Hi Daya,


Currently, all the flows corresponding to SG rules (irrespective of SG) have
same priority.

One basic question here, does ordering at a SG level or SG rules level
really matter? Becoz whatever we specify in SG rules are for allow traffic
only. There are no deny rules. So I believe sequencing shouldn't matter
unless if we are specifically looking for flow statistics.  Also there are
no attributes in openstack which specifically mention about the sequence
numbers. SG and rules are just passed as an array to ODL. So in case if we
have to maintain sequencing, we will be following the array indexing.


With your inputs on making use of priority, I think we can have different
priorities based on port + SG. This would create multiple flows on switch.
So the issue doesn't arise.

Hope SG priorities doesn't matter.


Please share your thoughts.






From: Dayavanti Gopal Kamath [mailto:dayavanti.gopal.kam...@ericsson.com] 
Sent: Thursday, October 13, 2016 2:18 PM
To: Somashekar Byrappa <somasheka...@altencalsoftlabs.com>;
jozef.baci...@pantheon.tech; netvirt-...@lists.opendaylight.org;
Subject: RE: [netvirt-dev] [openflowplugin-dev] Need inputs on handling
deletion of flows which have common attributes


Hi som,

I would question the need for this usecase itself.


sg rules would be an ordered list, which need to be applied in sequence, so
when these rules are programmed in the tables, we cannot have any
interleaving between rules from different SGs. I think this is a contract
that cannot be violated. For e.g

if SG1 has rule1, rule2, rule3 and SG2 has rule4,rule2, rule5. We need to
make sure the tables contain 2 instances of rule 2, in both these ordered
lists. The relative priority between all rules of SG1 and all rules of SG2
is a separate issue of course, and a separate discussion on whether these
prios are deterministic.

Basic point is, we need to ensure the sequencing is intact within a group,
either by adjusting the priorities or adding more specific match criteria,
for different SGs. 


2ndly, and more broadly, this does not sound typical to apply multiple SGs
to the same VM, and additionally have the same rule in each such SG. This
would call for some re-organization of the SG rules themselves, so from my
perspective, we need not have huge design changes in the code to support
such a use case.





From: netvirt-dev-boun...@lists.opendaylight.org
[mailto:netvirt-dev-boun...@lists.opendaylight.org] On Behalf Of Somashekar
Sent: Thursday, October 13, 2016 12:49 PM
To: jozef.baci...@pantheon.tech <mailto:jozef.baci...@pantheon.tech> ;
<mailto:netvirt-...@lists.opendaylight.org> ;
Subject: Re: [netvirt-dev] [openflowplugin-dev] Need inputs on handling
deletion of flows which have common attributes


Thanks Jozef for your inputs.

Maybe a common module needs to be written which can handle this scenario
instead of every application module handling on their own.


Anymore inputs from others? Or else for time being, I will handle this in
security groups module itself.





From: Jozef Bacigál [mailto:jozef.baci...@pantheon.tech] 
Sent: Friday, October 7, 2016 3:58 PM
To: Somashekar B <somasheka...@altencalsoftlabs.com
<mailto:somasheka...@altencalsoftlabs.com> >;
<mailto:netvirt-...@lists.opendaylight.org> ;
Subject: RE: [openflowplugin-dev] Need inputs on handling deletion of flows
which have common attributes


Hi Somashekar,


from Plugin POV it is quite impossible to handle this use case without a
performance impact. On the device you can't store two identical flows and
you can't store flow id as you mentioned below. But the plugins
reconciliation working on change event so if you delete one flow on
configuration it will be deleted on switch and reconciliation won't start
check all configuration unless you disconnect device. So yes, it would be
better approach to handle this use case from the application side instead to
let the plugin always check everything on each event.




From: Somashekar B [mailto:somasheka...@altencalsoftlabs.com] 
Sent: Thursday, October 6, 2016 1:09 PM
To: netvirt-...@lists.opendaylight.org
<mailto:netvirt-...@lists.opendaylight.org> ;
Subject: [openflowplugin-dev] Need inputs on handling deletion of flows
which have common attributes


Hi All,


I am looking for all your inputs for the below issue.


Issue: Create multiple flows with different flowId, keeping rest of the
attributes same.

In this case, there will be multiple flow entries in config DS, but a single
flow on the switch.

When we delete one of this overlapping flow, flow gets deleted on the


Use case:


We can associate multiple security groups to a VM from Openstack. 

Each rule in the security group (SG) generally gets translated to a flow in
one of the ACL tables (41/252) based on the direction (ingress/egress).

Let's say we create multiple SGs having few overlapping rules (highlighted
in yellow) among each other like below:


| sg1     | ingress, IPv4, 22/tcp, remote_ip_prefix:

|            | ingress, IPv4, icmp, remote_ip_prefix:

| sg2     | ingress, IPv4, 22/tcp, remote_ip_prefix:



When we associate both SGs (sg1 and sg2) to a VM, ACL module creates three
flow entries totally in config DS. 

For the above two overlapping rules, two flow entries are created in config
DS with different flowId, rest all the other attributes remains same.

This would result in a single flow on the switch as flowId is not a flow
attribute on the switch.


cookie=0x6900000, duration=11.895s, table=252, n_packets=0, n_bytes=0,

cookie=0x6900000, duration=75.237s, table=252, n_packets=0, n_bytes=0,
000,nw_src= actions=ct(commit,zone=5000),resubmit(,220)


Problem arises when we dissociate one of the SGs (let's say, sg2) from the
VM. In this case, we delete one of the overlapping flow from config DS.

This would result in deletion of flow from the switch. Even though there is
another flow entry (having same data with different flow ID) in the config
DS, this flow gets deleted from the switch.

This is how we generally handle all DCN/DTCN.


This is a common problem which might occur in other situations as well.


Question is how to handle this kind of scenario?

Which module should handle this? Plugin or applications?


In case, if we need to handle it from the applications side, we could think
of below option:


1.       When adding a flow to config DS,

a.       Construct the flow id using the match criteria which would generate
same flow ID for all the overlapping rules. So that only one flow will be
created for all overlapping rules.

b.       With the constructed flowId, query config DS to check if flow
already exists. 

                                                               i.      If
no, add this flow with flow name something like: ACL-<counter>. Counter
would signify the number of overlapping flows configured.

                                                             ii.      If
yes,  update the flow name by incrementing the counter. Eg: ACL-2

2.       In case of deleting flow from config DS,

a.       Construct the flow ID as mentioned in 1.a

b.        With the constructed flowId, query config DS to check if flow
already exists.

                                                               i.      If
no, ignore.

                                                             ii.      If
yes,  check the counter value in the flow name (ACL-2), if its value is 1,
delete the flow else decrement the counter and update the flow in config DS.


Cons of this approach: 

                One additional read call to config DS during
addition/deletion of every flow.


Please share your thoughts to handle it optimally. 






Software Engineer

Sídlo / Mlynské Nivy 56 / 821 05 Bratislava / Slovakia
R&D centrum / Janka Kráľa 9 /  974 01 Banská Bystrica / Slovakia
+421 908 766 972 / jozef.baci...@pantheon.tech
reception: +421 2 206 65 114 / www.pantheon.sk <http://www.pantheon.sk> 


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