Is My ISP Throttling My Bandwidth?

Categories: Networking

I had recently worked on a problem with a customer in which they had been experiencing  issues with the phone quality of their Voice-over-IP (VOIP) phone system at one of their branch offices (VPN connection).  During my review, I was told the Internet connection was supposed to be 20×2 (20 Mbps down and 2 Mbps up), but my speed tests were showing 3Mbps down/512 Kbps up.  What?!

I asked my customer to verify with their ISP what the contracted bandwidth was and they confirmed that they were paying for 20×2 service.  Many phone calls later, the customer determined “unofficially” from a friendly insider at the ISP that they may be throttling their bandwidth due to BitTorrent traffic.  A BitTorrent client was discovered in use by an employee at that location.  After the BitTorrent client was stopped, the bandwidth resumed to normal levels.

Well this situation was resolved for this particular customer, but how do you determine if your traffic is being throttled if you don’t have an “inside” connection?


Glasnost is a tool that will test to see if your ISP is suspected of throttling bandwidth.  It performs a series of tests that download/upload normal traffic and BitTorrent traffic, then compares the results of the two types of tests.  If any significant difference is detected, you can assume that your ISP is throttling your bandwidth.

According to their site, “Our test runs BitTorrent and TCP downloads as well as uploads on a well-known BitTorrent port and a non-BitTorrent port.”.

Bad ISPs

Another source of useful info is Bad ISPs.  This site maintains a list of ISPs known to throttle bandwidth for BitTorrent/P2P traffic, as well as other issues, such as high traffic volume.

Bottom Line

Of course, the main issue here is to restore your bandwidth levels.  You would think that ISPs would not throttle traffic on a “business” type account, but that’s not always the case.  Most likely any technician or higher up you speak with at the ISP will not be able to remove the throttling, so the best course of action is to find the offending workstation(s) on your network that may be causing the BitTorrent/P2P traffic and stop it or block the traffic directly on your firewall.  Tools such as Wireshark or Microsoft NetMon are useful for detecting, identifying, and analyzing network packets.