diff --git a/devstack/lib/ironic b/devstack/lib/ironic
index d1b5b7de52..c4584fde4f 100644
--- a/devstack/lib/ironic
+++ b/devstack/lib/ironic
@@ -955,7 +955,7 @@ function setup_qemu_log_hook {
 
 function create_bridge_and_vms {
     # Call libvirt setup scripts in a new shell to ensure any new group membership
-    sudo su $STACK_USER -c "$IRONIC_SCRIPTS_DIR/setup-network.sh $IRONIC_VM_NETWORK_BRIDGE"
+    sudo su $STACK_USER -c "$IRONIC_SCRIPTS_DIR/setup-network.sh $IRONIC_VM_NETWORK_BRIDGE $PUBLIC_BRIDGE_MTU"
     if [[ "$IRONIC_VM_LOG_CONSOLE" == "True" ]] ; then
         local log_arg="-l $IRONIC_VM_LOG_DIR"
 
diff --git a/devstack/settings b/devstack/settings
index f9ad9e655f..726919de3d 100644
--- a/devstack/settings
+++ b/devstack/settings
@@ -2,3 +2,12 @@ enable_service ironic ir-api ir-cond
 # TODO(jroll) this hacks around a bug, remove when fixed in devstack
 # https://bugs.launchpad.net/devstack/+bug/1629133
 SUBNETPOOL_PREFIX_V4=$FIXED_RANGE
+
+# NOTE(vsaienko) mtu calculation has been changed recently to 1450
+# https://github.com/openstack/neutron/commit/51a697
+# and caused https://bugs.launchpad.net/ironic/+bug/1631875
+# Get the smallest local MTU
+local_mtu=$(ip link show | sed -ne 's/.*mtu \([0-9]\+\).*/\1/p' | sort -n | head -1)
+# 50 bytes is overhead for vxlan (which is greater than GRE
+# allowing us to use either overlay option with this MTU.
+PUBLIC_BRIDGE_MTU=$((local_mtu - 50))
diff --git a/devstack/tools/ironic/scripts/setup-network.sh b/devstack/tools/ironic/scripts/setup-network.sh
index fc60da0820..3eb6ed80bf 100755
--- a/devstack/tools/ironic/scripts/setup-network.sh
+++ b/devstack/tools/ironic/scripts/setup-network.sh
@@ -12,6 +12,7 @@ LIBVIRT_CONNECT_URI=${LIBVIRT_CONNECT_URI:-"qemu:///system"}
 # Keep track of the DevStack directory
 TOP_DIR=$(cd $(dirname "$0")/.. && pwd)
 BRIDGE_NAME=${1:-brbm}
+PUBLIC_BRIDGE_MTU=${2:-1500}
 
 export VIRSH_DEFAULT_CONNECT_URI="$LIBVIRT_CONNECT_URI"
 
@@ -26,3 +27,5 @@ sudo ip link set dev ${BRIDGE_NAME} up
 virsh net-define <(sed s/brbm/$BRIDGE_NAME/ $TOP_DIR/templates/brbm.xml)
 virsh net-autostart ${BRIDGE_NAME}
 virsh net-start ${BRIDGE_NAME}
+
+sudo ip link set dev ${BRIDGE_NAME} mtu $PUBLIC_BRIDGE_MTU