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I am trying to understand how much data is flowing through a specific port on a Cisco (Stratix) switch. I have set up Port Mirroring so that I can capture the traffic on the target port via Wireshark. When viewing the Wireshark recording, I can see the network traffic in bits/s when viewing the Protocol Hierarchy Statistics. The data rate displayed in the 'Frame' row is 72Mb/s while the 'Ethernet' row shows 865kb/s. [Wireshark Protocol Hierarchy Statistics screenshot].

Can someone send me to school and help me understand which field I should be looking at to evaluate switch port data throughput? My target switch port is a 1GB/s port and I am trying to determine how close to it's throughput limit I am.

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    You cannot see the throughput of a different switch interface just from the mirrored traffic. There are switch commands that can help you with your goal, but mirroring traffic is just that.
    – Ron Maupin
    May 26, 2022 at 13:21
  • @RonMaupin - Thanks for the clarification. I have what is probably a very simple/unaware follow up question. How is the mirrored traffic different? I assume something is missing to properly measure the port throughput?
    – Greg Smith
    May 26, 2022 at 14:57
  • You cannot really get an accurate throughput of an interface unless you query the switch interface, and that is normally a simple command. I believe the default time period is five minutes, but you can probably change that.
    – Ron Maupin
    May 26, 2022 at 15:03

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which field I should be looking at to evaluate switch port data throughput?

You cannot use port mirroring to see that with precision because a monitoring port can carry more or less traffic than the mirrored port. You need to look at the port directly, within the switch. Most often, the value can be queried via command line, web interface, or SNMP.

Those values represent an average over a certain time period, commonly five minutes. If you need to know whether a port is overloaded, you need to look at its frame drop rate. Some switches also allow querying the (maximum) queueing depth, providing some indication for high load and impending frame loss.

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Statistics>Capture File Properties. will summarize your capture.

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