4.5. The “Capture Options” dialog box
When you select Figure 4.3, “The “Capture Options” dialog box”.
→ (or use the corresponding item in the
main toolbar), Wireshark pops up the “Capture Options” dialog box as shown in
Figure 4.3. The “Capture Options” dialog box
If you are unsure which options to choose in this dialog box just try keeping
the defaults as this should work well in many cases.
The table shows the settings for all available interfaces:
The name of the interface and its IP addresses. If no address could be
resolved from the system, “none” will be shown.
Loopback interfaces are not available on Windows platforms.
The link-layer header type.
The information whether promicuous mode is enabled or disabled.
The maximum amount of data that will be captured for each packet. The default
value is set to the 65535 bytes.
The size of the kernel buffer that is reserved to keep the captured packets.
The information whether packets will be captured in monitor mode (Unix/Linux
The chosen capture filter.
By marking the checkboxes in the first column the interfaces are selected to be
captured from. By double-clicking on an interface the “Edit Interface Settings”
dialog box as shown in Figure 4.4, “The “Edit Interface Settings” dialog box” will be opened.
Capture on all interfaces
As Wireshark can capture on multiple interfaces it is possible to choose to
capture on all available interfaces.
Capture all packets in promiscuous mode
This checkbox allows you to specify that Wireshark should put all interfaces in
promiscuous mode when capturing.
This field allows you to specify a capture filter for all interfaces that are
currently selected. Once a filter has been entered in this field, the newly
selected interfaces will inherit the filter. Capture filters are discussed in
more details in Section 4.13, “Filtering while capturing”. It defaults to empty, or no
You can also click on the Section 6.6, “Defining and saving filters” button and Wireshark will
bring up the Capture Filters dialog box and allow you to create and/or select a
filter. Please see
Compile selected BPFs
This button allows you to compile the capture filter into BPF code and pop up a
window showing you the resulting pseudo code. This can help in understanding the
working of the capture filter you created. The Figure 4.5, “The “Compile Results” dialog box”.
leads you to
Linux power user tip
The execution of BPFs can be sped up on Linux by turning on BPF JIT 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
4.5.2. Capture File(s) frame
An explanation about capture file usage can be found in Section 4.11, “Capture files and file modes”.
This field allows you to specify the file name that will be used for the capture
file. This field is left blank by default. If the field is left blank, the
capture data will be stored in a temporary file. See Section 4.11, “Capture files and file modes” for
You can also click on the button to the right of this field to browse through
Use multiple files
Instead of using a single file Wireshark will automatically switch to a new
one if a specific trigger condition is reached.
Use pcap-ng format
This checkbox allows you to specify that Wireshark saves the captured packets in
pcap-ng format. This next generation capture file format is currently in
development. If more than one interface is chosen for capturing, this checkbox
is set by default. See http://wiki.wireshark.org/Development/PcapNg for more details on
Next file every n megabyte(s)
Multiple files only. Switch to the next file after the given number of
byte(s)/kilobyte(s)/megabyte(s)/gigabyte(s) have been captured.
Next file every n minute(s)
Multiple files only: Switch to the next file after the given number of
second(s)/minutes(s)/hours(s)/days(s) have elapsed.
Ring buffer with n files
Multiple files only: Form a ring buffer of the capture files with the given
number of files.
Stop capture after n file(s)
Multiple files only: Stop capturing after switching to the next file the given
number of times.
4.5.3. Stop Capture… frame
… after n packet(s)
Stop capturing after the given number of packets have been captured.
… after n megabytes(s)
Stop capturing after the given number of
byte(s)/kilobyte(s)/megabyte(s)/gigabyte(s) have been captured. This option is
greyed out if “Use multiple files” is selected.
… after n minute(s)
Stop capturing after the given number of second(s)/minutes(s)/hours(s)/days(s)
4.5.4. Display Options frame
Update list of packets in real time
This option allows you to specify that Wireshark should update the packet list
pane in real time. If you do not specify this, Wireshark does 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.
Automatic scrolling in live capture
This option allows you to specify that Wireshark should scroll the packet list
pane as new packets come in, so you are always looking at the last packet. If
you do not specify this Wireshark simply adds new packets onto the end of the
list but does not scroll the packet list pane. This option is greyed out if
“Update list of packets in real time” is disabled.
Hide capture info dialog
If this option is checked, the capture info dialog described in Section 4.14, “While a Capture is running …” will be hidden.
4.5.5. Name Resolution frame
Enable MAC name resolution
This option allows you to control whether or not Wireshark translates MAC
addresses into names. See Section 7.7, “Name Resolution”.
Enable network name resolution
This option allows you to control whether or not Wireshark translates network
addresses into names. See Section 7.7, “Name Resolution”.
Enable transport name resolution
This option allows you to control whether or not Wireshark translates transport
addresses into protocols. See Section 7.7, “Name Resolution”.
Once you have set the values you desire and have selected the options you need,
simply click on
to commence the capture or to
cancel the capture.
If you start a capture, Wireshark allows you to stop capturing when you have
enough packets captured, for details see Section 4.14, “While a Capture is running …”.