[ovs-discuss] ovs fragment handling

Ben Pfaff blp at ovn.org
Tue Jul 2 17:33:33 UTC 2019

On Mon, Jul 01, 2019 at 10:00:15AM +0000, pei Jikui wrote:
> I have a question about how the ovs handling the ip fragments that is
> it possible that different actions will be enforced to the first
> fragment and the upcoming ones?
> For example, if we have an openflow rule to define the action A for
> udp packet with destination port 123. We also have the default
> "normal" action for the fragments.
> For this case, the action A will be conducted to the first ip fragment
> which has the udp destination port 123, and the action normal will be
> enforced to the other fragments?

The answer depends on how you configure Open vSwitch.  By default, OVS
treats all fragments (first or later) as if their L4 ports were zeroed.
This ensures that all associated fragments will be treated the same way.
But you can configure other modes.  I recommend reading the description
of the nw_frag field in ovs-fields(7), for complete information.

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