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blaze02

Connection Problems

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I've found one place in an office building that can not connect to my server at home. My app gets the server's IP from a text file, and the port is a known port. The machine in question sends a UDP packet to the server but the server never receives it. The machine has an Internet connection and other games can play multiplayer over the Internet from these machines. What reasons could there be for my app not connecting to my server? If it matters, the outgoing port for the machine is left at default. So what sort of a configuration would block my Internet traffic? My game seems to work fine from everywhere else.

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I'm assuming that your server works from other places.

Firewalls (local and net-centric), packet filtering and NAT can all get in the way. I suggest downloading a network sniffer and seeing what's going on.

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Yes, my server works from other places, but the specific port must be forwarded to the server.

This place that is unable to connect is an office building that I don't have access. I have had my program run and generate debug output. I know that my program sent a UDP packet to the server's ip:port. And, the server did not receive it.

What can I do to figure this out? My best guess is to have the machine run the ip tracer command and trace to the server ip (the name slips my mind for the moment, "tracert" or "iptrace"?).

Assuming the program did send everything correctly, what could be stopping the packet?

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Thanks for all the help h+. Is this a common thing to do, block UDP traffic?

I'm assuming I can determine if this is the case by making a tcp/ip app and server and retrying the same connection. If the tcp/ip program can connect, would it be feasible to fake a tcp/ip connection to punch through the firewall, then switch and use UDP packets? Or do you think the firewall will block UDP packets at any given time?

Again, thanks for the help.

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UDP and TCP are different name spaces, so even if the TCP connection made it through, the UDP will still be blocked. Your best fall-back is to open a TCP connection, and send your packets over that -- and live with the occasional stalls.

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Its hard for me to believe that they are blocking all UDP packets. I don't know of a game that can't be played on the Internet from the building. Battlefield 2 works from inside, and I can't imagine BF2 falling back on TCP/ip for all traffic.

I will write a simple tcp/ip prog and see if it works. And I will send an email to their helpdesk and see if they want to help.

Can you think of anything I should try?

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Talk to your network administrator. If they aren't deliberately blocking this traffic, arrange to place sensors at various locations to determine how far the packets get.

I'm assuming you're placing a sensor (e.g. tcpdump) on the server to find that no packets get through to it.

Either that, or you're finding that somehow the connection is being dynamically NAT'd in the outward direction only (which is wholly useless).

I recommend you discuss the whole thing with your network admin.

Mark

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Well thats the problem. I don't have access to the building or any computers in the building. I have a friend that tried to run my app, and he sent me the debug info.
I've chalked it up as a lost cause for now. I'll worry about it later. For now, it is the only place that can't connect to my server.

Oh well. Thanks for all the suggestions. Hopefully I'll get it working some day.

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