Red Hat Bugzilla – Bug 78193
Different Number of Packets
Last modified: 2008-05-01 11:38:04 EDT
From Bugzilla Helper: User-Agent: Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1) Description of problem: We are using the re-direct feature to print the results to a file tcpdump -e -x host A and Host b >testfile we are monitoring the traffic of a cetrain file. Version-Release number of selected component (if applicable): 3.6 How reproducible: Always Steps to Reproduce: 1. 2. 3. There not any. The problem arrizes for the number of packets that tcpdump report. using the screen as the standart output tcpdump -e -x host A and Host b the number of packets are 2.000 tcpdump -e -x host A and Host b > testfile using the file as the standart output the number of packets are 6.000 Please note that we are following the same procedure, monitoring the traffic of the same file Expected Results: Same number of packets at both scenarios. Additional info: Note that at 3.6.3 this problem does not exist!
Do not tell me that the shell ">" redirector changes any of the tcpdump behaviour :-) Show me how you can make a reproducible network traffic other than using a dump file and the -r argument. The shell ">" has nothing to do with tcpdump. If you are logged in from host A to the other host B and start tcpdump over the network you should experience _even_ less packets with ">" because the packets containing the output of tcpdump are not transferred over the network...
*** Bug 78192 has been marked as a duplicate of this bug. ***
You are right that the shell ">" redirector DOES NOT changes any of the tcpdump behaviour. Today i tried the following commands from HOST7. It is on the same subnet & hub with the HOST8. Host 8 download a 17 MB file using sftp. Tcpdump -x -w test1 host HOST8 and unix1 control C Packets 20.451! Immediately, same procedure but print to the screen Tcpdump -x host HOST8 and unix1 control C Packets 4.462 I have not mentioned that i am not logged as root. TCPdump requieres root priviledes to run propertly? The file is saved to my home directory where i have full privileges,
Yes, tcpdump requires root priveledges to run. Otherwise any user on the system could sniff network traffic, steal passwords, and capture other data going over the network. I fail to see any valid bug in this bug report. tcpdump is working properly as designed.