neutron/doc/source/ovn/gaps.rst
Jakub Libosvar 0817c42799 ovn: Document gap about IPv6 PD in OVN
ML2/OVN currently doesn't support IPv6 prefix delegation. This patch
adds it to the list of gaps.

Change-Id: Icf23cb9113d48322a4ba0db13a55c370e2bb14a4
Signed-off-by: Jakub Libosvar <libosvar@redhat.com>
2020-09-17 14:47:43 +02:00

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.. _ovn_gaps:
Gaps from ML2/OVS
=================
This is a list of some of the currently known gaps between ML2/OVS and OVN.
It is not a complete list, but is enough to be used as a starting point for
implementors working on closing these gaps. A TODO list for OVN is located
at [1]_.
* Security Groups logging API
Currently ML2/OVS, with the OpenvSwitch firewall, supports a log file where
security groups events are logged to be consumed by a security entity. This
allows users to have a way to check if an instance is trying to execute
restricted operations, or access restricted ports in remote servers.
This is a relatively new extension, support would need to be added to OVN.
* QoS DSCP support
Currently ML2/OVS supports QoS DSCP tagging and egress bandwidth limiting.
Those are basic QoS features that while integrated in the OVS/OVN C core
are not integrated (or fully tested) in the neutron OVN mechanism driver.
* QoS for Layer 3 IPs
Currently the Neutron L3-agent supports floating IP and gateway IP bandwidth
limiting based on Linux TC. Networking-ovn L3 had a prototype
implementation [2]_ based on the meter of openvswitch [3]_ utility that
has been abandoned. This is supported in user space datapath only, or
kernel versions 4.15+ [4]_.
* QoS Minimum Bandwidth support
Currently ML2/OVS supports QoS Minimum Bandwidth limiting, but it is
not supported in OVN.
* BGP support
Currently ML2/OVS supports making a tenant subnet routable via BGP, and
can announce host routes for both floating and fixed IP addresses.
* Baremetal provisioning with iPXE
The core OVN DHCP server implementation does not have support for
sending different boot options based on the ``gpxe`` DHCP Option
(no. 175). Also, Ironic uses dnsmasq syntax when configuring the DHCP
options for Neutron [5]_ which is not understood by the OVN driver.
* Availability Zones
Availability zones are used to make network resources highly available
by grouping nodes in separate zones which resources will be scheduled
to. Neutron supports two types of availability zones: Network (DHCP
agent) and router (L3 agent). The OVN team needs to assess each case
to see how they would fit in the OVN model. For example, in the router
availability zone case, the OVN driver should schedule the router
ports on a Chassis (a "node" in OVN terms) where the availability
zones match with the router availability zones [6]_.
* Routed provider networks
Routed provider networks allow for a single provider network to
represent multiple L2 domains (segments). The OVN driver does not
understand this feature yet and will need to account for multiple
physical networks associated with a single OVN Logical Switch (a
network in Neutron terms) [7]_.
* QoS minimum bandwidth allocation in Placement API
ML2/OVN integration with the Nova placement API to provide guaranteed
minimum bandwidth for ports [8]_.
* IPv6 Prefix Delegation
Currently ML2/OVN doesn't implement IPv6 prefix delegation. OVN logical
routers have this capability implemented in [9]_ and we have an open RFE to
fill this gap [10]_.
References
----------
.. [1] https://github.com/ovn-org/ovn/blob/master/TODO.rst
.. [2] https://review.opendev.org/#/c/539826/
.. [3] https://github.com/openvswitch/ovs/commit/66d89287269ca7e2f7593af0920e910d7f9bcc38
.. [4] https://github.com/torvalds/linux/blob/master/net/openvswitch/meter.h
.. [5] https://github.com/openstack/ironic/blob/123cb22c731f93d0c608d791b41e05884fe18c04/ironic/common/pxe_utils.py#L447-L462>
.. [6] https://docs.openstack.org/neutron/latest/admin/config-az.html
.. [7] https://bugs.launchpad.net/neutron/+bug/1865889
.. [8] https://specs.openstack.org/openstack/neutron-specs/specs/rocky/minimum-bandwidth-allocation-placement-api.html
.. [9] https://patchwork.ozlabs.org/project/openvswitch/patch/6aec0fb280f610a2083fbb6c61e251b1d237b21f.1576840560.git.lorenzo.bianconi@redhat.com/
.. [10] https://bugs.launchpad.net/neutron/+bug/1895972