Add top level content for configuration and testing

Change-Id: I710f402988fe0c6c6fa6c4b100fbfa752e8835ee
diff --git a/configuration.rst b/configuration.rst
index 7870475..6119f31 100644
--- a/configuration.rst
+++ b/configuration.rst
@@ -1,6 +1,24 @@
 Configuration Guide
 ===================
 
+There are several different types of configuration we use in SD-Fabric.
+We will explain every configuration in this section.
+
+Control plane configurations,
+including configuration for ONOS and SD-Fabric applications (``SegmentRouting``, ``UP4``, ``INT``)
+can be categorized as **network configuration** (sometimes shortened as ``netcfg``) and **component configuration**.
+
+  - **Network configurations** are network-related attributes,
+    including device, subnet, VLAN, routes...etc.
+  - **Component conofigurations** are application component attributes,
+    including feature flags, polling intervals, timeouts...etc.
+
+Data plane configurations, including port speed, breakout channel and queue configurations
+are done in Stratum **chassis config**.
+
+We have implemented config pusher in both ONOS and Stratum helm chart,
+fetching and applying configurations automatically once the system is ready.
+
 .. toctree::
    :maxdepth: 2
    :glob: