Query related to Port Mirror session

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Asad Raza

Nov 9, 2023, 1:15:01 AM11/9/23
to soni...@lists.sonicfoundation.dev, sonicp...@googlegroups.com
Hi folks! 

I am simulating Community SONiC version 202205 in GNS3 to test port mirroring function (specifically SPAN) of SONiC.

The sample topology attached is below where PC1 and PC2 are communicating with each other via Inter-VLAN routing. The monitor is attached to Ethernet0 interface which is configured to mirror traffic flowing through Ethernet4 interface (attached to PC1). To implement this, I configured a SPAN session with destination Ethernet0 and source Ethernet4. Complete configuration commands used for this topology are also attached below.

Unfortunately, no packets are flowing through the mirror session when PC1 pings PC2. Screenshots of Wireshark captures for the mirror session and normal are attached below. It can be seen that packets are visibly flowing in the normal port while none are being mirrored to the mirror session.

I need guidance from the community regarding this matter.

Thanks in advance.

Warm Regards,

Asad Raza
Network Design Engineer,
xFlow Research Inc.
Command History.png
Normal Branch Capture.png
Mirror Branch Capture.png

Chen Chenthanakij

Nov 16, 2023, 12:41:08 PM11/16/23
to Asad Raza, soni...@lists.sonicfoundation.dev, sonicp...@googlegroups.com

Hi Asad,


Sorry for the late response. I have done similar thing on 2019xx, 2021xx (don’t remember those digits with xx ) on a few different HW platforms and they work fine. I actually had a couple of scenarios that have the same exact topology like yours. Could this be something GNS3 specific? Have you tried this on any actual HW?





Apichai (Chen) Chenthanakij

Supermicro QA


From: soni...@lists.sonicfoundation.dev <soni...@lists.sonicfoundation.dev> On Behalf Of Asad Raza
Sent: Wednesday, November 8, 2023 10:15 PM
To: soni...@lists.sonicfoundation.dev; sonicp...@googlegroups.com
Subject: [sonic-dev] Query related to Port Mirror session


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Asad Raza

Nov 17, 2023, 1:15:47 AM11/17/23
to Chen Chenthanakij, All Sonic, soni...@lists.sonicfoundation.dev, sonicp...@googlegroups.com
Hi Chen,

Thanks a lot for your response.

You are correct as this seems to be an issue related to the VS version of SONiC, not with the topology itself. I have come to learn that VS-SONiC only supports control plane features and not data plane features (which include port mirroring) due to the absence of an actual ASIC. I will be testing the feature on physical hardware now.

Warm Regards,

Asad Raza
Network Design Engineer,
xFlow Research Inc.

Asad Raza

Nov 17, 2023, 1:21:40 AM11/17/23
to eddie...@alibaba-inc.com, soni...@lists.sonicfoundation.dev, sonicp...@googlegroups.com, All Sonic
Hi Eddie,

Thanks a lot for your response.

Yes, you are correct, thanks for the clarification. As a data plane feature, mirroring would require a physical ASIC itself or a data plane simulator.

I agree that it would be a great help from chip vendors if they could contribute some data plane simulators to the SONiC community. We should definitely look into this.

Thanks again for the reply, it is much appreciated.

Warm Regards,

Asad Raza
Network Design Engineer,
xFlow Research Inc.

On Thu, Nov 16, 2023 at 11:43 PM Eddie Ruan via lists.sonicfoundation.dev <eddie.ruan=alibaba...@lists.sonicfoundation.dev> wrote:
Mirror is a data plane feature. You need to build a vsonic VM with data plane simulator which provides from chip vendors. I am not sure if we could build it in public, although a lot of folks have already used it. 

It might be a good idea to see if we could get couple chip vendors to provide data plane simulator to public,  which would help to improve SONiC sanity in general. 



Sent At:2023 Nov. 16 (Thu.) 10:02
Subject:Re: [sonic-dev] Query related to Port Mirror session

[Edited Message Follows]

(I guess  my previous reply was sent privately, so resend it for all.)

HI All,

The SONiC VS VM does not support the mirroring feature. The SONiC VS is implemented on top of libsaivs which is just a stub for SAI, so there is no data-plane virtualization. As a result, most of the features that have corresponding configurations done in Linux are working. Not sure if somewhere is documented the list of supported/unsupported features, but from my experience, the VLAN, routing, and most of the control-plane features should work and the ACL, mirroring and other data-plane features will not.

Myron Sosyak, 


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