diff --git a/troubleshooting.rst b/troubleshooting.rst
index 0a50212..797c5e2 100644
--- a/troubleshooting.rst
+++ b/troubleshooting.rst
@@ -32,6 +32,142 @@
 - DHCP
 
 
+Network Information Base (NIB)
+==============================
+T3 analyzes network states that are stored in the NIB.
+A NIB is a collection of snapshots captured from various ONOS stores such as flows, groups, links...etc.
+The NIB, acting as a cache, allows T3 troubleshooting logic to avoid massive interaction with live ONOS subsystems,
+enabling near-runtime or postmortem analysis in a production environment.
+
+There are two methods of loading the network snapshots into the NIB:
+(1) from a live running system or (2) from a onos-diagnostics file dump.
+Users can choose one load command before troubleshooting commands,
+or can run troubleshooting commands alone (then the NIB is automatically loaded via (1)).
+
+
+t3-load-file
+=========================
+T3 offers this command to fill the NIB with files that represent snapshots of the network states in a certain time.
+
+t3-load-file Help
+------------------------------
+
+.. code-block:: console
+
+    onos> t3-load-file --help
+    DESCRIPTION
+            onos:t3-load-file
+
+            Load the NIB with onos-diagnostics dump files
+
+    SYNTAX
+            onos:t3-load-file [options] rootDir
+
+    ARGUMENTS
+            rootDir
+                    Specify the location of the directory where the previous onos-diagnostics command has extracted its dump files (e.g. /tmp/onos-diags/127.0.0.1)
+
+    OPTIONS
+            --help
+                    Display this help message
+            -j, --json
+                    Output JSON
+
+t3-load-file Example
+---------------------------------
+User is expected to run the tool ``onos-diagnostics`` [#onos-diagnostics_src]_ [#onos-diagnostics_man]_
+to generate target files first.
+
+.. code-block:: console
+
+    user$ onos-diagnostics -xj [IP_ONOS_INSTANCE_1 IP_ONOS_INSTANCE_2 ...]
+    Collecting diagnostics on [IP_ONOS_INSTANCE_1]...logs netcfg.json devices.json device-drivers.json links.json hosts.json ports.json edge-ports.json flows.json groups.json masters.json routes.json mcast-host-show.json  Done.
+    Collecting diagnostics on [IP_ONOS_INSTANCE_2]...logs netcfg.json devices.json device-drivers.json links.json hosts.json ports.json edge-ports.json flows.json groups.json masters.json routes.json mcast-host-show.json  Done.
+
+Then, execute this command with the path of the location where those JSON files are extracted.
+User can check the creation time and a summary of the NIB contents.
+
+.. code-block:: console
+
+    onos> t3-load-file /tmp/onos-diags/[IP_ONOS_INSTANCE_TARGET]
+    Load target files in: /tmp/onos-diags/[IP_ONOS_INSTANCE_TARGET]/
+    FlowNib created 03-06-2020 01:30 from FILE
+    GroupNib created 03-06-2020 01:30 from FILE
+    LinkNib created 03-06-2020 01:30 from FILE
+    HostNib created 03-06-2020 01:30 from FILE
+    DeviceNib created 03-06-2020 01:30 from FILE
+    DriverNib created 03-06-2020 01:30 from FILE
+    MastershipNib created 03-06-2020 01:30 from FILE
+    EdgePortNib created 03-06-2020 01:30 from FILE
+    RouteNib created 03-06-2020 01:30 from FILE
+    NetworkConfigNib created 03-06-2020 01:30 from FILE
+    MulticastRouteNib created 03-06-2020 01:30 from FILE
+
+t3-load-snapshot
+=============================
+T3 offers this command to fill the NIB with snapshots of the network states at the execution time.
+
+t3-load-snapshot Help
+----------------------------------
+
+.. code-block:: console
+
+    onos> t3-load-snapshot --help
+    DESCRIPTION
+            onos:t3-load-snapshot
+
+            Load the NIB with the network states stored in the ONOS instance where the T3 is running
+
+    SYNTAX
+            onos:t3-load-snapshot [options]
+
+    OPTIONS
+            --help
+                    Display this help message
+            -j, --json
+                    Output JSON
+
+t3-load-snapshot Example
+-------------------------------------
+User can check the creation time and a summary of the NIB contents.
+**SNAPSHOT** indicates that the source of the current NIB is the ONOS instance where the T3 is running.
+
+.. code-block:: console
+
+    onos> t3-load-snapshot
+    Load current network states from ONOS stores
+    FlowNib created 03-06-2020 01:40 from SNAPSHOT
+    GroupNib created 03-06-2020 01:40 from SNAPSHOT
+    LinkNib created 03-06-2020 01:40 from SNAPSHOT
+    HostNib created 03-06-2020 01:40 from SNAPSHOT
+    DeviceNib created 03-06-2020 01:40 from SNAPSHOT
+    DriverNib created 03-06-2020 01:40 from SNAPSHOT
+    MastershipNib created 03-06-2020 01:40 from SNAPSHOT
+    EdgePortNib created 03-06-2020 01:40 from SNAPSHOT
+    RouteNib created 03-06-2020 01:40 from SNAPSHOT
+    NetworkConfigNib created 03-06-2020 01:40 from SNAPSHOT
+    MulticastRouteNib created 03-06-2020 01:40 from SNAPSHOT
+
+If one of T3 commands below is used before loading the NIB from **SNAPSHOT** or **FILE** (so the NIB is empty),
+the command internally executes **t3-load-snapshot** to proceed with auto-filled NIB.
+
+.. code-block:: console
+
+    onos> t3-troubleshoot-simple 00:AA:00:00:00:01/None 00:AA:00:00:00:02/None
+    *** NIB is invalid. Snapshots for the NIB have been auto-filled: ***
+    Load current network states from ONOS stores
+    FlowNib created 03-06-2020 01:44 from SNAPSHOT
+    GroupNib created 03-06-2020 01:44 from SNAPSHOT
+    LinkNib created 03-06-2020 01:44 from SNAPSHOT
+    ...
+    Tracing between: 00:AA:00:00:00:01/None and 00:AA:00:00:00:02/None
+    Tracing Packet: DefaultTrafficSelector{criteria=[IN_PORT:3, ETH_DST:00:00:00:00:02:04, ETH_TYPE:ipv4, VLAN_VID:None, IPV4_SRC:10.0.2.1/32, IPV4_DST:10.0.2.2/32]}
+    Paths
+    [of:0000000000000204/3, of:0000000000000204/4]
+    Result:
+    Reached required destination Host of:0000000000000204/4
+
+
 t3-troubleshoot
 ===============
 
@@ -618,7 +754,7 @@
     DESCRIPTION
             onos:t3-troubleshoot-mcast
 
-     Traces all the mcast routes present in the system
+        Traces all the mcast routes present in the system
 
     SYNTAX
             onos:t3-troubleshoot-mcast [options]
@@ -681,12 +817,13 @@
 
 - **Diagnostics**.
 
-  We have built a tool ``onos-diagnostics`` (see `ONOS Remote Admin Tools
-  <https://wiki.onosproject.org/display/ONOS/ONOS+Remote+Admin+Tools>`_) to
-  help you easily collect and package ONOS diagnostics
+We have built a tool ``onos-diagnostics`` [#onos-diagnostics_src]_ [#onos-diagnostics_man]_
+to help you easily collect and package ONOS diagnostics
 
 
 Reference
 =========
 
+.. [#onos-diagnostics_src] `<https://github.com/opennetworkinglab/onos/blob/master/tools/package/runtime/bin/onos-diagnostics>`_
+.. [#onos-diagnostics_man] `<https://wiki.onosproject.org/display/ONOS/ONOS+Remote+Admin+Tools>`_
 .. [#trellis.py] `<https://github.com/opennetworkinglab/routing/blob/master/trellis/trellis.py>`_