openstack/neutron
Code Issues Proposed changes

ovn: Document fragmentation / pmtud gaps

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OVN does not correctly fragment packets or send ICMP
"packet too big" responses that would allow pmtud to work.

Related-Bug: #2032817
Change-Id: Ibc19ec6a9625124fb19e33c3bd6af40266aa5003
This commit is contained in:
Dr. Jens Harbott 2023-08-27 15:25:06 +02:00 committed by Brian Haley
parent 0e5c91c499
commit e4542bca80
1 changed files with 23 additions and 6 deletions

29
doc/source/ovn/gaps.rst

@ -28,12 +28,6 @@ at [1]_.
routers have this capability implemented in [4]_ and we have an open RFE to
fill this gap [5]_.
* 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.
* DHCP service for instances
ML2/OVS adds packet filtering rules to every instance that allow DHCP queries
@ -71,6 +65,26 @@ at [1]_.
The OVN metadata agent currently does not allow access via IPv6.
* East/West Fragmentation
The core OVN implementation does not support fragmentation of East/West
traffic using an OVN router between two private networks. This is being
tracked in [9]_ and [10]_.
* North/South Fragmentation and path MTU discovery
OVN does not correctly fragment IPv4 packets when the MTU of the target
network is smaller than the MTU of the source network. Instead, affected
packets could be silently dropped depending on the direction. OVN will
also not generate ICMP "packet too big" responses for packets that have
the DF bit set, even when the necessary configuration option is used
in ``ml2_conf.ini``::
[ovn]
ovn_emit_need_to_frag = true
This makes path MTU discovery fail, and is being tracked in [9]_ and [11]_.
References
----------
@ -82,3 +96,6 @@ References
.. [6] https://bugs.launchpad.net/neutron/+bug/1926515
.. [7] https://review.opendev.org/c/openstack/neutron/+/788594
.. [8] https://docs.openstack.org/neutron/latest/admin/config-dns-res.html
.. [9] https://bugs.launchpad.net/neutron/+bug/2032817
.. [10] https://bugzilla.redhat.com/show_bug.cgi?id=2238494
.. [11] https://bugzilla.redhat.com/show_bug.cgi?id=2238969