Connection slow but speed fast when connected

Question

I am experiencing an interesting type of slow connection buildup and would like to ask people more up to the topic on any ideas what could cause this and how to troubleshoot it. (On my background, I am an IT student fairly experienced with computers and networks)

On my network we have a router connected to the internet and serving multiple devices over wireless 802.11n. There is some interference with other WiFis but normally the connection is stable. Also all devices are in one room, less than 5 meters from the antenna, nothing blocking it.

There are times where everything works normal and there are times where it takes up to 30 seconds for a connection to finish the handshake, but once that is done, the connection speeds up to 20MBit/s.

You can see this extremely good on downloads like steam, where the graph has spikes every 10 or so seconds when one package clears. But youtube videos or http-downloads are fast once the initial connection is made.

This happens regardless of device or operation system (Windows, Linux, Android) and restarting the router, flushing dns does not resolve it.

Sending a ping to ip or domain goes in under 50ms and chat systems (probably working with sockets) are doing just fine.

While it seems to not be a dns issue, loading the exact same page a second time results in much faster connection.

• mysite.com?page=1 (10 seconds)
• mysite.com?page=2 (10 seconds)
• mysite.com?page=1 (0,5 seconds)

I am curious as to what could cause this and what tools I can use to analyse it. This is more a question for me to learn the technical background behind this and I would love to have an answer going into technical details.

If you need any more details I am happy to provide them!

Answer 1

I too am led to believe you have a problem with DNS. Your comment

nslookup on windows clears in under one second for random domains

did nothing to assuage these fears. I can offer a test, and a solution.

Dnscrypt is an extremely useful package, developed by the fine folks at OpenDNS.org, which will not only change the DNS port, but will also encrypt DNS queries. The point here is that your ISP may have enabled its own system of DNS and firewall which recognizes DNS queries based on port and/or protocol, so that just changing the port will not do. Encryption will allow you to bypass your ISP's DNS. On the Web site you will find download packages for both Windows and MacOs. Install one and see whether anything changes.

If this works, the simplest solution is to mount your own router behind the one given to you by your ISP, and route all of your traffic through this new router. To this end, you can either use a suitably crafted Linux version (even on old, second-hand hardware like I do), or buy yoursself a new router compatible with the Tomato by Shibby firmware, you may find a list here. This firmware has dnscrypt, which you may configure as you see fit, see for instance here.

Answer 2

This could also be an issue with IPv6. Maybe your Browser tries to connect via IPv6 and waits until that times out before retrying with IPv4.

That said, I'm also led to believe that this is a DNS issue.

Could you try to talk to an HTTP-Server directly via telnet?

Something like telnet www.google.com 80 should do it. Then look how long it takes to connect and also note if it tries to connect via IPv4 or IPv6.

Once connected you can do a handcrafted HTTP query like this and monitor the response time again.

GET / HTTP/1.1
Host: www.google.com
Connection: Close

The last line has to be terminated with 2(!) newlines to trigger the server response.