tcpdump is a most powerful and widely used command-line packets sniffer or package analyzer tool which is used to capture or filter TCP/IP packets that received or transferred over a network on a specific interface. It is available under most of the Linux/Unix based operating systems. tcpdump also gives us an option to save captured packets in a file for future analysis. It saves the file in a pcap format, that can be viewed by tcpdump command or an open source GUI based tool called Wireshark (Network Protocol Analyzer) that reads tcpdump pcap format files.
![]() What is tcpdump
One of the most common uses of tcpdump is to determine whether you are getting basic two-way communication. Lack of communication could be due to the following:
WinDump is TCPDump command line packet analyzer for windows. WinDump is fully compatible with TCPDUMP have same commands and features available on windows. If you want to traces the packets for some analysis purpose. We can easily capture packets on a particular network interface card as well as trace route of packet using Win Dump. Installing guacd¶ guacd is an optional service that provides the translation layer for RDP, VNC, and SSH for the remote control functionality in the Cuckoo web interface. Without it, remote control wonât work. Versions 0.9.9 and up will work, but we recommend installing the latest version.
WHY TCPDUMP?
tcpdump is the premier network analysis tool for information security professionals. Having a solid grasp of this über-powerful application is mandatory for anyone desiring a thorough understanding of TCP/IP. Many prefer to use higher level analysis tools such as Wireshark, but I believe this to usually be a mistake.
When using a tool that displays network traffic a more natural (raw) way the burden of analysis is placed directly on the human rather than the application. This approach cultivates a continued and elevated understanding of the TCP/IP suite, and for this reason, I strongly advocate using tcpdump instead of other tools whenever possible.
BASICS
Below are a few options you can use when configuring tcpdump. Theyâre easy to forget and/or confuse with other types of filters, e.g., Wireshark, so hopefully, this page can serve as a reference for you, as it does me. here are the main ones I like to keep in mind depending on what Iâm looking at.
OPTIONS:
-i any : Listen on all interfaces just to see if youâre seeing any traffic. -i eth0 : Listen on the eth0 interface. -D : Show the list of available interfaces -n : Donât resolve hostnames. -nn : Donât resolve hostnames or port names. -q : Be less verbose (more quiet) with your output. -t : Give human-readable timestamp output. -tttt : Give maximally human-readable timestamp output. -X : Show the packetâs contents in both hex and ASCII. -XX : Same as -X, but also shows the ethernet header. -v, -vv, -vvv : Increase the amount of packet information you get back. -c : Only get x number of packets and then stop. -s : Define the snaplength (size) of the capture in bytes. Use -s0 to get everything, unless you are intentionally capturing less. -S : Print absolute sequence numbers. -e : Get the ethernet header as well. -q : Show less protocol information. -E : Decrypt IPSEC traffic by providing an encryption key. EXPRESSIONS
In tcpdump, Expressions allow you to trim out various types of traffic and find exactly what youâre looking for. Mastering the expressions and learning to combine them creatively is what makes one truly powerful with tcpdump.
There are three main types of expression: type, dir, and proto.
How to Install tcpdump in Linux
Many of Linux distributions already shipped with tcpdump tool, if in case you donât have it on systems, you can install it using following Yum command for RedHat Based linux.
Once the tcpdump tool is installed on systems, you can continue to browse following commands with their examples.
Basic Examples
So, now that weâve seen what our options are, letâs look at some real-world examples that weâre likely to see in our everyday work.
1. BASIC COMMUNICATION
Just see whatâs going on, by looking at all interfaces.
2. SPECIFIC INTERFACE
Basic view of whatâs happening on a particular interface.
3. RAW OUTPUT VIEW
Verbose output, with no resolution of hostnames or port numbers, absolute sequence numbers, and human-readable timestamps.
4. FIND TRAFFIC BY IP
One of the most common queries, this will show you traffic from 1.2.3.4, whether itâs the source or the destination.
5. SEEING MORE OF THE PACKET WITH HEX OUTPUT
Hex output is useful when you want to see the content of the packets in question, and itâs often best used when youâre isolating a few candidates for closer scrutiny.
6. FILTERING BY SOURCE AND DESTINATION
Itâs quite easy to isolate traffic based on either source or destination using src and dst.
7. FINDING PACKETS BY NETWORK
To find packets going to or from a particular network, use the net option. You can combine this with the src or dst options as well.
8. SHOW TRAFFIC RELATED TO A SPECIFIC PORT
You can find specific port traffic by using the port option followed by the port number.
9. SHOW TRAFFIC OF ONE PROTOCOL
If youâre looking for one particular kind of traffic, you can use tcp, udp, icmp, and many others as well.
10. SHOW ONLY IP6 TRAFFIC
You can also find all IP6 traffic using the protocol option.
11. FIND TRAFFIC USING PORT RANGES
You can also use a range of ports to find traffic.
12. FIND TRAFFIC BASED ON PACKET SIZE
If youâre looking for packets of a particular size you can use these options. You can use less, greater, or their associated symbols that you would expect from mathematics.
13. WRITING CAPTURES TO A FILE
Itâs often useful to save packet captures into a file for analysis in the future. These files are known as PCAP (PEE-cap) files, and they can be processed by hundreds of different applications, including network analyzers, intrusion detection systems, and of course by tcpdump itself. Here weâre writing to a file called capture_file using the -w switch.
14. READING PCAP FILES
You can read PCAP files by using the -r switch. Note that you can use all the regular commands within tcpdump while reading in a file; youâre only limited by the fact that you canât capture and process what doesnât exist in the file already.
Advanced Examples
Now that weâve seen what we can do with the basics through some examples, letâs look at some more advanced stuff.
ITâS ALL ABOUT THE COMBINATIONS
Being able to do these various things individually is powerful, but the real magic of tcpdump comes from the ability to combine options in creative ways in order to isolate exactly what youâre looking for. There are three ways to do combinations, and if youâve studied programming at all theyâll be pretty familiar to you.
Here are some examples of combined commands.
1. FROM SPECIFIC IP AND DESTINED FOR A SPECIFIC PORT
Letâs find all traffic from 10.5.2.3 going to any host on port 3389.
2. FROM ONE NETWORK TO ANOTHER
Letâs look for all traffic coming from 192.168.x.x and going to the 10.x or 172.16.x.x networks, and weâre showing hex output with no hostname resolution and one level of extra verbosity.
3. NON ICMP TRAFFIC GOING TO A SPECIFIC IP
This will show us all traffic going to 192.168.0.2 that is not ICMP.
![]() 4. TRAFFIC FROM A HOST THAT ISNâT ON A SPECIFIC PORT
This will show us all traffic from a host that isnât SSH traffic (assuming default port usage).
As you can see, you can build queries to find just about anything you need. The key is to first figure out precisely what youâre looking for and then to build the syntax to isolate that specific type of traffic.
Summary
tcpdump is a valuable tool for anyone looking to get into networking or information security. The raw way it interfaces with traffic, combined with the precision it offers in inspecting packets make it the best possible tool for learning TCP/IP. Protocol Analyzers like Wireshark are great, but if you want to truly master packet-fu, you must become one with tcpdump first.
Well, this primer should get you going strong, but the man page should always be handy for the most advanced and one-off usage scenarios. I truly hope this has been useful to you.
MicroOLAP TCPDUMP for Windows accurately reproduces all features of the original tcpdump by LBNL's Network Research Group , developed for the UNIX systems.
Since MicroOLAP TCPDUMP for Windows is compiled with the Packet Sniffer SDK, it has the following advantages: does not require any third-party preinstalled drivers, works from the single 400K .EXE file, supports 1Gbit networks, may be launched remotely using Windows Terminal, Radmin, and other remote administration systems, it is portable, i.e. it works from removable devices, supports Loopback adapter. Currently MicroOLAP TCPDUMP supports the following operation systems: Windows 98, Windows ME, Windows NT, Windows 2000, Windows XP, Windows 2003, Wndows Vista, Windows LongHorn.
Features
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