Attempting to capture traffic but I don't know the write syntax to filter the output to a readable pcap file.
I need to use the syntax
tcpdump -r file.pcap
and to filter eth0 icmp traffic
tcpdump -i eth0 icmp -c 10 > file.pcap
is there a way to do this in one line of command?
Yes, but, if you're writing a pcap file rather than a text file, it doesn't involve the > character.
By default, tcpdump captures traffic from an interface, or reads a capture file, and writes out a human-readable dissection of the packets to the standard output.
You need the -w flag to write out a pcap file, so, in your case, the command is
tcpdump -r file.pcap -w file.pcap ICMP
Your command
tcpdump -i eth0 icmp -c 10 > file.pcap
wouldn't write out a pcap file, it writes out text such as
16:30:59.808885 IP 192.168.1.5 > example.com: ICMP echo request, id 40541, seq 0, length 64
16:30:59.841404 IP example.com > 192.168.1.5: ICMP echo reply, id 40541, seq 0, length 64
If you wanted to write the ICMP traffic to a pcap file, you would do
tcpdump -i eth0 icmp -c 10 -w file.pcap
Related
I would like to know that is there any option in Wireshark to capture packets in the streaming network dynamically. Since I need to capture packets with out doing the export each time and packets capture automatically in a CSV file without exporting it periodically. Thanks.
You should be able to use tshark to achieve this. For example, suppose you want to capture the frame number and source and destination IP addresses of each packet (to keep the example simple), you could use:
tshark -i foo -T fields -E separator=, -E quote=d -E header=y -Y ip -e frame.number -e ip.src -i ip.dst > output.csv
You can specify as many fields as you want using the -e option
I want filter first 100 packets inside a pcap file and show the result on stdout. for filtering first 100 packet I used below command:
editcap -r test.pcap output.pcap 1-100
for showing result and filtering packet for the further purpose I want to used tcpdump.
tcpdump -tttt tcp and host ip 192.168.1.1 -r inputfile.pcap
i want to redirect output of editcap to tcpdump, like this:
editcap -r test.pcap - | tcpdump -tttt tcp and host ip 192.168.1.1 -r -
but in this command I couldnt filter first 100 packets. Is it possible to do so??
If not is it possible to rediredt output of editcap to RAM and then the tcpdump read from RAM ??
thanks in advanced.
P.S by the way, I don't want to use the below command, because this command read the all Packet inside the file. I need the command read some packets inside he pcap file and shows then was finished the job.
tshark -r ~/test1.pcap -R "frame.number<20 and frame.number>10"
but in this command I couldnt filter first 100 packets
I.e., you don't see any packets?
Try doing
editcap -F pcap -r test.pcap - 1-100 | tcpdump -tttt tcp and host ip 192.168.1.1 -r -
as editcap might be writing out a pcap-ng file and there is a bug in some versions of libpcap when reading pcap-ng files that causes filtering in tcpdump not to work.
I have the following trace :
:
In the wireshark preferences I have the following option set to Off :
In TCP Prefs : Allow subdissector to reassemble TCP streams
In SIP prefs : Reassemble sIP headers spanning multiple TCP segments
In SIP prefs : Reassemble sIP bodies spanning multiple TCP segments
I am trying to analyze this trace with the tshark command given below. But in the output I am not shown any packets even though the packets are there in the trace :
[rishabh#pc Test]$tshark -T fields -E header=y -e ip.src -e tcp.srcport -e ip.dst -e tcp.dstport -R "sip.Status-Code eq 500" -r "4.cap"
ip.src tcp.srcport ip.dst tcp.dstport
[rishabh#pc Test]$
How do i modify the filter to capture the highlighted packet?
I found out that if I switch on all of the above wireshark options the TCP packets are shown as :
Maybe tshark allows reassembly by default and thus it is not able to filter the packet as a SIP message. Also I am able to capture the data with the tshark filter : "tcp contains '500 Responder'"
But I need to filter it as a sip status code only. How do I achieve this?
Note that the SIP status code is indeed 500, so the initial filter should work.
Found the solution:
tshark allows you to set the settings for the reassembly preferences. The preferences are :
Whether subdissector can request TCP streams to be reassembled
TRUE or FALSE (case-insensitive)
tcp.desegment_tcp_streams: TRUE
Whether the SIP dissector should reassemble headers of a request spanning multiple TCP segments. To use this option, you must also enable "Allow subdissectors to reassemble TCP streams" in the TCP protocol settings.
TRUE or FALSE (case-insensitive)
sip.desegment_headers: TRUE
Whether the SIP dissector should use the "Content-length:" value, if present, to reassemble the body of a request spanning multiple TCP segments, and reassemble chunked data spanning multiple TCP segments. To use this option, you must also enable "Allow subdissectors to reassemble TCP streams" in the TCP protocol settings.
TRUE or FALSE (case-insensitive)
sip.desegment_body: TRUE
Using these flags with -o option in tshark, preferences can be custiomized. I used the following tshark command for my problem :
/home/atsuser/Tools/wireshark/tshark -T fields -E header=y -e ip.src -e tcp.srcport -e ip.dst -e tcp.dstport -e frame.number -r 4.cap -o sip.desegment_headers:FALSE -o sip.desegment_body:FALSE -o tcp.desegment_tcp_streams:FALSE -R "sip.Status-Code eq 500"
I found the preference names at the location "%USERPROFILE%\Application Data\Wireshark" on my windows machine.
In my office firewall I use a command like this:
$ sudo tcpdump -v -s 1500 -i eth0 port 25 | grep 'smtp: S'
to monitor LAN clients sending mail (I need to early detect any possible spammer bot from some client, we have very looooose security policies, here... :-().
So far, so good: I have a continuous output as soon any client sends an email.
But, if I add some filter to get a cleaner output, something like this:
$ sudo tcpdump -v -s 1500 -i eth0 port 25 | grep 'smtp: S' | perl -pe 's/(.*?\)) (.*?)\.\d+ \>(.*)/$2/'
(here I intend to get only source ip/name), I do not get any output until tcpdump output is more than (bash?) buffer size... (or at least I suppose so...).
Nothing changes using 'sed' instead of 'perl'...
Any hint to get a continuous output of filtered data?
Put stdbuf before the first command:
sudo stdbuf -o0 tcpdump ...
But, if I add some filter to get a cleaner output, something like
this:
Use the --line-buffered option for grep:
--line-buffered
Use line buffering on output. This can cause a performance
penalty.
try maybe a sed --unbuffered (or -u sometimes like on AIX) to have a stram version (not waiting the EOF)
Okay, I want to have Nmap scan an IP range for computers with a certain port open (port 80 in this case) and have it output all the IP's it finds into a text file, stored in this format:
192.168.0.1
192.168.0.185
192.168.0.192
192.168.0.195
So to output the file, I tried using this command:
nmap -sT -p 80 -ttl 40 192.168.0.0-255 -oG - | grep "80/open" > output.txt
Where "output.txt" is the output file that contains the results. So a line of output.txt looks
like this:
Host: 192.168.0.1 () Ports: 80/open/tcp//http///
So I basically want it only to output the IP address with port 80 open, and nothing else.
I want it to not output the "Host: " or the "()" and "Ports: 80/open/tcp//http///" lines. So is there anyway I can have Nmap not put that stuff into the output file? Or make it only
output the IP addresses? I tried looking at the map page, it was of little help. And I looked all over the Internet and that wasn't very useful either. So does anyone know how I can do this? Thanks
Awk is your friend!
$ nmap -sT -p 80 192.168.0.0/24 -oG - | awk '/ 80\/open/{print $2}' > output.txt
This will find lines with port 80 open (notice the space before 80, if you plan to scan more than the one port!), and print field 2, splitting on whitespace. Another way to do it would be:
$ nmap -sT -p 80 --open 192.168.0.0/24 -oG - | awk '$4=="Ports:"{print $2}' > output.txt
This one uses the --open argument to Nmap to only produce output for hosts with open ports. The awk command checks that this is a "Ports" line, not a "Status" line (which may only show up when using -v, but I'm not positive) before printing the IP address.
Note that it is usually in your best interests to save the scan results to a file, to avoid needing to repeat the scan if you decide to extract some different information. If you choose to do this, I would recommend using the XML output (-oX), since there are lots of analysis tools that have parsers built for it already.
Having nmap produce exactly what you want would indeed be nice. But as a more general solution:
$ nmap ... | grep ... | tr '/' ' ' | awk '{ print $2,$5; }
192.168.0.1 80
Or maybe:
nmap ... | grep ... | tr '/' ' ' | cut -d' ' -f2,8
I found a script called scanreport.sh very useful. Although its not necessary, you could just use awk as suggested, but thought it might be of interest.
It gives the ability to output the nmap results nicely by service or port (with highlighting). It uses the grep-able output from nmap (-oG) after a quick tidy from grep -v ^# nmapoutput.txt > report.txt
Example
nmap -sS 192.168.1.22 -oG /directory/of/choice/results.txt
grep -v ^# results.txt > report.txt
./scanreport.sh -f report.txt
Host: 192.168.1.22 ()
22 open tcp ssh OpenSSH 5.3p1 Debian 3ubuntu4 (protocol 2.0)
80 open tcp http Apache httpd 2.2.14 ((Ubuntu))
./scanreport.sh -f report.txt -p 80
Host: 192.168.1.22 ()
80 open tcp http Apache httpd 2.2.14 ((Ubuntu))
./scanreport.sh -f report.txt -s ssh
Host: 192.168.1.22 ()
22 open tcp ssh OpenSSH 5.3p1 Debian 3ubuntu4 (protocol 2.0)
Plenty of stuff on google about it but here a link to one ref.
./scanreport.sh