Hi Ben,
Thank you very much for your answers. I have some comments that you can
find inline.
Again, thank you very much for your time and attention.
Regards,
Jordi
On 19/11/2020 18:35, Ben Pfaff wrote:
On Thu, Nov 19, 2020 at 12:20:01PM +0100, Jordi Baranda wrote:
If I use break-before-make, there is no problem because I replace the rules
and that is. However for the make-before-break approach, I foresee that there
will be some flow rules with the same match fields but different action
fields. (e.g, t0: in_port: 3 -> out_port: 2 vs t1: in_port: 3 -> out_port:4,
where t0 means time0 and t1 means time1 and t1 > t0 (older time instant) ). I
know I could handle that with priorities but I think this may add further
complexity to the SDN controller app.
I don't think this makes any sense. You cannot have two flows in a
table with the same match fields and the same priority. Those are the
same flow, and it has either one set of actions or another.
Yes, I understand. These entries will coexist for short time due to the
make-before-break approach. I will install the "new rule" with the same
match and different action and then remove the "old rule". My question
as you well described bellow is what happens while they coexist.
I am wondering if I can skip this treatment at the SDN controller app making
use of how OVS applies/evaluates rules in the flow table. More specifically,
rules in the flow table of OVS (for the same priority) are evaluated in any
time order? That is, OVS is considering "t1 rule" (which is more recent than
the one of t0) before than "t0 rule" (however, t0 rule will be erased
afterwards)? Or are the flow-rules in the flow table ordered/evaluated
"randomly"? Additionally, has this changed through the OVS versions?
I'm not sure I understand the question. Skipping by the problem above,
let me rephrase my understanding of it in another way, and you can
correct me if I get it wrong. I think you are saying, if a given packet
has two "best match" flows at the same priority, will OVS choose the one
added later by preference? No, OVS doesn't work that way; it has never
used the order in which flows are added as an input into the
classification process.
Yes, the problem is as you described. While the rules coexists, which
one will be applied? According to what I read, I suppose OVS checks the
rules in the flow table and applies the first one making match. However,
as I understand, OVS is not applying "any given order" to evaluate the
rules in the flow-table, it could be that sometimes applies one rule and
other time applies the other rule. Is my understanding correct? I have
found a thread in stackoverflow asking about the same issue
<https://stackoverflow.com/questions/45195182/what-if-there-are-multiple-forwarding-rules-for-the-same-flow-in-the-openflow-sw>
that I am presenting. They say OVS will match the new rule, but maybe it
was casual. Is the behaviour that they see consistent in OVS?
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