diff --git a/ansible/network.yml b/ansible/network.yml
index 1636fed3f..84aa105a7 100644
--- a/ansible/network.yml
+++ b/ansible/network.yml
@@ -74,7 +74,7 @@
   tags:
     - config
   vars:
-    veth_bridges: []
+    veth_bridge_mtu_map: {}
     veth_interfaces: []
   pre_tasks:
     # When these networks are VLANs, we need to use the underlying tagged
@@ -83,28 +83,30 @@
     # tagged interface may be shared between these networks.
     - name: Update a fact containing bridges to be patched to the Neutron OVS bridge
       set_fact:
-        veth_bridges: >
-          {{ veth_bridges | union([bridge_obj]) | list }}
+        veth_bridge_mtu_map: >
+          {{ veth_bridge_mtu_map | combine({interface: mtu}) }}
       with_items: "{{ [provision_wl_net_name] + external_net_names }}"
       when: item in network_interfaces
       vars:
         interface: "{{ item | net_interface | replace('.' ~ item | net_vlan | default('!nomatch!'), '') }}"
-        bridge_obj:
-          interface: "{{ interface }}"
-          mtu: "{{ item | net_mtu }}"
+        # Determine the MTU as the maximum of all subinterface MTUs. Only
+        # interfaces with an explicit MTU set will be taken account of. If no
+        # interface has an explicit MTU set, then the corresponding veth will
+        # not either.
+        mtu: "{{ [veth_bridge_mtu_map.get(interface), item | net_mtu] | max }}"
 
     - name: Update a fact containing veth interfaces
       set_fact:
         veth_interfaces: >
           {{ veth_interfaces +
-             [{'device': network_patch_prefix ~ item.interface ~ network_patch_suffix_phy,
+             [{'device': network_patch_prefix ~ item.key ~ network_patch_suffix_phy,
                'bootproto': 'static',
-               'bridge': item.interface,
-               'mtu': item.mtu,
-               'peer_device': network_patch_prefix ~ item.interface ~ network_patch_suffix_ovs,
+               'bridge': item.key,
+               'mtu': item.value,
+               'peer_device': network_patch_prefix ~ item.key ~ network_patch_suffix_ovs,
                'peer_bootproto': 'static',
-               'peer_mtu': item.mtu,
+               'peer_mtu': item.value,
                'onboot': 'yes'}] }}
-      with_items: "{{ veth_bridges }}"
+      with_dict: "{{ veth_bridge_mtu_map }}"
   roles:
     - role: veth