Index: xen-4.2.3-testing/tools/qemu-xen-traditional-dir-remote/i386-dm/qemu-ifup-Linux
===================================================================
--- xen-4.2.3-testing.orig/tools/qemu-xen-traditional-dir-remote/i386-dm/qemu-ifup-Linux
+++ xen-4.2.3-testing/tools/qemu-xen-traditional-dir-remote/i386-dm/qemu-ifup-Linux
@@ -20,4 +20,11 @@ then
 fi
 
 ifconfig $1 0.0.0.0 up
+
+mtu="`ip link show $bridge | awk '/mtu/ { print $5 }'`"
+if [ -n "$mtu" ] && [ "$mtu" -gt 0 ]
+then
+   ip link set $1 mtu $mtu || :
+fi
+
 brctl addif $bridge $1 || true