Customizing Ethereal
Introduction 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: How to start Ethereal with command line parameters How to colorize the Ethereal display How to use the various preference settings
Start Ethereal from the command line 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 (or something similar) should be printed. Help information available from Ethereal This is GNU ethereal 0.10.5 Compiled with GTK+ 2.4.3, with GLib 2.4.2, with WinPcap (version unknown), with libz 1.2.1, with libpcre 4.4, with Net-SNMP 5.1, with ADNS. Running with WinPcap version 3.0 (packet.dll version 3, 1, 0, 20), based on libpcap version 0.8 on Windows XP Service Pack 1, build 2600. ethereal [ -vh ] [ -klLnpQS ] [ -a <capture autostop condition> ] ... [ -b <number of ringbuffer files>[:<duration>] ] [ -B <byte view height> ] [ -c <count> ] [ -f <capture filter> ] [ -i <interface> ] [ -m <medium font> ] [ -N <resolving> ] [ -o <preference setting> ] ... [ -P <packet list height> ] [ -r <infile> ] [ -R <read filter> ] [ -s <snaplen> ] [ -t <time stamp format> ] [ -T <tree view height> ] [ -w <savefile> ] [ -y <link type> ] [ -z <statistics string> ] [ <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? -a <capture autostop condition> Specify a criterion that specifies when Ethereal is to stop writing to a capture file. The criterion is of the form test:value, where test is one of: duration Stop writing to a capture file after value of seconds have elapsed. filesize Stop writing to a capture file after it reaches a size of value kilobytes (where a kilobyte is 1000 bytes, not 1024 bytes). -b <number of ringbuffer files> If a maximum capture file size was specified, cause Ethereal to run in "ring buffer" mode, with the specified number of files. In "ring buffer" mode, Ethereal will write to several capture files. Their name is based on the number of the file and on the creation date and time. 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. -B <byte view height> This option sets the initial height of the "Packet Bytes" pane. This pane is usually the bottom pane in the Ethereal display. -c <count> This option specifies the maximum number of packets to capture when capturing live data. It would be used in conjunction with the -k option. -f <capture filter> This option sets the initial capture filter expression to be used when capturing packets. -h The -h option requests Ethereal to print its version and usage instructions (as shown above) and exit. -i <interface> The -i option allows you to specify, from the command line, which interface packet capture should occur on if capturing packets. 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. -k The -k option specifies that Ethereal should start capturing packets immediately. This option requires the use of the -i parameter to specify the interface that packet capture will occur from. -l This option turns on automatic scrolling if the packet list pane is being updated automatically as packets arrive during a capture ( as specified by the -S flag). -L List the data link types supported by the interface and exit. -m <medium font> This option sets the name of the font used for most text displayed by Ethereal. XXX - add an example! -n Disable network object name resolution (such as hostname, TCP and UDP port names). -N <resolving> Turns on name resolving for particular types of addresses and port numbers; the argument is a string that may contain the letters m to enable MAC address resolution, n to enable network address resolution, and t to enable transport-layer port number resolution. This overrides -n if both -N and -n are present. The letter C enables concurrent (asynchronous) DNS lookups. -o <preference settings> Sets a preference value, overriding the default value and any value read from a preference file. The argument to the flag is a string of the form prefname:value, where prefname is the name of the preference (which is the same name that would appear in the preference file), and value is the value to which it should be set. Multiple instances of -o <preference settings> can be given on a single command line. 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 Tip! You can get a list of all available preference strings from the preferences file, see . -p Don't put the interface into promiscuous mode. Note that the interface might be in promiscuous mode for some other reason; hence, -p cannot be used to ensure that the only traffic that is captured is traffic sent to or from the machine on which Ethereal is running, broadcast traffic, and multicast traffic to addresses received by that machine. -P <packet list height> This option sets the initial height of the "Packet List" pane, ie, the top pane. -Q This option forces Ethereal to exit when capturing is complete. It can be used with the -c option. It must be used in conjunction with the -i and -w options. -r <infile> This option provides the name of a capture file for Ethereal to read and display. This capture file can be in one of the formats Ethereal understands. -R <read filter> This option specifies a display filter to be applied when reading packets from a capture file. The syntax of this filter is that of the display filters discussed in . Packets not matching the filter are discarded. -s <snaplen> This option specifies the snapshot length to use when capturing packets. Ethereal will only capture <snaplen> bytes of data for each packet. -S This option specifies that Ethereal will display packets as it captures them. This is done by capturing in one process and displaying them in a separate process. This is the same as "Update list of packets in real time" in the Capture Options dialog box. -t <time stamp format> This option sets the format of packet timestamps that are displayed in the packet list window. The format can be one of: r relative, which specifies timestamps are displayed relative to the first packet captured. a absolute, which specifies that actual times be displayed for all packets. ad absolute with date, which specifies that actual dates and times be displayed for all packets. d delta, which specifies that timestamps are relative to the previous packet. -T <tree view height> This option sets the initial height of the "Packet Details" pane. -v The -v option requests Ethereal to print out its version information and exit. -w <savefile> This option sets the name of the savefile to be used when saving a capture file. -y <link type> If a capture is started from the command line with -k, set the data link type to use while capturing packets. The values reported by -L are the values that can be used. -z <statistics-string> Get Ethereal to collect various types of statistics and display the result in a window that updates in semi-real time. XXX - add more details here!
Packet colorization A very useful mechanism available in Ethereal is packet colorization. You can set Ethereal up so that it colorizes packets according to a filter. This allows you to emphasize the packets you are interested in. To colorize packets, select the Coloring Rules... menu item from the View menu, and Ethereal will pop up the "Coloring Rules" dialog box as shown in .
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. Note! You will need to carefully select the order that 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 .
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. 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 .
The "Choose color" dialog box
Select the color you desire for the selected packets and click on OK. Note! 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. 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.
Using color filters with Ethereal
Control Protocol dissection There are some ways, to let the user control how protocols are dissected. Each protocol has its own dissector, so dissecting a 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 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. Note! 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.
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. Warning! You have to use the Save button to save your settings. The OK or Apply buttons will not save your changes, so they will be lost when Ethereal is closed. You can choose from the following actions: Enable All Enable all protocols in the list. Disable All Disable all protocols in the list. Invert Toggle the state of all protocols in the list. OK Apply the changes and close the dialog box. Apply Apply the changes and keep the dialog box open. Save Save the settings to the disabled_protos, see for details. Cancel Cancel the changes and close the dialog box.
User Specified Decodes The "Decode As" functionality let you temporarily divert specific protocol dissections. This might be useful for example, if you do some uncommon things on your network.
The "Decode As" dialog box
The content of this dialog box depends on the selected packet when it was opened. Warning! The user specified decodes can not be saved. If you quit Ethereal, these settings will be lost. Decode Decode packets the selected way. Do not decode Do not decode packets the selected way. Link/Network/Transport Specify the way to decode packets. Which of these pages are available, depends on the content of the selected packet when this dialog box was opened. Show Current Open a dialog box showing the current list of user specified decodes. OK Apply the currently selected decode and close the dialog box. Apply Apply the currently selected decode and keep the dialog box open. Cancel Cancel the changes and close the dialog box.
Show User Specified Decodes This dialog box shows the currently active user specified decodes.
The "Decode As: Show" dialog box
OK Close this dialog box. Clear Removes all user specified decodes.
Preferences 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 , with the "User Interface" page as default. On the left side is a tree where you can select the page to be shown. XXX - add detailed descriptions of all the preferences pages. Warning! The OK or Apply button will not save the preference settings, you'll have to save the settings by clicking the Save button. The OK button will apply the preferences settings and close the dialog. The Apply button will apply the preferences settings and keep the dialog open. The Save button will apply the preferences settings, save the settings on the harddisk and keep the dialog open. The Cancel button will restore all preferences settings to the last saved state.
The "User Interface" page
The "User Interface" preferences page
This page allows you to configure various characteristics of the GUI.
The "User Interface: Layout" page
The "User Interface: Layout" preferences page
This page selects the GUI layout of the main window.
The "User Interface: Columns" page
The "User Interface: Columns" preferences page
This page allows you to select which columns appear in the "Packet List" Pane.
Note! Unlike all other preference changes, you will have to save the preferences and restart Ethereal in order for column changes to take effect!
The "User Interface: Font" page
The "User Interface: Font" preferences page
This page allows you to select which font to use.
The "User Interface: Colors" page
The "User Interface: Colors" preferences page
This page allows you to select which colors to use.
The "Capture" page
The "Capture" preferences page
This page allows you to select some defaults for the capture options dialog.
The "Printing" page
The "Printing" preferences page
This page allows you to select some defaults for the print dialog.
The "Name Resolution" page
The "Name Resolution" preferences page
This page allows you to select some defaults for the name resolution.
The "Protocols" pages These pages allows you to select settings for various protocols.