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We have a Logrhythm freemium network monitoring solution depending on port mirroring using span ports on switches to receive all traffic and analyze it. But I cannot understand the output.

If I am monitoring, for example, user A usage of YouTube, user A opens YouTube for 30 minutes, When I filter on user A and application YouTube I see around 20 flows each with duration less than 5 minutes, so I cannot figure from the output the total number of minutes spent on YouTube.

I need to know the definition for flow and why 20 flows appear for only one session. Also, for each flow I see a flag which indicates the flow completed or not, so I see 10 flows completed and others not completed. What is the meaning of flow completed or not ?

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    Netflow is the wrong tool to monitor usage. A user can spend lots of time reading a page/looking at an image without generating flows. If I'm watching a video or just reading comments, I'm still "using" YouTube. But in the latter case, I'm not generating flows. – Ron Trunk Feb 16 at 20:23
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An HTTP client often uses multiple socket connections (=flows) to fetch a full HTML page. Youtube might also do some complex buffering for the videos. It's not streaming real-time but fetches chunks in the background while playing - you can watch that in your browser's network inspector. Depending on the flow sampling, it can look pretty weird on a switch. The specifics largely depend on the application which I'm afraid is off-topic here.

If you need better control/monitoring of what your users do on the Internet you should run the analysis on the firewall. Next-generation firewalls can provide pretty exact control through policies on a very granular level.

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