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Port mirroring on SG300 questions


Hi all,

I'm troubleshooting a LAN issue I have, and I wanted to hook up wireshark to record traffic over the course of a couple of hours for later diagnostics. I went into the web administration interface, clicked Administration > Diagnostics > Port and VLAN Mirroring, and added a port mirror from the port I wanted to watch to a port to which I had connected a laptop. I picked the Tx and Rx options, and clicked Apply.

I did receive lots of traffic in wireshark, but I noticed immediately that the server on the port I had mirrored was suddenly unavailable on the network -- pings timed out. This lasted until I removed the mirror, then the server was suddenly reachable once again.

Does this feature not work the way I had thought it does? What I saw looked more like a forward than what I would call a mirror. The documentation leads me to believe mirroring is intended to be used in just the way I was attempting to use it.

Am I missing something?

1 Reply 1

David Hornstein
Rising star
Rising star

Hi Lamint,

I have a SG300-10P for my test,  I did the same thing you did in my GUI.

I was mirroring port 7 to port 8 ticking the item to mirror RX and TX

My PC with wireshark was residing on port 8.

I started a comtinuous oibg from my  PC on port 7 at IP address to my WAN routers LAN address, .

As you can see from my screen capture below, my PC on port 8 caprtured both RX and TX packets on port 7.

Because my wireshark  PC was on port 8, I could not access the management interface of the switch to show you my configuration, so I grabbed the configuration via hyperterminal.

See screen caopture below ( with some configuration items excluded)..

I would suggest, if you are having issues to allow the Small Business Support Center to assist you.

Hope this helps

regards Dave

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