diff --git a/doc/source/dev/dev-manual-devstack.rst b/doc/source/dev/dev-manual-devstack.rst
index 6b6c0df550..9db2801da1 100644
--- a/doc/source/dev/dev-manual-devstack.rst
+++ b/doc/source/dev/dev-manual-devstack.rst
@@ -85,9 +85,11 @@ Create a local.sh to automatically make necessary networking changes during
 the devstack deployment process. This will allow bays spawned by magnum to
 access the internet through PUBLIC_INTERFACE::
 
-    cat > local.sh << END_LOCAL_SH
+    cat > local.sh << 'END_LOCAL_SH'
     #!/bin/sh
-    sudo iptables -t nat -A POSTROUTING -o br-ex -j MASQUERADE
+    ROUTE_TO_INTERNET=$(ip route get 8.8.8.8)
+    OBOUND_DEV=$(echo ${ROUTE_TO_INTERNET#*dev} | awk '{print $1}')
+    sudo iptables -t nat -A POSTROUTING -o $OBOUND_DEV -j MASQUERADE
     END_LOCAL_SH
     chmod 755 local.sh