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tcp connection failure

Posted on 2008-10-04
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Last Modified: 2013-12-23
I just recently have experience a problem with two applications that interface with each other.  I have a call accounting system that interfaces with a property management system (call accounting passes phone charges to pms to charge on hotel bill).  This works off of a TCP connection.  All of a sudden (really after multiple updates that were installed at one time). the communication between the two systems have failed.  After a long support three way call with both vendors, nothing was resolved except for the possiblitiy of a communication error.  I do not know too much about tcp port connections, but there is multiple ports trying to connect from cas to the assigned port on the pms system, 5011.  The listing in netstat on call accounting show a long list of TIME_WAIT to the pms 5011 port ending in a FIN_WAIT_2 entry.  ON the PMS side, the netstat shows the 5011 as LISTENING.

Could a problem in tcp communication be my problem?  How can I troubleshoot this or try to reset the connection.  I have firewall on the xp machine (call accounting) off and the 2000 server which is the pms i believe has no firewall set.  

very confused right now any info would help
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Question by:dgoldfluss
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by:Shedding
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a few things.  Even without knowing how your systems works.  This is the first method of attack in your situation.

1. Ping your machines.  Make sure there is connectivity between them.  

2. If there is a ping between them, then you know at the very least that the two machines are connected  through tcpip.

3.  If this is the case, then the updates created the problem.  You need to go back to the vendor and let them know that there is a good connection between the two computers.  


If the ping does not come back (you sent 4 packets and 4 packets failed) then it will be an easier issue.  A few things to try is checking the switches (make sure they are on), make sure the cables are plugged in, make sure the two computers are in the same subnet .  If there is anything you don't understand, leave another message and I will be more detailed.  I just want to see if you get a ping or not.  Then we can figure this out from here.
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by:moorhouselondon
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Sounds like a Firewall issue, or the application is being isolated by the Operating System for doing suspicious things.  Make sure that Port 5011 is clear both ways on both pc's.  You can verify inwards communication by using the Shields Up facility on www.grc.com  Type 5011 into the ports to be scanned box and press the Custom Probe button.  You are looking for a Failed message.  If you get anything else then that is what your problem is.  

Make sure that your Firewall is forwarding the 5011 Port to the correct pc (which needs to have a fixed IP address).  To do this read the instructions on www.portforwarding.com for your router.

Checking outgoing communication, I would set up a Rule in your Firewall to Allow Always on Port 5011, and to switch logging on.  Try sending data, then check the log to see if you have packets being sent.
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by:Shedding
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He is in an internal network.. the only firewall he's got is his software firewall.  I made him ping the machine because if he has an aftermarket software firewall (blackice, zone alarm, norton 360, norton internet security, mcafee firewall, etc), most will deny ICMP requests.  Therefore it will not ping.  The other reason I asked him to please ping the machine is to make sure he has connectivity between the two machines.. otherwise there is no point in trying to troubleshoot ports.  Lets try the basics first.

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by:dgoldfluss
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sorry i did not mention that pings between the two machine are successful and that is not the issue.  NOt sure how i can test using SHields up ot port forward since both machines are within my local network.  I am running shields up now anyway to see what is going through my network firewall, but unfortunastely it will not help answer this question.  

My confiusion is that this should be a simple tcp connection but it is not working.  I wonder why there is such a long list of TIME_WAIT port connections.
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by:Shedding
Shedding earned 150 total points
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TIME_WAIT means that something was received and it is now closing the connection.  I got this from this site.. http://www.unixguide.net/network/socketfaq/2.7.shtml

Remember that TCP guarantees all data transmitted will be delivered,
  if at all possible.  When you close a socket, the server goes into a
  TIME_WAIT state, just to be really really sure that all the data has
  gone through.  When a socket is closed, both sides agree by sending
  messages to each other that they will send no more data.  This, it
  seemed to me was good enough, and after the handshaking is done, the
  socket should be closed.  The problem is two-fold.  First, there is no
  way to be sure that the last ack was communicated successfully.
  Second, there may be "wandering duplicates" left on the net that must
  be dealt with if they are delivered.

Here is a small question.. are you sure both programs are working on both computers?
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by:dgoldfluss
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Thanks for the info.  The last question is the real problem.  Since it is an interface involving two different systems, I am stuck in the middle of two vendors who will say that the problem is the other program, b ut in this case the one vendor was saying it was MY problem with TCP connectivity.  Therefore I have tried to see if actually the problem was on the network connectivity.  Right now they are not even starting to communicate.  

I will investigate further and let you all know what the solution is.
Thanks
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dgoldfluss earned 0 total points
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The issue ended up being a problem with a windows update that was installed for .net that caused a conflict with the Call Accounting software.  
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by:Shedding
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Good thing you found the problem.
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