Add Distributed DHCP documentation

Change-Id: I72428555cfddadab61b750b7ff6b8a825a8a83e6

doc/source/distributed_dhcp.rst

@@ -0,0 +1,50 @@
+==================
+Distributed DHCP
+==================
+
+Current Neutron Reference Implementation
+=========================================
+The DHCP server is implemented using the Dnsmasq server
+running in a namespace on the newtork-node per tenant subnet
+that is configured with DHCP enabled.
+
+Currently High availability is achieved by running multiple Dnsmasq
+servers on multiple Network nodes.
+
+There is a namespace with Dnsmasq server per tenant subnet
+
+Problems with current DHCP implementation:
+
+1) Management and Scalability
+   - Need to configure and mange multiple Dnsmasq instances
+2) Centralize solution depended on the network node
+
+DHCP agent
+-----------
+Same Concept as L3 agent and namespaces for virtual router.
+Using black boxes that implement functionality and using them as the IaaS
+backbone implementation
+
+
+Distributed DHCP In Dragonflow
+===============================
+Dragonflow distribute DHCP policy/configuration using the pluggable DB.
+Each controller read this DB and install hijacking OVS flows for DHCP traffic
+and send that traffic to the controller.
+
+The controller dispatch this to the local DHCP application which answer with local
+DHCP acks.
+
+The following diagrams demonstrate this process:
+
+.. image:: https://raw.githubusercontent.com/openstack/dragonflow/master/doc/images/dhcp1.jpg
+    :alt: Distributed DHCP 1
+    :width: 600
+    :height: 525
+    :align: center
+
+.. image:: https://raw.githubusercontent.com/openstack/dragonflow/master/doc/images/dhcp2.jpg
+    :alt: Distributed DHCP 1
+    :width: 600
+    :height: 525
+    :align: center

doc/source/distributed_dragonflow.rst

@@ -82,6 +82,7 @@ Dragonflow Pluggable DB
 
 Distributed DHCP Application
 ============================
+`Distributed DHCP Application <https://github.com/openstack/dragonflow/tree/master/doc/source/distributed_dhcp.rst>`_
 
 Containers and Dragonflow
 =========================

doc/source/index.rst

@@ -15,6 +15,7 @@ Contents:
    installation
    centralized_dragonflow
    distributed_dragonflow
+   distributed_dhcp
    usage
    contributing