diff --git a/Rantfile b/Rantfile
index 53d1f4b51..38aea0991 100644
--- a/Rantfile
+++ b/Rantfile
@@ -573,6 +573,12 @@ gen DirectedRule, topology_examples_objects_dir => [ topology_examples_source_di
   sys "gcc -I#{ Trema.include } -I#{ Trema.openflow } #{ var :CFLAGS } -c -o #{ t.name } #{ t.source }"
 end
 
+enable_discovery_objects = [
+  "enable_discovery.o",
+].collect do | each |
+  File.join topology_examples_objects_dir, each
+end
+
 show_topology_objects = [
   "show_topology.o",
 ].collect do | each |
@@ -586,6 +592,7 @@ show_switch_status_objects = [
 end
 
 topology_examples_binaries = {
+  "enable_discovery" => enable_discovery_objects,
   "show_topology" => show_topology_objects,
   "show_switch_status" => show_switch_status_objects,
 }
diff --git a/features/examples/topology.show_switch_status.feature b/features/examples/topology.show_switch_status.feature
index 26b267af0..b1ae61122 100644
--- a/features/examples/topology.show_switch_status.feature
+++ b/features/examples/topology.show_switch_status.feature
@@ -5,9 +5,13 @@ Feature: show_switch_status example.
   show_switch_status command will query for all the switch and port information 
   that the topology daemon hold and print them to standard output.
 
+  Background: 
+    Given I cd to "../../src/examples/topology/"
+
   @slow_process
   Scenario: [C API] Show switch and port information obtained from topology.
-    Given a file named "topology.conf" with:
+    Given I compile "show_switch_status.c" into "show_switch_status"
+    Given a file named "show_switch_status.conf" with:
       """
       vswitch("topology1") { datapath_id "0xe0" }
       vhost ("host1") {
@@ -24,23 +28,11 @@ Feature: show_switch_status example.
       
       link "topology1", "host1"
       link "topology1", "host2"
-      
-      run {
-        path "../../objects/topology/topology"
-        options "--always_run_discovery"
-      }
-      
-      run {
-        path "../../objects/examples/dumper/dumper"
-      }
-      
-      event :port_status => "topology", :packet_in => "filter", :state_notify => "topology"
-      filter :lldp => "topology", :packet_in => "dumper"
       """
-    And I run `trema run -c topology.conf -d`
-    And wait until "topology" is up
-    And *** sleep 16 ***
-    When I run `trema run ../../objects/examples/topology/show_switch_status`
+    And I run `trema run ../repeater_hub/repeater-hub.rb -c show_switch_status.conf -d`
+    And I run `trema run "../../../objects/topology/topology -d"`
+    And *** sleep 4 ***
+    When I run `trema run ./show_switch_status`
     Then the output should contain:
       """
       Switch status
@@ -50,5 +42,5 @@ Feature: show_switch_status example.
       """
       Port status
       """
-    And the output should match /dpid : 0xe0, port : 1\(.+\), status : up, external : true/
-    And the output should match /dpid : 0xe0, port : 2\(.+\), status : up, external : true/
+    And the output should match /  dpid : 0xe0, port : 1\(.+\), status : up, external : (true|false)/
+    And the output should match /  dpid : 0xe0, port : 2\(.+\), status : up, external : (true|false)/
diff --git a/features/examples/topology.show_topology.feature b/features/examples/topology.show_topology.feature
index 17b29e63d..4791bbb29 100644
--- a/features/examples/topology.show_topology.feature
+++ b/features/examples/topology.show_topology.feature
@@ -1,13 +1,26 @@
-Feature: show topology
-
-  As a Trema user
-  I want to control multiple openflow switches using topology application
-  So that I can show topology
+Feature: show_topology example.
+  
+  show_topology is a simple usage example of topology C API.
+  
+  show_topology command will query for all the link information that 
+  the topology daemon hold and print them in trema network DSL style.
+  
+  Topology daemon's link discovery feature must be enabled prior to running 
+  show_topology command in order to obtain non-empty result.
+  
+  Topology daemon's link discovery feature can be enabled 
+  by specifing "--always_run_discovery" option when starting topology daemon,
+  or by calling enable_topology_discovery() API from client application.  
+  
 
+  Background: 
+    Given I cd to "../../src/examples/topology/"
 
   @slow_process
-  Scenario: Four openflow switches, four servers
-    Given a file named "topology.conf" with:
+  Scenario: [C API] Show discovered link topology. (Directly start topology daemon)
+    Given I compile "show_topology.c" into "show_topology"
+    Given I compile "enable_discovery.c" into "enable_discovery"
+    Given a file named "show_topology.conf" with:
       """
       vswitch("topology1") { datapath_id "0x1" }
       vswitch("topology2") { datapath_id "0x2" }
@@ -20,23 +33,82 @@ Feature: show topology
       link "topology2", "topology3"
       link "topology2", "topology4"
       link "topology3", "topology4"
-      
-      run {
-        path "../../objects/topology/topology"
-        options "--always_run_discovery"
+      """
+    And I run `trema run ../repeater_hub/repeater-hub.rb -c show_topology.conf -d`
+    And I run `trema run "../../../objects/topology/topology -d --always_run_discovery"`
+    And *** sleep 4 ***
+    When I run `trema run ./show_topology`
+    Then the output should contain:
+      """
+      vswitch {
+        datapath_id "0x2"
       }
-      
-      run {
-        path "../../objects/examples/dumper/dumper"
+      """
+    And the output should contain:
+      """
+      vswitch {
+        datapath_id "0x3"
       }
+      """
+    And the output should contain:
+      """
+      vswitch {
+        datapath_id "0x1"
+      }
+      """
+    And the output should contain:
+      """
+      vswitch {
+        datapath_id "0x4"
+      }
+      """
+    And the output should contain:
+      """
+      link "0x2", "0x1"
+      """
+    And the output should contain:
+      """
+      link "0x3", "0x2"
+      """
+    And the output should contain:
+      """
+      link "0x3", "0x1"
+      """
+    And the output should contain:
+      """
+      link "0x4", "0x2"
+      """
+    And the output should contain:
+      """
+      link "0x4", "0x3"
+      """
+    And the output should contain:
+      """
+      link "0x4", "0x1"
+      """
+
+  @slow_process
+  Scenario: [C API] Show discovered link topology. (Enable link discovery by API)
+    Given I compile "show_topology.c" into "show_topology"
+    Given I compile "enable_discovery.c" into "enable_discovery"
+    Given a file named "show_topology.conf" with:
+      """
+      vswitch("topology1") { datapath_id "0x1" }
+      vswitch("topology2") { datapath_id "0x2" }
+      vswitch("topology3") { datapath_id "0x3" }
+      vswitch("topology4") { datapath_id "0x4" }
       
-      event :port_status => "topology", :packet_in => "filter", :state_notify => "topology"
-      filter :lldp => "topology", :packet_in => "dumper"
+      link "topology1", "topology2"
+      link "topology1", "topology3"
+      link "topology1", "topology4"
+      link "topology2", "topology3"
+      link "topology2", "topology4"
+      link "topology3", "topology4"
       """
-      And I run `trema run -c topology.conf -d`
-      And wait until "topology" is up
-      And *** sleep 4 ***
-      And I run `trema run ../../objects/examples/topology/show_topology`
+    And I run `trema run ../repeater_hub/repeater-hub.rb -c show_topology.conf -d`
+    And I run `trema run "./enable_discovery"`
+    And *** sleep 4 ***
+    When I run `trema run ./show_topology`
     Then the output should contain:
       """
       vswitch {
@@ -85,5 +157,3 @@ Feature: show topology
       """
       link "0x4", "0x1"
       """
-
-
diff --git a/src/examples/topology/.gitignore b/src/examples/topology/.gitignore
new file mode 100644
index 000000000..585d6b5ef
--- /dev/null
+++ b/src/examples/topology/.gitignore
@@ -0,0 +1,6 @@
+enable_discovery
+show_topology
+show_topology.conf
+show_switch_status
+show_switch_status.conf
+
diff --git a/src/examples/topology/README.md b/src/examples/topology/README.md
index bb4c8ef1c..94a9e6c04 100644
--- a/src/examples/topology/README.md
+++ b/src/examples/topology/README.md
@@ -9,14 +9,17 @@ This directory includes sample application using libtopology.
 - `show_swith_status` is a command line application, which retrieves 
   switch and port information from Topology daemon and print them to stdout.
 
+- `enable_discovery` is a command line application, which enables
+  link discovery feature using the topology API.
+
 
         +----------+           +-----------+           +------+    +------------------+
         |  switch  |  *    1   | packet in |  1    *   |dumper|    |show_topology/    |
         |  daemon  | --------> |  filter   | --------> |      |    |show_switch_status|
         +----------+ packet in +-----------+ packet in +------+    +------------------+
           ^ 1    ^                       |                               * ^ 
-          |      |                       |                     libtopology | 
-          |      `-------.               |                                 |
+          |      |                       |                                 | 
+          |      `-------.               |                    topology API |
           v 1            |               |                               1 v 
         +----------+     |               |   packet in(LLDP)        +-----------+
         | openflow |     |               `------------------------->| topology  |
@@ -32,19 +35,31 @@ How to run
         $ cd $TREMA_HOME
         $ ./build.rb
 
-2. Start topology daemon
+2. Start network to discover
+
+        $ ./trema run ./objects/examples/dumper/dumper -c src/examples/topology/topology_fullmesh.conf &
+ 
+   # dumper is used in the above example, only because trema cannot run without 
+   # any controller specified.
+
+3. Enable link discovery feature
+   by adding "--always_run_discovery" option when starting topology
+
+        $ ./trema run ./objects/examples/topology/topology -d --always_run_discovery
+
+   Or by using API call.
 
-        $ ./trema run -c src/examples/topology/topology_fullmesh.conf &
+        $ ./trema run ./objects/examples/topology/enable_discovery
 
-3. Run show_topology/show_switch_status from trema run 
+4. Run show_topology/show_switch_status from trema run 
 
         $ ./trema run objects/examples/topology/show_topology
         $ ./trema run objects/examples/topology/show_switch_status
 
    Or invoke each commands directly
 
-        $ env TREMA_HOME=`pwd` objects/examples/topology/show_topology
-        $ env TREMA_HOME=`pwd` objects/examples/topology/show_switch_status
+        $ env TREMA_HOME=`pwd` src/examples/topology/show_topology
+        $ env TREMA_HOME=`pwd` src/examples/topology/show_switch_status
 
 
 License & Terms
diff --git a/src/examples/topology/enable_discovery.c b/src/examples/topology/enable_discovery.c
new file mode 100644
index 000000000..464f605d0
--- /dev/null
+++ b/src/examples/topology/enable_discovery.c
@@ -0,0 +1,77 @@
+/*
+ * Copyright (C) 2012 NEC Corporation
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License, version 2, as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+
+#include <assert.h>
+#include <getopt.h>
+#include <stdio.h>
+#include <unistd.h>
+#include "trema.h"
+
+
+void
+usage() {
+  topology_service_interface_usage( get_executable_name(), "Show switch status", NULL );
+}
+
+
+static void
+timed_out( void *user_data ) {
+  UNUSED( user_data );
+
+  error( "timed out." );
+
+  stop_trema();
+}
+
+
+static void
+result_response( void *user_data, const topology_response *res ) {
+  UNUSED( user_data );
+  if ( res->status != TD_RESPONSE_OK ) {
+    error( "Enable topology discovery failed" );
+  } else {
+    info( "Enabled topology discovery" );
+  }
+  stop_trema();
+}
+
+int
+main( int argc, char *argv[] ) {
+  init_trema( &argc, &argv );
+  init_topology_service_interface_options( &argc, &argv );
+  init_libtopology( get_topology_service_interface_name() );
+
+  enable_topology_discovery( result_response, NULL );
+
+  add_periodic_event_callback( 15, timed_out, NULL );
+
+  start_trema();
+
+  finalize_libtopology();
+  finalize_topology_service_interface_options();
+
+  return 0;
+}
+
+
+/*
+ * Local variables:
+ * c-basic-offset: 2
+ * indent-tabs-mode: nil
+ * End:
+ */
diff --git a/src/examples/topology/topology.conf b/src/examples/topology/topology.conf
index 361183a1c..40bc482f9 100644
--- a/src/examples/topology/topology.conf
+++ b/src/examples/topology/topology.conf
@@ -17,15 +17,3 @@ vhost ("host2") {
 link "0xe0", "host1"
 link "0xe0", "host2"
 
-
-run {
-  path "./objects/topology/topology"
-  options "--always_run_discovery"
-}
-
-run {
-  path "./objects/examples/dumper/dumper"
-}
-
-event :port_status => "topology", :packet_in => "filter", :state_notify => "topology"
-filter :lldp => "topology", :packet_in => "dumper"
diff --git a/src/examples/topology/topology_fullmesh.conf b/src/examples/topology/topology_fullmesh.conf
index eda464f8a..17d4bed98 100644
--- a/src/examples/topology/topology_fullmesh.conf
+++ b/src/examples/topology/topology_fullmesh.conf
@@ -48,15 +48,3 @@ link "0xe0", "0xe3"
 link "0xe1", "0xe2"
 link "0xe1", "0xe3"
 link "0xe2", "0xe3"
-
-run {
-  path "./objects/topology/topology"
-  options "--always_run_discovery"
-}
-
-run {
-  path "./objects/examples/dumper/dumper"
-}
-
-event :port_status => "topology", :packet_in => "filter", :state_notify => "topology"
-filter :lldp => "topology", :packet_in => "dumper"
diff --git a/src/lib/topology.c b/src/lib/topology.c
index 92f86f344..76e4326c5 100644
--- a/src/lib/topology.c
+++ b/src/lib/topology.c
@@ -25,6 +25,10 @@
 #include <sys/time.h>
 #include <unistd.h>
 #include <netinet/in.h>
+#include <errno.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <dirent.h>
 #include "trema.h"
 #include "topology.h"
 
@@ -536,6 +540,86 @@ check_transaction_table( void *user_data ) {
 }
 
 
+static const char TOPOLOGY_DAEMON_PATH[] = "objects/topology/topology";
+
+static void
+maybe_start_topology_daemon( const char* service_name ) {
+  // topology daemon process check
+  if ( get_trema_process_from_name( service_name ) > 0 ) {
+    return;
+  }
+  // topology daemon not running
+
+  pid_t pid = fork();
+  if ( pid < 0 ) {
+    error( "Failed to fork. %s.", strerror( errno ) );
+    return;
+  }
+
+  if ( pid == 0 ) {
+    // child process
+
+    // close all open fd
+    DIR* dir = opendir( "/proc/self/fd" );
+    if ( dir == NULL ) {
+      error( "Failed to opendir. %s.", strerror( errno ) );
+    } else {
+      struct dirent *entry;
+      while ( ( entry = readdir( dir ) ) != NULL ) {
+        int openfd = atoi( entry->d_name );
+        close( openfd );
+      }
+      closedir( dir );
+      dir = NULL;
+    }
+
+    // exec
+    int in_fd = open( "/dev/null", O_RDONLY );
+    if ( in_fd != 0 ) {
+      dup2( in_fd, 0 );
+      close( in_fd );
+    }
+    int out_fd = open( "/dev/null", O_WRONLY );
+    if ( out_fd != 1 ) {
+      dup2( out_fd, 1 );
+      close( out_fd );
+    }
+    int err_fd = open( "/dev/null", O_WRONLY );
+    if ( err_fd != 2 ) {
+      dup2( err_fd, 2 );
+      close( err_fd );
+    }
+    char* daemon_path = xasprintf( "%s/%s", get_trema_home(),
+                                   TOPOLOGY_DAEMON_PATH );
+    char arg_daemonize[ ] = "-d";
+    char arg_name[ ] = "-n";
+    char* arg_name_opt = xstrdup( service_name );
+
+    char* argv[ 4 ];
+    argv[ 0 ] = daemon_path;
+    argv[ 1 ] = arg_daemonize;
+    argv[ 2 ] = arg_name;
+    argv[ 3 ] = arg_name_opt;
+
+    execvp( daemon_path, argv );
+    int err = errno;
+    error( "Failed to execvp: %s %s %s %s. %s.", argv[ 0 ], argv[ 1 ],
+           argv[ 2 ], argv[ 3 ], strerror( err ) );
+
+//      xfree( daemon_path );
+//      xfree( arg_name_opt );
+    UNREACHABLE();
+  } else {
+    // parent process
+    // wait for topology daemon to start
+    int try = 0;
+    const int max_try = 5;
+    while ( get_trema_process_from_name( service_name ) == -1 && ++try <= max_try ) {
+      sleep( 1 );
+    }
+  }
+}
+
 bool
 init_libtopology( const char *service_name ) {
   if ( topology_name != NULL || libtopology_queue_name != NULL ) {
@@ -543,6 +627,8 @@ init_libtopology( const char *service_name ) {
     return false;
   }
 
+  maybe_start_topology_daemon( service_name );
+
   const size_t server_name_len = strlen( service_name ) + strlen( ".t" ) + 1;
   if ( server_name_len > MESSENGER_SERVICE_NAME_LENGTH ) {
     die( "Service name too long to create topology service name ( %s ).", service_name );
diff --git a/unittests/lib/libtopology_test.c b/unittests/lib/libtopology_test.c
index e44b08d43..d51374670 100644
--- a/unittests/lib/libtopology_test.c
+++ b/unittests/lib/libtopology_test.c
@@ -1304,7 +1304,16 @@ main() {
 
     unit_test( test_respond_to_ping_from_topology ),
   };
+  setenv( "TREMA_HOME", ".", 0);
+  // call before leak detector to suppress false leak detection
+  pid_t pid = get_trema_process_from_name( TOPOLOGY_BASE_NAME );
+  if ( pid > 0 ) terminate_trema_process( pid ) ;
+
   setup_leak_detector();
-  return run_tests( tests );
+  int test_result = run_tests( tests );
+
+  pid = get_trema_process_from_name( TOPOLOGY_BASE_NAME );
+  if ( pid > 0 ) terminate_trema_process( pid ) ;
+  return test_result;
 }