diff --git a/roles/multi-node-bridge/README.rst b/roles/multi-node-bridge/README.rst
index fe6266f8b..aa1b0c35a 100644
--- a/roles/multi-node-bridge/README.rst
+++ b/roles/multi-node-bridge/README.rst
@@ -34,9 +34,12 @@ inventory in order to work:
    VXLAN Network Identifier offset (openvswitch key).
 
 .. zuul:rolevar:: bridge_mtu
-   :default: 1450
+   :default: Smallest mtu less 50 bytes for vxlan overhead
 
-   Bridge interface MTU.
+   Bridge interface MTU. By default we determine this value by checking
+   all interfaces on host, taking the smallest MTU and subtracting by
+   50 for vxlan overhead. Can be overridden explicitly if this does not
+   work.
 
 .. zuul:rolevar:: bridge_name
    :default: br-infra
diff --git a/roles/multi-node-bridge/defaults/main.yaml b/roles/multi-node-bridge/defaults/main.yaml
index dc93e7b81..1ba0c86ee 100644
--- a/roles/multi-node-bridge/defaults/main.yaml
+++ b/roles/multi-node-bridge/defaults/main.yaml
@@ -1,5 +1,4 @@
 bridge_vni_offset: 1000000
-bridge_mtu: 1450
 bridge_name: br-infra
 
 bridge_authorize_internal_traffic: false
diff --git a/roles/multi-node-bridge/tasks/common.yaml b/roles/multi-node-bridge/tasks/common.yaml
index 2cc66e18a..facd51a81 100644
--- a/roles/multi-node-bridge/tasks/common.yaml
+++ b/roles/multi-node-bridge/tasks/common.yaml
@@ -52,3 +52,37 @@
   when:
     - bridge_configure_address | bool
     - bridge_authorize_internal_traffic | bool
+
+- when: bridge_mtu is not defined
+  block:
+    - name: Determine bridge mtu
+      shell: |
+        # Find all interfaces with a permanent mac address type.
+        # Permanent mac addrs imply "real" hardware and not interfaces we have
+        # created through this system. This makes our MTU determination mostly
+        # idempotent allowing us to create multiple overlays without
+        # perpetually smaller MTUs.
+        SMALLEST_MTU=""
+        for X in $(ls /sys/class/net) ; do
+            MAC_TYPE=$(cat "/sys/class/net/${X}/addr_assign_type")
+            if [ "$MAC_TYPE" -ne "0" ] ; then
+                # Type 0 is a permanent address implying a "real"
+                # interface. We ignore other interfaces as that is what we
+                # create here
+                continue
+            fi
+            MTU=$(cat "/sys/class/net/${X}/mtu")
+            if [ -z "$SMALLEST_MTU" ] || [ "$SMALLEST_MTU" -gt "$MTU" ] ; then
+                SMALLEST_MTU=$MTU
+            fi
+        done
+        # 50 byte overhead for vxlan
+        echo $(( SMALLEST_MTU - 50 ))
+      args:
+        executable: /bin/bash
+      environment:
+        PATH: '{{ ansible_env.PATH }}:/bin:/sbin:/usr/sbin'
+      register: mtu_output
+    - name: Set bridge_mtu
+      set_fact:
+        bridge_mtu: "{{ mtu_output.stdout }}"
diff --git a/roles/multi-node-bridge/tasks/main.yaml b/roles/multi-node-bridge/tasks/main.yaml
index 70b1f79d8..384d1abf8 100644
--- a/roles/multi-node-bridge/tasks/main.yaml
+++ b/roles/multi-node-bridge/tasks/main.yaml
@@ -1,8 +1,10 @@
-- include: common.yaml
-
 # Note (dmsimard)
 # We explicitely declare a PATH environment variable because '/sbin' is not in
 # PATH when using 'become: yes' on some distributions
+- include: common.yaml
+  environment:
+    PATH: "{{ ansible_env.PATH }}:/sbin:/usr/sbin"
+
 - include: switch.yaml
   environment:
     PATH: "{{ ansible_env.PATH }}:/sbin:/usr/sbin"