I think of myself as an advanced user but this problem is driving me batty.

Windows XP (32bit Home) going through a WRT54G router, once or twice a day at completely different random times, refuses to connect to my main webserver on any port for a random amount of time, a few minutes to as long as 15+ minutes. Every other site works fine.

Here are the tricky catches though when this starts happening:

  1. Everyone else around the world can still connect just fine
  2. The router can directly connect (via shell I can wget, ssh etc)
  3. ping/traceroute WORKS from Windows - only http, ftp, ssh timesout (so UDP works?!)
  4. plug a netbook into the same router, the netbook CAN connect
  5. The webserver has several IPs - NONE of them connect when it starts doing this
  6. if I already have a ssh connection when this starts, IT WORKS, only new connection blocked
  7. I can connect to any other website/http/ftp just fine when this happens
  8. ipconfig /flushdns does NOT solve the problem (direct IP doesn't work either)

So, in summary, UDP seems to connect when this starts happening but not tcp/ip, router can talk to the webserver but not Windows.

So the router is either blocking TCP/IP from at random times from my PC to several different IPs but no others. Or Windows is refusing TCP/IP outbound to these specific IPs but not others for random times.

Can you spot anything else I should be looking for or trying?

added: discovered that resetting the Windows TCP/IP stack immediately allows me to re-connect to the server

netsh int ip reset

so it's something related or attached to the tcp/ip stack - but of course resetting it might cause other drivers or layers to also reset (windows firewall is not active)

  • Do you have any security software installed? – Moab Sep 18 '11 at 16:31
  • I use Outpost Firewall and Avast anti-virus and disabling them changes nothing unfortunately. Remember I have several IP addresses to connect to the server to, and none of them work once this starts happening. They don't even rDNS to the same address so how would the software even know? – ck_ Sep 18 '11 at 17:55
  • 1
    Firewall software makes many changes, one reason I stopped using ZoneAlarm years ago, I had several XP systems I actually had to reinstall, simply uninstalling ZA did not fix them, they were hosed, I don't think this is your issue, its a strange one indeed. You might put your XP ip in the router dmz zone temporarily to see if it is a router issue. – Moab Sep 18 '11 at 18:29
  • see if you spot anything with wireshark(a packet sniffer) – barlop Sep 19 '11 at 1:28

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