfaces_lagg_edit.php?id=' . $wancfg['if'][4] . '">interfaces_lagg.php</a></span>')
+	  ->setReadonly();
+} else {
+	$section->addInput(new Form_Input(
+		'mtu',
+		'MTU',
+		'number',
+		$pconfig['mtu']
+	))->setHelp('If you leave this field blank, the adapter\'s default MTU will be used. ' .
+				'This is typically 1500 bytes but can vary in some circumstances.');
+}
 
 $section->addInput(new Form_Input(
 	'mss',