diff --git a/lib/qemu-flags.nix b/lib/qemu-flags.nix
index 7831c8f149ab..5d8e898c534c 100644
--- a/lib/qemu-flags.nix
+++ b/lib/qemu-flags.nix
@@ -4,12 +4,6 @@
 
   qemuNICFlags = nic: net: machine:
     "-net nic,vlan=${toString nic},macaddr=52:54:00:12:${toString net}:${toString machine},model=virtio " +
-    # Use 232.0.1.<vlan> as the multicast address to connect VMs on
-    # the same vlan, but allow it to be overriden using the
-    # $QEMU_MCAST_ADDR_<vlan> environment variable.  The test driver
-    # sets this variable to prevent collisions between parallel
-    # builds.
-    "-net socket,vlan=${toString nic},mcast=" +
-    "\${QEMU_MCAST_ADDR_${toString net}:-232.0.1.${toString net}:1234} ";
-    
+    "-net vde,vlan=${toString nic},sock=$QEMU_VDE_SOCKET_${toString net} ";
+
 }
diff --git a/lib/test-driver/Machine.pm b/lib/test-driver/Machine.pm
index 81d96ee81e1a..7b48f26fb820 100644
--- a/lib/test-driver/Machine.pm
+++ b/lib/test-driver/Machine.pm
@@ -10,16 +10,6 @@ use Cwd;
 use File::Basename;
 
 
-# Stuff our PID in the multicast address/port to prevent collissions
-# with other NixOS VM networks.  See
-# http://www.iana.org/assignments/multicast-addresses/.
-my $mcastPrefix = "232.18";
-my $mcastSuffix = ($$ >> 8) . ":" . (64000 + ($$ & 0xff));
-print STDERR "using multicast addresses $mcastPrefix.<vlan>.$mcastSuffix\n";
-for (my $n = 0; $n < 256; $n++) {
-    $ENV{"QEMU_MCAST_ADDR_$n"} = "$mcastPrefix.$n.$mcastSuffix";
-}
-
 my $showGraphics = defined $ENV{'DISPLAY'};
 
 
diff --git a/lib/test-driver/test-driver.pl b/lib/test-driver/test-driver.pl
index 9f5054f77219..841017ea0a33 100644
--- a/lib/test-driver/test-driver.pl
+++ b/lib/test-driver/test-driver.pl
@@ -5,6 +5,7 @@ use Machine;
 use Term::ReadLine;
 use IO::File;
 use Logger;
+use Cwd;
 
 $SIG{PIPE} = 'IGNORE'; # because Unix domain sockets may die unexpectedly
 
@@ -13,6 +14,19 @@ STDERR->autoflush(1);
 my $log = new Logger;
 
 
+# Start vde_switch for each network required by the test.
+my %vlans;
+foreach my $vlan (split / /, $ENV{VLANS} || "") {
+    next if defined $vlans{$vlan};
+    $log->log("starting VDE switch for network $vlan");
+    my $socket = Cwd::abs_path "./vde$vlan.ctl";
+    system("vde_switch -d -s $socket") == 0
+        or die "cannot start vde_switch";
+    $ENV{"QEMU_VDE_SOCKET_$vlan"} = $socket;
+    $vlans{$vlan} = 1;
+}
+
+
 my %vms;
 my $context = "";
 
@@ -83,23 +97,26 @@ sub runTests {
 
     # Copy the kernel coverage data for each machine, if the kernel
     # has been compiled with coverage instrumentation.
-    foreach my $vm (values %vms) {
-        my $gcovDir = "/sys/kernel/debug/gcov";
+    $log->nest("collecting coverage data", sub {
+        foreach my $vm (values %vms) {
+            my $gcovDir = "/sys/kernel/debug/gcov";
 
-        next unless $vm->isUp();
+            next unless $vm->isUp();
 
-        my ($status, $out) = $vm->execute("test -e $gcovDir");
-        next if $status != 0;
+            my ($status, $out) = $vm->execute("test -e $gcovDir");
+            next if $status != 0;
 
-        # Figure out where to put the *.gcda files so that the report
-        # generator can find the corresponding kernel sources.
-        my $kernelDir = $vm->mustSucceed("echo \$(dirname \$(readlink -f /var/run/current-system/kernel))/.build/linux-*");
-        chomp $kernelDir;
-        my $coverageDir = "/hostfs" . $vm->stateDir() . "/coverage-data/$kernelDir";
+            # Figure out where to put the *.gcda files so that the
+            # report generator can find the corresponding kernel
+            # sources.
+            my $kernelDir = $vm->mustSucceed("echo \$(dirname \$(readlink -f /var/run/current-system/kernel))/.build/linux-*");
+            chomp $kernelDir;
+            my $coverageDir = "/hostfs" . $vm->stateDir() . "/coverage-data/$kernelDir";
 
-        # Copy all the *.gcda files.
-        $vm->execute("for d in $gcovDir/nix/store/*/.build/linux-*; do for i in \$(cd \$d && find -name '*.gcda'); do echo \$i; mkdir -p $coverageDir/\$(dirname \$i); cp -v \$d/\$i $coverageDir/\$i; done; done");
-    }
+            # Copy all the *.gcda files.
+            $vm->execute("for d in $gcovDir/nix/store/*/.build/linux-*; do for i in \$(cd \$d && find -name '*.gcda'); do echo \$i; mkdir -p $coverageDir/\$(dirname \$i); cp -v \$d/\$i $coverageDir/\$i; done; done");
+        }
+    });
 
     if ($nrTests != 0) {
         $log->log("$nrSucceeded out of $nrTests tests succeeded",
@@ -118,12 +135,14 @@ sub createDisk {
 
 
 END {
-    foreach my $vm (values %vms) {
-        if ($vm->{pid}) {
-            $log->log("killing " . $vm->{name} . " (pid " . $vm->{pid} . ")");
-            kill 9, $vm->{pid};
+    $log->nest("cleaning up", sub {
+        foreach my $vm (values %vms) {
+            if ($vm->{pid}) {
+                $log->log("killing " . $vm->{name} . " (pid " . $vm->{pid} . ")");
+                kill 9, $vm->{pid};
+            }
         }
-    }
+    });
     $log->close();
 }
 
diff --git a/lib/testing.nix b/lib/testing.nix
index 6f66ec72601d..7ed1ba042756 100644
--- a/lib/testing.nix
+++ b/lib/testing.nix
@@ -27,31 +27,27 @@ rec {
         cp ${./test-driver/Logger.pm} $libDir/Logger.pm
 
         wrapProgram $out/bin/nixos-test-driver \
-          --prefix PATH : "${imagemagick}/bin" \
+          --prefix PATH : "${pkgs.qemu_kvm}/bin:${pkgs.vde2}/bin:${imagemagick}/bin" \
           --prefix PERL5LIB : "${lib.makePerlPath [ perlPackages.TermReadLineGnu perlPackages.XMLWriter ]}:$out/lib/perl5/site_perl"
       '';
   };
 
 
   # Run an automated test suite in the given virtual network.
-  # `network' must be the result of a call to the
-  # `buildVirtualNetwork' function.  `tests' is a Perl fragment
-  # describing the tests.
-  runTests = network: tests:
+  # `driver' is the script that runs the network.
+  runTests = driver:
     stdenv.mkDerivation {
       name = "vm-test-run";
       
       requiredSystemFeatures = [ "kvm" ];
       
-      inherit tests;
-      
-      buildInputs = [ pkgs.qemu_kvm pkgs.libxslt ];
+      buildInputs = [ pkgs.libxslt ];
 
       buildCommand =
         ''
           mkdir -p $out/nix-support
 
-          LOGFILE=$out/log.xml ${testDriver}/bin/nixos-test-driver ${network}/vms/*/bin/run-*-vm || failed=1
+          LOGFILE=$out/log.xml tests="testScript" ${driver}/bin/nixos-test-driver || failed=1
 
           # Generate a pretty-printed log.          
           xsltproc --output $out/log.html ${./test-driver/log2html.xsl} $out/log.xml
@@ -138,10 +134,6 @@ rec {
       then t.testScript { inherit (vms) nodes; }
       else t.testScript;
       
-    test = runTests vms testScript;
-      
-    report = makeReport test;
-
     # Generate a convenience wrapper for running the test driver
     # interactively with the specified network.
     driver = runCommand "nixos-test-driver"
@@ -150,14 +142,19 @@ rec {
       }
       ''
         mkdir -p $out/bin
+        echo "$testScript" > $out/test-script
         ln -s ${vms}/bin/* $out/bin/
         ln -s ${testDriver}/bin/* $out/bin/
         wrapProgram $out/bin/nixos-test-driver \
           --add-flags "${vms}/vms/*/bin/run-*-vm" \
           --run "testScript=\"\$(cat $out/test-script)\"" \
-          --set testScript '"$testScript"'
-        echo "$testScript" > $out/test-script
+          --set testScript '"$testScript"' \
+          --set VLANS '"${toString (map (m: m.config.virtualisation.vlans) (lib.attrValues vms.nodes))}"' \
       ''; # "
+
+    test = runTests driver;
+      
+    report = makeReport test;
   };