0

I'm a software engineer, but I think my problem needs a network engineer...

For the software side of things, have a look at my Stack Overflow question: https://stackoverflow.com/questions/21641219/sending-and-receiving-over-network-using-tcpclient-socket-or-stream-fails-afte

I have the simplest possible length-prefixed string send-and-receive client and server. The client reads a line of input, sends it to the server, then waits to receive a response. The server reads the request string, then echoes it right back out.

I find that I can do five send-and-receives, and then on the sixth try, the client says it's sent the line of text, and it tries to receive the server response. The server gives no indication that it's received anything. And it's like clockwork, five times every time. Some time early yesterday it was consistently three times. Now it's five. What perverse system behaves like that?

The client runs in my office, Win7-64. The server runs in AWS, Win2k8R2.

I've tried disabling the client and server firewalls. I've tried a different AWS EC2s.

Wireshark says that it's doing TCP Retransmits in the hanging case. Eventually the client throws a "connection dropped" exception. Later, the server does likewise.

Any ideas?

4
  • 1
    If you can, throw a link up to a PCAP file with the interaction you're seeing in it, please. Feb 9, 2014 at 0:07
  • Here you go: dropbox.com/sh/jcds1kibkg9dzhf/bHy4tIsOSk Feb 9, 2014 at 2:39
  • I don't know why I didn't try this sooner, but I've found that the problem does not happen when two AWS EC2's communicate. They're both in us-west-1, so maybe that's not the best test. I'll try spinning up an EC2 on the east coast and try from there. At this point I'm thinking it's something in my client system that's blocking / gobbling something for some reason. Feb 9, 2014 at 2:43
  • I was able to verify that an East Coast client can access a West Coast server, so it's not a software problem, it's something amiss with my local networking. Hopefully y'all can find something interesting in the packet captures. It sure would be nice if I could communicate with my own servers... Feb 9, 2014 at 3:10

1 Answer 1

0

It turns out that our corporate network was blocking outgoing traffic going to the server's port. Not sure why it worked X times at all, but after the networking guys twiddled their bits, all worked well. Thanks for all your help and insights.

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .