vyos.ifconfig: T4330: MTU must be configured prior to any IPv6 option change

This extends the fix from 53e20097 ("vyos.ifconfig: T4330: bugfix changing MTU
when IPv6 is disabled") by ordering the execution in a way the Kernel does not
complain.

(cherry picked from commit 601ab19fd8c81a998b3c966cc83b85ed60ac5ae0)

1 files changed, 7 insertions, 4 deletions

diff --git a/python/vyos/ifconfig/interface.py b/python/vyos/ifconfig/interface.py
index e8278b103..214c8dcb1 100644
--- a/python/vyos/ifconfig/interface.py
+++ b/python/vyos/ifconfig/interface.py
@@ -1362,6 +1362,13 @@ class Interface(Control):
         value = tmp if (tmp != None) else '0'
         self.set_ipv4_source_validation(value)
 
+        # MTU - Maximum Transfer Unit has a default value. It must ALWAYS be set
+        # 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:
+            self.set_mtu(config.get('mtu'))
+
         # Only change IPv6 parameters if IPv6 was not explicitly disabled
         if is_ipv6_enabled():
             # IPv6 forwarding
@@ -1402,10 +1409,6 @@ class Interface(Control):
                 for addr in tmp:
                     self.add_ipv6_eui64_address(addr)
 
-        # MTU - Maximum Transfer Unit
-        if 'mtu' in config:
-            self.set_mtu(config.get('mtu'))
-
         # re-add ourselves to any bridge we might have fallen out of
         if 'is_bridge_member' in config:
             bridge_dict = config.get('is_bridge_member')