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diff --git a/docbook/wsug_src/wsug_capture.adoc b/docbook/wsug_src/wsug_capture.adoc new file mode 100644 index 00000000..c7ef8f1b --- /dev/null +++ b/docbook/wsug_src/wsug_capture.adoc @@ -0,0 +1,733 @@ +// WSUG Chapter Capture + +[#ChapterCapture] + +== Capturing Live Network Data + +[#ChCapIntroduction] + +=== Introduction + +Capturing live network data is one of the major features of Wireshark. + +The Wireshark capture engine provides the following features: + +* Capture from different kinds of network hardware such as Ethernet or 802.11. + +* Simultaneously capture from multiple network interfaces. + +* Stop the capture on different triggers such as the amount of captured data, + elapsed time, or the number of packets. + +* Simultaneously show decoded packets while Wireshark is capturing. + +* Filter packets, reducing the amount of data to be captured. See + <<ChCapCaptureFilterSection>>. + +* Save packets in multiple files while doing a long-term capture, optionally + rotating through a fixed number of files (a “ringbuffer”). See + <<ChCapCaptureFiles>>. + +The capture engine still lacks the following features: + +* Stop capturing (or perform some other action) depending on the captured data. + +[#ChCapPrerequisitesSection] + +=== Prerequisites + +Setting up Wireshark to capture packets for the first time can be +tricky. A comprehensive guide “How To setup a Capture” is available at +{wireshark-wiki-url}CaptureSetup. + +Here are some common pitfalls: + +* You may need special privileges to start a live capture. + +* You need to choose the right network interface to capture packet data from. + +* You need to capture at the right place in the network to see the traffic you + want to see. + +If you have any problems setting up your capture environment, you should have a +look at the guide mentioned above. + +[#ChCapCapturingSection] + +=== Start Capturing + +The following methods can be used to start capturing packets with Wireshark: + +* You can double-click on an interface in the <<ChCapInterfaceSection,welcome screen>>. + +* You can select an interface in the <<ChCapInterfaceSection,welcome screen>>, then select menu:Capture[Start] or click the first toolbar button. + +* You can get more detailed information about available interfaces using <<ChCapCaptureOptions>> (menu:Capture[Options...]). + +* If you already know the name of the capture interface you can start Wireshark from the command line: +-- +---- +$ wireshark -i eth0 -k +---- +-- +This will start Wireshark capturing on interface `eth0`. More details can be found at <<ChCustCommandLine>>. + +[#ChCapInterfaceSection] + +=== The “Capture” Section Of The Welcome Screen + +When you open Wireshark without starting a capture or opening a capture file it will display the “Welcome Screen,” which lists any recently opened capture files and available capture interfaces. +Network activity for each interface will be shown in a sparkline next to the interface name. +It is possible to select more than one interface and capture from them simultaneously. + +[#ChCapCaptureInterfacesMainWin32] + +.Capture interfaces on Microsoft Windows +image::images/ws-capture-interfaces-main-win32.png[{screenshot-attrs}] + +[#ChCapCaptureInterfacesMainMacos] + +.Capture interfaces on macOS +image::images/ws-capture-interfaces-main-macos.png[{screenshot-attrs}] + +Some interfaces allow or require configuration prior to capture. +This will be indicated by a configuration icon +(image:images/toolbar/x-capture-options.png[height=16,width=16]) +to the left of the interface name. +Clicking on the icon will show the configuration dialog for that interface. + +Hovering over an interface will show any associated IPv4 and IPv6 addresses and its capture filter. + +Wireshark isn't limited to just network interfaces -- on most systems you can also capture USB, Bluetooth, and other types of packets. +Note also that an interface might be hidden if it’s inaccessible to Wireshark or if it has been hidden as described in <<ChCapManageInterfacesSection>>. + +[#ChCapCaptureOptions] + +=== The “Capture Options” Dialog Box + +When you select menu:Capture[Options...] (or use the corresponding item in the +main toolbar), Wireshark pops up the “Capture Options” dialog box as shown in +<<ChCapCaptureOptionsDialog>>. +If you are unsure which options to choose in this dialog box, leaving the defaults settings as they are should work well in many cases. + +[#ChCapCaptureOptionsDialog] +.The “Capture Options” input tab +image::images/ws-capture-options.png[{screenshot-attrs}] + +The “Input” tab contains the “Interface” table, which shows the following columns: + +Interface:: +The interface name. ++ +Some interfaces allow or require configuration prior to capture. +This will be indicated by a configuration icon +(image:images/toolbar/x-capture-options.png[height=16,width=16]) +to the left of the interface name. +Clicking on the icon will show the configuration dialog for that interface. + +Traffic:: +A sparkline showing network activity over time. + +Link-layer Header:: +The type of packet captured by this interface. +In some cases it is possible to change this. +See <<ChCapLinkLayerHeader>> for more details. + +Promiscuous:: +Lets you put this interface in promiscuous mode while capturing. +Note that another application might override this setting. + +Snaplen:: +The snapshot length, or the number of bytes to capture for each packet. +You can set an explicit length if needed, e.g., for performance or privacy reasons. + +Buffer:: +The size of the kernel buffer that is reserved for capturing packets. +You can increase or decrease this as needed, but the default is usually sufficient. + +Monitor Mode:: +Lets you capture full, raw 802.11 headers. +Support depends on the interface type, hardware, driver, and OS. +Note that enabling this might disconnect you from your wireless network. + +Capture Filter:: +The capture filter applied to this interface. +You can edit the filter by double-clicking on it. +See <<ChCapCaptureFilterSection>> for more details about capture filters. + +Hovering over an interface or expanding it will show any associated IPv4 and IPv6 addresses. + +If “Enable promiscuous mode on all interfaces” is enabled, the individual promiscuous mode settings above will be overridden. + +“Capture filter for selected interfaces” can be used to set a filter for more than one interface at the same time. + +btn:[Manage Interfaces] opens the <<ChCapManageInterfacesDialog>> where pipes can be defined, local interfaces scanned or hidden, or remote interfaces added. + +btn:[Compile Selected BPFs] opens <<ChCapCompiledFilterOutputDialog>>, which shows you the compiled bytecode for your capture filter. +This can help to better understand the capture filter you created. + + +[TIP] +.Linux power user tip +==== +The execution of BPFs can be sped up on Linux by turning on BPF Just In Time compilation by executing + +---- +$ echo 1 >/proc/sys/net/core/bpf_jit_enable +---- + +if it is not enabled already. To make the change persistent you can use +link:{sysfs-main-url}[sysfsutils]. +==== + +.The “Capture Options” output tab +image::images/ws-capture-options-output.png[{screenshot-attrs}] + +The “Output” tab shows the following information: + +Capture to a permanent file:: + +File::: +This field allows you to specify the file name that will be used for the capture file. +It is left blank by default. +If left blank, the capture data will be stored in a temporary file. +See <<ChCapCaptureFiles>> for details. +You can also click on the button to the right of this field to browse through the filesystem. + +Output format::: +Allows you to set the format of the capture file. +pcapng is the default and is more flexible than pcap. +pcapng might be required, e.g., if more than one interface is chosen for capturing. +See {wireshark-wiki-url}Development/PcapNg for more details on pcapng. + +Create a new file automatically...:: +Sets the conditions for switching a new capture file. +A new capture file can be created based on the following conditions: + * The number of packets in the capture file. + * The size of the capture file. + * The duration of the capture file. + * The wall clock time. + +Use a ring buffer with:: +Multiple files only. +Form a ring buffer of the capture files with the given number of files. + +More details about capture files can be found in <<ChCapCaptureFiles>>. + +.The “Capture Options” options tab +image::images/ws-capture-options-options.png[{screenshot-attrs}] + +The “Options” tab shows the following information: + +Display Options:: + +Update list of packets in real-time::: +Updates the packet list pane in real time during capture. +If you do not enable this, Wireshark will not display any packets until you stop the capture. +When you check this, Wireshark captures in a separate process and feeds the captures to the display process. + +Automatically scroll during live capture::: +Scroll the packet list pane as new packets come in, so you are always looking at the most recent packet. +Automatic scrolling is temporarily disabled when manually scrolling upwards or performing a <<ChUseTabGo,"Go" action>> so that the selected packet can be examined. +It will resume upon manually scrolling to the end of the packet list. +If you do not specify this Wireshark adds new packets to the packet list but does not scroll the packet list pane. +This option has no effect if “Update list of packets in real-time” is disabled. + +Show capture information during capture::: +If this option is enabled, the capture information dialog described in <<ChCapRunningSection>> will be shown while packets are captured. + +Name Resolution:: + +Resolve MAC addresses::: +Translate MAC addresses into names. + +Resolve network names::: +Translate network addresses into names. + +Resolve transport names::: +Translate transport names (port numbers). + +See <<ChAdvNameResolutionSection>> for more details on each of these options. + +Stop capture automatically after...:: + +Capturing can be stopped based on the following conditions: + +* The number of packets in the capture file. +* The number of capture files. +* The capture file size. +* The capture file duration. + +You can double click on an interface row in the “Input“ tab or click btn:[Start] from any tab to commence the capture. You can click btn:[Cancel] to apply your changes and close the dialog. + +[#ChCapManageInterfacesSection] + +=== The “Manage Interfaces” Dialog Box + +[#ChCapManageInterfacesDialog] +.The “Manage Interfaces” dialog box +image::images/ws-manage-interfaces.png[{screenshot-attrs}] + +The “Manage Interfaces” dialog box initially shows the “Local Interfaces” tab, which lets you manage the following: + +Show:: +Whether or not to show or hide this interface in the welcome screen and the “Capture Options” dialog. + +Friendly Name:: +A name for the interface that is human readable. + +Interface Name:: +The device name of the interface. + +Comment:: +Can be used to add a descriptive comment for the interface. + +// [[ChCapManageInterfacesPipesDialog]] + +// .The “Pipes” tab +// image::images/ws-capture-options-manage-interfaces-pipes.png[{screenshot-attrs}] + +The “Pipes” tab lets you capture from a named pipe. +To successfully add a pipe, its associated named pipe must have already been created. +Click btn:[{plus}] and type the name of the pipe including its path. +Alternatively, btn:[Browse] can be used to locate the pipe. + +To remove a pipe from the list of interfaces, select it and press btn:[-]. + +// [[ChCapManageInterfacesDialog]] + +// === The “Add New Interfaces” dialog box + +// As a central point to manage interfaces this dialog box consists of three tabs +// to add or remove interfaces. + +// .The “Add New Interfaces” dialog box +// image::images/ws-capture-options-manage-interfaces.png[{screenshot-attrs}] + +// ==== Add or hide local interfaces + +// [[ChCapManageInterfacesLocalDialog]] +// .The “Add New Interfaces - Local Interfaces” dialog box +// image::images/ws-capture-options-manage-interfaces-local.png[{screenshot-attrs}] + +// The tab “Local Interfaces” contains a list of available local interfaces, +// including the hidden ones, which are not shown in the other lists. + +// If a new local interface is added, for example, a wireless interface has been +// activated, it is not automatically added to the list to prevent the constant +// scanning for a change in the list of available interfaces. To renew the list a +// rescan can be done. + +// One way to hide an interface is to change the preferences. If the “Hide” +// checkbox is activated and the btn:[Apply] button clicked, the interface will +// not be seen in the lists of the “Capture Interfaces” dialog box any more. The +// changes are also saved in the `preferences` file. + +// ==== Add or hide remote interfaces + +// [[ChCapManageInterfacesRemoteDialog]] +// .The “Add New Interfaces - Remote Interfaces” dialog box +// image::images/ws-capture-options-manage-interfaces-remote.png[{screenshot-attrs}] + +On Microsoft Windows, the “Remote Interfaces” tab lets you capture from an interface on a different machine. +The Remote Packet Capture Protocol service must first be running on the target platform before Wireshark can connect to it. + +On Linux or Unix you can capture (and do so more securely) through an SSH tunnel. + +To add a new remote capture interface, click btn:[{plus}] and specify the following: + +Host:: +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 blank 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. +This is exactly as secure as it appears, i.e., it is not secure at all. + +Password authentication:: +Lets you specify the username and password required to connect to the Remote Packet Capture Protocol service. + +Each interface can optionally be hidden. +In contrast to the local interfaces, they are not saved in the `preferences` file. + +[NOTE] +==== +Make sure you have outside access to port 2002 on the target platform. +This is the default port used by the Remote Packet Capture Protocol service. +==== + +To remove a host including all its interfaces from the list, select it and click the btn:[-] button. + +// To access the Remote Capture Interfaces dialog use the “Remote Interfaces” tab of the “Manage Interfaces” dialog. See <<ChCapManageInterfacesRemoteDialog>> and select btn:[Add]. + +// [[ChCapInterfaceRemoteDialog]] +// .The “Remote Capture Interfaces” dialog box +// image::images/ws-capture-options-manage-interfaces-remote-plus.png[{screenshot-attrs}] + + +// ==== Remote Capture Settings + +// The remote capture can be further fine tuned to match your situation. The +// btn:[Remote Interfaces] button in <<ChCapManageInterfacesDialog>> gives +// you this option. It pops up the dialog shown in +// <<ChCapInterfaceRemoteSettingsDialog>>. + +// [[ChCapInterfaceRemoteSettingsDialog]] +// .The “Remote Capture Settings” dialog box +// image::images/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 a 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::images/ws-capture-interface-details.png[{screenshot-attrs}] + +[#ChCapCompiledFilterOutputSection] + +=== The “Compiled Filter Output” Dialog Box + +This figure shows the results of compiling the BPF filter for the selected interfaces. + +[#ChCapCompiledFilterOutputDialog] + +.The “Compiled Filter Output” dialog box +image::images/ws-capture-options-compile-selected-bpfs.png[{medium-screenshot-attrs}] + +In the list on the left the interface names are listed. +The results of compiling a filter for the selected interface are shown on the right. + +[#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 +“Capture Options” dialog's “Output” tab. + +[#ChCapCaptureOptionsOutputDialog] +.Capture output options +image::images/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 the “Multiple files” option 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.pcap[ng] (where XXXXXX is a unique 6 character alphanumeric sequence) +|foo.cap|-|-|Single named file|foo.cap +|foo.cap|x|-|Multiple files, continuous|foo_00001_20230714110102.cap, foo_00002_20230714110318.cap, ... +|foo.cap|x|x|Multiple files, ring buffer|foo_00001_20230714110102.cap, foo_00002_20230714110318.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. +Choose this mode if you want to place the new capture file in a specific folder. + +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 exceptions +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 supports limiting the packet capture to packets that match a +_capture filter_. Wireshark capture filters are written in +libpcap filter language. Below is a brief overview of the libpcap filter +language's syntax. Complete documentation can be found at +the link:{pcap-filter-man-page-url}[pcap-filter man page]. You can find +many 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 +==== +---- +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 +==== +---- +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. + +[#ChCapRunningSection] + +=== While a Capture is running ... + +You might see the following dialog box while a capture is running: + +[#ChCapCaptureInfoDialog] +.The “Capture Information” dialog box +image::images/ws-capture-info.png[{small-screenshot-attrs}] + +This dialog box shows a list of protocols and their activity over time. +It can be enabled via the “capture.show_info” setting in the “Advanced” +preferences. + +[#ChCapStopSection] + +==== Stop the running capture + +A running capture session will be stopped in one of the following ways: + +. The btn:[Stop Capture] button in the “Capture Information” dialog box. + +. The menu:Capture[Stop] menu item. + +. 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 |