Yesterday there was an issue with Dr.TCP which caused problem in accessing the internet over the network. I was able to access the internet from the server, but when a request is made from other network machines they where not able to access the internet.
Every thing was working fine till we used Dr.TCP. later we found that the packets where send with local and destination port as 0 instead of port 80 when the request was made form other LAN computers.
Port 0 was blocked by the firewall. So the bowser loads indefinitely waiting to receive a replay from server.
And there was a surprise that when the request is send for google search engine it does not assign the request to port-0. It may be due to packet size. Packet size from google was always below 1000 and from other servers some time reached 1506. Once the size reached 1506 the reply from client become bizarre.
TCP Receive Window is set to 39204, other properties to default and MTU property. The issue was in fixing the MTU value.
The default MTU(maximum transmission unit) for broadband connection should be 1492.
but the Dr.TCP assigned it to 1465, we were trying a lot to change the MTU but all in vain.
We made call to customer care and they were also not able to resolve the issue.
Finally, just we stopped the firewall and made the change in MTU. Set the MTU value as 1492.
Now everything works fine.
Hope this helps some one....