Linux Basics, Security & Hacking
willi moser (2005-12-12)
Copyright © 2004-2005 Richard Sharpe, Ed Warnicke, Ulf Lamping
All logos and trademarks in this document are property of their respective owner.
Windows Software:
WinPcap_3_1.exe Please set it up first!
ethereal-setup-0.10.13.exe
Ethereal is one of those programs that many network managers would love to be able to use, but they are often prevented from getting what they would like from Ethereal because of the lack of documentation.
This document is part of an effort by the Ethereal team to improve the usability of Ethereal.
We hope that you find it useful, and look forward to your comments.
The intended audience of this book is anyone using Ethereal.
This book will explain all the basics and also some of the advanced features that Ethereal provides. As Ethereal has become a very complex program since the early days, not every feature of Ethereal might be explained in this book.
This book is not intended to explain network sniffing in general and it will not provide details about specific network protocols. A lot of useful information regarding these topics can be found at the Ethereal Wiki at http://wiki.ethereal.com
By reading this book, you will learn how to install Ethereal, how to use the basic elements of the graphical user interface (like the menu) and what's behind some of the advanced features that are maybe not that obvious at first sight. It will hopefully guide you around some common problems that frequently appears for new (and sometimes even advanced) users of Ethereal.
The authors would like to thank the whole Ethereal team for their assistance. In particular, the authors would like to thank:
The authors would also like to thank the following people for their helpful feedback on this document:
The authors would like to acknowledge those man page and README authors for the ethereal project from who sections of this document borrow heavily:
README.idl2eth
the section called “idl2eth:
Creating dissectors from Corba IDL files ” is derived.
This book was originally developed by Richard Sharpe with funds provided from the Ethereal Fund. It was updated by Ed Warnicke and more recently redesigned and updated by Ulf Lamping.
It is written in DocBook/XML.
You will find some specially marked parts in this book:
You should pay attention to a warning, as otherwise data loss might occur.
A note will point you to common mistakes and things that might not be obvious.
Tips will be helpful for your everyday work using Ethereal.
The latest copy of this documentation can always be found at: http://www.ethereal.com/docs/#usersguide.
Should you have any feedback about this document, please send them to the authors through ethereal-dev[AT]ethereal.com.
Ethereal is a network packet analyzer. A network packet analyzer will try to capture network packets and tries to display that packet data as detailed as possible.
You could think of a network packet analyzer as a measuring device used to examine what's going on inside a network cable, just like a voltmeter is used by an electrician to examine what's going on inside an electric cable (but at a higher level, of course).
In the past, such tools were either very expensive, proprietary, or both. However, with the advent of Ethereal, all that has changed.
Ethereal is perhaps one of the best open source packet analyzers available today.
Here are some examples people use Ethereal for:
Beside these examples, Ethereal can be helpful in many other situations too.
The following are some of the many features Ethereal provides:
However, to really appreciate its power, you have to start using it.
Figure 1.1, “ Ethereal captures packets and allows you to examine their content. ” shows Ethereal having captured some packets and waiting for you to examine them.
Figure 1.1. Ethereal captures packets and allows you to examine their content.
Despite its name, Ethereal can capture traffic from network media other than Ethernet. Which media types are supported, depends on many things like the operating system you are using. An overview of the supported media types can be found at: http://www.ethereal.com/media.html.
Ethereal can open packets captured from a large number of other capture programs. For a list of input formats see the section called “Input File Formats”.
Ethereal can save packets captured in a large number of formats of other capture programs. For a list of output formats see the section called “Output File Formats”.
There are protocol decoders (or dissectors, as they are known in Ethereal) for a great many protocols: see Appendix B, Protocols and Protocol Fields.
Ethereal is an open source software project, and is released under the GNU General Public Licence (GPL). You can freely use Ethereal on any number of computers you like, without worrying about license keys or fees or such. In addition, all source code is freely available under the GPL. Because of that, it is very easy for people to add new protocols to Ethereal, either as plugins, or built into the source, and they often do!
Here are some things Ethereal does not provide:
Ethereal currently runs on most UNIX platforms and various Windows platforms. It requires GTK+, GLib, libpcap and some other libraries in order to run.
If a binary package is not available for your platform, you should download the source and try to build it. Please report your experiences to ethereal-dev[AT]ethereal.com.
Binary packages are available for at least the following platforms:
Maintained:
Unsupported/Unmaintained (because lack of required libraries):
No experiences (fresh versions):
Please provide your experiences about these fresh versions to: ethereal-dev[AT]ethereal.com.
You can get the latest copy of the program from the Ethereal website: http://www.ethereal.com/download.html. The website allows you to choose from among several mirrors for downloading.
A new Ethereal version will typically become available every 4-8 weeks.
If you want to be notified about new Ethereal releases, you should subscribe to the ethereal-announce mailing list. You will find more details in the section called “Mailing Lists”.
William Shakespeare wrote: "A rose by any other name would smell as sweet." And so it is with Ethereal, as there appears to be two different ways that people pronounce the name.
Some people pronounce it ether-real, while others pronounce it e-the-real, as in ghostly, insubstantial, etc.
You are welcome to call it what you like, as long as you find it useful. The FAQ gives the official pronunciation as "e-the-real".
In late 1997, Gerald Combs needed a tool for tracking down networking problems and wanted to learn more about networking, so he started writing Ethereal as a way to solve both problems.
Ethereal was initially released, after several pauses in development, in July 1998 as version 0.2.0. Within days, patches, bug reports, and words of encouragement started arriving, so Ethereal was on its way to success.
Not long after that Gilbert Ramirez saw its potential and contributed a low-level dissector to it.
In October, 1998, Guy Harris of Network Appliance was looking for something better than tcpview, so he started applying patches and contributing dissectors to Ethereal.
In late 1998, Richard Sharpe, who was giving TCP/IP courses, saw its potential on such courses, and started looking at it to see if it supported the protocols he needed. While it didn't at that point, new protocols could be easily added. So he started contributing dissectors and contributing patches.
The list of people who have contributed to Ethereal has become very long since then, and almost all of them started with a protocol that they needed that Ethereal did not already handle. So they copied an existing dissector and contributed the code back to the team.
Ethereal was initially developed by Gerald Combs. Ongoing development and maintenance of Ethereal is handled by the Ethereal team, a loose group of individuals who fix bugs and provide new functionality.
There have also been a large number of people who have contributed protocol dissectors to Ethereal, and it is expected that this will continue. You can find a list of the people who have contributed code to Ethereal by checking the about dialog box of Ethereal, or at the authors page on the Ethereal web site.
Ethereal is an open source software project, and is released under the GNU General Public Licence (GPL). All source code is freely available under the GPL. You are welcome to modify Ethereal to suit your own needs, and it would be appreciated if you contribute your improvements back to the Ethereal team.
You gain three benefits by contributing your improvements back to the community:
The Ethereal source code and binary kits for some platforms are all available on the download page of the Ethereal website: http://www.ethereal.com/download.html.
If you have problems, or need help with Ethereal, there are several places that may be of interest to you (well, beside this guide of course).
You will find lot's of useful information on the Ethereal homepage at http://www.ethereal.com.
The Ethereal Wiki at http://wiki.ethereal.com provides a wide range of information related to Ethereal and packet capturing in general. You will find a lot of information not part of this user's guide. For example, there is an explanation how to capture on a switched network, an ongoing effort to build a protocol reference and a lot more.
And best of all, if you would like to contribute your knowledge on a specific topic (maybe a network protocol you know well), you can edit the wiki pages by simply using your webbrowser.
The "Frequently Asked Questions" will list often asked questions and the corresponding answers.
Before sending any mail to the mailing lists below, be sure to read the FAQ, as it will often answer the question(s) you might have. This will save yourself and others a lot of time (keep in mind that a lot of people are subscribed to the mailing lists).
You will find the FAQ inside Ethereal by clicking the menu item Help/Contents and selecting the FAQ page in the upcoming dialog.
An online version is available at the ethereal website: http://www.ethereal.com/faq.html. You might prefer this online version, as it's typically more up to date and the HTML format is easier to use.
There are several mailing lists of specific Ethereal topics available:
You can subscribe to each of these lists from the Ethereal web site: http://www.ethereal.com. Simply select the mailing lists link on the left hand side of the site. The lists are archived at the Ethereal web site as well.
You can search in the list archives to see if someone asked the same question some time before and maybe already got an answer. That way you don't have to wait until someone answers your question.
Before reporting any problems, please make sure you have installed the latest version of Ethereal.
When reporting problems with Ethereal, it is helpful if you supply the following information:
Do not send large files (>100KB) to the mailing lists, just place a note that further data is available on request. Large files will only annoy a lot of people on the list who are not interested in your specific problem. If required, you will be asked for further data by the persons who really can help you.
If you send captured data to the mailing lists, be sure they don't contain any sensitive or confidential information like passwords or such.
When reporting crashes with Ethereal, it is helpful if you supply the traceback information (besides the information mentioned in "Reporting Problems").
You can obtain this traceback information with the following commands:
$ gdb `whereis ethereal | cut -f2 -d: | cut -d' ' -f2` core >& bt.txt backtrace ^D $
Type the characters in the first line verbatim! Those are back-tics there!
backtrace is a gdb command. You
should enter it verbatim after the first line shown above, but it will
not be echoed. The ^D (Control-D, that is, press the Control key and
the D key together) will cause gdb to
exit. This will leave you with a file called
bt.txt
in the current directory. Include the file with your bug
report.
If you do not have gdb available, you will have to check out your operating system's debugger.
You should mail the traceback to the ethereal-dev[AT]ethereal.com mailing list.
The Windows distributions don't contain the symbol files (.pdb), because they are very large. For this reason it's not possible to create a meaningful backtrace file from it. You should report your crash just like other problems, using the mechanism described above.
As with all things, there must be a beginning, and so it is with Ethereal. To use Ethereal, you must:
Currently, only two or three Linux distributions ship Ethereal, and they are commonly shipping an out-of-date version. No other versions of UNIX ship Ethereal so far, and Microsoft does not ship it with any version of Windows. For that reason, you will need to know where to get the latest version of Ethereal and how to install it.
This chapter shows you how to obtain source and binary packages, and how to build Ethereal from source, should you choose to do so.
The following are the general steps you would use:
This may involve building and/or installing other necessary packages.
You can obtain both source and binary distributions from the Ethereal web site: http://www.ethereal.com. Simply select the download link, and then select either the source package or binary package of your choice from the mirror site closest to you.
In general, unless you have already downloaded Ethereal before, you will most likely need to download several source packages if you are building Ethereal from source. This is covered in more detail below.
Once you have downloaded the relevant files, you can go on to the next step.
While you will find a number of binary packages available on the Ethereal web site, you might not find one for your platform, and they often tend to be several versions behind the current released version, as they are contributed by people who have the platforms they are built for.
For this reason, you might want to pull down the source distribution and build it, as the process is relatively simple.
Before you build Ethereal from sources, or install a binary package, you must ensure that you have the following other packages installed:
You will also need Glib. Both can be obtained from www.gtk.org
You can obtain libpcap from www.tcpdump.org
Depending on your system, you may be able to install these from binaries, e.g. RPMs, or you may need to obtain them in source code form and build them.
If you have downloaded the source for GTK+, the instructions shown in Example 2.1, “Building GTK+ from source” may provide some help in building it:
Example 2.1. Building GTK+ from source
gzip -dc gtk+-1.2.10.tar.gz | tar xvf - <much output removed> cd gtk+-1.2.10 ./configure <much output removed> make <much output removed> make install <much output removed>
You may need to change the version number of gtk+ in Example 2.1, “Building GTK+ from source” to match the version of GTK+ you have downloaded. The directory you change to will change if the version of GTK+ changes, and in all cases, tar xvf - will show you the name of the directory you should change to.
If you use Linux, or have GNU tar installed, you can use tar zxvf gtk+-1.2.10.tar.gz. It is also possible to use gunzip -c or gzcat rather than gzip -dc on many UNIX systems.
If you downloaded gtk+ or any other tar file using Windows, you may find your file called gtk+-1_2_8_tar.gz.
You should consult the GTK+ web site if any errors occur in carrying out the instructions in Example 2.1, “Building GTK+ from source”.
If you have downloaded the source to libpcap, the general instructions shown in Example 2.2, “Building and installing libpcap” will assist in building it. Also, if your operating system does not support tcpdump, you might also want to download it from the tcpdump web site and install it.
Example 2.2. Building and installing libpcap
gzip -dc libpcap-0.8.3.tar.Z | tar xvf - <much output removed> cd libpcap_0_8_3 ./configure <much output removed> make <much output removed> make install <much output removed> make install-incl <much output removed>
The directory you should change to will depend on the version of libpcap you have downloaded. In all cases, tar xvf - will show you the name of the directory that has been unpacked.
When installing the include files, you might get the error shown in Example 2.3, “Errors while installing the libpcap include files” when you submit the command make install-incl.
Example 2.3. Errors while installing the libpcap include files
/usr/local/include/pcap.h /usr/bin/install -c -m 444 -o bin -g bin ./pcap-namedb.h \ /usr/local/include/pcap-namedb.h /usr/bin/install -c -m 444 -o bin -g bin ./net/bpf.h \ /usr/local/include/net/bpf.h /usr/bin/install: cannot create regular file \ `/usr/local/include/net/bpf.h': No such file or directory make: *** [install-incl] Error 1
If you do, simply create the missing directory with the following command:
mkdir /usr/local/include/net
and rerun the command make install-incl.
Under RedHat 6.x and beyond (and distributions based on it, like Mandrake) you can simply install each of the packages you need from RPMs. Most Linux systems will install GTK+ and GLib in anycase, however, you will probably need to install the devel versions of each of these packages. The commands shown in Example 2.4, “ Installing required RPMs under RedHat Linux 6.2 and beyond ” will install all the needed RPMs if they are not already installed.
Example 2.4. Installing required RPMs under RedHat Linux 6.2 and beyond
cd /mnt/cdrom/RedHat/RPMS rpm -ivh glib-1.2.6-3.i386.rpm rpm -ivh glib-devel-1.2.6-3.i386.rpm rpm -ivh gtk+-1.2.6-7.i386.rpm rpm -ivh gtk+-devel-1.2.6-7.i386.rpm rpm -ivh libpcap-0.4-19.i386.rpm
If you are using a version of RedHat later than 6.2, the required RPMs have most likely changed. Simply use the correct RPMs from your distribution.
Under Debian you can install Ethereal using apt-get. apt-get will handle any dependency issues for you. Example 2.5, “Installing debs under Debian” shows how to do this.
Example 2.5. Installing debs under Debian
apt-get install ethereal
Use the following general steps if you are building Ethereal from source under a UNIX operating system:
tar zxvf ethereal-0.10.12-tar.gz
For other versions of UNIX, You will want to use the following commands:
gzip -d ethereal-0.10.12-tar.gz tar xvf ethereal-0.10.12-tar
The pipeline gzip -dc ethereal-0.10.12-tar.gz | tar xvf - will work here as well.
If you have downloaded the Ethereal tarball under Windows, you may find that your browser has created a file with underscores rather than periods in its file name.
./configure
If this step fails, you will have to rectify the problems and rerun configure. Troubleshooting hints are provided in the section called “Troubleshooting during the install on Unix”.
make
make install
Once you have installed Ethereal with make install above, you should be able to run it by entering ethereal.
In general, installing the binary under your version of UNIX will be specific to the installation methods used with your version of UNIX. For example, under AIX, you would use smit to install the Ethereal binary package, while under Tru64 UNIX (formerly Digital UNIX) you would use setld.
Use the following command to install the Ethereal RPM that you have downloaded from the Ethereal web site:
rpm -ivh ethereal-0.10.5-0.2.2.i386.rpm
If the above step fails because of missing dependencies, install the dependencies first, and then retry the step above. See Example 2.4, “ Installing required RPMs under RedHat Linux 6.2 and beyond ” for information on what RPMs you will need to have installed.
Use the following command to install Ethereal under Debian:
apt-get install ethereal
apt-get should take care of all of the dependency issues for you.
A number of errors can occur during the installation process. Some hints on solving these are provided here.
If the configure stage fails, you will
need to find out why. You can check the file
config.log
in the source directory to find out what failed. The
last few lines of this file should help in determining the problem.
The standard problems are that you do not have GTK+ on your system, or you do not have a recent enough version of GTK+. The configure will also fail if you do not have libpcap (at least the required include files) on your system.
Another common problem is for the final compile and link stage to terminate with a complaint of: Output too long. This is likely to be caused by an antiquated sed (such as the one shipped with Solaris). Since sed is used by the libtool script to construct the final link command, this leads to mysterious problems. This can be resolved by downloading a recent version of sed from http://directory.fsf.org/GNU/sed.html.
If you cannot determine what the problems are, send mail to the
ethereal-dev mailing list explaining your
problem, and including the output from config.log
and anything else you think is relevant, like a trace of the
make stage.
It is recommended to use the binary installer for Windows, until you want to start developing Ethereal on the Windows platform.
For further information how to build Ethereal for Windows from the sources, have a look at the Development Wiki: http://wiki.ethereal.com/Development for the latest available development documentation.
In this section we explore installing Ethereal under Windows from the binary packages.
You may acquire a binary installer of Ethereal named something like:
ethereal-setup-x.y.z.exe
.
Simply download the Ethereal installer from: http://www.ethereal.com/download.html#releases and execute it.
Since Ethereal Version 0.10.12, the WinPcap installer has become part of the main Ethereal installer, so you don't need to download and install two separate packages any longer!
You can simply start the Ethereal installer without any command line parameters, it will show you the usual interactive installer.
There are some command line parameters available:
Example:
ethereal-setup-0.10.13.exe /NCRC /S /desktopicon=yes /quicklaunchicon=no /D=C:\Program Files\Foo
Beside the usual installer options like where to install the program, there are several optional components.
If you are unsure which settings to select, just keep the default settings.
The Components (both Ethereal GTK1 and 2 cannot be installed at the same time):
The dissection extensions for Ethereal and Tethereal:
The Tools:
The Additional Tasks:
As mentioned above, the Ethereal installer (since version 0.10.12) takes care of the installation of WinPcap, so usually you don't have to worry about WinPcap at all!
If you do not have WinPcap installed you will be able to open saved capture files, but you will not be able to capture live network traffic.
While running, the Ethereal installer detects which WinPcap version is currently installed and will install WinPcap, if none or an older version is detected.
More WinPcap info:
The following is only necessary if you want to try a different version than the one included in the Ethereal installer, e.g. because a new WinPcap (beta) version was released.
Additional WinPcap versions (including newer alpha or beta releases) can be downloaded from the following locations:
At the download page you will find a single installer exe called something like "auto-installer", which can be installed under various Windows systems, including 9x/Me/NT4.0/2000/XP.
From time to time you may want to update your installed Ethereal to a more recent version. If you join Ethereal's announce mailing list, you will be informed about new Ethereal versions, see the section called “Mailing Lists” for details how to subscribe to this list.
New versions of Ethereal usually become available every 4-8 weeks. Updating Ethereal is done the same way as installing it, you simply download and start the installer exe. A reboot is usually not required and all your personal settings remain unchanged.
New versions of WinPcap are less frequently available, maybe only once in a year. You will find WinPcap update instructions where you can download new WinPcap versions. Usually you have to reboot the machine after installing a new WinPcap version.
If you have an older version of WinPcap installed, you must un-install it before installing the current version. Recent versions of the WinPcap installer will take care of this.
You can uninstall Ethereal the usual way, using the "Add or Remove Programs" option inside the Control Panel. Select the "Ethereal" entry to start the uninstallation procedure.
The Ethereal uninstaller will provide several options which things to be uninstalled, the default is to remove the core components but keep the personal settings, WinPcap and alike.
WinPcap won't be uninstalled by default, as other programs than Ethereal may use it as well.
You can uninstall WinPcap independantly of Ethereal, using the "WinPcap" entry in the "Add or Remove Programs" of the Control Panel.
After uninstallation of WinPcap you can't capture anything with Ethereal.
It might be a good idea to reboot Windows afterwards.
By now you have installed Ethereal and are most likely keen to get started capturing your first packets. In the next chapters we will explore:
You can start Ethereal from your shell or window manager.
When starting Ethereal it's possible to specify optional settings using the command line. See the section called “Start Ethereal from the command line” for details.
In the following chapters, a lot of screenshots from Ethereal will be shown. As Ethereal runs on many different platforms and there are different versions of the underlying GUI toolkit (GTK 1.x / 2.x) used, your screen might look different from the provided screenshots. But as there are no real differences in functionality, these screenshots should still be well understandable.
Lets look at Ethereal's user interface. Figure 3.1, “The Main window” shows Ethereal as you would usually see it after some packets captured or loaded (how to do this will be described later).
Figure 3.1. The Main window
Ethereal's main window consist of parts that are commonly known from many other GUI programs.
The layout of the main window can be customized by changing preference settings. See the section called “Preferences” for details!
The Ethereal menu sits on top of the Ethereal window. An example is shown in Figure 3.2, “The Menu”.
Menu items will be greyed out if the corresponding feature isn't available. For example, you cannot save a capture file if you didn't capture or load any data before.
Figure 3.2. The Menu
It contains the following items:
Each of these menu items is described in more detail in the sections that follow.
You can access menu items directly or by pressing the corresponding accelerator keys, which are shown at the right side of the menu. For example, you can press the Control (or Strg in German) and the K keys together to open the capture dialog.
The Ethereal file menu contains the fields shown in Table 3.1, “File menu items”.
Figure 3.3. The "File" Menu
Table 3.1. File menu items
Menu Item | Accelerator | Description |
---|---|---|
Open... | Ctrl+O | This menu item brings up the file open dialog box that allows you to load a capture file for viewing. It is discussed in more detail in the section called “The "Open Capture File" dialog box”. |
Open Recent | This menu item shows a submenu containing the recently opened capture files. Clicking on one of the submenu items will open the corresponding capture file directly. | |
Merge... | This menu item brings up the merge file dialog box that allows you to merge a capture file into the currently loaded one. It is discussed in more detail in the section called “Merging capture files”. | |
Close | Ctrl+W | This menu item closes the current capture. If you haven't saved the capture, you will be asked to do so first (this can be disabled by a preference setting). |
------ | ||
Save | Ctrl+S | This menu item saves the current capture. If you have not set a
default capture file name (perhaps with the -w <capfile> option),
Ethereal pops up the Save Capture File As dialog box (which is
discussed further in
the section called “The "Save Capture File As" dialog box”).
Note!If you have already saved the current capture, this menu item will be greyed out. Note!You cannot save a live capture while it is in progress. You must stop the capture in order to save. |
Save As... | Shift+Ctrl+S | This menu item allows you to save the current capture file to whatever file you would like. It pops up the Save Capture File As dialog box (which is discussed further in the section called “The "Save Capture File As" dialog box”). |
------ | ||
File Set > List Files | This menu item allows you to show a list of files in a file set. It pops up the Ethereal List File Set dialog box (which is discussed further in the section called “File Sets”). | |
File Set > Next File | If the currently loaded file is part of a file set, jump to the next file in the set. If it isn't part of a file set or just the last file in that set, this item is greyed out. | |
File Set > Previous File | If the currently loaded file is part of a file set, jump to the previous file in the set. If it isn't part of a file set or just the first file in that set, this item is greyed out. | |
------ | ||
Export > as "Plain Text" file... | This menu item allows you to export all, or some, of the packets in the capture file to a plain ASCII text file. It pops up the Ethereal Export dialog box (which is discussed further in the section called “The "Export as Plain Text File" dialog box”). | |
Export > as "PostScript" file... | This menu item allows you to export the (or some) of the packets in the capture file to a PostScript file. It pops up the Ethereal Export dialog box (which is discussed further in the section called “The "Export as PostScript File" dialog box”). | |
Export > as "CSV" (Comma Separated Values packet summary) file... | This menu item allows you to export the (or some) of the packet summaries in the capture file to a .csv file (e.g. used by spreadsheet programs). It pops up the Ethereal Export dialog box (which is discussed further in the section called “The "Export as CSV (Comma Seperated Values) File" dialog box”). | |
Export > as "PSML" file... | This menu item allows you to export the (or some) of the packets in the capture file to a PSML (packet summary markup language) XML file. It pops up the Ethereal Export dialog box (which is discussed further in the section called “The "Export as PSML File" dialog box”). | |
Export > as "PDML" file... | This menu item allows you to export the (or some) of the packets in the capture file to a PDML (packet details markup language) XML file. It pops up the Ethereal Export dialog box (which is discussed further in the section called “The "Export as PDML File" dialog box”). | |
Export > Selected Packet Bytes... | Ctrl+H | This menu item allows you to export the currently selected bytes in the packet bytes pane to a binary file. It pops up the Ethereal Export dialog box (which is discussed further in the section called “The "Export selected packet bytes" dialog box”) |
------ | ||
Print... | Ctrl+P | This menu item allows you to print all (or some of) the packets in the capture file. It pops up the Ethereal Print dialog box (which is discussed further in the section called “Printing packets”). |
------ | ||
Quit | Ctrl+Q | This menu item allows you to quit from Ethereal. Ethereal will ask to save your capture file if you haven't saved it before (this can be disabled by a preference setting). |
The Ethereal Edit menu contains the fields shown in Table 3.2, “Edit menu items”.
Figure 3.4. The "Edit" Menu
Table 3.2. Edit menu items
Menu Item | Accelerator | Description |
---|---|---|
Find Packet... | Ctrl+F | This menu item brings up a dialog box that allows you to find a packet by many criteria. There is further information on finding packets in the section called “Finding packets”. |
Find Next | Ctrl+N | This menu item tries to find the next packet matching the settings from "Find Packet...". |
Find Previous | Ctrl+B | This menu item tries to find the previous packet matching the settings from "Find Packet...". |
------ | ||
Time Reference > Set Time Reference (toggle) | Ctrl+T | This menu item set a time reference on the currently selected packet. See the section called “Packet time referencing” for more information about the time referenced packets. |
Time Reference > Find Next | This menu item tries to find the next time referenced packet. | |
Time Reference > Find Previous | This menu item tries to find the previous time referenced packet. | |
Mark Packet (toggle) | Ctrl+M | This menu item "marks" the currently selected packet. See the section called “Marking packets” for details. |
Mark All Packets | This menu item "marks" all packets. | |
Unmark All Packets | This menu item "unmarks" all marked packets. | |
------ | ||
Preferences... | Shift+Ctrl+P | This menu item brings up a dialog box that allows you to set preferences for many parameters that control Ethereal. You can also save your preferences so Ethereal will use them the next time you start it. More detail is provided in the section called “Preferences”. |
The Ethereal View menu contains the fields shown in Table 3.3, “View menu items”.
Figure 3.5. The "View" Menu
Table 3.3. View menu items
Menu Item | Accelerator | Description |
---|---|---|
Main Toolbar | This menu item hides or shows the main toolbar, see the section called “The "Main" toolbar”. | |
Filter Toolbar | This menu item hides or shows the filter toolbar, see the section called “The "Filter" toolbar”. | |
Statusbar | This menu item hides or shows the statusbar, see the section called “The Statusbar”. | |
------ | ||
Packet List | This menu item hides or shows the packet list pane, see the section called “The "Packet List" pane”. | |
Packet Details | This menu item hides or shows the packet details pane, see the section called “The "Packet Details" pane”. | |
Packet Bytes | This menu item hides or shows the packet bytes pane, see the section called “The "Packet Bytes" pane”. | |
------ | ||
Time Display Format > Time of Day | Selecting this tells Ethereal to display time stamps in time of
day format, see
the section called “Time display
formats and time references”.
Note!The fields "Time of Day", "Date and Time of Day", "Seconds Since Beginning of Capture" and "Seconds Since Previous Packet" are mutually exclusive.
|
|
Time Display Format > Date and Time of Day | Selecting this tells Ethereal to display the time stamps in date and time of day format, see the section called “Time display formats and time references”. | |
Time Display Format > Seconds Since Beginning of Capture | Selecting this tells Ethereal to display time stamps in seconds since beginning of capture format, see the section called “Time display formats and time references”. | |
Time Display Format > Seconds Since Previous Packet | Selecting this tells Ethereal to display time stamps in seconds since previous packet format, see the section called “Time display formats and time references”. | |
Name Resolution > Resolve Name | This item allows you to trigger a name resolve of the current packet only, see the section called “Name Resolution”. | |
Name Resolution > Enable for MAC Layer | This item allows you to control whether or not Ethereal translates MAC addresses into names, see the section called “Name Resolution”. | |
Name Resolution > Enable for Network Layer | This item allows you to control whether or not Ethereal translates network addresses into names, see the section called “Name Resolution”. | |
Name Resolution > Enable for Transport Layer | This item allows you to control whether or not Ethereal translates transport addresses into names, see the section called “Name Resolution”. | |
Colorize Packet List | This item allows you to control wether or not Ethereal should
colorize the packet list.Note!Enabling colorization will slow down the display of new packets while capturing / loading capture files. |
|
Auto Scroll in Live Capture | This item allows you to specify that Ethereal should scroll the packet list pane as new packets come in, so you are always looking at the last packet. If you do not specify this, Ethereal simply adds new packets onto the end of the list, but does not scroll the packet list pane. | |
------ | ||
Zoom In | Ctrl++ | Zoom into the packet data (increase the font size). |
Zoom Out | Ctrl+- | Zoom out of the packet data (decrease the font size). |
Normal Size | Ctrl+= | Set zoom level back to 100% (set font size back to normal). |
Resize All Columns | Resize all column widths so the content will fit into it.
Note!Resizing may take a significant amount of time, especially if a large capture file is loaded. |
|
------ | ||
Expand Subtrees | This menu item expands the currently selected subtree in the packet details tree. | |
Expand All | Ethereal keeps a list of all the protocol subtrees that are expanded, and uses it to ensure that the correct subtrees are expanded when you display a packet. This menu item expands all subtrees in all packets in the capture. | |
Collapse All | This menu item collapses the tree view of all packets in the capture list. | |
------ | ||
Coloring Rules... | This menu item brings up a dialog box that allows you to color packets in the packet list pane according to filter expressions you choose. It can be very useful for spotting certain types of packets, see the section called “Packet colorization”. | |
------ | ||
Show Packet in New Window | This menu item brings up the selected packet in a separate window. The separate window shows only the tree view and byte view panes. | |
Reload | Ctrl-R | This menu item allows you to reload the current capture file. |
The Ethereal Go menu contains the fields shown in Table 3.4, “Go menu items”.
Figure 3.6. The "Go" Menu
Table 3.4. Go menu items
Menu Item | Accelerator | Description |
---|---|---|
Back | Alt+Left | Jump to the recently visited packet in the packet history, much like the page history in a web browser. |
Forward | Alt+Right | Jump to the next visited packet in the packet history, much like the page history in a web browser. |
Go to Packet... | Ctrl-G | Bring up a dialog box that allows you to specify a packet number, and then goes to that packet. See the section called “Go to a specific packet” for details. |
Go to Corresponding Packet | Go to the corresponding packet of the currently selected protocol field. If the selected field doesn't correspond to a packet, this item is greyed out. | |
------ | ||
First Packet | Jump to the first packet of the capture file. | |
Last Packet | Jump to the last packet of the capture file. |
The Ethereal Capture menu contains the fields shown in Table 3.5, “Capture menu items”.
Figure 3.7. The "Capture" Menu
Table 3.5. Capture menu items
Menu Item | Accelerator | Description |
---|---|---|
Interfaces... | This menu item brings up a dialog box that shows what's going on at the network interfaces Ethereal knows of, see the section called “The "Capture Interfaces" dialog box”) . | |
Options... | Ctrl+K | This menu item brings up the Capture Options dialog box (discussed further in the section called “The "Capture Options" dialog box”) and allows you to start capturing packets. |
Start | Immediately start capturing packets with the same settings than the last time. | |
Stop | Ctrl+E | This menu item stops the currently running capture, see the section called “Stop the running capture”) . |
Restart | This menu item stops the currently running capture and starts again with the same options, this is just for convenience. | |
Capture Filters... | This menu item brings up a dialog box that allows you to create and edit capture filters. You can name filters, and you can save them for future use. More detail on this subject is provided in the section called “Defining and saving filters” |
The Ethereal Analyze menu contains the fields shown in Table 3.6, “Analyze menu items”.
Figure 3.8. The "Analyze" Menu
Table 3.6. Analyze menu items
Menu Item | Accelerator | Description |
---|---|---|
Display Filters... | This menu item brings up a dialog box that allows you to create and edit display filters. You can name filters, and you can save them for future use. More detail on this subject is provided in the section called “Defining and saving filters” | |
Apply as Filter > ... | These menu items will change the current display filter and apply the changed filter immediately. Depending on the chosen menu item, the current display filter string will be replaced or appended to by the selected protocol field in the packet details pane. | |
Prepare a Filter > ... | These menu items will change the current display filter but won't apply the changed filter. Depending on the chosen menu item, the current display filter string will be replaced or appended to by the selected protocol field in the packet details pane. | |
------ | ||
Enabled Protocols... | Shift+Ctrl+R | This menu item allows the user to enable/disable protocol dissectors, see the section called “The "Enabled Protocols" dialog box” |
Decode As... | This menu item allows the user to force Ethereal to decode certain packets as a particular protocol, see the section called “User Specified Decodes” | |
User Specified Decodes... | This menu item allows the user to force Ethereal to decode certain packets as a particular protocol, see the section called “Show User Specified Decodes” | |
------ | ||
Follow TCP Stream | This menu item brings up a separate window and displays all the TCP segments captured that are on the same TCP connection as a selected packet, see the section called “Following TCP streams” |
The Ethereal Statistics menu contains the fields shown in Table 3.7, “Statistics menu items”.
Figure 3.9. The "Statistics" Menu
All menu items will bring up a new window showing specific statistical information.
Table 3.7. Statistics menu items
The Ethereal Help menu contains the fields shown in Table 3.8, “Help menu items”.
Figure 3.10. The "Help" Menu
Table 3.8. Help menu items
Menu Item | Accelerator | Description |
---|---|---|
Contents | F1 | This menu item brings up a basic help system. |
Supported Protocols | This menu item brings up a dialog box showing the supported protocols and protocol fields. | |
Manual Pages > ... | This menu item starts a Web browser showing one of the locally installed html manual pages. | |
Ethereal Online > ... | This menu item starts a Web browser showing the chosen webpage from: http://www.ethereal.com. | |
------ | ||
About Ethereal | This menu item brings up an information window that provides some information on Ethereal, such as the plugins, the used folders, ... |
Calling a Web browser might be unsupported in your version of Ethereal. If this is the case, the corresponding menu items will be hidden.
If calling a Web browser fails on your machine, maybe because just nothing happens or the browser is started but no page is shown, have a look at the webbrowser setting in the preferences dialog.
The main toolbar provides quick access to frequently used items from the menu. This toolbar cannot be customized by the user, but it can be hidden using the View menu, if the space on the screen is needed to show even more packet data.
As in the menu, only the items useful in the current program state will be available. The others will be greyed out (e.g. you cannot save a capture file if you haven't loaded one).
Figure 3.11. The "Main" toolbar
Table 3.9. Main toolbar items
Toolbar Icon | Toolbar Item | Corresponding Menu Item | Description |
---|---|---|---|
|
Interfaces... | Capture/Interfaces... | This item brings up the Capture Interfaces List dialog box (discussed further in the section called “Start Capturing”). |
|
Options... | Capture/Options... | This item brings up the Capture Options dialog box (discussed further in the section called “Start Capturing”) and allows you to start capturing packets. |
|
Start | Capture/Start | This item starts capturing packets with the options form the last time. |
|
Stop | Capture/Stop | This item stops the currently running live capture process the section called “Start Capturing”). |
|
Restart | Capture/Restart | This item stops the currently running live capture process and restarts it again, for convenience. |
------ | |||
|
Open... | File/Open... | This item brings up the file open dialog box that allows you to load a capture file for viewing. It is discussed in more detail in the section called “The "Open Capture File" dialog box”. |
|
Save As... | File/Save As... | This item allows you to save the current capture file to
whatever file you would like. It pops up the Save Capture File As
dialog box (which is discussed further in
the section called “The "Save Capture File As" dialog box”).
Note!If you currently have a temporary capture file, the Save icon will be shown instead. |
|
Close | File/Close | This item closes the current capture. If you have not saved the capture, you will be asked to save it first. |
|
Reload | View/Reload | This item allows you to reload the current capture file. |
|
Print... | File/Print... | This item allows you to print all (or some of) the packets in the capture file. It pops up the Ethereal Print dialog box (which is discussed further in the section called “Printing packets”). |
------ | |||
|
Find Packet... | Edit/Find Packet... | This item brings up a dialog box that allows you to find a packet. There is further information on finding packets in the section called “Finding packets”. |
|
Go Back | Go/Go Back | This item jumps back in the packet history. |
|
Go Forward | Go/Go Forward | This item jumps forward in the packet history. |
|
Go to Packet... | Go/Go to Packet... | This item brings up a dialog box that allows you to specify a packet number to go to that packet. |
|
Go To First Packet | Go/First Packet | This item jumps to the first packet of the capture file. |
|
Go To Last Packet | Go/Last Packet | This item jumps to the last packet of the capture file. |
------ | |||
|
Colorize | View/Colorize | Colorize the packet list (or not). |
|
Auto Scroll in Live Capture | View/Auto Scroll in Live Capture | Auto scroll packet list while doing a live capture (or not). |
------ | |||
|
Zoom In | View/Zoom In | Zoom into the packet data (increase the font size). |
|
Zoom Out | View/Zoom Out | Zoom out of the packet data (decrease the font size). |
|
Normal Size | View/Normal Size | Set zoom level back to 100%. |
|
Resize Columns | View/Resize Columns | Resize columns, so the content fits into them. |
------ | |||
|
Capture Filters... | Capture/Capture Filters... | This item brings up a dialog box that allows you to create and edit capture filters. You can name filters, and you can save them for future use. More detail on this subject is provided in the section called “Defining and saving filters”. |
|
Display Filters... | Analyze/Display Filters... | This item brings up a dialog box that allows you to create and edit display filters. You can name filters, and you can save them for future use. More detail on this subject is provided in the section called “Defining and saving filters”. |
|
Coloring Rules... | View/Coloring Rules... | This item brings up a dialog box that allows you color packets in the packet list pane according to filter expressions you choose. It can be very useful for spotting certain types of packets. More detail on this subject is provided in the section called “Packet colorization”. |
|
Preferences... | Edit/Preferences | This item brings up a dialog box that allows you to set preferences for many parameters that control Ethereal. You can also save your preferences so Ethereal will use them the next time you start it. More detail is provided in the section called “Preferences” |
------ | |||
|
Help | Help/Contents | This item brings up help dialog box. |
The filter toolbar lets you quickly edit and apply display filters. More information on display filters is available in the section called “Filtering packets while viewing”.
Figure 3.12. The "Filter" toolbar
After you've changed something in this field, don't forget to press the Apply button (or the Enter/Return key), to apply this filter string to the display.
This field is also where the current filter in effect is displayed.
Applying a display filter on large capture files might take quite a long time!
The packet list pane displays all the packets in the current capture file.
Figure 3.13. The "Packet List" pane
Each line in the packet list corresponds to one packet in the capture file. If you select a line in this pane, more details will be displayed in the "Packet Details" and "Packet Bytes" panes.
While dissecting a packet, Ethereal will place information from the protocol dissectors into the columns. As higher level protocols might overwrite information from lower levels, you will typically see the information from the highest possible level only.
For example, let's look at a packet containing TCP inside IP inside an Ethernet packet. The Ethernet dissector will write its data (such as the Ethernet addresses), the IP dissector will overwrite this by its own (such as the IP addresses), the TCP dissector will overwrite the IP information, and so on.
There are a lot of different columns available. Which columns are displayed can be selected by preference settings, see the section called “Preferences”.
The default columns will show:
There is a context menu (right mouse click) available, see details in Figure 6.3, “Pop-up menu of "Packet List" pane”.
The packet details pane shows the current packet (selected in the "Packet List" pane) in a more detailed form.
Figure 3.14. The "Packet Details" pane
This pane shows the protocols and protocol fields of the packet selected in the "Packet List" pane. The protocols and fields of the packet are displayed using a tree, which can be expanded and collapsed.
There is a context menu (right mouse click) available, see details in Figure 6.4, “Pop-up menu of "Packet Details" pane”.
Some protocol fields are specially displayed.
The packet bytes pane shows the data of the current packet (selected in the "Packet List" pane) in a hexdump style.
Figure 3.15. The "Packet Bytes" pane
As usual for a hexdump, the left side shows the offset in the packet data, in the middle the packet data is shown in a hexadecimal representation and on the right the corresponding ASCII characters (or . if not appropriate) are displayed.
There is a context menu (right mouse click) available, see details in Figure 6.5, “Pop-up menu of "Packet Bytes" pane”.
Depending on the packet data, sometimes more than one page is available, e.g. when Ethereal has reassembled some packets into a single chunk of data, see the section called “Packet Reassembling”. In this case there are some additional tabs shown at the bottom of the pane to let you select the page you want to see.
Figure 3.16. The "Packet Bytes" pane with tabs
The additional pages might contain data picked from multiple packets.
The context menu (right mouse click) of the tab labels will show a list of all available pages. This can be helpful if the size in the pane is too small for all the tab labels.
The statusbar displays informational messages.
In general, the left side will show context related information, while the right side will show the current number of packets.
Figure 3.17. The initial Statusbar
This statusbar is shown while no capture file is loaded, e.g. when Ethereal is started.
Figure 3.18. The Statusbar with a loaded capture file
The left side shows information about the capture file, its name, its size and the elapsed time while it was being captured.
The right side shows the current number of packets in the capture file. The following values are displayed:
Figure 3.19. The Statusbar with a selected protocol field
This is displayed if you have selected a protocol field from the "Packet Details" pane.
The value between the brackets (in this example arp.opcode) can be used as a display filter string, representing the selected protocol field.
Capturing live network data is one of the major features of Ethereal.
The Ethereal capture engine provides the following features:
The capture engine still lacks the following features:
Setting up Ethereal to capture packets for the first time can be tricky.
A comprehensive guide "How To setup a Capture" is available at: http://wiki.ethereal.com/CaptureSetup.
Here are some common pitfalls:
If you have any problems setting up your capture environment, you should have a look at the guide mentioned above.
One of the following methods can be used to start capturing packets with Ethereal:
ethereal -i eth0 -k
This will start Ethereal capturing on interface eth0, more details can be found at: the section called “Start Ethereal from the command line”.
When you select "Interfaces..." from the Capture menu, Ethereal pops up the "Capture Interfaces" dialog box as shown in Figure 4.1, “The "Capture Interfaces" dialog box”.
As the "Capture Interfaces" dialog is showing live captured data, it is consuming a lot of system ressources. Close this dialog as soon as possible to prevent excessive system load.
This dialog box will only show the local interfaces Ethereal knows of. As Ethereal might not be able to detect all local interfaces, and it cannot detect the remote interfaces available, there could be more capture interfaces available than listed.
Figure 4.1. The "Capture Interfaces" dialog box
When you select Start... from the Capture menu (or use the corresponding item in the "Main" toolbar), Ethereal pops up the "Capture Options" dialog box as shown in Figure 4.2, “The "Capture Options" dialog box”.
Figure 4.2. The "Capture Options" dialog box
If you are unsure which options to choose in this dialog box, just try keeping the defaults as this should work well in many cases.
You can set the following fields in this dialog box:
This field performs the same function as the -i <interface> command line option.
This option is only available on Windows platforms.
If some other process has put the interface in promiscuous mode you may be capturing in promiscuous mode even if you turn off this option
Even in promiscuous mode you still won't necessarily see all packets on your LAN segment, see http://www.ethereal.com/faq#promiscsniff for some more explanations.
You can also click on the button labelled Capture Filter, and Ethereal will bring up the Capture Filters dialog box and allow you to create and/or select a filter. Please see the section called “Defining and saving filters”
An explanation about capture file usage can be found in the section called “Capture files and file modes”.
You can also click on the button to the right of this field to browse through the filesystem.
Once you have set the values you desire and have selected the options you need, simply click on OK to commence the capture, or Cancel to cancel the capture.
If you start a capture, Ethereal allows you to stop capturing when you have enough packets captured, for details see the section called “While a Capture is running ...”.
While capturing, the underlying libpcap capturing engine will grab the packets from the network card and keep the packet data in a (relatively) small kernel buffer. This data is read by Ethereal and saved into the capture file(s) the user specified.
Different modes of operation are available when saving this packet data to the capture file(s).
Working with large files (several 100 MB's) can be quite slow. If you plan to do a long term capture or capturing from a high traffic network, think about using one of the "Multiple files" options. This will spread the captured packets over several smaller files which can be much more pleasant to work with.
Using Multiple files may cut context related information. Ethereal keeps context information of the loaded packet data, so it can report context related problems (like a stream error) and keeps information about context related protocols (e.g. where data is exchanged at the establishing phase and only referred to in later packets). As it keeps this information only for the loaded file, using one of the multiple file modes may cut these contexts. If the establishing phase is saved in one file and the things you would like to see is in another, you might not see some of the valuable context related information.
Information about the folders used for the capture file(s), can be found in Appendix A, Configuration (and other) Files and Folders.
Table 4.1. Capture file mode selected by capture options
"File" option | "Use multiple files" option | "Ring buffer with n files" option | Mode | Resulting filename(s) used |
---|---|---|---|---|
- | - | - | Single temporary file | etherXXXXXX (where XXXXXX is a unique number) |
foo.cap | - | - | Single named file | foo.cap |
foo.cap | x | - | Multiple files, continuous | foo_00001_20040205110102.cap, foo_00002_20040205110102.cap, ... |
foo.cap | x | x | Multiple files, ring buffer | foo_00001_20040205110102.cap, foo_00002_20040205110102.cap, ... |
This mode will limit the maximum disk usage, even for an unlimited amount of capture input data, keeping the latest captured data.
In the usual case, you won't have to choose this link-layer header type. The following paragraphs describe the exceptional cases, where selecting this type is possible, so you will have a guide what to do:
If you are capturing on an 802.11 device on some versions of BSD, this might offer a choice of "Ethernet" or "802.11". "Ethernet" will cause the captured packets to have fake Ethernet headers; "802.11" will cause them to have IEEE 802.11 headers. Unless the capture needs to be read by an application that doesn't support 802.11 headers, you should select "802.11".
If you are capturing on an Endace DAG card connected to a synchronous serial line, this might offer a choice of "PPP over serial" or "Cisco HDLC"; if the protocol on the serial line is PPP, select "PPP over serial", and if the protocol on the serial line is Cisco HDLC, select "Cisco HDLC".
If you are capturing on an Endace DAG card connected to an ATM network, this might offer a choice of "RFC 1483 IP-over-ATM" or "Sun raw ATM". If the only traffic being captured is RFC 1483 LLC-encapsulated IP, or if the capture needs to be read by an application that doesn't support SunATM headers, select "RFC 1483 IP-over-ATM", otherwise select "Sun raw ATM".
If you are capturing on an Ethernet device, this might offer a choice of "Ethernet" or "DOCSIS". If you are capturing traffic from a Cisco Cable Modem Termination System that is putting DOCSIS traffic onto the Ethernet to be captured, select "DOCSIS", otherwise select "Ethernet".
Ethereal uses the libpcap filter language for capture filters. This is explained in the tcpdump man page, which can be hard to understand, so it's explained here to some extent.
You will find a lot of Capture Filter examples at http://wiki.ethereal.com/CaptureFilters.
You enter the capture filter into the Filter field of the Ethereal Capture Options dialog box, as shown in Figure 4.2, “The "Capture Options" dialog box”. The following is an outline of the syntax of the tcpdump capture filter language. See the expression option at the tcpdump manual page for details: http://www.tcpdump.org/tcpdump_man.html.
A capture filter takes the form of a series of primitive expressions connected by conjunctions (and/or) and optionally preceded by not:
[not] primitive [and|or [not] primitive ...]
An example is shown in Example 4.1, “ A capture filter for telnet than captures traffic to and from a particular host ”.
Example 4.1. A capture filter for telnet than captures traffic to and from a particular host
tcp port 23 and host 10.0.0.5
This example captures telnet traffic to and from the host 10.0.0.5, and shows how to use two primitives and the and conjunction. Another example is shown in Example 4.2, “ Capturing all telnet traffic not from 10.0.0.5”, and shows how to capture all telnet traffic except that from 10.0.0.5.
Example 4.2. Capturing all telnet traffic not from 10.0.0.5
tcp port 23 and not host 10.0.0.5
XXX - add examples to the following list.
A primitive is simply one of the following:
If these are not specified, packets will be selected for both the TCP and UDP protocols and when the specified address appears in either the source or destination port field.
While a capture is running, the following dialog box is shown:
Figure 4.3. The "Capture Info" dialog box
This dialog box will inform you about the number of captured packets and the time since the capture was started. The selection which protocols are counted cannot be changed.
This Capture Info dialog box can be hidden, using the "Hide capture info dialog" option in the Capture Options dialog box.
A running capture session will be stopped in one of the following ways:
The Capture Info dialog box might be hidden, if the option "Hide capture info dialog" is used.
A running capture session can be restarted with the same capture options than the last time, this will remove all packets previously captured. This can be useful, if some uninteresting packets are captured and there's no need to keep them.
Restart is a convenience function and equivalent to a capture stop following by an immediate capture start. A restart can be triggered in one of the following ways:
This chapter will describe input and output of capture data.
Ethereal can read in previously saved capture files. To read them, simply select the menu or toolbar item: "File/ Open". Ethereal will then pop up the File Open dialog box, which is discussed in more detail in the section called “The "Open Capture File" dialog box”.
You can also use drag-and-drop to open a file, by simply dropping the desired file from your file manager onto Ethereal's main window. However, drag-and-drop is not available/won't work in all desktop environments.
If you didn't save the current capture file before, you will be asked to do so, to prevent data loss (this behaviour can be disabled in the preferences).
In addition to its native file format (libpcap format, also used by tcpdump/WinDump and other libpcap/WinPcap-based programs), Ethereal can read capture files from a large number of other packet capture programs as well. See the section called “Input File Formats” for the list of capture formats Ethereal understands.
The "Open Capture File" dialog box allows you to search for a capture file containing previously captured packets for display in Ethereal. Figure 5.1, “The "Open Capture File" Dialog box” shows an example of the Ethereal Open File Dialog box.
Ethereal uses the open dialog box from the version of the GTK+ toolkit that it's using. This dialog was completely redesigned in GTK version 2.4. Depending on the installed GTK version, your dialog box might look different. However, as the functionality remains almost the same, much of this description will work with your version of Ethereal.
Figure 5.1. The "Open Capture File" Dialog box
With this dialog box, you can perform the following actions:
You can also change the display filter and name resolution settings later while viewing the packets. However, for very large capture files it can take a significant amount of extra time changing these settings later, so it might be a good idea to set at least the filter in advance here.
The following file formats from other capture tools can be opened by Ethereal:
It may not be possible to read some formats dependent on the packet types captured. Ethernet captures are usually supported for most file formats, but other packet types (e.g. token ring packets) may not be possible to read from all file formats.
You can save captured packets simply by using the Save As... menu item from the File menu under Ethereal. You can choose which packets to save and which file format to be used.
The "Save Capture File As" dialog box allows you to save the current capture to a file. Figure 5.2, “The "Save Capture File As" dialog box” shows an example of this dialog box.
Ethereal uses the open dialog box from the version of the GTK+ toolkit that it's using. This dialog was completely redesigned in the GTK version 2.4. Depending on the installed GTK version, your dialog box might look different. However, as the functionality remains almost the same, much of this description will work with your version of Ethereal.
Figure 5.2. The "Save Capture File As" dialog box
With this dialog box, you can perform the following actions:
Some capture formats may not be available, depending on the packet types captured.
You can convert capture files from one format to another by reading in a capture file and writing it out using a different format.
The following file formats can be saved by Ethereal, so other capture tools can read the capture data from:
Other protocol analyzers may require that the file has a certain suffix in order to read the files you generate with Ethereal, e.g.:
".DMP" for Tcpdump/libpcap
".CAP" for Network Associates Sniffer Windows
Sometimes you need to merge several capture files into one. For example this can be useful, if you have captured simultaneously from multiple interfaces at once (e.g. using multiple instances of Ethereal).
Merging capture files can be done in three ways:
This dialog box let you select a file to be merged into the currently loaded file.
If your current data wasn't saved before, you will be asked to save it first, before this dialog box is shown.
Figure 5.3. The "Merge with Capture File" dialog box
All other controls will work the same way as in the "Open Capture File" dialog box, see the section called “The "Open Capture File" dialog box”.
When using the "Multiple Files" option while doing a capture, the capture data is spreaded over several capture files, called a file set. Ethereal tries to find the files matching the same filename pattern than the currently loaded file. This will only work, if all the files of the file set are located in the same directory.
As it can become tedious to work with a file set by hand, Ethereal provides some features in the "File" menu to handle these file sets in a more convenient way:
XXX - add icons from the menu
XXX - add screenshot
Each line contains information about a file of the file set:
The last line will contain info about the currently used directory where all of the files in the file set can be found.
The content of this dialog box is updated each time a capture file is opened/closed.
If you click on the radio button to the left of the line, the corresponding capture file will be opened. The Close button will, well, close the dialog box.
Ethereal provides several ways and formats to export packet data. This section describes general ways to export data from Ethereal.
There are more specialized functions to export specific data, which will be described at the appropriate places.
XXX - add detailed descriptions of the output formats and some sample output, too.
Export packet data into a plain ASCII text file, much like the format used to print packets.
Figure 5.4. The "Export as Plain Text File" dialog box
Export packet data into PostScript, much like the format used to print packets.
You can easily convert PostScript files to PDF files using ghostscript. For example: export to a file named foo.ps and then call: ps2pdf foo.ps
Figure 5.5. The "Export as PostScript File" dialog box
XXX - add screenshot
Export packet summary into CSV, used e.g. by spreadsheet programs to im-/export data.
Export packet data into PSML. This is an XML based format including only the packet summary.
Figure 5.6. The "Export as PSML File" dialog box
There's no such thing as a packet details frame for PSML export, as the packet format is defined by the PSML specification.
Export packet data into PDML. This is an XML based format including the packet details. The PDML file specification is available at: PDML specification.
The PDML specification is not officially released and Ethereal's implementation of it is still in an early beta state, so please expect changes in future Ethereal versions.
Figure 5.7. The "Export as PDML File" dialog box
There's no such thing as a packet details frame for PDML export, as the packet format is defined by the PDML specification.
Export the bytes selected in the "Packet Bytes" pane into a raw binary file.
Figure 5.8. The "Export Selected Packet Bytes" dialog box
To print packets, select the "Print..." menu item from the File menu. When you do this, Ethereal pops up the Print dialog box as shown in Figure 5.9, “The "Print" dialog box”.
Figure 5.9. The "Print" dialog box
The following fields are available in the Print dialog box:
This field is where you enter the file to print to if you have selected Print to a file, or you can click the button to browse the filesystem. It is greyed out if Print to a file is not selected.
These Print command fields are not available on windows platforms.
This field specifies the command to use for printing. It is typically lpr. You would change it to specify a particular queue if you need to print to a queue other than the default. An example might be:
lpr -Pmypostscript
This field is greyed out if Output to file: is checked above.
The packet range frame is a part of various output related dialog boxes. It provides options to select which packets should be processed by the output function.
Figure 5.10. The "Packet Range" frame
If the Captured button is set (default), all packets from the selected rule will be processed. If the Displayed button is set, only the currently displayed packets are taken into account to the selected rule.
The packet format frame is a part of various output related dialog boxes. It provides options to select which parts of a packet should be used for the output function.
Figure 5.11. The "Packet Format" frame
Once you have captured some packets, or you have opened a previously saved capture file, you can view the packets that are displayed in the packet list pane by simply clicking on a packet in the packet list pane, which will bring up the selected packet in the tree view and byte view panes.
You can then expand any part of the tree view by clicking on the plus sign (the symbol itself may vary) to the left of that part of the payload, and you can select individual fields by clicking on them in the tree view pane. An example with a TCP packet selected is shown in Figure 6.1, “Ethereal with a TCP packet selected for viewing”. It also has the Acknowledgment number in the TCP header selected, which shows up in the byte view as the selected bytes.
Figure 6.1. Ethereal with a TCP packet selected for viewing
You can also select and view packets the same way, while Ethereal is capturing, if you selected "Update list of packets in real time" in the Ethereal Capture Preferences dialog box.
In addition, you can view individual packets in a separate window as shown in Figure 6.2, “Viewing a packet in a separate window”. Do this by selecting the packet you are interested in the packet list pane, and then select "Show Packet in New Windows" from the Display menu. This allows you to easily compare two or even more packets.
Figure 6.2. Viewing a packet in a separate window
Finally, you can bring up a pop-up menu over either the "Packet List", "Packet Details" or "Packet Bytes" pane by clicking your right mouse button.
The following table gives an overview which functions are available in the panes, where to find the corresponding function in the menu, and a short description of each item.
Table 6.1. Function overview of the pop-up menus
Item | List | Details | Bytes | Menu | Description |
---|---|---|---|---|---|
Mark Packet (toggle) | X | - | - | Edit | Mark a packet. |
Time Reference | X | - | - | Edit | Set/reset and find time references. |
Expand Subtrees | - | X | - | View | Expand the currently selected subtree. |
Expand All | - | X | - | View | Expand all subtrees in all packets in the capture. |
Collapse All | - | X | - | View | Ethereal keeps a list of all the protocol subtrees that are expanded, and uses it to ensure that the correct subtrees are expanded when you display a packet. This menu item collapses the tree view of all packets in the capture list. |
Apply as Filter | X | X | - | Analyze | . |
Prepare a Filter | X | X | - | Analyze | . |
Follow TCP stream | X | X | - | Analyze | View all the data on a TCP stream between a pair of nodes. |
Wiki Protocol Page | - | X | - | - | Show the wiki page corresponding to the currently selected protocol in your web browser. |
Filter Field Reference | - | X | - | - | Show the filter field reference web page corresponding to the currently selected protocol in your web browser. |
Protocol Preferences... | - | X | - | - | The menu item takes you to the preferences dialog and selects the page corresponding to the protocol if there are settings associated with the highlighted field. More information on preferences can be found in the section called “Preferences”. |
Decode As... | X | X | - | Analyze | . |
Print... | X | - | - | File | Print (the selected) packet(s). |
Show Packet in New Window | X | - | - | View | Display the selected packet in another window. |
Resolve name | - | X | - | View/Name Resolution | Cause a name resolution to be performed for the selected packet, but NOT for every packet in the capture. |
Go to Corresponding Packet | - | X | - | Go | If the selected field has a packet number in it, go to it. The corresponding packet will often be a response which is requested by this packet, or the request for which this packet is a response. |
Copy | - | - | X | - | Copy the selected packet data to the clipboard (XXX - in which format). |
Export Selected Packet Bytes... | - | - | X | File->Export | Export raw packet bytes to a binary file. |
Figure 6.3. Pop-up menu of "Packet List" pane
Figure 6.4. Pop-up menu of "Packet Details" pane
Figure 6.5. Pop-up menu of "Packet Bytes" pane
Ethereal has two filtering languages: One used when capturing packets, and one used when displaying packets. In this section we explore that second type of filter: Display filters. The first one has already been dealt with in the section called “Filtering while capturing”.
Display filters allow you to concentrate on the packets you are interested in while hiding the currently uninteresting ones. They allow you to select packets by:
To select packets based on protocol type, simply type the protocol you are interested in in the Filter: field in the filter toolbar of the Ethereal window and press enter to initiate the filter. Figure 6.6, “Filtering on the TCP protocol” shows an example of what happens when you type tcp in the filter field.
All protocol and field names are entered in lowercase. Also, don't forget to press enter after entering the filter expression.
Figure 6.6. Filtering on the TCP protocol
As you might have noticed, only packets of the TCP protocol are displayed now (e.g. packets 1-10 are hidden). The packet numbering will remain as before, so the first packet shown is now packet number 11.
When using a display filter, all packets remain in the capture file. The display filter only changes the display of the capture file but not its content!
You can filter on any protocol that Ethereal understands. You can also filter on any field that a dissector adds to the tree view, but only if the dissector has added an abbreviation for the field. A list of such fields is available in the Ethereal in the Add Expression... dialog box. You can find more information on the Add Expression... dialog box in the section called “The "Filter Expression" dialog box”.
For example, to narrow the packet list pane down to only those packets to or from the IP address 192.168.0.1, use ip.addr==192.168.0.1.
To remove the filter, click on the Clear button to the right of the filter field.
Ethereal provides a simple but powerful display filter language that you can build quite complex filter expressions with. You can compare values in packets as well as combine expressions into more specific expressions. The following sections provide more information on doing this.
You will find a lot of Display Filter examples at the Ethereal Wiki Display Filter page at http://wiki.ethereal.com/DisplayFilters.
Every field in the packet details pane can be used as a filter string, this will result in showing only the packets where this field exists. For example: the filter string: tcp will show all packets containing the tcp protocol.
There is a complete list of all filter fields available through the menu item "Help/Supported Protocols" in the page "Display Filter Fields" of the upcoming dialog.
XXX - add some more info here and a link to the statusbar info.
You can build display filters that compare values using a number of different comparison operators. They are shown in Table 6.2, “Display Filter comparison operators”.
You can use English and C-like terms in the same way, they can even be mixed in a filter string!
Table 6.2. Display Filter comparison operators
English | C-like | Description and example |
---|---|---|
eq |
== |
Equal
ip.addr==10.0.0.5
|
ne |
!= |
Not equal
ip.addr!=10.0.0.5
|
gt |
> |
Greater than
frame.pkt_len > 10
|
lt |
< |
Less than
frame.pkt_len < 128
|
ge |
>= |
Greater than or equal to
frame.pkt_len ge 0x100
|
le |
<= |
Less than or equal to
frame.pkt_len <= 0x20
|
In addition, all protocol fields are typed. Table 6.3, “Display Filter Field Types” provides a list of the types and example of how to express them.
Table 6.3. Display Filter Field Types
Type | Example |
---|---|
Unsigned integer (8-bit, 16-bit, 24-bit, 32-bit) | You can express integers in decimal, octal, or hexadecimal.
The following display filters are equivalent:
ip.len le 1500 ip.len le 02734 ip.len le 0x436
|
Signed integer (8-bit, 16-bit, 24-bit, 32-bit) | |
Boolean | A boolean field is present in the protocol decode only if its
value is true. For example, tcp.flags.syn
is present, and thus true, only if the SYN flag is present in a
TCP segment header. Thus the filter expression tcp.flags.syn will select only those packets for which this flag exists, that is, TCP segments where the segment header contains the SYN flag. Similarly, to find source-routed token ring packets, use a filter expression of tr.sr. |
Ethernet address (6 bytes) | eth.addr == ff:ff:ff:ff:ff:ff |
IPv4 address | ip.addr == 192.168.0.1 |
IPv6 address | |
IPX network number | |
String (text) | |
Double-precision floating point number |
You can combine filter expressions in Ethereal using the logical operators shown in Table 6.4, “Display Filter Logical Operations”
Table 6.4. Display Filter Logical Operations
English | C-like | Description and example |
---|---|---|
and | && | Logical AND
ip.addr==10.0.0.5 and tcp.flags.fin
|
or | || | Logical OR
ip.addr==10.0.0.5 or ip.addr==192.1.1.1
|
xor | ^^ | Logical XOR
tr.dst[0:3] == 0.6.29 xor tr.src[0:3] == 0.6.29
|
not | ! | Logical NOT
not llc
|
[...] | Substring Operator Ethereal allows you to select subsequences of a sequence in rather elaborate ways. After a label you can place a pair of brackets [] containing a comma separated list of range specifiers.
eth.src[0:3] == 00:00:83 The example above uses the n:m format to specify a single range. In this case n is the beginning offset and m is the length of the range being specified.
eth.src[1-2] == 00:83 The example above uses the n-m format to specify a single range. In this case n is the beginning offset and m is the ending offset.
eth.src[:4] == 00:00:83:00 The example above uses the :m format, which takes everything from the beginning of a sequence to offset m. It is equivalent to 0:m
eth.src[4:] == 20:20 The example above uses the n: format, which takes everything from offset n to the end of the sequence.
eth.src[2] == 83 The example above uses the n format to specify a single range. In this case the element in the sequence at offset n is selected. This is equivalent to n:1.
eth.src[0:3,1-2,:4,4:,2] == 00:00:83:00:83:00:00:83:00:20:20:83 Ethereal allows you to string together single ranges in a comma separated list to form compound ranges as shown above. |
Using the != operator on combined expressions like: eth.addr, ip.addr, tcp.port, udp.port and alike will probably not work as expected!
Often people use a filter string to display something like ip.addr == 1.2.3.4 which will display all packets containing the IP address 1.2.3.4.
Then they use ip.addr != 1.2.3.4 to see all packets not containing the IP address 1.2.3.4 in it. Unfortunately, this does not do the expected.
Instead, that expression will even be true for packets where either source or destination IP address equals 1.2.3.4. The reason for this, is that the expression ip.addr != 1.2.3.4 must be read as "the packet contains a field named ip.addr with a value different from 1.2.3.4". As an IP datagram contains both a source and a destination address, the expression will evaluate to true whenever at least one of the two addresses differs from 1.2.3.4.
If you want to filter out all packets containing IP datagrams to or from IP address 1.2.3.4, then the correct filter is !(ip.addr == 1.2.3.4) as it reads "show me all the packets for which it is not true that a field named ip.addr exists with a value of 1.2.3.4", or in other words, "filter out all packets for which there are no occurrences of a field named ip.addr with the value 1.2.3.4".
When you are accustomed to Ethereal's filtering system and know what labels you wish to use in your filters it can be very quick to simply type a filter string. However if you are new to Ethereal or are working with a slightly unfamiliar protocol it can be very confusing to try to figure out what to type. The Filter Expression dialog box helps with this.
The "Filter Expression" dialog box is an excellent way to learn how to write Ethereal display filter strings.
Figure 6.7. The "Filter Expression" dialog box
When you first bring up the Filter Expression dialog box you are shown a tree list of field names, organized by protocol, and a box for selecting a relation.
When you select a field from the field name list and select a binary relation (such as the equality relation ==) you will be given the opportunity to enter a value, and possibly some range information.
You can define filters with Ethereal and give them labels for later use. This can save time in remembering and retyping some of the more complex filters you use.
To define a new filter or edit an existing one, select the Capture Filters... menu item from the Capture menu or the Display Filters... menu item from the Analyze menu. Ethereal will then pop up the Filters dialog as shown in Figure 6.8, “The "Capture Filters" and "Display Filters" dialog boxes”.
The mechanisms for defining and saving capture filters and display filters are almost identical. So both will be described here, differences between these two will be marked as such.
You must use Save to save your filters permanently. Ok or Apply will not save the filters, so they will be lost when you close Ethereal.
Figure 6.8. The "Capture Filters" and "Display Filters" dialog boxes
The filter name will only be used in this dialog to identify the filter for your convenience, it will not be used elsewhere. You can add multiple filters with the same name, but this is not very useful.
You can easily find packets once you have captured some packets or have read in a previously saved capture file. Simply select the Find Packet... menu item from the Edit menu. Ethereal will pop up the dialog box shown in Figure 6.9, “The "Find Packet" dialog box”.
Figure 6.9. The "Find Packet" dialog box
You might first select the kind of thing to search for:
Simply enter a display filter string into the Filter: field, select a direction, and click on OK.
For example, to find the three way handshake for a connection from host 192.168.0.1, use the following filter string:
ip.addr==192.168.0.1 and tcp.flags.syn
For more details on display filters, see the section called “Filtering packets while viewing”
Search for a specific byte sequence in the packet data.
For example, use "00:00" to find the next packet including two null bytes in the packet data.
Find a string in the packet data, with various options.
The value to be found will by syntax checked while you type it in. If the syntax check of your value succeeded, the background of the entry field will turn green, if it fails, it will turn red.
You can choose the direction to be searched for:
Search upwards in the packet list (decreasing packet numbers).
Search downwards in the packet list (increasing packet numbers).
"Find Next" will continue searching with the same options like in the last "Find Packet" run.
"Find Previous" will do the same thing as "Find Next", but with reverse search direction.
You can easily jump to specific packets with one of the menu items in the Go menu.
Go back in the packet history, works much like the page history in current web browsers.
Go forward in the packet history, works much like the page history in current web browsers.
Figure 6.10. The "Go To Packet" dialog box
This dialog box will let you enter a packet number. When you press OK, Ethereal will jump to that packet.
If a protocol field is selected which points to another packet in the capture file, this command will jump to that packet.
As these protocol fields now work like links (just as in your Web browser), it's easier to simply double-click on the field to jump to the corresponding field.
This command will simply jump to the first packet displayed.
This command will simply jump to the last packet displayed.
You can mark packets in the "Packet List" pane. A marked packet will be shown with black background, regardless of the coloring rules set. Marking a packet can be useful to find it later while analyzing in a large capture file.
The packet marks are not stored in the capture file or anywhere else, so all packet marks will be lost if you close the capture file.
You can use packet marking to control the output of packets when saving/exporting/printing. To do so, an option in the packet range is available, see the section called “The Packet Range frame”.
There are three functions to manipulate the marked state of a packet:
These mark function are available from the "Edit" menu, and the "Mark packet (toggle)" function is also available from the pop-up menu of the "Packet List" pane.
While packets are captured, each packet is timestamped. These timestamps will be saved to the capture file, so they will be available for later analysis.
When the packets are displayed, the presentation of these timestamps can be chosen by the user. There are four presentation formats available:
The time format can be selected from the View menu, see Figure 3.5, “The "View" Menu”.
XXX - how is the GMT / localtime thing handled.
The user can set time references to packets. A time reference is the starting point for all subsequent packet time calculations. It will be useful, if you want to see the time values relative to a special packet, e.g. the start of a new request. It's possible to set multiple time references in the capture file.
The time references will not be saved permanently and will be lost when you close the capture file.
Time referencing will only be useful, if the time display format is set to "Seconds Since Beginning of Capture". If one of the other time display formats are used, time referencing will have no effect (and will make no sense either).
To work with time references, choose one of the "Time Reference" items in the "Edit" menu , see the section called “The "Edit" menu”, or from the pop-up menu of the "Packet List" pane.
Figure 6.11. Ethereal showing a time referenced packet
A time referenced packet will be marked with the string *REF* in the Time column (see packet number 10). All subsequent packets will show the time since the last time reference.
In this chapter some advanced features of Ethereal will be described.
There will be occasions when you would like to see the data from a TCP session in the order that the application layer sees it. Perhaps you are looking for passwords in a Telnet stream, or you are trying to make sense of a data stream. If so, Ethereal's ability to follow a TCP stream will be useful to you.
Simply select a TCP packet in the stream/connection you are interested in and then select the Follow TCP Stream menu item from the Ethereal Tools menu. Ethereal will pop up a separate window with all the data from the TCP stream laid out in order, as shown in Figure 7.1, “The "Follow TCP Stream" dialog box”.
Figure 7.1. The "Follow TCP Stream" dialog box
You can choose from the following actions:
You can then choose to view the data in one of the following formats:
It is worthwhile noting that Follow TCP Stream installs a filter to select all the packets in the TCP stream you have selected.
Often network protocols needs to transport large chunks of data, which are complete in itself, e.g. when transferring a file. The underlying protocol might not be able to handle that chunk size (e.g. limitation of the network packet size), or is stream-based like TCP, which doesn't know data chunks at all.
In that case the network protocol has to handle that chunks itself and (if required) spreading the data over multiple packets. It also needs a mechanism to find back the chunk boundaries on the receiving side.
Ethereal calls this mechanism reassembling, although a specific protocol specification might use a different term for this.
For some of the network protocols Ethereal knows of, a mechanism is implemented to find, decode and display this chunks of data. Ethereal will try to find the corresponding packets of this chunk, and will show the combined data as additional pages in the "Packet Bytes" pane, see the section called “The "Packet Bytes" pane”.
Reassembling might take place in several protocol layers, so it's possible that multiple tabs in the "Packet Bytes" pane appear.
You will find the reassembled data in the last packet of the chunk.
An example: In a HTTP GET response, the requested data (e.g. a HTML page) is returned. Ethereal will show the hex dump of the data in a new tab "Uncompressed entity body" in the "Packet Bytes" pane.
Reassembling is usually disabled in the preferences by default, as it slows down packet processing a bit.
Enabling reassembling of a protocol typically requires two things:
The tooltip of the higher level protocol setting will note you if and which lower level protocol setting has to be considered too.
Name resolution tries to resolve some of the numerical address values to human readable names. There are two possible ways to do this conversations, depending on the resolution to be done: calling system/network services (like the gethostname function) and/or evaluate from Ethereal specific configuration files. If there are both features available, Ethereal will first try the system services and then fall back to it's own configuration files. XXX - is this really true? For details about the configuration files Ethereal uses for name resolution and alike, see Appendix A, Configuration (and other) Files and Folders.
However, be prepared that this conversion often will fail, e.g. the name to be resolved might simply be unknown by the servers asked and not found in the configuration files.
You may see packets to/from your machine in your capture file, which are caused by name resolution network services (e.g. DNS packets).
The resolved names are not stored in the capture file or somewhere else, so the resolved names might not be available if you open the capture file later or on a different machine.
The name resolution in the packet list is done while the list is filled. If a name could be resolved after a packet was added to the list, that entry won't be changed. As the name resolution results are cached, you can use "View/Reload" to rebuild the packet list, this time with the correctly resolved names.
The name resolution feature can be en-/disabled separately for the following protocol layers (in brackets):
ARP name resolution (system service) Ethereal will ask the operating system to convert an ethernet address to the corresponding IP address (e.g. 00:09:5b:01:02:03 -> 192.168.0.1).
Ethernet codes (ethers file) If the ARP name resolution failed, Ethereal tries to convert the ethernet address to a known device name, which has been assigned by the user using an ethers file (e.g. 00:09:5b:01:02:03 -> homerouter).
Ethernet manufacturer codes (manuf file) If both ARP and ethers didn't returned a result, Ethereal tries to convert the first 3 bytes of an ethernet address to an abbreviated manufacturer name, which has been assigned by the IETF (e.g. 00:09:5b:01:02:03 -> Netgear_01:02:03).
DNS/ADNS name resolution (system/library service) Ethereal will ask the operating system (or the ADNS library), to convert an IP address to the hostname associated with it (e.g. 65.208.228.223 -> www.ethereal.com). The DNS service is using synchronous calls to the DNS server. So Ethereal will stop responding until a response to a DNS request is returned. If possible, you might consider using the ADNS library (which won't wait for a network response).
Enabling network name resolution when your name server is unavailable may significantly slow down Ethereal while it waits for all of the name server requests to time out. Use ADNS in that case.
DNS vs. ADNS here's a short comparison: Both mechanisms are used to convert an IP address to some human readable (domain) name. The usual DNS call gethostname() will try to convert the address to a name. To do this, it will first ask the systems hosts file (e.g. /etc/hosts) if it finds a matching entry. If that fails, it will ask the configured DNS server(s) about the name.
So the real difference between DNS and ADNS comes when the system has to wait for the DNS server about a name resolution. The system call gethostname() will wait until a name is resolved or an error occurs. If the DNS server is unavailable, this might take quite a while (several seconds). The ADNS service will work a bit differently. It will also ask the DNS server, but it won't wait for the answer. It will just return to Ethereal in a very short amount of time. XXX - what does happen with the actual address field at that run? Will the response be ignored for that field?
hosts name resolution (hosts file) If DNS name resolution failed, Ethereal will try to convert an IP address to the hostname associated with it, using an hosts file provided by the user (e.g. 65.208.228.223 -> www.ethereal.com).
ipxnet name resolution (ipxnets file) XXX - add ipxnets name resolution explanation.
TCP/UDP port conversion (system service) Ethereal will ask the operating system to convert a TCP or UDP port to its well known name (e.g. 80 -> http).
Ethereal provides a wide range of network statistics.
These statistics range from general information about the loaded capture file (like the number of captured packets), to statistics about specific protocols (e.g. statistics about the number of HTTP requests and responses captured).
The protocol specific statistics requires detailed knowledge about the specific protocol. Unless you are familiar with that protocol, statistics about it will be pretty hard to understand.
General statistics about the current capture file.
Figure 8.1. The "Summary" window
The protocol hierarchy of the captured packets.
Figure 8.2. The "Protocol Hierarchy" window
This is a tree of all the protocols in the capture. You can collapse or expand subtrees, by clicking on the plus / minus icons. By default, all trees are expanded.
Each row contains the statistical values of one protocol.
The following columns containing the statistical values are available:
Packets will usually contain multiple protocols, so more than one protocol will be counted for each packet. Example: In the screenshot IP has 99,17% and TCP 85,83% (which is together much more than 100%).
A single packet can contain the same protocol more than once. In this case, the protocol is counted more than once. For example: in some tunneling configurations the IP layer can appear twice.
Statistics of the endpoints captured.
If you are looking for a feature other network tools call a hostlist, here is the right place to look. The list of Ethernet or IP endpoints is usually what you're looking for.
A network endpoint is the logical endpoint of separate protocol traffic of a specific protocol layer. The endpoint statistics of Ethereal will take the following endpoints into account:
Broadcast / multicast traffic will be shown separately as additional endpoints. Of course, as these endpoints are virtual endpoints, the real traffic will be received by all (multicast: some) of the listed unicast endpoints.
This window shows statistics about the endpoints captured.
Figure 8.3. The "Endpoints" window
For each supported protocol, a tab is shown in this window. The tab labels shows the number of endpoints captured (e.g. the tab label "Ethernet: 5" tells you that five ethernet endpoints have been captured). If no endpoints of a specific protocol were captured, the tab label will be grayed out (although the related page can still be selected).
Each row in the list shows the statistical values for exactly one endpoint.
Name resolution will be done if selected in the window and if it is active for the specific protocol layer (MAC layer for the selected Ethernet endpoints page). As you might have noticed, the first row has a name resolution of the first three bytes "Netgear", the second row's address was resolved to an IP address (using ARP) and the third was resolved to a broadcast (unresolved this would still be: ff:ff:ff:ff:ff:ff), the last two Ethernet addresses remain unresolved.
This window will be updated frequently, so it will be useful, even if you open it before (or while) you are doing a live capture.
Before the combined window described above was available, each of its pages were shown as separate windows. Even though the combined window is much more convenient to use, these separate windows are still available. The main reason is, they might process faster for very large capture files. However, as the functionality is exactly the same as in the combined window, they won't be discussed in detail here.
Statistics of the captured conversations.
A network conversation is the traffic between two specific endpoints. For example, an IP conversation is all the traffic between two IP addresses. The description of the known endpoint types can be found in the section called “What is an Endpoint?”.
Beside the list content, the conversations window work the same way as the endpoint ones, see the section called “The "Endpoints" window” for a description how it works.
Figure 8.4. The "Conversations" window
Before the combined window described above was available, each of its pages were shown as separate windows. Even though the combined window is much more convenient to use, these separate windows are still available. The main reason is, they might process faster for very large capture files. However, as the functionality is exactly the same as in the combined window, they won't be discussed in detail here.
User configurable graph of the captured network packets.
You can define up to five differently colored graphs.
Figure 8.5. The "IO Graphs" window
The user can configure the following things:
XXX - describe the Advanced feature.
The service response time is the time between a request and the corresponding response. This information is available for many protocols.
Service response time statistics are currently available for the following protocols:
As an example, the DCE-RPC service response time is described in more detail.
The other Service Response Time windows will work the same way (or only slightly different) compared to the following description.
The service response time of DCE-RPC is the time between the request and the corresponding response.
First of all, you have to select the DCE-RPC interface:
Figure 8.6. The "Compute DCE-RPC statistics" window
You can optionally set a display filter, to reduce the amount of packets.
Figure 8.7. The "DCE-RPC Statistic for ..." window
Each row corresponds to a method of the interface selected (so the EPM interface in version 3 has 7 methods). For each method the number of calls, and the statistics of the SRT time is calculated.
The protocol specific statistics windows display detailed information of specific protocols and might be described in a later version of this document.
Some of these statistics are described at the http://wiki.ethereal.com/Statistics pages.
Ethereal's default behaviour will usually suit your needs pretty well. However, as you become more familiar with Ethereal, it can be customized in various ways to suit your needs even better. In this chapter we explore:
You can start Ethereal from the command line, but it can also be started from most Window managers as well. In this section we will look at starting it from the command line.
Ethereal supports a large number of command line parameters. To see what they are, simply enter the command ethereal -h and the help information shown in Example 9.1, “Help information available from Ethereal” (or something similar) should be printed.
Example 9.1. Help information available from Ethereal
This is GNU ethereal 0.10.11 (C) 1998-2005 Gerald Combs <gerald@ethereal.com> Compiled with GTK+ 2.4.14, with GLib 2.4.7, with WinPcap (version unknown), with libz 1.2.2, with libpcre 4.4, with Net-SNMP 5.1.2, with ADNS. Running with WinPcap version 3.1 beta4 (packet.dll version 3, 1, 0, 24), based o n libpcap version 0.8.3 on Windows XP Service Pack 1, build 2600. ethereal [ -vh ] [ -klLnpQS ] [ -a <capture autostop condition> ] ... [ -b <capture ring buffer option> ] ...] [ -B capture buffer size (Win32 only) ] [ -c <capture packet count> ] [ -f <capture filter> ] [ -g <packet number> ] [ -i <capture interface> ] [ -m <font> ] [ -N <name resolving flags> ] [ -o <preference/recent setting> ] ... [ -r <infile> ] [ -R <read (display) filter> ] [ -s <capture snaplen> ] [ -t <time stamp format> ] [ -w <savefile> ] [ -y <capture link type> ] [ -z <statistics> ] [ <infile> ]
We will examine each of the command line options in turn.
The first thing to notice is that issuing the command ethereal by itself will bring up Ethereal. However, you can include as many of the command line parameters as you like. Their meanings are as follows ( in alphabetical order ): XXX - is the alphabetical order a good choice? Maybe better task based?
When the first capture file fills up, Ethereal will switch to writing to the next file, until it fills up the last file, at which point it'll discard the data in the first file (unless 0 is specified, in which case, the number of files is unlimited) and start writing to that file and so on.
If the optional duration is specified, Ethereal will switch also to the next file when the specified number of seconds has elapsed even if the current file is not completely fills up.
An example would be: ethereal -i eth0.
To get a listing of all the interfaces you can capture on, use the command ifconfig -a or netstat -i. Unfortunately, some versions of UNIX do not support ifconfig -a, so you will have to use netstat -i in these cases.
An example of setting a single preference would be:
ethereal -o mgcp.display_dissect_tree:TRUE
An example of setting multiple preferences would be:
ethereal -o mgcp.display_dissect_tree:TRUE -o mgcp.udp.callagent_port:2627
You can get a list of all available preference strings from the preferences file, see Appendix A, Configuration (and other) Files and Folders.
A very useful mechanism available in Ethereal is packet colorization. You can set-up Ethereal so that it will colorize packets according to a filter. This allows you to emphasize the packets you are usually interested in.
You will find a lot of Coloring Rule examples at the Ethereal Wiki Coloring Rules page at http://wiki.ethereal.com/ColoringRules.
To colorize packets, select the Coloring Rules... menu item from the View menu, Ethereal will pop up the "Coloring Rules" dialog box as shown in Figure 9.1, “The "Coloring Rules" dialog box”.
Figure 9.1. The "Coloring Rules" dialog box
Once the Coloring Rules dialog box is up, there are a number of buttons you can use, depending on whether or not you have any color filters installed already.
You will need to carefully select the order the coloring rules are listed (and thus applied) as they are applied in order from top to bottom. So, more specific rules need to be listed before more general rules. For example, if you have a color rule for UDP before the one for DNS, the color rule for DNS will never be applied (as DNS uses UDP, so the UDP rule will be matching first).
If this is the first time you have used Coloring Rules, click on the New button which will bring up the Edit color filter dialog box as shown in Figure 9.2, “The "Edit Color Filter" dialog box”.
Figure 9.2. The "Edit Color Filter" dialog box
In the Edit Color dialog box, simply enter a name for the color filter, and enter a filter string in the Filter text field. Figure 9.2, “The "Edit Color Filter" dialog box” shows the values arp and arp which means that the name of the color filter is arp and the filter will select protocols of type arp. Once you have entered these values, you can choose a foreground and background color for packets that match the filter expression. Click on Foreground color... or Background color... to achieve this and Ethereal will pop up the Choose foreground/background color for protocol dialog box as shown in Figure 9.3, “The "Choose color" dialog box”.
Figure 9.3. The "Choose color" dialog box
Select the color you desire for the selected packets and click on OK.
You must select a color in the colorbar next to the colorwheel to load values into the RGB values. Alternatively, you can set the values to select the color you want.
Figure 9.4, “Using color filters with Ethereal” shows an example of several color filters being used in Ethereal. You may not like the color choices, however, feel free to choose your own.
Figure 9.4. Using color filters with Ethereal
The user can control how protocols are dissected.
Each protocol has its own dissector, so dissecting a complete packet will typically involve several dissectors. As Ethereal tries to find the right dissector for each packet (using static "routes" and heuristics "guessing"), it might choose the wrong dissector in your specific case. For example, Ethereal won't know if you use a common protocol on an uncommon TCP port, e.g. using HTTP on TCP port 800 instead of the standard port 80.
There are two ways to control the relations between protocol dissectors: disable a protocol dissector completely or temporarily divert the way Ethereal calls the dissectors.
The Enabled Protocols dialog box lets you enable or disable specific protocols, all protocols are enabled by default. When a protocol is disabled, Ethereal stops processing a packet whenever that protocol is encountered.
Disabling a protocol will prevent information about higher-layer protocols from being displayed. For example, suppose you disabled the IP protocol and selected a packet containing Ethernet, IP, TCP, and HTTP information. The Ethernet information would be displayed, but the IP, TCP and HTTP information would not - disabling IP would prevent it and the other protocols from being displayed.
Figure 9.5. The "Enabled Protocols" dialog box
To disable or enable a protocol, simply click on it using the mouse or press the space bar when the protocol is highlighted.
You have to use the Save button to save your settings. The OK or Apply buttons will not save your changes permanently, so they will be lost when Ethereal is closed.
You can choose from the following actions:
The "Decode As" functionality let you temporarily divert specific protocol dissections. This might be useful for example, if you do some uncommon experiments on your network.
Figure 9.6. The "Decode As" dialog box
The content of this dialog box depends on the selected packet when it was opened.
The user specified decodes can not be saved. If you quit Ethereal, these settings will be lost.
This dialog box shows the currently active user specified decodes.
Figure 9.7. The "Decode As: Show" dialog box
There are a number of preferences you can set. Simply select the Preferences... menu item from the Edit menu, and Ethereal will pop up the Preferences dialog box as shown in Figure 9.8, “The preferences dialog box”, with the "User Interface" page as default. On the left side is a tree where you can select the page to be shown.
Preference settings are added frequently. For a recent explanation of the preference pages and their settings have a look at the Ethereal Wiki Preferences page at http://wiki.ethereal.com/Preferences.
The OK or Apply button will not save the preference settings, you'll have to save the settings by clicking the Save button.
Figure 9.8. The preferences dialog box
Ethereal uses a number of files and folders while it is running. Some of these reside in the personal configuration folder and are used to maintain information between runs of Ethereal, while some of them are maintained in system areas.
A list of the folders Ethereal actually uses can be found under the Folders tab in the dialog box coming up, when you select About Ethereal from the Help menu.
The content format of the configuration files is the same on all platforms. However, to match the different policies for unix and windows platforms, different folders for these files are used.
Table A.1. Configuration files and folders overview
File/Folder | Description | Unix/Linux folders | Windows folders |
---|---|---|---|
preferences | Settings from the Preferences dialog box. | /etc/ethereal.conf, $HOME/.ethereal/preferences | %ETHEREAL%\ethereal.conf, %APPDATA%\Ethereal\preferences |
recent | Recent GUI settings (e.g. recent files lists). | $HOME/.ethereal/recent | %APPDATA%\Ethereal\recent |
cfilters | Capture filters. | $HOME/.ethereal/cfilters | %ETHEREAL%\cfilters, %APPDATA%\Ethereal\cfilters |
dfilters | Display filters. | $HOME/.ethereal/dfilters | %ETHEREAL%\dfilters, %APPDATA%\Ethereal\dfilters |
colorfilters | Coloring rules. | $HOME/.ethereal/colorfilters | %ETHEREAL%\colorfilters, %APPDATA%\Ethereal\colorfilters |
disabled_protos | Disabled protocols. | $HOME/.ethereal/disabled_protos | %ETHEREAL%\disabled_protos, %APPDATA%\Ethereal\disabled_protos |
ethers | Ethernet name resolution. | /etc/ethers, $HOME/.ethereal/ethers | %ETHEREAL%\ethers, %APPDATA%\Ethereal\ethers |
manuf | Ethernet name resolution. | /etc/manuf | %ETHEREAL%\manuf |
hosts | IPv4 and IPv6 name resolution. | $HOME/.ethereal/hosts | %APPDATA%\hosts |
ipxnets | IPX name resolution. | $HOME/.ethereal/ipxnets | %ETHEREAL%\ipxnets |
plugins | Plugin directories. | /usr/share/ethereal/plugins, /usr/local/share/ethereal/plugins, $HOME/.ethereal/plugins | %ETHEREAL%\plugins\<version>, %APPDATA%\Ethereal\plugins |
temp | Temporary files. | Environment: TMPDIR | Environment: TMPDIR or TEMP |
%APPDATA% points to the personal configuration folder, typically
C:\Documents and Settings\<username>\Application
Data
(for further details, have a look at
the section called
“Windows profiles”), %ETHEREAL% points to the Ethereal program folder,
typically C:\Program Files\Ethereal
The /etc
folder is the global Ethereal
configuration folder. The folder actually used on your system may vary,
maybe something like: /usr/local/etc
.
variable: value
The settings from this file are read in at program start and written to disk when you press the Save button in the "Preferences" dialog box.
variable: value
It is read at program start and written at program exit.
"<filter name>" <filter string>
The settings from this file are read in at program start and written to disk when you press the Save button in the "Capture Filters" dialog box.
"<filter name>" <filter string>
The settings from this file are read in at program start and written to disk when you press the Save button in the "Display Filters" dialog box.
@<filter name>@<filter string> @[<bg RGB(16-bit)>][<fg RGB(16-bit)>]
The settings from this file are read in at program start and written to disk when you press the Save button in the "Coloring Rules" dialog box.
tcp udp
The settings from this file are read in at program start and written to disk when you press the Save button in the "Enabled Protocols" dialog box.
Each line in these files consists of one hardware address and name separated by whitespace. The digits of hardware addresses are separated by colons (:), dashes (-) or periods(.). The following are some examples:
ff-ff-ff-ff-ff-ff Broadcast c0-00-ff-ff-ff-ff TR_broadcast 00.2b.08.93.4b.a1 Freds_machine
The settings from this file are read in at program start and never written by Ethereal.
An example is:
00:00:01 Xerox # XEROX CORPORATION
The settings from this file are read in at program start and never written by Ethereal.
This file has the same format as the usual /etc/hosts file in unix systems.
An example is:
# Comments must be prepended by the # sign! 192.168.0.1 homeserver
The settings from this file are read in at program start and never written by Ethereal.
An example is:
C0.A8.2C.00 HR c0-a8-1c-00 CEO 00:00:BE:EF IT_Server1 110f FileServer3
The settings from this file are read in at program start and never written by Ethereal.
Here you will find some details about the folders used in Ethereal on different Windows versions.
As already mentioned, you can find the currently used folders in the About Ethereal dialog.
Windows uses some special directories to store user configuration files in, named the user profile. This can be confusing, as the default directory location changed from version to version and might also be different for english and internationalized versions of windows.
If you upgraded to a new windows version, your profile might be kept in the former location, so the defaults mentioned here might not apply.
The following will try to guide you to the right place where to look for Ethereals profile data.
C:\windows\Application Data\Ethereal
C:\windows\Profiles\<username>\Application Data\Ethereal
is
used. C:\WINNT\Profiles\<username>\Application
Data\Ethereal
C:\Documents and
Settings\<username>\Application Data
, "Documents and
Settings" and "Application Data" might be internationalized.
The following will only be applicable if you are using roaming profiles. This might be the case, if you work in a Windows domain environment (used in huge company networks). The configurations of all programs you use won't be saved on the local harddrive of the computer you are currently working on, but on the domain server.
As Ethereal is using the correct places to store it's profile data, your settings will travel with you, if you logon to a different computer the next time.
There is an exception to this: The "Local Settings" folder in your
profile data (typically something like:
C:\Documents and Settings\<username>\Local Settings
) will not be
transferred to the domain server. This is the default for temporary
capture files.
Ethereal uses the folder which is set by the TMPDIR or TEMP environment variable. This variable will be set by the windows installer.
The default location for temporary files on NT 4 is just
C:\TEMP
, and in 2000 the default location
is some directory under your profile directory but it might have
"Temporary Files" in the path name.
Ethereal distinguishes between protocols (e.g. tcp) and protocol fields (e.g. tcp.port).
A comprehensive list of all protocols and protocol fields can be found at: http://www.ethereal.com/docs/dfref/
Beside the Ethereal GUI application, there are some command line tools, which can be helpful for doing some more specialized things. These tools will be described in this chapter.
There are occasions when you want to capture packets using tcpdump rather than ethereal, especially when you want to do a remote capture and do not want the network load associated with running Ethereal remotely (not to mention all the X traffic polluting your capture).
However, the default tcpdump parameters result in a capture file where each packet is truncated, because tcpdump, by default, does only capture the first 68 bytes of each packet.
To ensure that you capture complete packets, use the following command:
tcpdump -i <interface> -s 1500 -w <some-file>
You will have to specify the correct interface and the name of a file to save into. In addition, you will have to terminate the capture with ^C when you believe you have captured enough packets.
tcpdump is not part of the Ethereal distribution. You can get it from: http://www.tcpdump.org for various platforms.
Tethereal is a terminal oriented version of ethereal designed for capturing and displaying packets when an interactive user interface isn't necessary or available. It supports the same options as ethereal. For more information on tethereal, see the manual pages (man tethereal).
Included with Ethereal is a small utility called capinfos, which is a command-line utility to print information about binary capture files.
Example C.1. Help information available from capinfos
$ capinfos -h Usage: capinfos [-t] [-c] [-s] [-d] [-u] [-a] [-e] [-y] [-i] [-z] [-h] <capfile> where -t display the capture type of <capfile> -c count the number of packets -s display the size of the file -d display the total length of all packets in the file (in bytes) -u display the capture duration (in seconds) -a display the capture start time -e display the capture end time -y display average data rate (in bytes) -i display average data rate (in bits) -z display average packet size (in bytes) -h produces this help listing. If no data flags are given, default is to display all statistics
Included with Ethereal is a small utility called editcap, which is a command-line utility for working with capture files. Its main function is to remove packets from capture files, but it can also be used to convert capture files from one format to another, as well as print information about capture files.
Example C.2. Help information available from editcap
$ editcap.exe -h Usage: editcap [-r] [-h] [-v] [-T <encap type>] [-E <probability>] [-F <capture type>]> [-s <snaplen>] [-t <time adjustment>] <infile> <outfile> [ <record#>[-<record#>] ... ] where -E <probability> specifies the probability (between 0 and 1) that a particular byte will will have an error. -F <capture type> specifies the capture file type to write: libpcap - libpcap (tcpdump, Ethereal, etc.) rh6_1libpcap - RedHat Linux 6.1 libpcap (tcpdump) suse6_3libpcap - SuSE Linux 6.3 libpcap (tcpdump) modlibpcap - modified libpcap (tcpdump) nokialibpcap - Nokia libpcap (tcpdump) lanalyzer - Novell LANalyzer ngsniffer - Network Associates Sniffer (DOS-based) snoop - Sun snoop netmon1 - Microsoft Network Monitor 1.x netmon2 - Microsoft Network Monitor 2.x ngwsniffer_1_1 - Network Associates Sniffer (Windows-based) 1.1 ngwsniffer_2_0 - Network Associates Sniffer (Windows-based) 2.00x nettl - HP-UX nettl trace visual - Visual Networks traffic capture 5views - Accellent 5Views capture niobserverv9 - Network Instruments Observer version 9 default is libpcap -h produces this help listing. -r specifies that the records specified should be kept, not deleted, default is to delete -s <snaplen> specifies that packets should be truncated to <snaplen> bytes of data -t <time adjustment> specifies the time adjustment to be applied to selected packets -T <encap type> specifies the encapsulation type to use: ether - Ethernet tr - Token Ring slip - SLIP ppp - PPP fddi - FDDI fddi-swapped - FDDI with bit-swapped MAC addresses rawip - Raw IP arcnet - ARCNET arcnet_linux - Linux ARCNET atm-rfc1483 - RFC 1483 ATM linux-atm-clip - Linux ATM CLIP lapb - LAPB atm-pdus - ATM PDUs atm-pdus-untruncated - ATM PDUs - untruncated null - NULL ascend - Lucent/Ascend access equipment isdn - ISDN ip-over-fc - RFC 2625 IP-over-Fibre Channel ppp-with-direction - PPP with Directional Info ieee-802-11 - IEEE 802.11 Wireless LAN prism - IEEE 802.11 plus Prism II monitor mode header ieee-802-11-radio - IEEE 802.11 Wireless LAN with radio information ieee-802-11-radiotap - IEEE 802.11 plus radiotap WLAN header ieee-802-11-avs - IEEE 802.11 plus AVS WLAN header linux-sll - Linux cooked-mode capture frelay - Frame Relay frelay-with-direction - Frame Relay with Directional Info chdlc - Cisco HDLC ios - Cisco IOS internal ltalk - Localtalk pflog-old - OpenBSD PF Firewall logs, pre-3.4 hhdlc - HiPath HDLC docsis - Data Over Cable Service Interface Specification cosine - CoSine L2 debug log whdlc - Wellfleet HDLC sdlc - SDLC tzsp - Tazmen sniffer protocol enc - OpenBSD enc(4) encapsulating interface pflog - OpenBSD PF Firewall logs chdlc-with-direction - Cisco HDLC with Directional Info bluetooth-h4 - Bluetooth H4 mtp2 - SS7 MTP2 mtp3 - SS7 MTP3 irda - IrDA user0 - USER 0 user1 - USER 1 user2 - USER 2 user3 - USER 3 user4 - USER 4 user5 - USER 5 user6 - USER 6 user7 - USER 7 user8 - USER 8 user9 - USER 9 user10 - USER 10 user11 - USER 11 user12 - USER 12 user13 - USER 13 user14 - USER 14 user15 - USER 15 symantec - Symantec Enterprise Firewall ap1394 - Apple IP-over-IEEE 1394 bacnet-ms-tp - BACnet MS/TP raw-icmp-nettl - Raw ICMP with nettl headers raw-icmpv6-nettl - Raw ICMPv6 with nettl headers gprs-llc - GPRS LLC juniper-atm1 - Juniper ATM1 juniper-atm2 - Juniper ATM2 redback - Redback SmartEdge rawip-nettl - Raw IP with nettl headers ether-nettl - Ethernet with nettl headers tr-nettl - Token Ring with nettl headers fddi-nettl - FDDI with nettl headers unknown-nettl - Unknown link-layer type with nettl headers mtp2-with-phdr - MTP2 with pseudoheader juniper-pppoe - Juniper PPPoE gcom-tie1 - GCOM TIE1 gcom-serial - GCOM Serial x25-nettl - X25 with nettl headers default is the same as the input file -v specifies verbose operation, default is silent A range of records can be specified as well
Where each option has the following meaning:
It is mainly for converting funny captures to something that Ethereal can deal with.
The default frame encapsulation type is the same as the input encapsulation.
The default is libpcap format.
Mergecap is a program that combines multiple saved capture files into a single output file specified by the -w argument. Mergecap knows how to read libpcap capture files, including those of tcpdump. In addition, Mergecap can read capture files from snoop (including Shomiti) and atmsnoop, LanAlyzer, Sniffer (compressed or uncompressed), Microsoft Network Monitor, AIX's iptrace, NetXray, Sniffer Pro, RADCOM's WAN/LAN analyzer, Lucent/Ascend router debug output, HP-UX's nettl, and the dump output from Toshiba's ISDN routers. There is no need to tell Mergecap what type of file you are reading; it will determine the file type by itself. Mergecap is also capable of reading any of these file formats if they are compressed using gzip. Mergecap recognizes this directly from the file; the '.gz' extension is not required for this purpose.
By default, it writes the capture file in libpcap format, and writes all of the packets in both input capture files to the output file. The -F flag can be used to specify the format in which to write the capture file; it can write the file in libpcap format (standard libpcap format, a modified format used by some patched versions of libpcap, the format used by Red Hat Linux 6.1, or the format used by SuSE Linux 6.3), snoop format, uncompressed Sniffer format, Microsoft Network Monitor 1.x format, and the format used by Windows-based versions of the Sniffer software.
Packets from the input files are merged in chronological order based on each frame's timestamp, unless the -a flag is specified. Mergecap assumes that frames within a single capture file are already stored in chronological order. When the -a flag is specified, packets are copied directly from each input file to the output file, independent of each frame's timestamp.
If the -s flag is used to specify a snapshot length, frames in the input file with more captured data than the specified snapshot length will have only the amount of data specified by the snapshot length written to the output file. This may be useful if the program that is to read the output file cannot handle packets larger than a certain size (for example, the versions of snoop in Solaris 2.5.1 and Solaris 2.6 appear to reject Ethernet frames larger than the standard Ethernet MTU, making them incapable of handling gigabit Ethernet captures if jumbo frames were used).
If the -T flag is used to specify an encapsulation type, the encapsulation type of the output capture file will be forced to the specified type, rather than being the type appropriate to the encapsulation type of the input capture file. Note that this merely forces the encapsulation type of the output file to be the specified type; the packet headers of the packets will not be translated from the encapsulation type of the input capture file to the specified encapsulation type (for example, it will not translate an Ethernet capture to an FDDI capture if an Ethernet capture is read and '-T fddi' is specified).
Example C.3. Help information available from mergecap
$ mergecap.exe -h mergecap version 0.10.5 Usage: mergecap [-hva] [-s <snaplen>] [-T <encap type>] [-F <capture type>] -w <outfile> <infile> [...] where -h produces this help listing. -v verbose operation, default is silent -a files should be concatenated, not merged Default merges based on frame timestamps -s <snaplen>: truncate packets to <snaplen> bytes of data -w <outfile>: sets output filename to <outfile> -T <encap type> encapsulation type to use: ether - Ethernet tr - Token Ring slip - SLIP ppp - PPP fddi - FDDI fddi-swapped - FDDI with bit-swapped MAC addresses rawip - Raw IP arcnet - ARCNET arcnet_linux - Linux ARCNET atm-rfc1483 - RFC 1483 ATM linux-atm-clip - Linux ATM CLIP lapb - LAPB atm-pdus - ATM PDUs atm-pdus-untruncated - ATM PDUs - untruncated null - NULL ascend - Lucent/Ascend access equipment isdn - ISDN ip-over-fc - RFC 2625 IP-over-Fibre Channel ppp-with-direction - PPP with Directional Info ieee-802-11 - IEEE 802.11 Wireless LAN prism - IEEE 802.11 plus Prism II monitor mode header ieee-802-11-radio - IEEE 802.11 Wireless LAN with radio information ieee-802-11-bsd - IEEE 802.11 plus BSD WLAN header ieee-802-11-avs - IEEE 802.11 plus AVS WLAN header linux-sll - Linux cooked-mode capture frelay - Frame Relay frelay-with-direction - Frame Relay with Directional Info chdlc - Cisco HDLC ios - Cisco IOS internal ltalk - Localtalk pflog-old - OpenBSD PF Firewall logs, pre-3.4 hhdlc - HiPath HDLC docsis - Data Over Cable Service Interface Specification cosine - CoSine L2 debug log whdlc - Wellfleet HDLC sdlc - SDLC tzsp - Tazmen sniffer protocol enc - OpenBSD enc(4) encapsulating interface pflog - OpenBSD PF Firewall logs chdlc-with-direction - Cisco HDLC with Directional Info bluetooth-h4 - Bluetooth H4 mtp2 - SS7 MTP2 mtp3 - SS7 MTP3 irda - IrDA user0 - USER 0 user1 - USER 1 user2 - USER 2 user3 - USER 3 user4 - USER 4 user5 - USER 5 user6 - USER 6 user7 - USER 7 user8 - USER 8 user9 - USER 9 user10 - USER 10 user11 - USER 11 user12 - USER 12 user13 - USER 13 user14 - USER 14 user15 - USER 15 symantec - Symantec Enterprise Firewall ap1394 - Apple IP-over-IEEE 1394 bacnet-ms-tp - BACnet MS/TP default is the same as the first input file -F <capture type> capture file type to write: libpcap - libpcap (tcpdump, Ethereal, etc.) rh6_1libpcap - RedHat Linux 6.1 libpcap (tcpdump) suse6_3libpcap - SuSE Linux 6.3 libpcap (tcpdump) modlibpcap - modified libpcap (tcpdump) nokialibpcap - Nokia libpcap (tcpdump) lanalyzer - Novell LANalyzer ngsniffer - Network Associates Sniffer (DOS-based) snoop - Sun snoop netmon1 - Microsoft Network Monitor 1.x netmon2 - Microsoft Network Monitor 2.x ngwsniffer_1_1 - Network Associates Sniffer (Windows-based) 1.1 ngwsniffer_2_0 - Network Associates Sniffer (Windows-based) 2.00x visual - Visual Networks traffic capture 5views - Accellent 5Views capture niobserverv9 - Network Instruments Observer version 9 default is libpcap
A simple example merging dhcp-capture.libpcap
and imap-1.libpcap
into
outfile.libpcap
is shown below.
Example C.4. Simple example of using mergecap
$ mergecap -w outfile.libpcap dhcp-capture.libpcap imap-1.libpcap
There may be some occasions when you wish to convert a hex dump of some network traffic into a libpcap file.
Text2pcap is a program that reads in an ASCII hex dump and writes the data described into a libpcap-style capture file. text2pcap can read hexdumps with multiple packets in them, and build a capture file of multiple packets. text2pcap is also capable of generating dummy Ethernet, IP and UDP headers, in order to build fully processable packet dumps from hexdumps of application-level data only.
Text2pcap understands a hexdump of the form generated by od -t x1. In other words, each byte is individually displayed and surrounded with a space. Each line begins with an offset describing the position in the file. The offset is a hex number (can also be octal - see -o), of more than two hex digits. Here is a sample dump that text2pcap can recognize:
000000 00 e0 1e a7 05 6f 00 10 ........ 000008 5a a0 b9 12 08 00 46 00 ........ 000010 03 68 00 00 00 00 0a 2e ........ 000018 ee 33 0f 19 08 7f 0f 19 ........ 000020 03 80 94 04 00 00 10 01 ........ 000028 16 a2 0a 00 03 50 00 0c ........ 000030 01 01 0f 19 03 80 11 01 ........
There is no limit on the width or number of bytes per line. Also the text dump at the end of the line is ignored. Bytes/hex numbers can be uppercase or lowercase. Any text before the offset is ignored, including email forwarding characters '>'. Any lines of text between the bytestring lines is ignored. The offsets are used to track the bytes, so offsets must be correct. Any line which has only bytes without a leading offset is ignored. An offset is recognized as being a hex number longer than two characters. Any text after the bytes is ignored (e.g. the character dump). Any hex numbers in this text are also ignored. An offset of zero is indicative of starting a new packet, so a single text file with a series of hexdumps can be converted into a packet capture with multiple packets. Multiple packets are read in with timestamps differing by one second each. In general, short of these restrictions, text2pcap is pretty liberal about reading in hexdumps and has been tested with a variety of mangled outputs (including being forwarded through email multiple times, with limited line wrap etc.)
There are a couple of other special features to note. Any line where the first non-whitespace character is '#' will be ignored as a comment. Any line beginning with #TEXT2PCAP is a directive and options can be inserted after this command to be processed by text2pcap. Currently there are no directives implemented; in the future, these may be used to give more fine grained control on the dump and the way it should be processed e.g. timestamps, encapsulation type etc.
Text2pcap also allows the user to read in dumps of application-level data, by inserting dummy L2, L3 and L4 headers before each packet. The user can elect to insert Ethernet headers, Ethernet and IP, or Ethernet, IP and UDP headers before each packet. This allows Ethereal or any other full-packet decoder to handle these dumps.
Example C.5. Help information available for text2pcap
$ text2pcap.exe -h Usage: text2pcap.exe [-h] [-d] [-q] [-o h|o] [-l typenum] [-e l3pid] [-i proto] [-m max-packet] [-u srcp,destp] [-T srcp,destp] [-s srcp,destp,tag] [-S srcp,destp,tag] [-t timefmt] <input-filename> <output-filename> where <input-filename> specifies input filename (use - for standard input) <output-filename> specifies output filename (use - for standard output) [options] are one or more of the following -h : Display this help message -d : Generate detailed debug of parser states -o hex|oct : Parse offsets as (h)ex or (o)ctal. Default is hex -l typenum : Specify link-layer type number. Default is 1 (Ethernet). See net/bpf.h for list of numbers. -q : Generate no output at all (automatically turns off -d) -e l3pid : Prepend dummy Ethernet II header with specified L3PID (in HEX) Example: -e 0x800 -i proto : Prepend dummy IP header with specified IP protocol (in DECIMAL). Automatically prepends Ethernet header as well. Example: -i 46 -m max-packet : Max packet length in output, default is 64000 -u srcp,destp : Prepend dummy UDP header with specified dest and source ports (in DECIMAL). Automatically prepends Ethernet and IP headers as well Example: -u 30,40 -T srcp,destp : Prepend dummy TCP header with specified dest and source ports (in DECIMAL). Automatically prepends Ethernet and IP headers as well Example: -T 50,60 -s srcp,dstp,tag: Prepend dummy SCTP header with specified dest/source ports and verification tag (in DECIMAL). Automatically prepends Ethernet and IP headers as well Example: -s 30,40,34 -S srcp,dstp,ppi: Prepend dummy SCTP header with specified dest/source ports and verification tag 0. It also prepends a dummy SCTP DATA chunk header with payload protocol identifier ppi. Example: -S 30,40,34 -t timefmt : Treats the text before the packet as a date/time code; the specified argument is a format string of the sort supported by strptime. Example: The time "10:15:14.5476" has the format code "%H:%M:%S." NOTE: The subsecond component delimiter must be specified (.) but no pattern is required; the remaining number is assumed to be fractions of a second.
For IP packets, instead of generating a fake Ethernet header you can also use -l 12 to indicate a raw IP packet to Ethereal. Note that -l 12 does not work for any non-IP Layer 3 packet (e.g. ARP), whereas generating a dummy Ethernet header with -e works for any sort of L3 packet.
In an ideal world idl2eth would be mentioned in the users guide in passing and documented in the developers guide. As the developers guide has not yet been completed it will be documented here.
As you have probably guessed from the name, idl2eth takes a user specified IDL file and attempts to build a dissector that can decode the IDL traffic over GIOP. The resulting file is "C" code, that should compile okay as an ethereal dissector.
idl2eth basically parses the data struct given to it by the omniidl compiler, and using the GIOP API available in packet-giop.[ch], generates get_CDR_xxx calls to decode the CORBA traffic on the wire.
It consists of 4 main files.
README.idl2eth
ethereal_be.py
ethereal_gen.py
idl2eth
It is important to understand what CORBA traffic looks like over GIOP/IIOP, and to help build a tool that can assist in troubleshooting CORBA interworking. This was especially the case after seeing a lot of discussions about how particular IDL types are represented inside an octet stream.
I have also had comments/feedback that this tool would be good for say a CORBA class when teaching students what CORBA traffic looks like "on the wire".
It is also COOL to work on a great Open Source project such as the case with "Ethereal" ( http://www.ethereal.com )
To use the idl2eth to generate ethereal dissectors, you need the following:
Prerequisites to using idl2eth
To use idl2eth to generate an ethereal dissector from an idl file use the following procedure:
Procedure for converting a Corba idl file into an ethereal dissector
idl2eth <your file.idl>
eg:
idl2eth echo.idl
idl2eth echo.idl > packet-test-idl.c
You may wish to comment out the register_giop_user_module() code and that will leave you with heuristic dissection.
If you don't want to use the shell script wrapper, then try steps 3 or 4 instead.
Usage: omniidl -p ./ -b ethereal_be <your file.idl>
eg:
omniidl -p ./ -b ethereal_be echo.idl
omniidl -p ./ -b ethereal_be echo.idl > packet-test-idl.c
You may wish to comment out the register_giop_user_module() code and that will leave you with heuristic dissection.
cp packet-test-idl.c /dir/where/ethereal/lives/ edit Makefile.am edit Makefile.nmake
./configure (or ./autogen.sh)
make
See the TODO list inside packet-giop.c
As with the original licence and documentation distributed with Ethereal, this document is covered by the GNU General Public Licence (GNU GPL).
If you haven't read the GPL before, please do so. It explains all the things that you are allowed to do with this code and documentation.
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Linux Basics, Security & Hacking
willi moser (2005-12-12)