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Lucas Alvares Gomes 4e325088d3 [OVN] Document Network Availability Zones

This patch adds the documentation to the Network Availability Zones
support in OVN. Instead of having two documentation pages, one for router
AZs and another one for network AZs, this patch merges both guides into
one single documentation. Setting up AZs in OVN is the same for both
types and the differences between the two are documented within their
own sections.

The patch also removes a limitation listed in the SR-IOV documentation
for OVN since we no longer have a default HA Chassis Group. This
limitation was removed as part of the Network AZ work.

Change-Id: I55f27a5473dcd1e6e2255007108c2008acfb6dec
Signed-off-by: Lucas Alvares Gomes <lucasagomes@gmail.com>

2021-08-16 11:59:48 +01:00

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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 at¹.

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 implementation² based on the meter of openvswitch³ 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 Neutron⁵ which is not understood by the OVN driver.
QoS minimum bandwidth allocation in Placement API

ML2/OVN integration with the Nova placement API to provide guaranteed minimum bandwidth for ports⁶.
IPv6 Prefix Delegation

Currently ML2/OVN doesn't implement IPv6 prefix delegation. OVN logical routers have this capability implemented in⁷ and we have an open RFE to fill this gap⁸.
East/West Fragmentation

The core OVN implementation does not support east/west fragmentation. There is no known production use-case for this feature hence we don't even have an RFE open for it and it's not on the roadmap to be implemented.

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Gaps from ML2/OVS

References

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