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I am using ADSL2+, and the sustained connection can go up to 1.3MB/s, but recently the HTTP connection has been quite slow ( other port i.e. ftp, torrent, etc are fine).

I am using Netgear modem/router for my ADSL connection, and am using Netgear switches for my LAN (connected to the modem).

What can go wrong and how can I investigate?

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Any possibility that your ISP could be using transparent proxies to route web traffic? I've a WiMAX connection where this happens. The web traffic is routed through a web proxy at the ISP's end. I get slow speeds when browsing, but fast speeds when using any other services. I have started using an SSH tunnel to re-route my web traffic, and sure enough, have seen faster speeds.

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Not sure. I guess I have to ask my ISP – portoalet May 30 '10 at 8:19

Do you mean you are hosting a HTTP service and people are complaining it's slow or do you mean you are trying to browse the Internet and this is were you see it is slow ? If the former, it is due to your upload rate. If the latter, maybe that's because of DNS resolution ?

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It is the latter. how can I check my DNS connection? – portoalet May 30 '10 at 8:08
You could try to nslookup a few well-known domains for example (using your ISP DNS servers). – Xavier Maillard May 30 '10 at 8:28
You should most likely clear the DNS cache before you do those tests – Svish Jun 9 '10 at 8:51
  1. Use Speedtest.Net for checking your bandwidth availability
  2. Try OpenDNS to check if your ISP DNS is not in good shape
    The Basic form is free.
    This is how you can setup your computer to use it.
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+1. This is very useful to me. Thanks. – Xavierjazz May 30 '10 at 16:27

It was all ok now, so I can only assume that it was my ISP's fault that it was slow on port 80.

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