How to capture packets using wireshark
About
Wireshark is the world's foremost network protocol analyzer.
It let you capture and interactively browse the traffic running on a computer network.
More information about Wireshark can be found here
Install
To install Wireshark put this command to Terminal:
yum -y install wireshark
Usage
Capture all traffic
After that you can use command:
tethereal -i eth0 -w /home/capture.pcap
Please note that in this example and other examples bellow we are using network interface eth0. When you run this command in your server, your interface can have other name (eth1, em1, etc), so you need to put your server actual interface name.
To save a dump of packets please stop capturing by pressing ctrl+c
Packets will be saved to directory /home/capture.pcap
You can send captured file capture.pcap from your server and open with Wireshark GUI and analyse the packets.
Capture only SIP traffic
If you have many calls, capturing all traffic will result in huge file after few minutes. Often, we are only interested in SIP traffic (which by default is sent/received on 5060 port), so to capture only SIP traffic you can use this command:
tethereal -i eth0 -w /home/capture.pcap port 5060
Capture SIP Traffic only for specific IP
tethereal -i eth0 -w /home/siptrace.pcap port 5060 and host 123.123.123.123
Capture SIP traffic on port 5060 and RTP traffic
tcpdump -i eth0 udp port 5060 or udp portrange 10000-20000 -s 0 -w capture.cap
Capture SIP traffic on port 5060 and RTP traffic into split files
tcpdump -i eth0 udp port 5060 or portrange 10000-20000 -s 0 -C 200 -Z root -w capture
Capture SIP traffic on port 5060 and RTP traffic for specific IP address
tcpdump -i eth0 port 5060 and host 192.168.0.192 or 192.168.0.8 or udp portrange 10000-20000 -s 0 -w capture.pcap
Capture traffic into split files
If complete traffic trace is needed, and you need to leave trace for a long time it is convenient to split trace into smaller files and cycle the files after certain amount of files, as otherwise Wireshark can take very long time or crash if we want to open very large file. This can be achieved using tcppdump -W and -C options. -C specify size of file (in MB) and -W specify the file count after new files start overwrite old ones. For example, this command:
tcpdump -i eth0 -s 0 -C 200 -W 40 -Z root -w capture
This command will create a new file once current file reach 200MB and after 40 files will be created, news one will overwrite oldest one and so on, thus using max 200*40 = 8000MB of disk space.
To capture traffic from/to specific IP you can use this command:
tcpdump -i eth0 host 1.2.3.4 -s 0 -C 200 -W 40 -Z root -w capture
To capture only SIP traffic you can use this command:
tcpdump -i eth0 port 5060 -s 0 -C 200 -W 40 -Z root -w capture
Additional notes
You can analyse network packets on real time on server using command:
tshark
More options with command tshark you can find here.
