Merge "DHCP port per lswitch spec "

doc/source/specs/dhcp_port_per_network.rst

@@ -0,0 +1,89 @@
+=====================
+DHCP port per network
+=====================
+
+Problem Description
+===================
+
+Currently dragonflow creates one dhcp-port per enable-dhcp-subnet.
+
+DF does not save information about packet subnet in the ovs metadata/registers.
+For forwarding packets toward the dhcp-port its needs to install flow for
+each port in the subnet.
+
+This behaviour causes complexity in the code and create a performance penalty,
+that because every change in subnet (updated/add/delete/enabled-dhcp/disabled-dhcp)
+raises the need to do diff with the previous state, and install/remove all relevant flows.
+
+Proposed Change
+===============
+
+Instead of creating dhcp-port per subnet, DF will create one port per
+enabled-dhcp network (when enabled-dhcp-network defined as a network that
+have at least one enable-dhcp-subnet).
+
+This port will contain multiple ips - one for each dhcp subnet that
+connected to the port. All port CUD operation will done with neutron
+plugin for using it's ip-address-managemnt.
+
+Neutron data-model impact
+-------------------------
+Instead of one dhcp logical port subnet, there will be
+one dhcp-port per network.That port will be connected to all enabled-dhcp-subnet,
+and will hold an ip for each subnet (The port owner will remain "neutron:dhcp").
+
+Dragonflow data-model impact
+----------------------------
+Instead dhcp-lport per logical-subnet, there will be one dhcp-port
+per logical-switch. enable_dhcp trait will be removed from logical-subnet.
+(an upgrade code should be supplied).
+
+Dragonflow controller impact
+----------------------------
+For forwarding the dhcp requests to the controller - the dhcp-app will install
+one flow per lswitch (The lswitch can be identified in the ovs tables
+by the OXM_OF_METADATA field).
+
+when packets arrived to the dhcp-app,  the subnet of the packets
+will be identified by the lport (that information stored in reg6).
+Packets that belong to subnet that not enabled dhcp will be dropped.
+
+Advantage of that change
+------------------------
+
+* Remove the code complication that described above
+
+* Reduce mumber of flows in dhcp tables
+
+* Reduce the number of lports in the DB
+
+
+Separate the DHCP logic
+=======================
+
+As part of the effort to reduce the coupling between components in
+the system, this spec suggests moving all the dhpc-logic from the
+mech_driver code to a separate code module.
+
+This module will be invoked by the ml2-driver, and will function
+independently. It's will use neutron registry _[1] for subscribing
+to sunbet and lswitch CUD event's, and will be responsible to maintain
+the dhcp-port according to the logic that described above.
+
+
+References
+==========
+.. [1] https://docs.openstack.org/neutron-lib/latest/contributor/callbacks.html
+
+
+
+
+
+
+
+
+
+
+
+
+

doc/source/specs/index.rst

@@ -74,6 +74,7 @@ Specs
     tunneling_app
     logical_port_locality
     extra_dhcp_opts
+    dhcp_port_per_network
 
 Templates
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