vxlan: T5759: change default MTU from 1450 -> 1500 bytes

Found an odd behavior on Linux and the VyOS CLI implementation. If adding VXLAN
interfaces using iproute2 the MTU differs depending on the creation syntax:

ip -4 link add vxlan100 type vxlan dstport 4789 external df unset tos inherit \
  ttl 16 nolearning vnifilter local 172.16.33.201
ip -4 link add vxlan200 type vxlan id 200 dstport 4789 local 172.16.33.201 dev eth0
ip -6 link add vxlan300 type vxlan id 300 dstport 4789 local 2001:db8:1::1 dev eth0

132: vxlan300: <BROADCAST,MULTICAST> mtu 1430 qdisc noop state DOWN group default qlen 1000
    link/ether 4e:fb:e3:f5:d9:59 brd ff:ff:ff:ff:ff:ff
133: vxlan200: <BROADCAST,MULTICAST> mtu 1450 qdisc noop state DOWN group default qlen 1000
    link/ether 0e:4e:f4:76:59:3f brd ff:ff:ff:ff:ff:ff
134: vxlan100: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN group default qlen 1000
    link/ether ba:b6:b7:0c:b1:37 brd ff:ff:ff:ff:ff:ff

VyOS always sets a default MTU of 1450 bytes which is correct for IPv4 p2p links
or multicast, but invalid for IPv6 p2p. Also this will break EVPN deployments
as ethernet bridges with MTU < 1500 bytes are less fun.

Increase default MTU to 1500 bytes. Migrate old configurations to use 1450
bytes if not specified otherwise on the CLI.

(cherry picked from commit 4a163b016333e58fee9d6ec6b53a09e0160b3213)

2 files changed, 10 insertions, 8 deletions

diff --git a/smoketest/scripts/cli/base_interfaces_test.py b/smoketest/scripts/cli/base_interfaces_test.py
index 6862207e3..dfdfd3736 100644
--- a/smoketest/scripts/cli/base_interfaces_test.py
+++ b/smoketest/scripts/cli/base_interfaces_test.py
@@ -412,10 +412,9 @@ class BasicInterfaceTest:
 
             for intf in self._interfaces:
                 base = self._base_path + [intf]
-                self.cli_set(base + ['mtu', self._mtu])
-
                 for option in self._options.get(intf, []):
                     self.cli_set(base + option.split())
+                self.cli_set(base + ['mtu', self._mtu])
 
             # check validate() - can not set low MTU if 'no-default-link-local'
             # is not set on CLI
diff --git a/smoketest/scripts/cli/test_interfaces_vxlan.py b/smoketest/scripts/cli/test_interfaces_vxlan.py
index be1fa9d7f..18676491b 100755
--- a/smoketest/scripts/cli/test_interfaces_vxlan.py
+++ b/smoketest/scripts/cli/test_interfaces_vxlan.py
@@ -18,6 +18,7 @@ import unittest
 
 from vyos.configsession import ConfigSessionError
 from vyos.ifconfig import Interface
+from vyos.ifconfig import Section
 from vyos.utils.network import get_bridge_fdb
 from vyos.utils.network import get_interface_config
 from vyos.utils.network import interface_exists
@@ -32,12 +33,13 @@ class VXLANInterfaceTest(BasicInterfaceTest.TestCase):
         cls._base_path = ['interfaces', 'vxlan']
         cls._options = {
             'vxlan10': ['vni 10', 'remote 127.0.0.2'],
-            'vxlan20': ['vni 20', 'group 239.1.1.1', 'source-interface eth0'],
+            'vxlan20': ['vni 20', 'group 239.1.1.1', 'source-interface eth0', 'mtu 1450'],
             'vxlan30': ['vni 30', 'remote 2001:db8:2000::1', 'source-address 2001:db8:1000::1', 'parameters ipv6 flowlabel 0x1000'],
             'vxlan40': ['vni 40', 'remote 127.0.0.2', 'remote 127.0.0.3'],
             'vxlan50': ['vni 50', 'remote 2001:db8:2000::1', 'remote 2001:db8:2000::2', 'parameters ipv6 flowlabel 0x1000'],
         }
         cls._interfaces = list(cls._options)
+        cls._mtu = '1450'
         # call base-classes classmethod
         super(VXLANInterfaceTest, cls).setUpClass()
 
@@ -139,7 +141,7 @@ class VXLANInterfaceTest(BasicInterfaceTest.TestCase):
     def test_vxlan_vlan_vni_mapping(self):
         bridge = 'br0'
         interface = 'vxlan0'
-        source_interface = 'eth0'
+        source_address = '192.0.2.99'
 
         vlan_to_vni = {
             '10': '10010',
@@ -152,8 +154,7 @@ class VXLANInterfaceTest(BasicInterfaceTest.TestCase):
         }
 
         self.cli_set(self._base_path + [interface, 'parameters', 'external'])
-        self.cli_set(self._base_path + [interface, 'parameters', 'vni-filter'])
-        self.cli_set(self._base_path + [interface, 'source-interface', source_interface])
+        self.cli_set(self._base_path + [interface, 'source-address', source_address])
 
         for vlan, vni in vlan_to_vni.items():
             self.cli_set(self._base_path + [interface, 'vlan-to-vni', vlan, 'vni', vni])
@@ -189,11 +190,12 @@ class VXLANInterfaceTest(BasicInterfaceTest.TestCase):
     def test_vxlan_neighbor_suppress(self):
         bridge = 'br555'
         interface = 'vxlan555'
-        source_interface = 'eth0'
+        source_interface = 'dum0'
+
+        self.cli_set(['interfaces', Section.section(source_interface), source_interface, 'mtu', '9000'])
 
         self.cli_set(self._base_path + [interface, 'parameters', 'external'])
         self.cli_set(self._base_path + [interface, 'source-interface', source_interface])
-
         self.cli_set(self._base_path + [interface, 'parameters', 'neighbor-suppress'])
 
         # This must fail as this VXLAN interface is not associated with any bridge
@@ -223,6 +225,7 @@ class VXLANInterfaceTest(BasicInterfaceTest.TestCase):
         self.assertTrue(tmp['linkinfo']['info_slave_data']['learning'])
 
         self.cli_delete(['interfaces', 'bridge', bridge])
+        self.cli_delete(['interfaces', Section.section(source_interface), source_interface])
 
     def test_vxlan_vni_filter(self):
         interfaces = ['vxlan987', 'vxlan986', 'vxlan985']