Simple Question: Does High Bandwidth usage affect Speedtest.net Results?

  • In an office building with 20-some employees, our internet service sometimes drops to about .3 Mbits/sec from 5 Mbits/sec. I use speedtest.net to test the speed. When the speed drops, how can I tell the source of the issue? Namely, are my speedtest results affected by employee streaming/downloading/etc, as opposed to an ISP problem? Would I need a virtually quiet network to accurately test speed?

  • Geekman

    Geekman Correct answer

    8 years ago

    To answer your first question, yes high bandwidth use will affect speedtest.net results. And yes, you would be best to wait until a time of low traffic to get a better/more accurate reading of your maximum possible speed.

    Another metric of maximum possible speed would be (assuming you are connecting via ADSL) the line sync speed as reported by your modem. Although it may not be as accurate, this would allow you to find out the maximum without having to wait until low bandwidth periods.

    In terms of determining the source of the internet traffic, you will need to use some mechanism to examine the traffic going between your LAN and the internet. There are a number of ways you could do this, depending on what you have available:

    • You could issue "show ip flow top-talkers" from your router, if it is a Cisco IOS router and you have Netflow configured properly. This is probably the easiest way to determine who is using the most traffic, and where it's going.

    • You could examine the NAT translations table on your router (assuming you use NAT), to show you which internal IPs have the most translations. This would give you a rough idea as to where your bandwidth is going. But it's hardly the best indicator.

    • You could setup a mirror port on your LAN switch, to mirror traffic to/from the router, and then use a packet capture utility such as Wirekshark to analyse the traffic.

    • You could setup a PC as a bridge to sit between your router and your LAN, with internet traffic passing through it, allowing you to again run a packet capture utility and analyse it to find the culprit(s). NOTE: In this case, you risk slowing down your internet speed while you do the capture. This would be best left until after-hours if done.

    Cisco 'Top Talkers' Example Config

    ! Configure top-talkers
    ip flow-top-talkers
     top 100
     sort-by bytes
    
    ! Configure NetFlow on the appropriate interface on the router
    interface Vlan1
     ip flow ingress
     ip flow egress
    

License under CC-BY-SA with attribution


Content dated before 7/24/2021 11:53 AM

Tags used