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 
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 B
Sent: Thursday, October 13, 2016 12:49 PM
To: 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

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>; 
netvirt-...@lists.opendaylight.org; openflowplugin-dev@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
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 switch.

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, 

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 

                                                               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 

                                                               i.      If no, 

                                                             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 / 
reception: +421 2 206 65 114 / www.pantheon.sk<http://www.pantheon.sk>

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