string destination_address = host->get_address();
         uint16_t destination_port = host->get_port();
         string host_network_interface = host->get_source_network_interface();
-        string network_interface = ( default_network_interface.empty() ) ?
-                host_network_interface :
-                default_network_interface;
+        string network_interface = ( host_network_interface == "default" ) ?
+                default_network_interface :
+                host_network_interface;
         PingProtocolList protocol_list = host->get_ping_protocol_list();
         int ping_interval_in_sec = host->get_interval_in_sec();
         PingSchedulerItem scheduler(