From 29b0ee30bf2622a40ca3d17e3f6b9e94e5b62072 Mon Sep 17 00:00:00 2001
From: Viacheslav Hletenko <v.gletenko@vyos.io>
Date: Mon, 1 Aug 2022 13:19:53 +0000
Subject: mtu: T4572: Add DHCP-option MTU to get values from DHCP-server

Ability to get MTU from DHCP-server and don't touch it per
any interface change if interface 'dhcp-options mtu' is
configured
---
 interface-definitions/include/interface/dhcp-options.xml.i | 6 ++++++
 python/vyos/ifconfig/interface.py                          | 2 +-
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/interface-definitions/include/interface/dhcp-options.xml.i b/interface-definitions/include/interface/dhcp-options.xml.i
index 914b60503..2ed5fd403 100644
--- a/interface-definitions/include/interface/dhcp-options.xml.i
+++ b/interface-definitions/include/interface/dhcp-options.xml.i
@@ -14,6 +14,12 @@
         <help>Override system host-name sent to DHCP server</help>
       </properties>
     </leafNode>
+    <leafNode name="mtu">
+      <properties>
+        <help>Use MTU value from DHCP server - ignore interface setting</help>
+        <valueless/>
+      </properties>
+    </leafNode>
     <leafNode name="vendor-class-id">
       <properties>
         <help>Identify the vendor client type to the DHCP server</help>
diff --git a/python/vyos/ifconfig/interface.py b/python/vyos/ifconfig/interface.py
index 555494f80..c50ead89f 100644
--- a/python/vyos/ifconfig/interface.py
+++ b/python/vyos/ifconfig/interface.py
@@ -1535,7 +1535,7 @@ class Interface(Control):
         # before mangling any IPv6 option. If MTU is less then 1280 IPv6 will be
         # automatically disabled by the kernel. Also MTU must be increased before
         # configuring any IPv6 address on the interface.
-        if 'mtu' in config:
+        if 'mtu' in config and dict_search('dhcp_options.mtu', config) == None:
             self.set_mtu(config.get('mtu'))
 
         # Configure MSS value for IPv6 TCP connections
-- 
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