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Thread: Am I being throttled?

  1. #1
    Junior Member
    Join Date
    Nov 2012

    Am I being throttled?

    Hello Philip. It is so good to know there is a reliable expert around here when we need one. I'm having a little....situation, because I really shouldnt complain. My internet service is ATT fiber, the cheapest at $35, now upgraded to 300Mbps. I enjoyed that for a few days until my lawn service ripped the fiber off the outside wall. Needless to say I was boiling! After the repair my speed seems to be what they upgraded it to, around 300Mbps (meassured using, which uses a test based on HTML5, just like your test here), but my dissapointment starts when I connect thru my NordVpn, which was giving me 120Mbps before, and now barely hits the 50Mbps mark. The only thing I see different in all this is that when I am vpn connected, your analyzer says that my MTU is 1364, MSS is 1324, scaling of 6 bits, factor is 64, unscaled TCP receive window is 2050. These numbers are not all that bad, problem is for a brief moment my scaling was 9 bits, which is a lot better. I know that these numbers mean not much in terms of streaming movies, which is what I use it for, I couldnt tell the difference, but WHAT IN THE WORLD can be happening now when I connect thru the vpn? How and why would they be changing my MTU? Can they do that? Is that what is happening here?
    Do you see something obvious, off the top of your head, that I'm missing? I've been using your analyzer for years, never seen anything like this before, and the only thing I see is that all of this has happened now that I am using an IMac. I jumped into the Macworld when my PC had a catastrophic failure, which gave me the chance to take a little break from Microsoft and learn a little about Apple. Among other things I learned that the TCP protocol is universal, anything that wants to connect to the internet has to use it, and that the MacOS doesnt let me touch most of the stack, unless I become a programmer, a coder in my old age, which I dont see happening...Any thoughts? I suppose I can live with the service I have, but it would be great to know what is going on here.....Thanks.....your fan...... Armando O.

  2. #2
    Administrator Philip's Avatar
    Join Date
    May 1999
    Jacksonville, Florida
    Blog Entries
    Hi Armando,

    VPN adds some additional headers to packets, so if you start with a 1500-byte packet (MTU), minus TCP/IP headers (40 bytes), you usually have up to 1460-bytes useful load (MSS). Any other type of encapsulation eats up from that by adding another envelope around it with its own headers, usually another 20-30 bytes for VPN, 8+ bytes, for PPPoE, etc.

    The MTU itself is not that big of an issue, neither is the scaling of the TCP Window. What's probably happening is that your VPN service is connecting you to a different server. I am not very familiar with Nord VPN, I use IPVanish myself sometimes, but they should give you options to choose your servers, I'd play with those settings. Also, the type of VPN matters a lot, I would use either "IKEv2" or "WireGuard" as the type of VPN.

    Best of luck with it

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