openstack/neutron
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Update OVN gap document

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Signed-off-by: Dr. Jens Harbott <harbott@osism.tech>
Change-Id: Ifa315feac2702c305949363b201e8a0ceabf2507
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Dr. Jens Harbott 2021-11-22 12:02:16 +01:00
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doc/source/ovn/gaps.rst
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@ -28,8 +28,9 @@ at [1]_.
* 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.
Neutron-dynamic-routing supports making a tenant subnet routable via BGP, and
can announce host routes for both floating and fixed IP addresses. These
functions are not supported in OVN.
* Baremetal provisioning with iPXE
@ -55,6 +56,27 @@ at [1]_.
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.
* DHCP service for instances
ML2/OVS adds packet filtering rules to every instance that allow DHCP queries
from instances to reach the DHCP agent. For OVN this traffic has to be explicitly
allowed by security group rules attached to the instance. Note that the default
security group does allow all outgoing traffic, so this only becomes relevant
when using custom security groups [6]_.
* DNS resolution for instances
OVN cannot use the host's networking for DNS resolution, so Case 2b in [7]_ can
only be used when additional DHCP agents are deployed. For Case 2a a different
configuration option has to be used in ``ml2_conf.ini``::
[ovn]
dns_servers = 203.0.113.8, 198.51.100.53
Note that this option currently only works for IPv4 nameservers [8]_.
In addition, with ML2/OVS setting the name-server option for a subnet to ``0.0.0.0``
or ``::`` respectively has the effect that no nameservers are announced via DHCP for
this subnet. This currently does not work with OVN [9]_.
References
----------
@ -64,3 +86,7 @@ References
.. [3] https://specs.openstack.org/openstack/neutron-specs/specs/rocky/minimum-bandwidth-allocation-placement-api.html
.. [4] https://patchwork.ozlabs.org/project/openvswitch/patch/6aec0fb280f610a2083fbb6c61e251b1d237b21f.1576840560.git.lorenzo.bianconi@redhat.com/
.. [5] https://bugs.launchpad.net/neutron/+bug/1895972
.. [6] https://bugs.launchpad.net/neutron/+bug/1926515
.. [7] https://docs.openstack.org/neutron/latest/admin/config-dns-res.html
.. [8] https://bugs.launchpad.net/neutron/+bug/1951816
.. [9] https://bugs.launchpad.net/neutron/+bug/1950686