ifconfig: mtu: disallow MTU < 1280 bytes when IPv6 is enabled on the interface

Using an MTU less then the required 1280 bytes (as per RFC) on an interface
where IPv6 is not explicitly disabled by:

- set interfaces ethernet eth1 ipv6 address no-default-link-local
- not having any other IPv6 address configured

Will now trigger a commit error via verify() instead of raising
FileNotFoundError!

10 files changed, 49 insertions, 0 deletions

diff --git a/python/vyos/configverify.py b/python/vyos/configverify.py
index 6e5ba1df0..944fc4294 100644
--- a/python/vyos/configverify.py
+++ b/python/vyos/configverify.py
@@ -44,6 +44,36 @@ def verify_mtu(config):
             raise ConfigError(f'Interface MTU too high, ' \
                               f'maximum supported MTU is {max_mtu}!')
 
+def verify_mtu_ipv6(config):
+    """
+    Common helper function used by interface implementations to perform
+    recurring validation if the specified MTU can be used when IPv6 is
+    configured on the interface. IPv6 requires a 1280 bytes MTU.
+    """
+    from vyos.validate import is_ipv6
+    from vyos.util import vyos_dict_search
+    # IPv6 minimum required link mtu
+    min_mtu = 1280
+
+    if int(config['mtu']) < min_mtu:
+        interface = config['ifname']
+        error_msg = f'IPv6 address will be configured on interface "{interface}" ' \
+                    f'thus the minimum MTU requirement is {min_mtu}!'
+
+        if not vyos_dict_search('ipv6.address.no_default_link_local', config):
+            raise ConfigError('link-local ' + error_msg)
+
+        for address in (vyos_dict_search('address', config) or []):
+            if address in ['dhcpv6'] or is_ipv6(address):
+                raise ConfigError(error_msg)
+
+        if vyos_dict_search('ipv6.address.autoconf', config):
+            raise ConfigError(error_msg)
+
+        if vyos_dict_search('ipv6.address.eui64', config):
+            raise ConfigError(error_msg)
+
+
 def verify_vrf(config):
     """
     Common helper function used by interface implementations to perform
diff --git a/src/conf_mode/interfaces-bonding.py b/src/conf_mode/interfaces-bonding.py
index aece2a04b..9763620ac 100755
--- a/src/conf_mode/interfaces-bonding.py
+++ b/src/conf_mode/interfaces-bonding.py
@@ -28,6 +28,7 @@ from vyos.configverify import verify_address
 from vyos.configverify import verify_bridge_delete
 from vyos.configverify import verify_dhcpv6
 from vyos.configverify import verify_source_interface
+from vyos.configverify import verify_mtu_ipv6
 from vyos.configverify import verify_vlan_config
 from vyos.configverify import verify_vrf
 from vyos.ifconfig import BondIf
@@ -141,6 +142,7 @@ def verify(bond):
             raise ConfigError('Option primary - mode dependency failed, not'
                               'supported in mode {mode}!'.format(**bond))
 
+    verify_mtu_ipv6(bond)
     verify_address(bond)
     verify_dhcpv6(bond)
     verify_vrf(bond)
diff --git a/src/conf_mode/interfaces-bridge.py b/src/conf_mode/interfaces-bridge.py
index 485decb17..4ac9c8963 100755
--- a/src/conf_mode/interfaces-bridge.py
+++ b/src/conf_mode/interfaces-bridge.py
@@ -25,6 +25,7 @@ from vyos.configdict import node_changed
 from vyos.configdict import is_member
 from vyos.configdict import is_source_interface
 from vyos.configverify import verify_dhcpv6
+from vyos.configverify import verify_mtu_ipv6
 from vyos.configverify import verify_vrf
 from vyos.ifconfig import BridgeIf
 from vyos.validate import has_address_configured
@@ -95,6 +96,7 @@ def verify(bridge):
     if 'deleted' in bridge:
         return None
 
+    verify_mtu_ipv6(bridge)
     verify_dhcpv6(bridge)
     verify_vrf(bridge)
 
diff --git a/src/conf_mode/interfaces-ethernet.py b/src/conf_mode/interfaces-ethernet.py
index 5468c7bda..1f622c003 100755
--- a/src/conf_mode/interfaces-ethernet.py
+++ b/src/conf_mode/interfaces-ethernet.py
@@ -24,6 +24,7 @@ from vyos.configverify import verify_address
 from vyos.configverify import verify_dhcpv6
 from vyos.configverify import verify_interface_exists
 from vyos.configverify import verify_mtu
+from vyos.configverify import verify_mtu_ipv6
 from vyos.configverify import verify_vlan_config
 from vyos.configverify import verify_vrf
 from vyos.ifconfig import EthernetIf
@@ -42,6 +43,7 @@ def get_config(config=None):
         conf = Config()
     base = ['interfaces', 'ethernet']
     ethernet = get_interface_dict(conf, base)
+
     return ethernet
 
 def verify(ethernet):
@@ -59,6 +61,7 @@ def verify(ethernet):
             raise ConfigError('If duplex is hardcoded, speed must be hardcoded, too')
 
     verify_mtu(ethernet)
+    verify_mtu_ipv6(ethernet)
     verify_dhcpv6(ethernet)
     verify_address(ethernet)
     verify_vrf(ethernet)
diff --git a/src/conf_mode/interfaces-geneve.py b/src/conf_mode/interfaces-geneve.py
index af7c121f4..979a5612e 100755
--- a/src/conf_mode/interfaces-geneve.py
+++ b/src/conf_mode/interfaces-geneve.py
@@ -22,6 +22,7 @@ from netifaces import interfaces
 from vyos.config import Config
 from vyos.configdict import get_interface_dict
 from vyos.configverify import verify_address
+from vyos.configverify import verify_mtu_ipv6
 from vyos.configverify import verify_bridge_delete
 from vyos.ifconfig import GeneveIf
 from vyos import ConfigError
@@ -47,6 +48,7 @@ def verify(geneve):
         verify_bridge_delete(geneve)
         return None
 
+    verify_mtu_ipv6(geneve)
     verify_address(geneve)
 
     if 'remote' not in geneve:
diff --git a/src/conf_mode/interfaces-l2tpv3.py b/src/conf_mode/interfaces-l2tpv3.py
index 2653ff19c..1118143e4 100755
--- a/src/conf_mode/interfaces-l2tpv3.py
+++ b/src/conf_mode/interfaces-l2tpv3.py
@@ -24,6 +24,7 @@ from vyos.configdict import get_interface_dict
 from vyos.configdict import leaf_node_changed
 from vyos.configverify import verify_address
 from vyos.configverify import verify_bridge_delete
+from vyos.configverify import verify_mtu_ipv6
 from vyos.ifconfig import L2TPv3If
 from vyos.util import check_kmod
 from vyos.validate import is_addr_assigned
@@ -80,6 +81,7 @@ def verify(l2tpv3):
         raise ConfigError('L2TPv3 local-ip address '
                           '"{local_ip}" is not configured!'.format(**l2tpv3))
 
+    verify_mtu_ipv6(l2tpv3)
     verify_address(l2tpv3)
     return None
 
diff --git a/src/conf_mode/interfaces-macsec.py b/src/conf_mode/interfaces-macsec.py
index a224c540e..0a20a121b 100755
--- a/src/conf_mode/interfaces-macsec.py
+++ b/src/conf_mode/interfaces-macsec.py
@@ -27,6 +27,7 @@ from vyos.util import call
 from vyos.configverify import verify_vrf
 from vyos.configverify import verify_address
 from vyos.configverify import verify_bridge_delete
+from vyos.configverify import verify_mtu_ipv6
 from vyos.configverify import verify_source_interface
 from vyos import ConfigError
 from vyos import airbag
@@ -71,6 +72,7 @@ def verify(macsec):
 
     verify_source_interface(macsec)
     verify_vrf(macsec)
+    verify_mtu_ipv6(macsec)
     verify_address(macsec)
 
     if not (('security' in macsec) and
diff --git a/src/conf_mode/interfaces-pppoe.py b/src/conf_mode/interfaces-pppoe.py
index 1b4b9e4ee..ee3b142c8 100755
--- a/src/conf_mode/interfaces-pppoe.py
+++ b/src/conf_mode/interfaces-pppoe.py
@@ -24,6 +24,7 @@ from vyos.config import Config
 from vyos.configdict import get_interface_dict
 from vyos.configverify import verify_source_interface
 from vyos.configverify import verify_vrf
+from vyos.configverify import verify_mtu_ipv6
 from vyos.template import render
 from vyos.util import call
 from vyos import ConfigError
@@ -57,6 +58,7 @@ def verify(pppoe):
 
     verify_source_interface(pppoe)
     verify_vrf(pppoe)
+    verify_mtu_ipv6(pppoe)
 
     if {'connect_on_demand', 'vrf'} <= set(pppoe):
         raise ConfigError('On-demand dialing and VRF can not be used at the same time')
diff --git a/src/conf_mode/interfaces-vxlan.py b/src/conf_mode/interfaces-vxlan.py
index 850ea28d7..002f40aef 100755
--- a/src/conf_mode/interfaces-vxlan.py
+++ b/src/conf_mode/interfaces-vxlan.py
@@ -23,6 +23,7 @@ from vyos.config import Config
 from vyos.configdict import get_interface_dict
 from vyos.configverify import verify_address
 from vyos.configverify import verify_bridge_delete
+from vyos.configverify import verify_mtu_ipv6
 from vyos.configverify import verify_source_interface
 from vyos.ifconfig import VXLANIf, Interface
 from vyos import ConfigError
@@ -77,6 +78,7 @@ def verify(vxlan):
             raise ConfigError('VXLAN has a 50 byte overhead, underlaying device ' \
                               f'MTU is to small ({underlay_mtu} bytes)')
 
+    verify_mtu_ipv6(vxlan)
     verify_address(vxlan)
     return None
 
diff --git a/src/conf_mode/interfaces-wireguard.py b/src/conf_mode/interfaces-wireguard.py
index e7c22da1a..d5800264f 100755
--- a/src/conf_mode/interfaces-wireguard.py
+++ b/src/conf_mode/interfaces-wireguard.py
@@ -27,6 +27,7 @@ from vyos.configdict import leaf_node_changed
 from vyos.configverify import verify_vrf
 from vyos.configverify import verify_address
 from vyos.configverify import verify_bridge_delete
+from vyos.configverify import verify_mtu_ipv6
 from vyos.ifconfig import WireGuardIf
 from vyos.util import check_kmod
 from vyos import ConfigError
@@ -71,6 +72,7 @@ def verify(wireguard):
         verify_bridge_delete(wireguard)
         return None
 
+    verify_mtu_ipv6(wireguard)
     verify_address(wireguard)
     verify_vrf(wireguard)