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How to analyze dropped packets info in ethereal?

Posted on 2004-10-13
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Last Modified: 2013-12-07
Hello, I use Ethereal 0.10.6, and someone has sent me a .cap file to analyze for dropped packets. I am kinda new to Ethereal and would like to know how to analyze and find dropped packet info including the reasons behind it. Is there an easier way to do it? Thanks in advance.

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Question by:yasmagic
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by:NashvilleGuitarPicker
ID: 12299525
You might want to explain your situation further.  Perhaps the simplest form of "dropped" packets are where there is simply no response from the server, and your capture would not show a response (ACK) for the request.  In this case, the .CAP file may not be enough to figure out WHY the packet was ignored.  You may have to do some diagnosis on the server to find out why it dropped the packet.  If instead, you are referring to random problems where a connection that was working is suddenly interrupted, such as from a cabling problem, then you might get some hints from the .CAP file, but a hardware probe ($$$) might be better.  Another cause of dropped packets is network flooding.  You can use the graphing tools in Ethereal to see if there is a period of high activity right before the problem occurs.

Describe the problem a bit more, and we might be able to help better.

- Will
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by:yasmagic
ID: 12301015
Hello Will,

Well, the SAP application server looses it's connection with the other server throwing the following error message,

*                                                                                                                              
*  LOCATION    SAP-Gateway on host TEST3SAP / sapgw00                                                                      
*  ERROR       connection to partner broken                                                                                    
*                                                                                                                              
*  TIME        Sat Sep 25 21:52:12 2004                                                                                        
*  RELEASE     620                                                                                                              
*  COMPONENT   NI (network interface)                                                                                          
*  VERSION     36                                                                                                              
*  RC          -6                                                                                                              
*  MODULE      ninti.c                                                                                                          
*  LINE        1074                                                                                                            
*  DETAIL      NiPRead (192.168.0.1/4337)                                                                                    
*  SYSTEM CALL recv                                                                                                            
*  COUNTER     393                                                                                                              
*                      

and so we put a trace on the gateway to see why it is getting disconnected. I am not sure what to look for in the .CAP trace file to fix this issue. Is this info helpful?
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NashvilleGuitarPicker earned 2000 total points
ID: 12303180
Hmmm, does it disconnect at a predictable interval?  Some iritating firewalls will disconnect sessions that are open for long periods of time, even if they are active.

If there is a bad cable somewhere, it is unlikely that a software sniffer will be able to tell you much, since there will usually be no packet to sniff.  I would start the trace, and start a stopwatch.  If you know exactly when the session disconnected, you can find the corresponding entry in the .CAP file and look for any packet patterns which seem different than while it was running correctly.  These issues can be hard to diagnose.  Also, scour the event logs on the gateways and the computers involved, looking for errors.

- Will
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by:NashvilleGuitarPicker
ID: 12495996
Thanks for the points.  I assume that the issue is resolved or at least identified.  What turned out the be the problem?

- Will
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