Super User is a question and answer site for computer enthusiasts and power users. It's 100% free, no registration required.

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

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.

share|improve this question
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.

share|improve this answer
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...

share|improve this answer
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

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.