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I'm writing this using a 3G connection on my phone.

At lunch time yesterday, the ports above and a few additional other ports like 40001 and 4089 stopped working on my internet connection at work.

SSH access still works and MySQL connections too I believe.

Using Wireshark on a Windows 7 laptop I can see loads of [TCP Retransmission] requests on the ports which don't work.

We have a Ethernet from our laptops (Windows, Mac and Linux) connected to a switch connected to a Draytek router connected to an ADSL line.

As far as I know there is no firewall turned on, on the router.

Ask if you need any more info, but how do I go about debugging this problem. Our ISP can't see any problems on the line.

EDIT: we've tried two completely different brand routers with no difference in what we observe. I can SSH out on a non-standard port and view my http requests being unsuccessfully ACK'd. Skype works fine BTW, just in case anyone was wondering.

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I would suspect the router configuration has been changed and a mistake has been made. I would compare the router's actual configuration with change-management records of it's configuration. – RedGrittyBrick Feb 2 '12 at 10:11
    
we've reset the router to factory defaults and added in our isp/ADSL connection details but that made no difference. – Jon Feb 2 '12 at 11:31
up vote 1 down vote accepted

Turns out we hit our ISP's download limit and they'd not told us.

Good times.

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You have a download limit on a business connection? I'd look at changing this quick. – Joe Taylor Feb 2 '12 at 12:41

Backup router configuration, do a heavy-handed reset and reload configuration

Maybe ... just maybe.... you enabled SPI on your (not so popular) router and it is running out of memory...

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we've reset the router, and tried a new one of a different brand with no difference. I can SSH out on a non-standard port and view TCP connections inbound to the same server, but it just keeps sending ACKs and I keep not receiving them, so my laptop keeps sending TCP retransmissions – Jon Feb 2 '12 at 11:34

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