[openstack-dev] [neutron] blueprint ovs-firewall-driver: OVS implementation of security groups

Carl Baldwin carl at ecbaldwin.net
Tue Jun 3 14:01:02 UTC 2014

How does ovs handle tcp flows?  Does it include stateful tracking of tcp --
as your wording below implies -- or does it do stateless inspection of
returning tcp packets?  It appears it is the latter.  This isn't the same
as providing a stateful ESTABLISHED feature.  Many users may not fully
understand the differences.

One of the most basic use cases, which is to ping an outside Ip address
from inside a nova instance would not work without connection tracking with
the default security groups which don't allow ingress except related and
established.  This may surprise many.

 Hi all,

 In the Neutron weekly meeting today[0], we discussed the
ovs-firewall-driver blueprint[1]. Moving forward, OVS features today will
give us "80%" of the iptables security groups behavior. Specifically, OVS
lacks connection tracking so it won’t have a RELATED feature or stateful
rules for non-TCP flows. (OVS connection tracking is currently under
development, to be released by 2015[2]). To make the “20%" difference more
explicit to the operator and end user, we have proposed feature
configuration to provide security group rules API validation that would
validate based on connection tracking ability, for example.

 Several ideas floated up during the chat today, I wanted to expand the
discussion to the mailing list for further debate. Some ideas include:
- marking ovs-firewall-driver as experimental in Juno
- What does it mean to be marked as “experimental”?
- performance improvements under a new OVS firewall driver untested so far
(vthapar is working on this)
- incomplete implementation will cause confusion, educational burden
- debugging OVS is new to users compared to debugging old iptables
- waiting for upstream OVS to implement (OpenStack K- or even L- cycle)

 In my humble opinion, merging the blueprint for Juno will provide us a
viable, more performant security groups implementation than what we have
available today.


[1] https://review.openstack.org/#/c/89712/
[2] http://openvswitch.org/pipermail/dev/2014-May/040567.html

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