Assert source/target L2XC are the same MTU

unittest/error-l2xc7.yaml

@@ -0,0 +1,36 @@
+test:
+  description: "L2 cross connect source and target must have the same MTU"
+  errors:
+    expected:
+     - "interface .* l2xc target MTU .* does not match source MTU .*"
+     - "sub-interface .* l2xc target MTU .* does not match source MTU .*"
+    count: 6
+---
+interfaces:
+  GigabitEthernet1/0/0:
+    mtu: 9216
+    l2xc: GigabitEthernet1/0/1
+  GigabitEthernet1/0/1:
+    mtu: 9215
+    l2xc: GigabitEthernet1/0/0
+
+  GigabitEthernet2/0/0:
+    mtu: 9216
+    sub-interfaces:
+      100:
+        mtu: 1500
+        l2xc: GigabitEthernet2/0/0.200
+      200:
+        mtu: 1501
+        l2xc: GigabitEthernet2/0/0.100
+
+  GigabitEthernet3/0/0:
+    mtu: 9000
+    l2xc: GigabitEthernet3/0/1.100
+
+  GigabitEthernet3/0/1:
+    mtu: 3000
+    sub-interfaces:
+      100:
+        mtu: 2000
+        l2xc: GigabitEthernet3/0/0

validator/interface.py

@@ -393,6 +393,10 @@ def validate_interfaces(yaml):
             if not get_by_name(yaml, iface['l2xc']):
                 msgs.append("interface %s l2xc target %s does not exist" % (ifname, iface['l2xc']))
                 result = False
+            target_mtu = get_mtu(yaml, iface['l2xc'])
+            if target_mtu != iface_mtu:
+                msgs.append("interface %s l2xc target MTU %d does not match source MTU %d" % (ifname, target_mtu, iface_mtu))
+                result = False
             if not is_l2xc_target_interface_unique(yaml, iface['l2xc']):
                 msgs.append("interface %s l2xc target %s is not unique" % (ifname, iface['l2xc']))
                 result = False
@@ -455,6 +459,10 @@ def validate_interfaces(yaml):
                     if not get_by_name(yaml, sub_iface['l2xc']):
                         msgs.append("sub-interface %s l2xc target %s does not exist" % (sub_ifname, sub_iface['l2xc']))
                         result = False
+                    target_mtu = get_mtu(yaml, sub_iface['l2xc'])
+                    if target_mtu != sub_mtu:
+                        msgs.append("sub-interface %s l2xc target MTU %d does not match source MTU %d" % (ifname, target_mtu, sub_mtu))
+                        result = False
                     if not is_l2xc_target_interface_unique(yaml, sub_iface['l2xc']):
                         msgs.append("sub-interface %s l2xc target %s is not unique" % (sub_ifname, sub_iface['l2xc']))
                         result = False