fix bug when looking up one vtn
diff --git a/xos/core/xoslib/methods/vtn.py b/xos/core/xoslib/methods/vtn.py
index 14dd458..1a2af53 100644
--- a/xos/core/xoslib/methods/vtn.py
+++ b/xos/core/xoslib/methods/vtn.py
@@ -55,7 +55,7 @@
 
     def get_service(self, request, pk=None, service=None):
         for xos_service in Service.objects.all():
-            if service in xos_service.get_vtn_ids():
+            if service in xos_service.get_vtn_src_ids():
                 return Response(xos_service.get_vtn_dependencies_ids())
         raise DoesNotExist()