OFAgent: Merge br-int and br-tun

Change-Id: I7d7dd17a7938d67627e817a6e5c6310c320e638c

specs/juno/ofagent-merge-bridges.rst

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+..
+ This work is licensed under a Creative Commons Attribution 3.0 Unported
+ License.
+
+ http://creativecommons.org/licenses/by/3.0/legalcode
+
+==========================================
+OFAgent: Merge br-int and br-tun
+==========================================
+
+https://blueprints.launchpad.net/neutron/+spec/ofagent-merge-bridges
+
+merge br-int and br-tun and stop using OVS patch ports feature.
+this involves drastic flow table changes.
+
+Problem description
+===================
+
+ofagent aims to be portable among switch implementations.
+currently it uses some of OVS specific features.
+patch ports is one of them.
+
+Proposed change
+===============
+
+merge br-int and br-tun into a single bridge.
+
+Alternatives
+------------
+
+* give up and declare that tunnel support is only for OVS.  this is not
+  what we want to do.
+
+* use veth pair instead.  this is not ideal as it still requires
+  multiple logical bridge feature.  besides that, it likely involve
+  some performance loss because patch ports is better optimized than
+  veth pair.
+
+Data model impact
+-----------------
+
+none
+
+REST API impact
+---------------
+
+none
+
+Security impact
+---------------
+
+none
+
+Notifications impact
+--------------------
+
+none
+
+Other end user impact
+---------------------
+
+none
+
+Performance Impact
+------------------
+
+because OVS patch ports hardly have negative performace effects for fast path,
+this change is not expected to improve performance.
+
+Other deployer impact
+---------------------
+
+when upgrading the agent, deployer might want to remove br-tun.
+
+Developer impact
+----------------
+
+none
+
+Implementation
+==============
+
+Assignee(s)
+-----------
+
+Primary assignee:
+  yamamoto
+
+Other contributors:
+  kakuma
+
+Work Items
+----------
+
+* design flow table.  see `flow_table`_ for WIP design.
+
+.. _flow_table: https://wiki.openstack.org/wiki/Neutron/OFAgent/FlowTable
+
+* implement it in ofagent neutron agent
+
+* document the upgrade procedure
+
+Dependencies
+============
+
+strictly speaking, none.
+but the following items are nice to have before this.
+
+* `ofagent-l2pop`_ blueprint (our WIP implementation relies on this)
+
+.. _ofagent-l2pop: https://blueprints.launchpad.net/neutron/+spec/l2-population
+
+* matrohon's `get_device_details-enhancement`_.
+  or other way to obtain device's mac_address.
+  (for example, make l2pop provide device-id for entries.)
+  we want to use it for node local routing of packets.
+
+.. _get_device_details-enhancement: https://review.openstack.org/#/c/96181/
+
+Testing
+=======
+
+* unit tests
+
+* existing third party testing
+
+Documentation Impact
+====================
+
+* document the upgrade procedure
+
+References
+==========
+
+* WIP flow table for this blueprint
+  https://wiki.openstack.org/wiki/Neutron/OFAgent/FlowTable
+
+* WIP implementation of the above
+  https://github.com/yamt/neutron/tree/ofagent-merge-bridges
+