diff --git a/lib/test-driver/Machine.pm b/lib/test-driver/Machine.pm
index 46fbf6d60cdf..9f5971d70a1c 100644
--- a/lib/test-driver/Machine.pm
+++ b/lib/test-driver/Machine.pm
@@ -28,7 +28,7 @@ sub new {
         # !!! merge with qemu-vm.nix.
         $startCommand =
             "qemu-system-x86_64 -m 384 " .
-            "-net nic,model=virtio -net user \$QEMU_OPTS ";
+            "-net nic,model=virtio -net user,\$QEMU_NET_OPTS \$QEMU_OPTS ";
         $startCommand .= "-drive file=" . Cwd::abs_path($args->{hda}) . ",if=virtio,boot=on,werror=report "
             if defined $args->{hda};
         $startCommand .= "-cdrom $args->{cdrom} "
diff --git a/modules/testing/test-instrumentation.nix b/modules/testing/test-instrumentation.nix
index 2515edf6192b..655cda31ed65 100644
--- a/modules/testing/test-instrumentation.nix
+++ b/modules/testing/test-instrumentation.nix
@@ -24,7 +24,8 @@ in
   config = {
 
     jobs.backdoor =
-      { startOn = "started network-interfaces";
+      { startOn = "ip-up";
+        stopOn = "never";
         
         script =
           ''
@@ -35,10 +36,12 @@ in
             source /etc/profile
             cd /tmp
             echo "connecting to host..." > /dev/ttyS0
-            exec ${pkgs.socat}/bin/socat tcp:10.0.2.6:23 exec:${rootShell} 2> /dev/ttyS0
+            ${pkgs.socat}/bin/socat tcp:10.0.2.6:23 exec:${rootShell} 2> /dev/ttyS0 || poweroff -f
           '';
+
+        respawn = false;
       };
-  
+
     boot.postBootCommands =
       ''
         # Panic on out-of-memory conditions rather than letting the