forked from osmocom/wireshark
946 lines
35 KiB
Plaintext
946 lines
35 KiB
Plaintext
// WSUG Chapter Capture
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[[ChapterCapture]]
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== Capturing Live Network Data
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[[ChCapIntroduction]]
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=== Introduction
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Capturing live network data is one of the major features of Wireshark.
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The Wireshark capture engine provides the following features:
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* Capture from different kinds of network hardware such as Ethernet or 802.11.
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* Stop the capture on different triggers such as the amount of captured data,
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elapsed time, or the number of packets.
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* Simultaneously show decoded packets while Wireshark is capturing.
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* Filter packets, reducing the amount of data to be captured. See
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<<ChCapCaptureFilterSection>>.
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* Save packets in multiple files while doing a long term capture, optionally
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rotating through a fixed number of files (a “ringbuffer”). See
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<<ChCapCaptureFiles>>.
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* Simultaneously capture from multiple network interfaces.
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The capture engine still lacks the following features:
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* Stop capturing (or perform some other action) depending on the captured data.
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[[ChCapPrerequisitesSection]]
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=== Prerequisites
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Setting up Wireshark to capture packets for the first time can be
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tricky. A comprehensive guide ``How To setup a Capture'' is available at
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{wireshark-wiki-url}CaptureSetup.
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Here are some common pitfalls:
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* You may need special privileges to start a live capture.
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* You need to choose the right network interface to capture packet data from.
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* You need to capture at the right place in the network to see the traffic you
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want to see.
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If you have any problems setting up your capture environment you should have a
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look at the guide mentioned above.
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[[ChCapCapturingSection]]
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=== Start Capturing
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The following methods can be used to start capturing packets with Wireshark:
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* You can double-click on an interface in the main window.
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* You can get an overview of the available interfaces using the ``Capture
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Interfaces'' dialog box (menu:Capture[Options...]). See
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<<ChCapCaptureInterfacesDialogWin32>> or <<ChCapCaptureInterfacesDialog>> for
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more information. You can start a capture from this dialog box using the
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btn:[Start] button.
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* You can immediately start a capture using your current settings by selecting
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menu:Capture[Start] or by cliking the first toolbar button.
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* If you already know the name of the capture interface you can start Wireshark
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from the command line:
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--
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----
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$ wireshark -i eth0 -k
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----
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--
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This will start Wireshark capturing on interface eth0. More details can be found
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at <<ChCustCommandLine>>.
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[[ChCapInterfaceSection]]
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=== The ``Capture Interfaces'' dialog box
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When you select menu:Capture[Options...] from the main menu Wireshark pops up
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the ``Capture Interfaces'' dialog box as shown in
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<<ChCapCaptureInterfacesDialogWin32>> or <<ChCapCaptureInterfacesDialog>>.
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// XXX Not sure this is the case any more
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//[WARNING]
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//.This dialog consumes lots of system resources
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//====
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//As the ``Capture Interfaces'' dialog is showing live captured data, it is
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//consuming a lot of system resources. Close this dialog as soon as possible to
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//prevent excessive system load.
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//====
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[NOTE]
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.Both you and your OS can hide interfaces
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====
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This dialog box will only show the local interfaces Wireshark can access. It
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will also hide interfaces marked as hidden in <<ChCustInterfaceOptionsSection>>.
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As Wireshark might not be able to detect all local interfaces and it cannot
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detect the remote interfaces available there could be more capture interfaces
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available than listed.
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====
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It is possible to select more than one interface and capture from them
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simultaneously.
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[[ChCapCaptureInterfacesDialogWin32]]
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.The ``Capture Interfaces'' dialog box on Microsoft Windows
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image::wsug_graphics/ws-capture-interfaces-win32.png[{screenshot-attrs}]
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[[ChCapCaptureInterfacesDialog]]
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.The ``Capture Interfaces'' dialog box on Unix/Linux
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image::wsug_graphics/ws-capture-interfaces.png[{screenshot-attrs}]
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_Device (Unix/Linux only)_::
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The interface device name.
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_Description_::
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The interface description provided by the operating system, or the user defined
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comment added in <<ChCustInterfaceOptionsSection>>.
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_IP_::
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The first IP address Wireshark could find for this interface. You can click on
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the address to cycle through other addresses assigned to it, if available. If no
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address could be found “none” will be displayed.
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_Packets_::
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The number of packets captured from this interface, since this dialog was
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opened. Will be greyed out, if no packet was captured in the last second.
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_Packets/s_::
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Number of packets captured in the last second. Will be greyed out, if no packet
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was captured in the last second.
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_Stop_::
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Stop a currently running capture.
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_Start_::
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Start a capture on all selected interfaces immediately, using the settings from
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the last capture or the default settings, if no options have been set.
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_Options_::
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Open the Capture Options dialog with the marked interfaces selected. See
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<<ChCapCaptureOptions>>.
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_Details (Microsoft Windows only)_::
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Open a dialog with detailed information about the interface. See
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<<ChCapInterfaceDetailsSection>>.
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_Help_::
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Show this help page.
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_Close_::
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Close this dialog box.
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[[ChCapCaptureOptions]]
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=== The ``Capture Options'' dialog box
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When you select menu:Capture[Options...] (or use the corresponding item in the
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main toolbar), Wireshark pops up the ``Capture Options'' dialog box as shown in
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<<ChCapCaptureOptionsDialog>>.
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[[ChCapCaptureOptionsDialog]]
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.The ``Capture Options'' dialog box
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image::wsug_graphics/ws-capture-options.png[{screenshot-attrs}]
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[TIP]
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====
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If you are unsure which options to choose in this dialog box just try keeping
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the defaults as this should work well in many cases.
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====
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==== Capture frame
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The table shows the settings for all available interfaces:
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* The name of the interface and its IP addresses. If no address could be
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resolved from the system, “none” will be shown.
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--
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[NOTE]
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====
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Loopback interfaces are not available on Windows platforms.
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====
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--
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* The link-layer header type.
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* The information whether promicuous mode is enabled or disabled.
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* The maximum amount of data that will be captured for each packet. The default
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value is set to the 262144 bytes.
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* The size of the kernel buffer that is reserved to keep the captured packets.
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* The information whether packets will be captured in monitor mode (Unix/Linux
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only).
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* The chosen capture filter.
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By marking the checkboxes in the first column the interfaces are selected to be
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captured from. By double-clicking on an interface the ``Edit Interface Settings''
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dialog box as shown in <<ChCapEditInterfacesSettingsDialog>> will be opened.
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_Capture on all interfaces_::
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As Wireshark can capture on multiple interfaces it is possible to choose to
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capture on all available interfaces.
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_Capture all packets in promiscuous mode_::
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This checkbox allows you to specify that Wireshark should put all interfaces in
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promiscuous mode when capturing.
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_Capture Filter_::
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This field allows you to specify a capture filter for all interfaces that are
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currently selected. Once a filter has been entered in this field, the newly
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selected interfaces will inherit the filter. Capture filters are discussed in
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more details in <<ChCapCaptureFilterSection>>. It defaults to empty, or no
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filter.
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+
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You can also click on the btn:[Capture Filter] button and Wireshark will
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bring up the Capture Filters dialog box and allow you to create and/or select a
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filter. Please see <<ChWorkDefineFilterSection>>
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_Compile selected BPFs_::
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This button allows you to compile the capture filter into BPF code and pop up a
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window showing you the resulting pseudo code. This can help in understanding the
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working of the capture filter you created. The btn:[Compile Selected BPFs] button
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leads you to <<ChCapCompileSelectedBpfsDialog>>.
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[TIP]
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Linux power user tip
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====
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The execution of BPFs can be sped up on Linux by turning on BPF JIT by executing
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----
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$ echo 1 >/proc/sys/net/core/bpf_jit_enable
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----
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if it is not enabled already. To make the change persistent you can use
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link:{sysfs-main-url}[sysfsutils].
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====
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_Manage Interfaces_::
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The btn:[Manage Interfaces] button opens the <<ChCapManageInterfacesDialog>>
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where pipes can be defined, local interfaces scanned or hidden, or remote
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interfaces added (Windows only).
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==== Capture File(s) frame
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An explanation about capture file usage can be found in <<ChCapCaptureFiles>>.
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_File_::
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This field allows you to specify the file name that will be used for the capture
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file. This field is left blank by default. If the field is left blank, the
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capture data will be stored in a temporary file. See <<ChCapCaptureFiles>> for
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details.
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+
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You can also click on the button to the right of this field to browse through
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the filesystem.
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_Use multiple files_::
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Instead of using a single file Wireshark will automatically switch to a new
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one if a specific trigger condition is reached.
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_Use pcapng format_:: This checkbox allows you to specify that
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Wireshark saves the captured packets in pcapng format. This next
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generation capture file format is currently in development. If more than
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one interface is chosen for capturing, this checkbox is set by default.
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See {wireshark-wiki-url}Development/PcapNg for more details on
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pcapng.
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_Next file every n megabyte(s)_::
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Multiple files only. Switch to the next file after the given number of
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byte(s)/kilobyte(s)/megabyte(s)/gigabyte(s) have been captured.
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_Next file every n minute(s)_::
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Multiple files only: Switch to the next file after the given number of
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second(s)/minutes(s)/hours(s)/days(s) have elapsed.
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_Ring buffer with n files_::
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Multiple files only: Form a ring buffer of the capture files with the given
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number of files.
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_Stop capture after n file(s)_::
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Multiple files only: Stop capturing after switching to the next file the given
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number of times.
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==== Stop Capture... frame
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_... after n packet(s)_::
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Stop capturing after the given number of packets have been captured.
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_... after n megabytes(s)_::
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Stop capturing after the given number of
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byte(s)/kilobyte(s)/megabyte(s)/gigabyte(s) have been captured. This option is
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greyed out if ``Use multiple files'' is selected.
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_... after n minute(s)_::
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Stop capturing after the given number of second(s)/minutes(s)/hours(s)/days(s)
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have elapsed.
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==== Display Options frame
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_Update list of packets in real time_::
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This option allows you to specify that Wireshark should update the packet list
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pane in real time. If you do not specify this, Wireshark does not display any
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packets until you stop the capture. When you check this, Wireshark captures in a
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separate process and feeds the captures to the display process.
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_Automatic scrolling in live capture_::
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This option allows you to specify that Wireshark should scroll the packet list
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pane as new packets come in, so you are always looking at the last packet. If
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you do not specify this Wireshark simply adds new packets onto the end of the
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list but does not scroll the packet list pane. This option is greyed out if
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``Update list of packets in real time'' is disabled.
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// XXX ChCapRunningSection currently disabled
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//_Hide capture info dialog_::
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//If this option is checked, the capture info dialog described in <<ChCapRunningSection>> will be hidden.
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==== Name Resolution frame
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_Enable MAC name resolution_::
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This option allows you to control whether or not Wireshark translates MAC
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addresses into names. See <<ChAdvNameResolutionSection>>.
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_Enable network name resolution_::
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This option allows you to control whether or not Wireshark translates network
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addresses into names. See <<ChAdvNameResolutionSection>>.
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_Enable transport name resolution_::
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This option allows you to control whether or not Wireshark translates transport
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addresses into protocols. See <<ChAdvNameResolutionSection>>.
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==== Buttons
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Once you have set the values you desire and have selected the options you need,
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simply click on btn:[Start] to commence the capture or btn:[Cancel] to
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cancel the capture.
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// XXX ChCapRunningSection currently disabled
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//If you start a capture, Wireshark allows you to stop capturing when you have
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//enough packets captured, for details see <<ChCapRunningSection>>.
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[[ChCapEditInterfaceSettingsSection]]
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=== The ``Edit Interface Settings'' dialog box
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If you double-click on an interface in <<ChCapCaptureOptionsDialog>> the following dialog box pops up.
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[[ChCapEditInterfacesSettingsDialog]]
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.The ``Edit Interface Settings'' dialog box
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image::wsug_graphics/ws-capture-options-settings.png[{screenshot-attrs}]
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You can set the following fields in this dialog box:
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_IP address_::
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The IP address(es) of the selected interface. If no address could be resolved
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from the system “none” will be shown.
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_Link-layer header type_::
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Unless you are in the rare situation that requires this keep the default setting.
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For a detailed description. See <<ChCapLinkLayerHeader>>
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_Wireless settings (Windows only)_::
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Here you can set the settings for wireless capture using the AirPCap adapter.
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For a detailed description see the AirPCap Users Guide.
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_Remote settings (Windows only)_::
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Here you can set the settings for remote capture. For a detailed description
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see <<ChCapInterfaceRemoteSection>>
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_Capture packets in promiscuous mode_::
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This checkbox allows you to specify that Wireshark should put the interface in
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promiscuous mode when capturing. If you do not specify this Wireshark will only
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capture the packets going to or from your computer (not all packets on your LAN
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segment).
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[NOTE]
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====
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If some other process has put the interface in promiscuous mode you may be
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capturing in promiscuous mode even if you turn off this option.
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Even in promiscuous mode you still won't necessarily see all packets on your LAN
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segment. See link:{wireshark-faq-url}#promiscsniff[the Wireshark FAQ] for more information.
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====
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_Limit each packet to n bytes_::
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This field allows you to specify the maximum amount of data that will be
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captured for each packet, and is sometimes referred to as the _snaplen_. If
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disabled the value is set to the maximum 65535 which will be sufficient for
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most protocols. Some rules of thumb:
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* If you are unsure just keep the default value.
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* If you don't need or don't want all of the data in a packet - for example, if
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you only need the link-layer, IP, and TCP headers - you might want to choose a
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small snapshot length, as less CPU time is required for copying packets, less
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buffer space is required for packets, and thus perhaps fewer packets will be
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dropped if traffic is very heavy.
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* If you don't capture all of the data in a packet you might find that the
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packet data you want is in the part that’s dropped or that reassembly isn't
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possible as the data required for reassembly is missing.
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_Buffer size: n megabyte(s)_::
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Enter the buffer size to be used while capturing. This is the size of the kernel
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buffer which will keep the captured packets, until they are written to disk. If
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you encounter packet drops, try increasing this value.
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_Capture packets in monitor mode (Unix/Linux only)_::
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This checkbox allows you to setup the Wireless interface to capture all traffic
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it can receive, not just the traffic on the BSS to which it is associated, which
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can happen even when you set promiscuous mode. Also it might be necessary to
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turn this option on in order to see IEEE 802.11 headers and/or radio information
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from the captured frames.
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[NOTE]
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====
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In monitor mode the adapter might disassociate itself from the network it was
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associated to.
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====
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_Capture Filter_::
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This field allows you to specify a capture filter. Capture filters are discussed
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in more details in <<ChCapCaptureFilterSection>>. It defaults to empty, or no
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filter.
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+
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You can also click on the btn:[Capture Filter] button and Wireshark will
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bring up the ``Capture Filters'' dialog box and allow you to create and/or
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select a filter. Please see <<ChWorkDefineFilterSection>>
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_Compile BPF_::
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This button allows you to compile the capture filter into BPF code and pop up a
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window showing you the resulting pseudo code. This can help in understanding the
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working of the capture filter you created.
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[[ChCapCompileSelectedBpfsSection]]
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=== The ``Compile Results'' dialog box
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This figure shows the compile results of the selected interfaces.
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[[ChCapCompileSelectedBpfsDialog]]
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.The ``Compile Results'' dialog box
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image::wsug_graphics/ws-capture-options-compile-selected-bpfs.png[{screenshot-attrs}]
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In the left window the interface names are listed. The results of an individual
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interface are shown in the right window when it is selected.
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[[ChCapManageInterfacesSection]]
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=== The ``Add New Interfaces'' dialog box
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As a central point to manage interfaces this dialog box consists of three tabs
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to add or remove interfaces.
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[[ChCapManageInterfacesDialog]]
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.The ``Add New Interfaces'' dialog box
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image::wsug_graphics/ws-capture-options-manage-interfaces.png[{screenshot-attrs}]
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==== Add or remove pipes
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[[ChCapManageInterfacesPipesDialog]]
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.The ``Add New Interfaces - Pipes'' dialog box
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image::wsug_graphics/ws-capture-options-manage-interfaces-pipes.png[{screenshot-attrs}]
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To successfully add a pipe, this pipe must have already been created. Click the
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btn:[New] button and type the name of the pipe including its path.
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Alternatively, the btn:[Browse] button can be used to locate the pipe. With
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the btn:[Save] button the pipe is added to the list of available interfaces.
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Afterwards, other pipes can be added.
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To remove a pipe from the list of interfaces it first has to be selected. Then
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click the btn:[Delete] button.
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==== Add or hide local interfaces
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[[ChCapManageInterfacesLocalDialog]]
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.The ``Add New Interfaces - Local Interfaces'' dialog box
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image::wsug_graphics/ws-capture-options-manage-interfaces-local.png[{screenshot-attrs}]
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The tab ``Local Interfaces'' contains a list of available local interfaces,
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including the hidden ones, which are not shown in the other lists.
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If a new local interface is added, for example, a wireless interface has been
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activated, it is not automatically added to the list to prevent the constant
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scanning for a change in the list of available interfaces. To renew the list a
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rescan can be done.
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One way to hide an interface is to change the preferences. If the “Hide”
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checkbox is activated and the btn:[Apply] button clicked, the interface will
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not be seen in the lists of the ``Capture Interfaces'' dialog box any more. The
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changes are also saved in the `preferences` file.
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==== Add or hide remote interfaces
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||
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[[ChCapManageInterfacesRemoteDialog]]
|
||
.The ``Add New Interfaces - Remote Interfaces'' dialog box
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image::wsug_graphics/ws-capture-options-manage-interfaces-remote.png[{screenshot-attrs}]
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In this tab interfaces on remote hosts can be added. One or more of these
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interfaces can be hidden. In contrast to the local interfaces they are not saved
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in the `preferences` file.
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To remove a host including all its interfaces from the list, it has to be
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selected. Then click the btn:[Delete] button.
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For a detailed description see <<ChCapInterfaceRemoteSection>>
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||
|
||
[[ChCapInterfaceRemoteSection]]
|
||
|
||
=== The ``Remote Capture Interfaces'' dialog box
|
||
|
||
Besides doing capture on local interfaces Wireshark is capable of reaching out
|
||
across the network to a so called capture daemon or service processes to receive
|
||
captured data from.
|
||
|
||
[NOTE]
|
||
.Microsoft Windows only
|
||
====
|
||
This dialog and capability is only available on Microsoft Windows. On Linux/Unix
|
||
you can achieve the same effect (securely) through an SSH tunnel.
|
||
====
|
||
|
||
The Remote Packet Capture Protocol service must first be running on the
|
||
target platform before Wireshark can connect to it. The easiest way is
|
||
to install WinPcap from {winpcap-download-url} on the target. Once
|
||
installation is completed go to the Services control panel, find the
|
||
Remote Packet Capture Protocol service and start it.
|
||
|
||
[NOTE]
|
||
====
|
||
Make sure you have outside access to port 2002 on the target platform. This is
|
||
the port where the Remote Packet Capture Protocol service can be reached by
|
||
default.
|
||
====
|
||
|
||
To access the Remote Capture Interfaces dialog use the ``Add New Interfaces -
|
||
Remote'' dialog. See <<ChCapManageInterfacesRemoteDialog>> and select btn:[Add].
|
||
|
||
==== Remote Capture Interfaces
|
||
|
||
[[ChCapInterfaceRemoteDialog]]
|
||
.The ``Remote Capture Interfaces'' dialog box
|
||
image::wsug_graphics/ws-capture-options-manage-interfaces-remote-plus.png[{screenshot-attrs}]
|
||
|
||
You have to set the following parameters in this dialog:
|
||
|
||
_Host_::
|
||
Enter the IP address or host name of the target platform where the Remote Packet
|
||
Capture Protocol service is listening. The drop down list contains the hosts
|
||
that have previously been successfully contacted. The list can be emptied by
|
||
choosing ``Clear list'' from the drop down list.
|
||
|
||
_Port_::
|
||
Set the port number where the Remote Packet Capture Protocol service is
|
||
listening on. Leave open to use the default port (2002).
|
||
|
||
_Null authentication_::
|
||
Select this if you don't need authentication to take place for a remote capture
|
||
to be started. This depends on the target platform. Configuring the target
|
||
platform like this makes it insecure.
|
||
|
||
_Password authentication_::
|
||
This is the normal way of connecting to a target platform. Set the credentials
|
||
needed to connect to the Remote Packet Capture Protocol service.
|
||
|
||
==== Remote Capture Settings
|
||
|
||
The remote capture can be further fine tuned to match your situation. The
|
||
btn:[Remote Settings] button in <<ChCapEditInterfacesSettingsDialog>> gives
|
||
you this option. It pops up the dialog shown in
|
||
<<ChCapInterfaceRemoteSettingsDialog>>.
|
||
|
||
[[ChCapInterfaceRemoteSettingsDialog]]
|
||
.The ``Remote Capture Settings'' dialog box
|
||
image::wsug_graphics/ws-capture-options-remote-settings.png[{screenshot-attrs}]
|
||
|
||
You can set the following parameters in this dialog:
|
||
|
||
_Do not capture own RPCAP traffic_::
|
||
This option sets a capture filter so that the traffic flowing back from the
|
||
Remote Packet Capture Protocol service to Wireshark isn't captured as well and
|
||
also send back. The recursion in this saturates the link with duplicate traffic.
|
||
+
|
||
You only should switch this off when capturing on an interface other than the
|
||
interface connecting back to Wireshark.
|
||
|
||
_Use UDP for data transfer_::
|
||
Remote capture control and data flows over a TCP connection. This option allows
|
||
you to choose an UDP stream for data transfer.
|
||
|
||
_Sampling option None_::
|
||
This option instructs the Remote Packet Capture Protocol service to send back
|
||
all captured packets which have passed the capture filter. This is usually not a
|
||
problem on a remote capture session with sufficient bandwidth.
|
||
|
||
_Sampling option 1 of x packets_::
|
||
This option limits the Remote Packet Capture Protocol service to send only a sub
|
||
sampling of the captured data, in terms of number of packets. This allows
|
||
capture over a narrow band remote capture session of a higher bandwidth
|
||
interface.
|
||
|
||
|
||
_Sampling option 1 every x milliseconds_::
|
||
This option limits the Remote Packet Capture Protocol service to send only a sub
|
||
sampling of the captured data in terms of time. This allows capture over a
|
||
narrow band capture session of a higher bandwidth interface.
|
||
|
||
[[ChCapInterfaceDetailsSection]]
|
||
|
||
=== The ``Interface Details'' dialog box
|
||
|
||
When you select Details from the Capture Interface menu, Wireshark pops up the
|
||
``Interface Details'' dialog box as shown in <<ChCapInterfaceDetailsDialog>>. This
|
||
dialog shows various characteristics and statistics for the selected interface.
|
||
|
||
[NOTE]
|
||
.Microsoft Windows only
|
||
====
|
||
This dialog is only available on Microsoft Windows
|
||
====
|
||
|
||
[[ChCapInterfaceDetailsDialog]]
|
||
.The ``Interface Details'' dialog box
|
||
image::wsug_graphics/ws-capture-interface-details.png[{screenshot-attrs}]
|
||
|
||
[[ChCapCaptureFiles]]
|
||
|
||
=== Capture files and file modes
|
||
|
||
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 Wireshark and saved into a capture file.
|
||
|
||
By default Wireshark saves packets to a temporary file. You can also tell
|
||
Wireshark to save to a specific (“permanent”) file and switch to a
|
||
different file after a given time has elapsed or a given number of packets
|
||
have been captured. These options are controlled in the “Output” tab in
|
||
the ``Capture Options'' dialog.
|
||
|
||
[[ChCapCaptureOptionsOutputDialog]]
|
||
.Capture output options
|
||
image::wsug_graphics/ws-capture-options-output.png[{screenshot-attrs}]
|
||
|
||
[TIP]
|
||
====
|
||
Working with large files (several hundred MB) 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. Wireshark 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 capture files can be found in
|
||
<<AppFiles>>.
|
||
|
||
[[ChCapTabCaptureFiles]]
|
||
.Capture file mode selected by capture options
|
||
[options="header",cols="2,2,2,3,5"]
|
||
|===============
|
||
|File Name|``Create a new file...''|``Use a ring buffer...''|Mode|Resulting filename(s) used
|
||
|-|-|-|_Single temporary file_|wiresharkXXXXXX (where XXXXXX is a unique number)
|
||
|foo.cap|-|-|_Single named file_|foo.cap
|
||
|foo.cap|x|-|_Multiple files, continuous_|foo_00001_20100205110102.cap, foo_00002_20100205110318.cap, ...
|
||
|foo.cap|x|x|_Multiple files, ring buffer_|foo_00001_20100205110102.cap, foo_00002_20100205110318.cap, ...
|
||
|===============
|
||
|
||
_Single temporary file_::
|
||
A temporary file will be created and used (this is the default). After capturing
|
||
is stopped this file can be saved later under a user specified name.
|
||
|
||
_Single named file_::
|
||
A single capture file will be used. If you want to place the new capture file in
|
||
a specific folder choose this mode.
|
||
|
||
_Multiple files, continuous_::
|
||
Like the ``Single named file'' mode, but a new file is created and used after
|
||
reaching one of the multiple file switch conditions (one of the ``Next file every
|
||
...'' values).
|
||
|
||
_Multiple files, ring buffer_::
|
||
Much like ``Multiple files continuous'', reaching one of the multiple files switch
|
||
conditions (one of the ``Next file every ...'' values) will switch to the next
|
||
file. This will be a newly created file if value of ``Ring buffer with n files''
|
||
is not reached, otherwise it will replace the oldest of the formerly used files
|
||
(thus forming a “ring”).
|
||
+
|
||
This mode will limit the maximum disk usage, even for an unlimited amount of
|
||
capture input data, only keeping the latest captured data.
|
||
|
||
[[ChCapLinkLayerHeader]]
|
||
|
||
=== Link-layer header type
|
||
|
||
In most cases you won't have to modify link-layer header type. Some exceaptions
|
||
are as follows:
|
||
|
||
If you are capturing on an Ethernet device you might be offered 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”.
|
||
|
||
If you are capturing on an 802.11 device on some versions of BSD you might be
|
||
offered a choice of “Ethernet” or “802.11”. “Ethernet” will cause the
|
||
captured packets to have fake (“cooked”) Ethernet headers. “802.11” will
|
||
cause them to have full 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 you might be offered 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 you might
|
||
be offered 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''.
|
||
|
||
[[ChCapCaptureFilterSection]]
|
||
|
||
=== Filtering while capturing
|
||
|
||
Wireshark uses the libpcap filter language for capture filters. A brief
|
||
overview of the syntax follows. Complete documentation can be found in
|
||
the link:{pcap-filter-man-page-url}[pcap-filter man page]. You can find
|
||
a lot of Capture Filter examples at {wireshark-wiki-url}CaptureFilters.
|
||
|
||
You enter the capture filter into the “Filter” field of the Wireshark
|
||
``Capture Options'' dialog box, as shown in <<ChCapCaptureOptionsDialog>>.
|
||
|
||
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 <<ChCapExFilt1>>.
|
||
|
||
[[ChCapExFilt1]]
|
||
.A capture filter for telnet that captures traffic to and from a particular host
|
||
====
|
||
A capture filter for telnet that 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 <<ChCapExFilt2>>, and shows how to capture all telnet traffic except that
|
||
from 10.0.0.5.
|
||
|
||
[[ChCapExFilt2]]
|
||
.Capturing all telnet traffic not from 10.0.0.5
|
||
====
|
||
Capturing all telnet traffic not from 10.0.0.5
|
||
|
||
----
|
||
tcp port 23 and not src host 10.0.0.5
|
||
----
|
||
====
|
||
|
||
// XXX - add examples to the following list.
|
||
|
||
A primitive is simply one of the following: _[src|dst] host <host>_::
|
||
This primitive allows you to filter on a host IP address or name. You can
|
||
optionally precede the primitive with the keyword _src|dst_ to specify that you
|
||
are only interested in source or destination addresses. If these are not
|
||
present, packets where the specified address appears as either the source or the
|
||
destination address will be selected.
|
||
|
||
_ether [src|dst] host <ehost>_::
|
||
This primitive allows you to filter on Ethernet host addresses. You can
|
||
optionally include the keyword _src|dst_ between the keywords _ether_ and _host_
|
||
to specify that you are only interested in source or destination addresses. If
|
||
these are not present, packets where the specified address appears in either the
|
||
source or destination address will be selected.
|
||
|
||
_gateway host <host>_::
|
||
This primitive allows you to filter on packets that used _host_ as a gateway.
|
||
That is, where the Ethernet source or destination was _host_ but neither the
|
||
source nor destination IP address was _host_.
|
||
|
||
_[src|dst] net <net> [{mask <mask>}|{len <len>}]_::
|
||
This primitive allows you to filter on network numbers. You can optionally
|
||
precede this primitive with the keyword _src|dst_ to specify that you are only
|
||
interested in a source or destination network. If neither of these are present,
|
||
packets will be selected that have the specified network in either the source or
|
||
destination address. In addition, you can specify either the netmask or the CIDR
|
||
prefix for the network if they are different from your own.
|
||
|
||
|
||
_[tcp|udp] [src|dst] port <port>_::
|
||
This primitive allows you to filter on TCP and UDP port numbers. You can
|
||
optionally precede this primitive with the keywords _src|dst_ and _tcp|udp_
|
||
which allow you to specify that you are only interested in source or destination
|
||
ports and TCP or UDP packets respectively. The keywords _tcp|udp_ must appear
|
||
before _src|dst_.
|
||
+
|
||
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.
|
||
|
||
_less|greater <length>_::
|
||
This primitive allows you to filter on packets whose length was less than or
|
||
equal to the specified length, or greater than or equal to the specified length,
|
||
respectively.
|
||
|
||
_ip|ether proto <protocol>_::
|
||
This primitive allows you to filter on the specified protocol at either the
|
||
Ethernet layer or the IP layer.
|
||
|
||
_ether|ip broadcast|multicast_::
|
||
This primitive allows you to filter on either Ethernet or IP broadcasts or
|
||
multicasts.
|
||
|
||
_<expr> relop <expr>_:: This primitive allows you to create
|
||
complex filter expressions that select bytes or ranges of bytes in
|
||
packets. Please see the pcap-filter man page at
|
||
{pcap-filter-man-page-url} for more details.
|
||
|
||
|
||
[[ChCapCaptureAutoFilterSection]]
|
||
|
||
==== Automatic Remote Traffic Filtering
|
||
|
||
If Wireshark is running remotely (using e.g. SSH, an exported X11 window, a
|
||
terminal server, ...), the remote content has to be transported over the
|
||
network, adding a lot of (usually unimportant) packets to the actually
|
||
interesting traffic.
|
||
|
||
To avoid this, Wireshark tries to figure out if it’s remotely connected (by
|
||
looking at some specific environment variables) and automatically creates a
|
||
capture filter that matches aspects of the connection.
|
||
|
||
The following environment variables are analyzed:
|
||
|
||
_$$SSH_CONNECTION$$_ (ssh)::
|
||
<remote IP> <remote port> <local IP> <local port>
|
||
|
||
|
||
_$$SSH_CLIENT$$_ (ssh)::
|
||
<remote IP> <remote port> <local port>
|
||
|
||
|
||
_REMOTEHOST_ (tcsh, others?)::
|
||
<remote name>
|
||
|
||
_DISPLAY_ (x11)::
|
||
[remote name]:<display num>
|
||
|
||
|
||
_SESSIONNAME_ (terminal server)::
|
||
<remote name>
|
||
|
||
On Windows it asks the operating system if it’s running in a Remote Desktop Services environment.
|
||
|
||
////
|
||
|
||
// XXX Capture Info is currently disabled, but might be resurrected. See
|
||
// capture_info.[ch] and their git logs for details.
|
||
|
||
[[ChCapRunningSection]]
|
||
|
||
=== While a Capture is running ...
|
||
|
||
While a capture is running, the following dialog box is shown:
|
||
|
||
[[ChCapCaptureInfoDialog]]
|
||
.The ``Capture Info'' dialog box
|
||
image::wsug_graphics/ws-capture-info.png[{screenshot-attrs}]
|
||
|
||
This dialog box will inform you about the number of captured packets and the
|
||
time since the capture was started. The selection of which protocols are counted
|
||
cannot be changed.
|
||
|
||
[TIP]
|
||
====
|
||
This ``Capture Info'' dialog box can be hidden using the ``Hide capture info
|
||
dialog'' option in the Capture Options dialog box.
|
||
====
|
||
////
|
||
|
||
[[ChCapStopSection]]
|
||
|
||
==== Stop the running capture
|
||
|
||
A running capture session will be stopped in one of the following ways:
|
||
|
||
. Using the btn:[Stop] button from the ``Capture Info'' dialog box.
|
||
|
||
[NOTE]
|
||
====
|
||
The ``Capture Info'' dialog box might be hidden if the ``Hide capture info
|
||
dialog'' option is used.
|
||
====
|
||
|
||
. Using the menu:Capture[Stop] menu item.
|
||
|
||
. Using the btn:[Stop] toolbar button.
|
||
|
||
. Pressing kbd:[Ctrl+E].
|
||
|
||
. The capture will be automatically stopped if one of the _Stop Conditions_ is
|
||
met, e.g. the maximum amount of data was captured.
|
||
|
||
[[ChCapRestartSection]]
|
||
|
||
==== Restart a running capture
|
||
|
||
A running capture session can be restarted with the same capture options as 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:
|
||
|
||
. Using the menu:Capture[Restart] menu item.
|
||
|
||
. Using the btn:[Restart] toolbar button.
|
||
|
||
// End of WSUG Chapter Capture
|