From Bingyao Du:

[obnox/wireshark/wip.git] / FAQ

   The Wireshark FAQ

   Note: This is just an ASCII snapshot of the faq and may not be up to
         date. Please go to http://www.wireshark.org/faq.html for the up
         to date version. The version of this snapshot can be found at
         the end of this document.

   INDEX


1. General Questions:

   1.1 What is Wireshark?

   1.2 What's up with the name change? Is Wireshark a fork?

   1.3 Where can I get help?

   1.4 How much does Wireshark cost?

   1.5 Can I use Wireshark commercially?

   1.6 Can I use Wireshark as part of my commercial product?

   1.7 What protocols are currently supported?

   1.8 Are there any plans to support {your favorite protocol}?

   1.9 Can Wireshark read capture files from {your favorite network
   analyzer}?

   1.10 What devices can Wireshark use to capture packets?

   1.11 Does Wireshark work on Windows Me?

   1.12 Does Wireshark work on Windows XP?

2. Downloading Wireshark:

   2.1 Why do I get an error when I try to run the Win32 installer?

3. Installing Wireshark:

   3.1 I installed the Wireshark RPM (or other package); why did it
   install TShark but not Wireshark?

4. Building Wireshark:

   4.1 I have libpcap installed; why did the configure script not find
   pcap.h or bpf.h?

   4.2 Why do I get the error

     dftest_DEPENDENCIES was already defined in condition TRUE, which
     implies condition HAVE_PLUGINS_TRUE

   when I try to build Wireshark from SVN or a SVN snapshot?

   4.3 Why does the linker fail with a number of "Output line too long."
   messages followed by linker errors when I try to buil Wireshark?

   4.4 When I try to build Wireshark on Solaris, why does the link fail
   complaining that plugin_list is undefined?

   4.5 When I try to build Wireshark on Windows, why does the build fail
   because of conflicts between winsock.h and winsock2.h?

5. Starting Wireshark:

   5.1 Why does Wireshark crash with a Bus Error when I try to run it on
   Solaris 8?

   5.2 When I run Wireshark on Windows NT, why does it die with a Dr.
   Watson error, reporting an "Integer division by zero" exception, when I
   start it?

   5.3 When I try to run Wireshark, why does it complain about
   sprint_realloc_objid being undefined?

   5.4 When I try to run Wireshark on Windows, why does it fail to run
   with a complaint that it can't find packet.dll?

   5.5 I've installed Wireshark from Fink on Mac OS X; why is it very slow
   to start up?

6. Crashes and other fatal errors:

   6.1 I have an XXX network card on my machine; if I try to capture on
   it, why does my machine crash or reset itself?

   6.2 Why does my machine crash or reset itself when I select "Start"
   from the "Capture" menu or select "Preferences" from the "Edit" menu?

7. Capturing packets:

   7.1 When I use Wireshark to capture packets, why do I see only packets
   to and from my machine, or not see all the traffic I'm expecting to see
   from or to the machine I'm trying to monitor?

   7.2 When I capture with Wireshark, why can't I see any TCP packets
   other than packets to and from my machine, even though another analyzer
   on the network sees those packets?

   7.3 Why am I only seeing ARP packets when I try to capture traffic?

   7.4 Why am I not seeing any traffic when I try to capture traffic?

   7.5 Can Wireshark capture on (my T1/E1 line, SS7 links, etc.)?

   7.6 How do I put an interface into promiscuous mode?

   7.7 I can set a display filter just fine; why don't capture filters
   work?

   7.8 I'm entering valid capture filters; why do I still get "parse
   error" errors?

   7.9 How can I capture packets with CRC errors?

   7.10 How can I capture entire frames, including the FCS?

   7.11 I'm capturing packets on a machine on a VLAN; why don't the
   packets I'm capturing have VLAN tags?

   7.12 Why does Wireshark hang after I stop a capture?

8. Capturing packets on Windows:

   8.1 I'm running Wireshark on Windows; why does some network interface
   on my machine not show up in the list of interfaces in the "Interface:"
   field in the dialog box popped up by "Capture->Start", and/or why does
   Wireshark give me an error if I try to capture on that interface?

   8.2 I'm running Wireshark on Windows; why do no network interfaces show
   up in the list of interfaces in the "Interface:" field in the dialog
   box popped up by "Capture->Start"?

   8.3 I'm running Wireshark on Windows; why doesn't my serial port/ADSL
   modem/ISDN modem show up in the list of interfaces in the "Interface:"
   field in the dialog box popped up by "Capture->Start"?

   8.4 I'm running Wireshark on Windows NT 4.0/Windows 2000/Windows
   XP/Windows Server 2003; my machine has a PPP (dial-up POTS, ISDN, etc.)
   interface, and it shows up in the "Interface" item in the "Capture
   Options" dialog box. Why can no packets be sent on or received from
   that network while I'm trying to capture traffic on that interface?

   8.5 I'm running Wireshark on Windows 95/98/Me, on a machine with more
   than one network adapter of the same type; why does Wireshark show all
   of those adapters with the same name, not letting me use any of those
   adapters other than the first one?

   8.6 I'm running Wireshark on Windows; why am I not seeing any traffic
   being sent by the machine running Wireshark?

   8.7 When I capture on Windows in promiscuous mode, I can see packets
   other than those sent to or from my machine; however, those packets
   show up with a "Short Frame" indication, unlike packets to or from my
   machine. What should I do to arrange that I see those packets in their
   entirety?

   8.8 I'm capturing packets on {Windows 95, Windows 98, Windows Me}; why
   are the time stamps on packets wrong?

   8.9 I'm trying to capture 802.11 traffic on Windows; why am I not
   seeing any packets?

   8.10 I'm trying to capture 802.11 traffic on Windows; why am I seeing
   packets received by the machine on which I'm capturing traffic, but not
   packets sent by that machine?

   8.11 I'm trying to capture Ethernet VLAN traffic on Windows, and I'm
   capturing on a "raw" Ethernet device rather than a "VLAN interface", so
   that I can see the VLAN headers; why am I seeing packets received by
   the machine on which I'm capturing traffic, but not packets sent by
   that machine?

9. Capturing packets on UN*Xes:

   9.1 I'm running Wireshark on a UNIX-flavored OS; why does some network
   interface on my machine not show up in the list of interfaces in the
   "Interface:" field in the dialog box popped up by "Capture->Start",
   and/or why does Wireshark give me an error if I try to capture on that
   interface?

   9.2 I'm running Wireshark on a UNIX-flavored OS; why do no network
   interfaces show up in the list of interfaces in the "Interface:" field
   in the dialog box popped up by "Capture->Start"?

   9.3 I'm capturing packets on Linux; why do the time stamps have only
   100ms resolution, rather than 1us resolution?

10. Capturing packets on wireless LANs:

   10.1 How can I capture raw 802.11 frames, including non-data
   (management, beacon) frames?

   10.2 How do I capture on an 802.11 device in monitor mode?

11. Viewing traffic:

   11.1 Why am I seeing lots of packets with incorrect TCP checksums?

   11.2 I've just installed Wireshark, and the traffic on my local LAN is
   boring. Where can I find more interesting captures?

   11.3 Why doesn't Wireshark correctly identify RTP packets? It shows
   them only as UDP.

   11.4 Why doesn't Wireshark show Yahoo Messenger packets in captures
   that contain Yahoo Messenger traffic?

12. Filtering traffic:

   12.1 I saved a filter and tried to use its name to filter the display;
   why do I get an "Unexpected end of filter string" error?

   12.2 How can I search for, or filter, packets that have a particular
   string anywhere in them?

   12.3 How do I filter a capture to see traffic for virus XXX?

1. General Questions

   Q 1.1: What is Wireshark?

   A: Gerald Combs, the creator of Ethereal®, has initiated the Wireshark
   network protocol analyzer project, a successor to Ethereal®. The
   Ethereal® core developer team has moved with Gerald to the Wireshark
   project. It is the world's most popular network protocol analyzer. It
   has a rich and powerful feature set, and runs on most computing
   platforms including Windows, OS X, and Linux. It is freely available as
   open source, and is released under the GNU General Public License.

   For more information, please see the About Wireshark page.

   Q 1.2: What's up with the name change? Is Wireshark a fork?

   A: In May of 2006, the original author of Ethereal® went to work for
   CACE Technologies (best known for WinPcap). Unfortunately, he had to
   leave the Ethereal® trademarks behind.

   This left the project in an awkward position. The only reasonable way
   to ensure the continued success of the project was to change the name.
   This is how Wireshark was born.

   Wireshark is almost (but not quite) a fork. Normally a "fork" of an
   open source project results in two names, web sites, development teams,
   support infrastructures, etc. This is the case with Wireshark except
   for one notable exception -- every member of the core development team
   is now working on Wireshark. As far as anyone knows, there has been no
   active development on Ethereal since the name change. More information
   on the name change can be found here:
     *
     *

   Q 1.3: Where can I get help?

   A: Community support is available on the wireshark-users mailing list.
   Subscription information and archives for all of Wireshark's mailing
   lists can be found at http://www.wireshark.org/mailman/listinfo. An IRC
   channel dedicated to Wireshark can be found at
   irc://irc.freenode.net/wireshark.

   Commercial support, training, and development services are available
   from CACE Technologies.

   Q 1.4: How much does Wireshark cost?

   A: Wireshark is "free software"; you can download it without paying any
   license fee. The version of Wireshark you download isn't a "demo"
   version, with limitations not present in a "full" version; it is the
   full version.

   The license under which Wireshark is issued is the GNU General Public
   License. See the GNU GPL FAQ for some more information.

   Q 1.5: Can I use Wireshark commercially?

   A: Yes, if, for example, you mean "I work for a commercial
   organization; can I use Wireshark to capture and analyze network
   traffic in our company's networks or in our customer's networks?"

   If you mean "Can I use Wireshark as part of my commercial product?",
   see the next entry in the FAQ.

   Q 1.6: Can I use Wireshark as part of my commercial product?

   A: As noted, Wireshark is licensed under the GNU General Public
   License. The GPL imposes conditions on your use of GPL'ed code in your
   own products; you cannot, for example, make a "derived work" from
   Wireshark, by making modifications to it, and then sell the resulting
   derived work and not allow recipients to give away the resulting work.
   You must also make the changes you've made to the Wireshark source
   available to all recipients of your modified version; those changes
   must also be licensed under the terms of the GPL. See the GPL FAQ for
   more details; in particular, note the answer to the question about
   modifying a GPLed program and selling it commercially, and the question
   about linking GPLed code with other code to make a proprietary program.

   You can combine a GPLed program such as Wireshark and a commercial
   program as long as they communicate "at arm's length", as per this item
   in the GPL FAQ.

   Q 1.7: What protocols are currently supported?

   A: There are currently hundreds of supported protocols and media.
   Details can be found in the wireshark(1) man page.

   Q 1.8: Are there any plans to support {your favorite protocol}?

   A: Support for particular protocols is added to Wireshark as a result
   of people contributing that support; no formal plans for adding support
   for particular protocols in particular future releases exist.

   Q 1.9: Can Wireshark read capture files from {your favorite network
   analyzer}?

   A: Support for particular protocols is added to Wireshark as a result
   of people contributing that support; no formal plans for adding support
   for particular protocols in particular future releases exist.

   If a network analyzer writes out files in a format already supported by
   Wireshark (e.g., in libpcap format), Wireshark may already be able to
   read them, unless the analyzer has added its own proprietary extensions
   to that format.

   If a network analyzer writes out files in its own format, or has added
   proprietary extensions to another format, in order to make Wireshark
   read captures from that network analyzer, we would either have to have
   a specification for the file format, or the extensions, sufficient to
   give us enough information to read the parts of the file relevant to
   Wireshark, or would need at least one capture file in that format AND a
   detailed textual analysis of the packets in that capture file (showing
   packet time stamps, packet lengths, and the top-level packet header) in
   order to reverse-engineer the file format.

   Note that there is no guarantee that we will be able to
   reverse-engineer a capture file format.

   Q 1.10: What devices can Wireshark use to capture packets?

   A: Wireshark can read live data from Ethernet, Token-Ring, FDDI, serial
   (PPP and SLIP) (if the OS on which it's running allows Wireshark to do
   so), 802.11 wireless LAN (if the OS on which it's running allows
   Wireshark to do so), ATM connections (if the OS on which it's running
   allows Wireshark to do so), and the "any" device supported on Linux by
   recent versions of libpcap.

   It can also read a variety of capture file formats, including:
     * AG Group/WildPackets EtherPeek/TokenPeek/AiroPeek/EtherHelp/Packet
       Grabber captures
     * AIX's iptrace captures
     * Accellent's 5Views LAN agent output
     * Cinco Networks NetXRay captures
     * Cisco Secure Intrusion Detection System IPLog output
     * CoSine L2 debug output
     * DBS Etherwatch VMS text output
     * Endace Measurement Systems' ERF format captures
     * EyeSDN USB S0 traces
     * HP-UX nettl captures
     * ISDN4BSD project i4btrace captures
     * Linux Bluez Bluetooth stack hcidump -w traces
     * Lucent/Ascend router debug output
     * Microsoft Network Monitor captures
     * Network Associates Windows-based Sniffer captures
     * Network General/Network Associates DOS-based Sniffer (compressed or
       uncompressed) captures
     * Network Instruments Observer version 9 captures
     * Novell LANalyzer captures
     * RADCOM's WAN/LAN analyzer captures
     * Shomiti/Finisar Surveyor captures
     * Toshiba's ISDN routers dump output
     * VMS TCPIPtrace/TCPtrace/UCX$TRACE output
     * Visual Networks' Visual UpTime traffic capture
     * libpcap, tcpdump and various other tools using tcpdump's capture
       format
     * snoop and atmsnoop output

   so that it can read traces from various network types, as captured by
   other applications or equipment, even if it cannot itself capture on
   those network types.

   Q 1.11: Does Wireshark work on Windows Me?

   A: Yes, but if you want to capture packets, you will need to install
   the latest version of WinPcap, as 2.02 and earlier versions of WinPcap
   didn't support Windows Me. You should also install the latest version
   of Wireshark as well.

   Q 1.12: Does Wireshark work on Windows XP?

   A: Yes, but if you want to capture packets, you will need to install
   the latest version of WinPcap, as 2.2 and earlier versions of WinPcap
   didn't support Windows XP.

2. Downloading Wireshark

   Q 2.1: Why do I get an error when I try to run the Win32 installer?

   A: The program you used to download it may have downloaded it
   incorrectly. Web browsers sometimes may do this.

   Try downloading it with, for example:
     * Wget, for which Windows binaries are available on the SunSITE FTP
       server at sunsite.tk or Heiko Herold's windows wget spot - wGetGUI
       offers a GUI interface that uses wget;
     * WS_FTP from Ipswitch,
     * the ftp command that comes with Windows.

   If you use the ftp command, make sure you do the transfer in binary
   mode rather than ASCII mode, by using the binary command before
   transferring the file.

3. Installing Wireshark

   Q 3.1: I installed the Wireshark RPM (or other package); why did it
   install TShark but not Wireshark?

   A: Many distributions have separate Wireshark packages, one for non-GUI
   components such as TShark, editcap, dumpcap, etc. and one for the GUI.
   If this is the case on your system, there's probably a separate package
   named wireshark-gnome or wireshark-gtk+. Find it and install it.

4. Building Wireshark

   Q 4.1: I have libpcap installed; why did the configure script not find
   pcap.h or bpf.h?

   A: Are you sure pcap.h and bpf.h are installed? The official
   distribution of libpcap only installs the libpcap.a library file when
   "make install" is run. To install pcap.h and bpf.h, you must run "make
   install-incl". If you're running Debian or Redhat, make sure you have
   the "libpcap-dev" or "libpcap-devel" packages installed.

   It's also possible that pcap.h and bpf.h have been installed in a
   strange location. If this is the case, you may have to tweak
   aclocal.m4.

   Q 4.2: Why do I get the error

     dftest_DEPENDENCIES was already defined in condition TRUE, which
     implies condition HAVE_PLUGINS_TRUE

   when I try to build Wireshark from SVN or a SVN snapshot?

   A: You probably have automake 1.5 installed on your machine (the
   command automake --version will report the version of automake on your
   machine). There is a bug in that version of automake that causes this
   problem; upgrade to a later version of automake (1.6 or later).

   Q 4.3: Why does the linker fail with a number of "Output line too
   long." messages followed by linker errors when I try to buil Wireshark?

   A: The version of the sed command on your system is incapable of
   handling very long lines. On Solaris, for example, /usr/bin/sed has a
   line length limit too low to allow libtool to work; /usr/xpg4/bin/sed
   can handle it, as can GNU sed if you have it installed.

   On Solaris, changing your command search path to search /usr/xpg4/bin
   before /usr/bin should make the problem go away; on any platform on
   which you have this problem, installing GNU sed and changing your
   command path to search the directory in which it is installed before
   searching the directory with the version of sed that came with the OS
   should make the problem go away.

   Q 4.4: When I try to build Wireshark on Solaris, why does the link fail
   complaining that plugin_list is undefined?

   A: This appears to be due to a problem with some versions of the GTK+
   and GLib packages from www.sunfreeware.org; un-install those packages,
   and try getting the 1.2.10 versions from that site, or the versions
   from The Written Word, or the versions from Sun's GNOME distribution,
   or the versions from the supplemental software CD that comes with the
   Solaris media kit, or build them from source from the GTK Web site.
   Then re-run the configuration script, and try rebuilding Wireshark. (If
   you get the 1.2.10 versions from www.sunfreeware.org, and the problem
   persists, un-install them and try installing one of the other versions
   mentioned.)

   Q 4.5: When I try to build Wireshark on Windows, why does the build
   fail because of conflicts between winsock.h and winsock2.h?

   A: As of Wireshark 0.9.5, you must install WinPcap 2.3 or later, and
   the corresponding version of the developer's pack, in order to be able
   to compile Wireshark; it will not compile with older versions of the
   developer's pack. The symptoms of this failure are conflicts between
   definitions in winsock.h and in winsock2.h; Wireshark uses winsock2.h,
   but pre-2.3 versions of the WinPcap developer's packet use winsock.h.
   (2.3 uses winsock2.h, so if Wireshark were to use winsock.h, it would
   not be able to build with current versions of the WinPcap developer's
   pack.)

   Note that the installed version of the developer's pack should be the
   same version as the version of WinPcap you have installed.

5. Starting Wireshark

   Q 5.1: Why does Wireshark crash with a Bus Error when I try to run it
   on Solaris 8?

   A: Some versions of the GTK+ library from www.sunfreeware.org appear to
   be buggy, causing Wireshark to drop core with a Bus Error. Un-install
   those packages, and try getting the 1.2.10 version from that site, or
   the version from The Written Word, or the version from Sun's GNOME
   distribution, or the version from the supplemental software CD that
   comes with the Solaris media kit, or build it from source from the GTK
   Web site. Update the GLib library to the 1.2.10 version, from the same
   source, as well. (If you get the 1.2.10 versions from
   www.sunfreeware.org, and the problem persists, un-install them and try
   installing one of the other versions mentioned.)

   Similar problems may exist with older versions of GTK+ for earlier
   versions of Solaris.

   Q 5.2: When I run Wireshark on Windows NT, why does it die with a Dr.
   Watson error, reporting an "Integer division by zero" exception, when I
   start it?

   A: In at least some case, this appears to be due to using the default
   VGA driver; if that's not the correct driver for your video card, try
   running the correct driver for your video card.

   Q 5.3: When I try to run Wireshark, why does it complain about
   sprint_realloc_objid being undefined?

   A: Wireshark can only be linked with version 4.2.2 or later of UCD
   SNMP. Your version of Wireshark was dynamically linked with such a
   version of UCD SNMP; however, you have an older version of UCD SNMP
   installed, which means that when Wireshark is run, it tries to link to
   the older version, and fails. You will have to replace that version of
   UCD SNMP with version 4.2.2 or a later version.

   Q 5.4: When I try to run Wireshark on Windows, why does it fail to run
   with a complaint that it can't find packet.dll?

   A: In older versions of Wireshark, there were two binary distributions
   available for Windows, one that supported capturing packets, and one
   that didn't. The version that supported capturing packets required that
   you install the WinPcap driver; if you didn't install it, it would fail
   to run because it couldn't find packet.dll.

   The current version of Wireshark has only one binary distribution for
   Windows; that version will check whether WinPcap is installed and, if
   it's not, will disable support for packet capture.

   The WinPcap driver and libraries can be downloaded from the WinPcap Web
   site or the Wiretapped.net mirror of the WinPcap site.

   Q 5.5: I've installed Wireshark from Fink on Mac OS X; why is it very
   slow to start up?

   A: When an application is installed on OS X, prior to 10.4, it is
   usually "prebound" to speed up launching the application. (That's what
   the "Optimizing" phase of installation is.) Fink normally performs
   prebinding automatically when you install a package. However, in some
   rare cases, for whatever reason the prebinding caches get corrupt, and
   then not only does prebinding fail, but startup actually becomes much
   slower, because the system tries in vain to perform prebinding "on the
   fly" as you launch the application. This fails, causing sometimes huge
   delays. To fix the prebinding caches, run the command
        sudo /sw/var/lib/fink/prebound/update-package-prebinding.pl -f

6. Crashes and other fatal errors

   Q 6.1: I have an XXX network card on my machine; if I try to capture on
   it, why does my machine crash or reset itself?

   A: This is almost certainly a problem with one or more of:
     * the operating system you're using;
     * the device driver for the interface you're using;
     * the libpcap/WinPcap library and, if this is Windows, the WinPcap
       device driver;

   so:
     * if you are using Windows, see the WinPcap support page - check the
       "Submitting bugs" section;
     * if you are using some Linux distribution, some version of BSD, or
       some other UNIX-flavored OS, you should report the problem to the
       company or organization that produces the OS (in the case of a
       Linux distribution, report the problem to whoever produces the
       distribution).

   Q 6.2: Why does my machine crash or reset itself when I select "Start"
   from the "Capture" menu or select "Preferences" from the "Edit" menu?

   A: Both of those operations cause Wireshark to try to build a list of
   the interfaces that it can open; it does so by getting a list of
   interfaces and trying to open them. There is probably an OS, driver,
   or, for Windows, WinPcap bug that causes the system to crash when this
   happens; see the previous question.

7. Capturing packets

   Q 7.1: When I use Wireshark to capture packets, why do I see only
   packets to and from my machine, or not see all the traffic I'm
   expecting to see from or to the machine I'm trying to monitor?

   A: This might be because the interface on which you're capturing is
   plugged into an Ethernet or Token Ring switch; on a switched network,
   unicast traffic between two ports will not necessarily appear on other
   ports - only broadcast and multicast traffic will be sent to all ports.

   Note that even if your machine is plugged into a hub, the "hub" may be
   a switched hub, in which case you're still on a switched network.

   Note also that on the Linksys Web site, they say that their
   auto-sensing hubs "broadcast the 10Mb packets to the port that operate
   at 10Mb only and broadcast the 100Mb packets to the ports that operate
   at 100Mb only", which would indicate that if you sniff on a 10Mb port,
   you will not see traffic coming sent to a 100Mb port, and vice versa.
   This problem has also been reported for Netgear dual-speed hubs, and
   may exist for other "auto-sensing" or "dual-speed" hubs.

   Some switches have the ability to replicate all traffic on all ports to
   a single port so that you can plug your analyzer into that single port
   to sniff all traffic. You would have to check the documentation for the
   switch to see if this is possible and, if so, to see how to do this.
   See the switch reference page on the Wireshark Wiki for information on
   some switches. (Note that it's a Wiki, so you can update or fix that
   information, or add additional information on those switches or
   information on new switches, yourself.)

   Note also that many firewall/NAT boxes have a switch built into them;
   this includes many of the "cable/DSL router" boxes. If you have a box
   of that sort, that has a switch with some number of Ethernet ports into
   which you plug machines on your network, and another Ethernet port used
   to connect to a cable or DSL modem, you can, at least, sniff traffic
   between the machines on your network and the Internet by plugging the
   Ethernet port on the router going to the modem, the Ethernet port on
   the modem, and the machine on which you're running Wireshark into a hub
   (make sure it's not a switching hub, and that, if it's a dual-speed
   hub, all three of those ports are running at the same speed.

   If your machine is not plugged into a switched network or a dual-speed
   hub, or it is plugged into a switched network but the port is set up to
   have all traffic replicated to it, the problem might be that the
   network interface on which you're capturing doesn't support
   "promiscuous" mode, or because your OS can't put the interface into
   promiscuous mode. Normally, network interfaces supply to the host only:
     * packets sent to one of that host's link-layer addresses;
     * broadcast packets;
     * multicast packets sent to a multicast address that the host has
       configured the interface to accept.

   Most network interfaces can also be put in "promiscuous" mode, in which
   they supply to the host all network packets they see. Wireshark will
   try to put the interface on which it's capturing into promiscuous mode
   unless the "Capture packets in promiscuous mode" option is turned off
   in the "Capture Options" dialog box, and TShark will try to put the
   interface on which it's capturing into promiscuous mode unless the -p
   option was specified. However, some network interfaces don't support
   promiscuous mode, and some OSes might not allow interfaces to be put
   into promiscuous mode.

   If the interface is not running in promiscuous mode, it won't see any
   traffic that isn't intended to be seen by your machine. It will see
   broadcast packets, and multicast packets sent to a multicast MAC
   address the interface is set up to receive.

   You should ask the vendor of your network interface whether it supports
   promiscuous mode. If it does, you should ask whoever supplied the
   driver for the interface (the vendor, or the supplier of the OS you're
   running on your machine) whether it supports promiscuous mode with that
   network interface.

   In the case of token ring interfaces, the drivers for some of them, on
   Windows, may require you to enable promiscuous mode in order to capture
   in promiscuous mode. See the Wireshark Wiki item on Token Ring
   capturing for details.

   In the case of wireless LAN interfaces, it appears that, when those
   interfaces are promiscuously sniffing, they're running in a
   significantly different mode from the mode that they run in when
   they're just acting as network interfaces (to the extent that it would
   be a significant effor for those drivers to support for promiscuously
   sniffing and acting as regular network interfaces at the same time), so
   it may be that Windows drivers for those interfaces don't support
   promiscuous mode.

   Q 7.2: When I capture with Wireshark, why can't I see any TCP packets
   other than packets to and from my machine, even though another analyzer
   on the network sees those packets?

   A: You're probably not seeing any packets other than unicast packets to
   or from your machine, and broadcast and multicast packets; a switch
   will normally send to a port only unicast traffic sent to the MAC
   address for the interface on that port, and broadcast and multicast
   traffic - it won't send to that port unicast traffic sent to a MAC
   address for some other interface - and a network interface not in
   promiscuous mode will receive only unicast traffic sent to the MAC
   address for that interface, broadcast traffic, and multicast traffic
   sent to a multicast MAC address the interface is set up to receive.

   TCP doesn't use broadcast or multicast, so you will only see your own
   TCP traffic, but UDP services may use broadcast or multicast so you'll
   see some UDP traffic - however, this is not a problem with TCP traffic,
   it's a problem with unicast traffic, as you also won't see all UDP
   traffic between other machines.

   I.e., this is probably the same question as this earlier one; see the
   response to that question.

   Q 7.3: Why am I only seeing ARP packets when I try to capture traffic?

   A: You're probably on a switched network, and running Wireshark on a
   machine that's not sending traffic to the switch and not being sent any
   traffic from other machines on the switch. ARP packets are often
   broadcast packets, which are sent to all switch ports.

   I.e., this is probably the same question as this earlier one; see the
   response to that question.

   Q 7.4: Why am I not seeing any traffic when I try to capture traffic?

   A: Is the machine running Wireshark sending out any traffic on the
   network interface on which you're capturing, or receiving any traffic
   on that network, or is there any broadcast traffic on the network or
   multicast traffic to a multicast group to which the machine running
   Wireshark belongs?

   If not, this may just be a problem with promiscuous sniffing, either
   due to running on a switched network or a dual-speed hub, or due to
   problems with the interface not supporting promiscuous mode; see the
   response to this earlier question.

   Otherwise, on Windows, see the response to this question and, on a
   UNIX-flavored OS, see the response to this question.

   Q 7.5: Can Wireshark capture on (my T1/E1 line, SS7 links, etc.)?

   A: Wireshark can only capture on devices supported by libpcap/WinPcap.
   On most OSes, only devices that can act as network interfaces of the
   type that support IP are supported as capture devices for
   libpcap/WinPcap, although the device doesn't necessarily have to be
   running as an IP interface in order to support traffic capture.

   On Linux and FreeBSD, libpcap 0.8 and later support the API for Endace
   Measurement Systems' DAG cards, so that a system with one of those
   cards, and its driver and libraries, installed can capture traffic with
   those cards with libpcap-based applications. You would either have to
   have a version of Wireshark built with that version of libpcap, or a
   dynamically-linked version of Wireshark and a shared libpcap library
   with DAG support, in order to do so with Wireshark. You should ask
   Endace whether that could be used to capture traffic on, for example,
   your T1/E1 link. See the SS7 capture setup page on the Wireshark Wiki
   for current information on capturing SS7 traffic on TDM links.

   Q 7.6: How do I put an interface into promiscuous mode?

   A: By not disabling promiscuous mode when running Wireshark or TShark.

   Note, however, that:
     * the form of promiscuous mode that libpcap (the library that
       programs such as tcpdump, Wireshark, etc. use to do packet capture)
       turns on will not necessarily be shown if you run ifconfig on the
       interface on a UNIX system;
     * some network interfaces might not support promiscuous mode, and
       some drivers might not allow promiscuous mode to be turned on - see
       this earlier question for more information on that;
     * the fact that you're not seeing any traffic, or are only seeing
       broadcast traffic, or aren't seeing any non-broadcast traffic other
       than traffic to or from the machine running Wireshark, does not
       mean that promiscuous mode isn't on - see this earlier question for
       more information on that.

   I.e., this is probably the same question as this earlier one; see the
   response to that question.

   Q 7.7: I can set a display filter just fine; why don't capture filters
   work?

   A: Capture filters currently use a different syntax than display
   filters. Here's the corresponding section from the wireshark(1) man
   page:

   "Display filters in Wireshark are very powerful; more fields are
   filterable in Wireshark than in other protocol analyzers, and the
   syntax you can use to create your filters is richer. As Wireshark
   progresses, expect more and more protocol fields to be allowed in
   display filters.

   Packet capturing is performed with the pcap library. The capture filter
   syntax follows the rules of the pcap library. This syntax is different
   from the display filter syntax."

   The capture filter syntax used by libpcap can be found in the
   tcpdump(8) man page.

   Q 7.8: I'm entering valid capture filters; why do I still get "parse
   error" errors?

   A: There is a bug in some versions of libpcap/WinPcap that cause it to
   report parse errors even for valid expressions if a previous filter
   expression was invalid and got a parse error.

   Try exiting and restarting Wireshark; if you are using a version of
   libpcap/WinPcap with this bug, this will "erase" its memory of the
   previous parse error. If the capture filter that got the "parse error"
   now works, the earlier error with that filter was probably due to this
   bug.

   The bug was fixed in libpcap 0.6; 0.4[.x] and 0.5[.x] versions of
   libpcap have this bug, but 0.6[.x] and later versions don't.

   Versions of WinPcap prior to 2.3 are based on pre-0.6 versions of
   libpcap, and have this bug; WinPcap 2.3 is based on libpcap 0.6.2, and
   doesn't have this bug.

   If you are running Wireshark on a UNIX-flavored platform, run
   "wireshark -v", or select "About Wireshark..." from the "Help" menu in
   Wireshark, to see what version of libpcap it's using. If it's not 0.6
   or later, you will need either to upgrade your OS to get a later
   version of libpcap, or will need to build and install a later version
   of libpcap from the tcpdump.org Web site and then recompile Wireshark
   from source with that later version of libpcap.

   If you are running Wireshark on Windows with a pre-2.3 version of
   WinPcap, you will need to un-install WinPcap and then download and
   install WinPcap 2.3.

   Q 7.9: How can I capture packets with CRC errors?

   A: Wireshark can capture only the packets that the packet capture
   library - libpcap on UNIX-flavored OSes, and the WinPcap port to
   Windows of libpcap on Windows - can capture, and libpcap/WinPcap can
   capture only the packets that the OS's raw packet capture mechanism (or
   the WinPcap driver, and the underlying OS networking code and network
   interface drivers, on Windows) will allow it to capture.

   Unless the OS always supplies packets with errors such as invalid CRCs
   to the raw packet capture mechanism, or can be configured to do so,
   invalid CRCs to the raw packet capture mechanism, Wireshark - and other
   programs that capture raw packets, such as tcpdump - cannot capture
   those packets. You will have to determine whether your OS needs to be
   so configured and, if so, can be so configured, configure it if
   necessary and possible, and make whatever changes to libpcap and the
   packet capture program you're using are necessary, if any, to support
   capturing those packets.

   Most OSes probably do not support capturing packets with invalid CRCs
   on Ethernet, and probably do not support it on most other link-layer
   types. Some drivers on some OSes do support it, such as some Ethernet
   drivers on FreeBSD; in those OSes, you might always get those packets,
   or you might only get them if you capture in promiscuous mode (you'd
   have to determine which is the case).

   Note that libpcap does not currently supply to programs that use it an
   indication of whether the packet's CRC was invalid (because the drivers
   themselves do not supply that information to the raw packet capture
   mechanism); therefore, Wireshark will not indicate which packets had
   CRC errors unless the FCS was captured (see the next question) and
   you're using Wireshark 0.9.15 and later, in which case Wireshark will
   check the CRC and indicate whether it's correct or not.

   Q 7.10: How can I capture entire frames, including the FCS?

   A: Wireshark can only capture data that the packet capture library -
   libpcap on UNIX-flavored OSes, and the WinPcap port to Windows of
   libpcap on Windows - can capture, and libpcap/WinPcap can capture only
   the data that the OS's raw packet capture mechanism (or the WinPcap
   driver, and the underlying OS networking code and network interface
   drivers, on Windows) will allow it to capture.

   For any particular link-layer network type, unless the OS supplies the
   FCS of a frame as part of the frame, or can be configured to do so,
   Wireshark - and other programs that capture raw packets, such as
   tcpdump - cannot capture the FCS of a frame. You will have to determine
   whether your OS needs to be so configured and, if so, can be so
   configured, configure it if necessary and possible, and make whatever
   changes to libpcap and the packet capture program you're using are
   necessary, if any, to support capturing the FCS of a frame.

   Most OSes do not support capturing the FCS of a frame on Ethernet, and
   probably do not support it on most other link-layer types. Some drivres
   on some OSes do support it, such as some (all?) Ethernet drivers on
   NetBSD and possibly the driver for Apple's gigabit Ethernet interface
   in Mac OS X; in those OSes, you might always get the FCS, or you might
   only get the FCS if you capture in promiscuous mode (you'd have to
   determine which is the case).

   Versions of Wireshark prior to 0.9.15 will not treat an Ethernet FCS in
   a captured packet as an FCS. 0.9.15 and later will attempt to determine
   whether there's an FCS at the end of the frame and, if it thinks there
   is, will display it as such, and will check whether it's the correct
   CRC-32 value or not.

   Q 7.11: I'm capturing packets on a machine on a VLAN; why don't the
   packets I'm capturing have VLAN tags?

   A: You might be capturing on what might be called a "VLAN interface" -
   the way a particular OS makes VLANs plug into the networking stack
   might, for example, be to have a network device object for the physical
   interface, which takes VLAN packets, strips off the VLAN header and
   constructs an Ethernet header, and passes that packet to an internal
   network device object for the VLAN, which then passes the packets onto
   various higher-level protocol implementations.

   In order to see the raw Ethernet packets, rather than "de-VLANized"
   packets, you would have to capture not on the virtual interface for the
   VLAN, but on the interface corresponding to the physical network
   device, if possible. See the Wireshark Wiki item on VLAN capturing for
   details.

   Q 7.12: Why does Wireshark hang after I stop a capture?

   A: The most likely reason for this is that Wireshark is trying to look
   up an IP address in the capture to convert it to a name (so that, for
   example, it can display the name in the source address or destination
   address columns), and that lookup process is taking a very long time.

   Wireshark calls a routine in the OS of the machine on which it's
   running to convert of IP addresses to the corresponding names. That
   routine probably does one or more of:
     * a search of a system file listing IP addresses and names;
     * a lookup using DNS;
     * on UNIX systems, a lookup using NIS;
     * on Windows systems, a NetBIOS-over-TCP query.

   If a DNS server that's used in an address lookup is not responding, the
   lookup will fail, but will only fail after a timeout while the system
   routine waits for a reply.

   In addition, on Windows systems, if the DNS lookup of the address
   fails, either because the server isn't responding or because there are
   no records in the DNS that could be used to map the address to a name,
   a NetBIOS-over-TCP query will be made. That query involves sending a
   message to the NetBIOS-over-TCP name service on that machine, asking
   for the name and other information about the machine. If the machine
   isn't running software that responds to those queries - for example,
   many non-Windows machines wouldn't be running that software - the
   lookup will only fail after a timeout. Those timeouts can cause the
   lookup to take a long time.

   If you disable network address-to-name translation - for example, by
   turning off the "Enable network name resolution" option in the "Capture
   Options" dialog box for starting a network capture - the lookups of the
   address won't be done, which may speed up the process of reading the
   capture file after the capture is stopped. You can make that setting
   the default by selecting "Preferences" from the "Edit" menu, turning
   off the "Enable network name resolution" option in the "Name
   resolution" options in the preferences disalog box, and using the
   "Save" button in that dialog box; note that this will save all your
   current preference settings.

   If Wireshark hangs when reading a capture even with network name
   resolution turned off, there might, for example, be a bug in one of
   Wireshark's dissectors for a protocol causing it to loop infinitely. If
   you're not running the most recent release of Wireshark, you should
   first upgrade to that release, as, if there's a bug of that sort, it
   might've been fixed in a release after the one you're running. If the
   hang occurs in the most recent release of Wireshark, the bug should be
   reported to the Wireshark developers' mailing list at
   wireshark-dev@wireshark.org.

   On UNIX-flavored OSes, please try to force Wireshark to dump core, by
   sending it a SIGABRT signal (usually signal 6) with the kill command,
   and then get a stack trace if you have a debugger installed. A stack
   trace can be obtained by using your debugger (gdb in this example), the
   Wireshark binary, and the resulting core file. Here's an example of how
   to use the gdb command backtrace to do so.
        $ gdb wireshark core
        (gdb) backtrace
        ..... prints the stack trace
        (gdb) quit
        $

   The core dump file may be named "wireshark.core" rather than "core" on
   some platforms (e.g., BSD systems).

   Also, if at all possible, please send a copy of the capture file that
   caused the problem; when capturing packets, Wireshark normally writes
   captured packets to a temporary file, which will probably be in /tmp or
   /var/tmp on UNIX-flavored OSes, \TEMP on the main system disk (normally
   C:) on Windows 9x/Me/NT 4.0, and \Documents and Settings\your login
   name\Local Settings\Temp on the main system disk on Windows
   2000/Windows XP/Windows Server 2003, so the capture file will probably
   be there. It will have a name beginning with ether, with some mixture
   of letters and numbers after that. Please don't send a trace file
   greater than 1 MB when compressed; instead, make it available via FTP
   or HTTP, or say it's available but leave it up to a developer to ask
   for it. If the trace file contains sensitive information (e.g.,
   passwords), then please do not send it.

8. Capturing packets on Windows

   Q 8.1: I'm running Wireshark on Windows; why does some network
   interface on my machine not show up in the list of interfaces in the
   "Interface:" field in the dialog box popped up by "Capture->Start",
   and/or why does Wireshark give me an error if I try to capture on that
   interface?

   A: If you are running Wireshark on Windows NT 4.0, Windows 2000,
   Windows XP, or Windows Server 2003, and this is the first time you have
   run a WinPcap-based program (such as Wireshark, or TShark, or WinDump,
   or Analyzer, or...) since the machine was rebooted, you need to run
   that program from an account with administrator privileges; once you
   have run such a program, you will not need administrator privileges to
   run any such programs until you reboot.

   If you are running on Windows 95/98/Me, or if you are running on
   Windows NT 4.0/Windows 2000/Windows XP/Windows Server 2003 and have
   administrator privileges or a WinPcap-based program has been run with
   those privileges since the machine rebooted, this problem might clear
   up if you completely un-install WinPcap and then re-install it.

   If that doesn't work, then note that Wireshark relies on the WinPcap
   library, on the WinPcap device driver, and on the facilities that come
   with the OS on which it's running in order to do captures.

   Therefore, if the OS, the WinPcap library, or the WinPcap driver don't
   support capturing on a particular network interface device, Wireshark
   won't be able to capture on that device.

   Note that:
    1. 2.02 and earlier versions of the WinPcap driver and library that
       Wireshark uses for packet capture didn't support Token Ring
       interfaces; versions 2.1 and later support Token Ring, and the
       current version of Wireshark works with (and, in fact, requires)
       WinPcap 2.1 or later.
       If you are having problems capturing on Token Ring interfaces, and
       you have WinPcap 2.02 or an earlier version of WinPcap installed,
       you should uninstall WinPcap, download and install the current
       version of WinPcap, and then install the latest version of
       Wireshark.
    2. On Windows 95, 98, or Me, sometimes more than one interface will be
       given the same name; if that is the case, you will only be able to
       capture on one of those interfaces - it's not clear to which one
       the name, when used in a WinPcap-based application, will refer. For
       example, if you have a PPP serial interface and a VPN interface,
       they might show up with the same name, for example "ppp-mac", and
       if you try to capture on "ppp-mac", it might not capture on the
       interface you're currently using. In that case, you might, for
       example, have to remove the VPN interface from the system in order
       to capture on the PPP serial interface.
    3. WinPcap 2.3 has problems supporting PPP WAN interfaces on Windows
       NT 4.0, Windows 2000, Windows XP, and Windows Server 2003, and, to
       avoid those problems, support for PPP WAN interfaces on those
       versions of Windows has been disabled in WinPcap 3.0. Regular
       dial-up lines, ISDN lines, ADSL connections using PPPoE or PPPoA,
       and various other lines such as T1/E1 lines are all PPP interfaces,
       so those interfaces might not show up on the list of interfaces in
       the "Capture Options" dialog on those OSes.
       On Windows 2000, Windows XP, and Windows Server 2003, but not
       Windows NT 4.0 or Windows Vista Beta 1, you should be able to
       capture on the "GenericDialupAdapter" with WinPcap 3.1. (3.1 beta
       releases called it the "NdisWanAdapter"; if you're using a 3.1 beta
       release, you should un-install it and install the final 3.1
       release.) See the Wireshark Wiki item on PPP capturing for details.
    4. WinPcap prior to 3.0 does not support multiprocessor machines (note
       that machines with a single multi-threaded processor, such as
       Intel's new multi-threaded x86 processors, are multiprocessor
       machines as far as the OS and WinPcap are concerned), and recent
       2.x versions of WinPcap refuse to operate if they detect that
       they're running on a multiprocessor machine, which means that they
       may not show any network interfaces. You will need to use WinPcap
       3.0 to capture on a multiprocessor machine.

   If an interface doesn't show up in the list of interfaces in the
   "Interface:" field, and you know the name of the interface, try
   entering that name in the "Interface:" field and capturing on that
   device.

   If the attempt to capture on it succeeds, the interface is somehow not
   being reported by the mechanism Wireshark uses to get a list of
   interfaces. Try listing the interfaces with WinDump; see the WinDump
   Web site for information on using WinDump.

   You would run WinDump with the -D flag; if it lists the interface,
   please report this to wireshark-dev@wireshark.org giving full details
   of the problem, including
     * the operating system you're using, and the version of that
       operating system;
     * the type of network device you're using;
     * the output of WinDump.

   If WinDump does not list the interface, this is almost certainly a
   problem with one or more of:
     * the operating system you're using;
     * the device driver for the interface you're using;
     * the WinPcap library and/or the WinPcap device driver;

   so first check the WinPcap FAQ or the Wiretapped.net mirror of that
   FAQ, to see if your problem is mentioned there. If not, then see the
   WinPcap support page - check the "Submitting bugs" section.

   If you are having trouble capturing on a particular network interface,
   first try capturing on that device with WinDump; see the WinDump Web
   site for information on using WinDump.

   If you can capture on the interface with WinDump, send mail to
   wireshark-users@wireshark.org giving full details of the problem,
   including
     * the operating system you're using, and the version of that
       operating system;
     * the type of network device you're using;
     * the error message you get from Wireshark.

   If you cannot capture on the interface with WinDump, this is almost
   certainly a problem with one or more of:
     * the operating system you're using;
     * the device driver for the interface you're using;
     * the WinPcap library and/or the WinPcap device driver;

   so first check the WinPcap FAQ or the Wiretapped.net mirror of that
   FAQ, to see if your problem is mentioned there. If not, then see the
   WinPcap support page - check the "Submitting bugs" section.

   You may also want to ask the wireshark-users@wireshark.org and the
   winpcap-users@winpcap.org mailing lists to see if anybody happens to
   know about the problem and know a workaround or fix for the problem.
   (Note that you will have to subscribe to that list in order to be
   allowed to mail to it; see the WinPcap support page for information on
   the mailing list.) In your mail, please give full details of the
   problem, as described above, and also indicate that the problem occurs
   with WinDump, not just with Wireshark.

   Q 8.2: I'm running Wireshark on Windows; why do no network interfaces
   show up in the list of interfaces in the "Interface:" field in the
   dialog box popped up by "Capture->Start"?

   A: This is really the same question as the previous one; see the
   response to that question.

   Q 8.3: I'm running Wireshark on Windows; why doesn't my serial
   port/ADSL modem/ISDN modem show up in the list of interfaces in the
   "Interface:" field in the dialog box popped up by "Capture->Start"?

   A: Internet access on those devices is often done with the
   Point-to-Point (PPP) protocol; WinPcap 2.3 has problems supporting PPP
   WAN interfaces on Windows NT 4.0, Windows 2000, Windows XP, and Windows
   Server 2003, and, to avoid those problems, support for PPP WAN
   interfaces on those versions of Windows has been disabled in WinPcap
   3.0.

   On Windows 2000, Windows XP, and Windows Server 2003, but not Windows
   NT 4.0 or Windows Vista Beta 1, you should be able to capture on the
   "GenericDialupAdapter" with WinPcap 3.1. (3.1 beta releases called it
   the "NdisWanAdapter"; if you're using a 3.1 beta release, you should
   un-install it and install the final 3.1 release.) See the Wireshark
   Wiki item on PPP capturing for details.

   Q 8.4: I'm running Wireshark on Windows NT 4.0/Windows 2000/Windows
   XP/Windows Server 2003; my machine has a PPP (dial-up POTS, ISDN, etc.)
   interface, and it shows up in the "Interface" item in the "Capture
   Options" dialog box. Why can no packets be sent on or received from
   that network while I'm trying to capture traffic on that interface?

   A: Some versions of WinPcap have problems with PPP WAN interfaces on
   Windows NT 4.0, Windows 2000, Windows XP, and Windows Server 2003; one
   symptom that may be seen is that attempts to capture in promiscuous
   mode on the interface cause the interface to be incapable of sending or
   receiving packets. You can disable promiscuous mode using the -p
   command-line flag or the item in the "Capture Preferences" dialog box,
   but this may mean that outgoing packets, or incoming packets, won't be
   seen in the capture.

   On Windows 2000, Windows XP, and Windows Server 2003, but not Windows
   NT 4.0 or Windows Vista Beta 1, you should be able to capture on the
   "GenericDialupAdapter" with WinPcap 3.1. (3.1 beta releases called it
   the "NdisWanAdapter"; if you're using a 3.1 beta release, you should
   un-install it and install the final 3.1 release.) See the Wireshark
   Wiki item on PPP capturing for details.

   Q 8.5: I'm running Wireshark on Windows 95/98/Me, on a machine with
   more than one network adapter of the same type; why does Wireshark show
   all of those adapters with the same name, not letting me use any of
   those adapters other than the first one?

   A: Unfortunately, Windows 95/98/Me gives the same name to multiple
   instances of the type of same network adapter. Therefore, WinPcap
   cannot distinguish between them, so a WinPcap-based application can
   capture only on the first such interface; Wireshark is a
   libpcap/WinPcap-based application.

   Q 8.6: I'm running Wireshark on Windows; why am I not seeing any
   traffic being sent by the machine running Wireshark?

   A: If you are running some form of VPN client software, it might be
   causing this problem; people have seen this problem when they have
   Check Point's VPN software installed on their machine. If that's the
   cause of the problem, you will have to remove the VPN software in order
   to have Wireshark (or any other application using WinPcap) see outgoing
   packets; unfortunately, neither we nor the WinPcap developers know any
   way to make WinPcap and the VPN software work well together.

   Also, some drivers for Windows (especially some wireless network
   interface drivers) apparently do not, when running in promiscuous mode,
   arrange that outgoing packets are delivered to the software that
   requested that the interface run promiscuously; try turning promiscuous
   mode off.

   Q 8.7: When I capture on Windows in promiscuous mode, I can see packets
   other than those sent to or from my machine; however, those packets
   show up with a "Short Frame" indication, unlike packets to or from my
   machine. What should I do to arrange that I see those packets in their
   entirety?

   A: In at least some cases, this appears to be the result of PGPnet
   running on the network interface on which you're capturing; turn it off
   on that interface.

   Q 8.8: I'm capturing packets on {Windows 95, Windows 98, Windows Me};
   why are the time stamps on packets wrong?

   A: This is due to a bug in WinPcap. The bug should be fixed in WinPcap
   3.0 and later releases.

   Q 8.9: I'm trying to capture 802.11 traffic on Windows; why am I not
   seeing any packets?

   A: At least some 802.11 card drivers on Windows appear not to see any
   packets if they're running in promiscuous mode. Try turning promiscuous
   mode off; you'll only be able to see packets sent by and received by
   your machine, not third-party traffic, and it'll look like Ethernet
   traffic and won't include any management or control frames, but that's
   a limitation of the card drivers.

   See MicroLogix's list of cards supported with WinPcap for information
   on support of various adapters and drivers with WinPcap.

   Q 8.10: I'm trying to capture 802.11 traffic on Windows; why am I
   seeing packets received by the machine on which I'm capturing traffic,
   but not packets sent by that machine?

   A: This appears to be another problem with promiscuous mode; try
   turning it off.

   Q 8.11: I'm trying to capture Ethernet VLAN traffic on Windows, and I'm
   capturing on a "raw" Ethernet device rather than a "VLAN interface", so
   that I can see the VLAN headers; why am I seeing packets received by
   the machine on which I'm capturing traffic, but not packets sent by
   that machine?

   A: The way the Windows networking code works probably means that
   packets are sent on a "VLAN interface" rather than the "raw" device, so
   packets sent by the machine will only be seen when you capture on the
   "VLAN interface". If so, you will be unable to see outgoing packets
   when capturing on the "raw" device, so you are stuck with a choice
   between seeing VLAN headers and seeing outgoing packets.

9. Capturing packets on UN*Xes

   Q 9.1: I'm running Wireshark on a UNIX-flavored OS; why does some
   network interface on my machine not show up in the list of interfaces
   in the "Interface:" field in the dialog box popped up by
   "Capture->Start", and/or why does Wireshark give me an error if I try
   to capture on that interface?

   A: You may need to run Wireshark from an account with sufficient
   privileges to capture packets, such as the super-user account, or may
   need to give your account sufficient privileges to capture packets.
   Only those interfaces that Wireshark can open for capturing show up in
   that list; if you don't have sufficient privileges to capture on any
   interfaces, no interfaces will show up in the list. See the Wireshark
   Wiki item on capture privileges for details on how to give a particular
   account or account group capture privileges on platforms where that can
   be done.

   If you are running Wireshark from an account with sufficient
   privileges, then note that Wireshark relies on the libpcap library, and
   on the facilities that come with the OS on which it's running in order
   to do captures. On some OSes, those facilities aren't present by
   default; see the Wireshark Wiki item on adding capture support for
   details.

   And, even if you're running with an account that has sufficient
   privileges to capture, and capture support is present in your OS, if
   the OS or the libpcap library don't support capturing on a particular
   network interface device or particular types of devices, Wireshark
   won't be able to capture on that device.

   On Solaris, note that libpcap 0.6.2 and earlier didn't support Token
   Ring interfaces; the current version, 0.7.2, does support Token Ring,
   and the current version of Wireshark works with libcap 0.7.2 and later.

   If an interface doesn't show up in the list of interfaces in the
   "Interface:" field, and you know the name of the interface, try
   entering that name in the "Interface:" field and capturing on that
   device.

   If the attempt to capture on it succeeds, the interface is somehow not
   being reported by the mechanism Wireshark uses to get a list of
   interfaces; please report this to wireshark-dev@wireshark.org giving
   full details of the problem, including
     * the operating system you're using, and the version of that
       operating system (for Linux, give both the version number of the
       kernel and the name and version number of the distribution you're
       using);
     * the type of network device you're using.

   If you are having trouble capturing on a particular network interface,
   and you've made sure that (on platforms that require it) you've
   arranged that packet capture support is present, as per the above,
   first try capturing on that device with tcpdump.

   If you can capture on the interface with tcpdump, send mail to
   wireshark-users@wireshark.org giving full details of the problem,
   including
     * the operating system you're using, and the version of that
       operating system (for Linux, give both the version number of the
       kernel and the name and version number of the distribution you're
       using);
     * the type of network device you're using;
     * the error message you get from Wireshark.

   If you cannot capture on the interface with tcpdump, this is almost
   certainly a problem with one or more of:
     * the operating system you're using;
     * the device driver for the interface you're using;
     * the libpcap library;

   so you should report the problem to the company or organization that
   produces the OS (in the case of a Linux distribution, report the
   problem to whoever produces the distribution).

   You may also want to ask the wireshark-users@wireshark.org and the
   tcpdump-workers@tcpdump.org mailing lists to see if anybody happens to
   know about the problem and know a workaround or fix for the problem. In
   your mail, please give full details of the problem, as described above,
   and also indicate that the problem occurs with tcpdump not just with
   Wireshark.

   Q 9.2: I'm running Wireshark on a UNIX-flavored OS; why do no network
   interfaces show up in the list of interfaces in the "Interface:" field
   in the dialog box popped up by "Capture->Start"?

   A: This is really the same question as the previous one; see the
   response to that question.

   Q 9.3: I'm capturing packets on Linux; why do the time stamps have only
   100ms resolution, rather than 1us resolution?

   A: Wireshark gets time stamps from libpcap/WinPcap, and libpcap/WinPcap
   get them from the OS kernel, so Wireshark - and any other program using
   libpcap, such as tcpdump - is at the mercy of the time stamping code in
   the OS for time stamps.

   At least on x86-based machines, Linux can get high-resolution time
   stamps on newer processors with the Time Stamp Counter (TSC) register;
   for example, Intel x86 processors, starting with the Pentium Pro, and
   including all x86 processors since then, have had a TSC, and other
   vendors probably added the TSC at some point to their families of x86
   processors.

   The Linux kernel must be configured with the CONFIG_X86_TSC option
   enabled in order to use the TSC. Make sure this option is enabled in
   your kernel.

   In addition, some Linux distributions may have bugs in their versions
   of the kernel that cause packets not to be given high-resolution time
   stamps even if the TSC is enabled. See, for example, bug 61111 for Red
   Hat Linux 7.2. If your distribution has a bug such as this, you may
   have to run a standard kernel from kernel.org in order to get
   high-resolution time stamps.

10. Capturing packets on wireless LANs

   Q 10.1: How can I capture raw 802.11 frames, including non-data
   (management, beacon) frames?

   A: That depends on the operating system on which you're running, and on
   the 802.11 interface on which you're capturing.

   This would probably require that you capture in promiscuous mode or in
   the mode called "monitor mode" or "RFMON mode". On some platforms, or
   with some cards, this might require that you capture in monitor mode -
   promiscuous mode might not be sufficient. If you want to capture
   traffic on networks other than the one with which you're associated,
   you will have to capture in monitor mode.

   Not all operating systems support capturing non-data packets and, even
   on operating systems that do support it, not all drivers, and thus not
   all interfaces, support it. Even on those that do, monitor mode might
   not be supported by the operating system or by the drivers for all
   interfaces.

   NOTE: an interface running in monitor mode will, on most if not all
   platforms, not be able to act as a regular network interface; putting
   it into monitor mode will, in effect, take your machine off of whatever
   network it's on as long as the interface is in monitor mode, allowing
   it only to passively capture packets.

   This means that you should disable name resolution when capturing in
   monitor mode; otherwise, when Wireshark (or TShark, or tcpdump) tries
   to display IP addresses as host names, it will probably block for a
   long time trying to resolve the name because it will not be able to
   communicate with any DNS or NIS servers.

   See the Wireshark Wiki item on 802.11 capturing for details.

   Q 10.2: How do I capture on an 802.11 device in monitor mode?

   A: Whether you will be able to capture in monitor mode depends on the
   operating system, adapter, and driver you're using. See the previous
   question for information on monitor mode, including a link to the
   Wireshark Wiki page that gives details on 802.11 capturing.

11. Viewing traffic

   Q 11.1: Why am I seeing lots of packets with incorrect TCP checksums?

   A: If the packets that have incorrect TCP checksums are all being sent
   by the machine on which Wireshark is running, this is probably because
   the network interface on which you're capturing does TCP checksum
   offloading. That means that the TCP checksum is added to the packet by
   the network interface, not by the OS's TCP/IP stack; when capturing on
   an interface, packets being sent by the host on which you're capturing
   are directly handed to the capture interface by the OS, which means
   that they are handed to the capture interface without a TCP checksum
   being added to them.

   The only way to prevent this from happening would be to disable TCP
   checksum offloading, but
    1. that might not even be possible on some OSes;
    2. that could reduce networking performance significantly.

   However, you can disable the check that Wireshark does of the TCP
   checksum, so that it won't report any packets as having TCP checksum
   errors, and so that it won't refuse to do TCP reassembly due to a
   packet having an incorrect TCP checksum. That can be set as an
   Wireshark preference by selecting "Preferences" from the "Edit" menu,
   opening up the "Protocols" list in the left-hand pane of the
   "Preferences" dialog box, selecting "TCP", from that list, turning off
   the "Check the validity of the TCP checksum when possible" option,
   clicking "Save" if you want to save that setting in your preference
   file, and clicking "OK".

   It can also be set on the Wireshark or TShark command line with a -o
   tcp.check_checksum:false command-line flag, or manually set in your
   preferences file by adding a tcp.check_checksum:false line.

   Q 11.2: I've just installed Wireshark, and the traffic on my local LAN
   is boring. Where can I find more interesting captures?

   A: We have a collection of strange and exotic sample capture files at
   http://wiki.wireshark.org/SampleCaptures

   Q 11.3: Why doesn't Wireshark correctly identify RTP packets? It shows
   them only as UDP.

   A: Wireshark can identify a UDP datagram as containing a packet of a
   particular protocol running atop UDP only if
    1. The protocol in question has a particular standard port number, and
       the UDP source or destination port number is that port
    2. Packets of that protocol can be identified by looking for a
       "signature" of some type in the packet - i.e., some data that, if
       Wireshark finds it in some particular part of a packet, means that
       the packet is almost certainly a packet of that type.
    3. Some other traffic earlier in the capture indicated that, for
       example, UDP traffic between two particular addresses and ports
       will be RTP traffic.

   RTP doesn't have a standard port number, so 1) doesn't work; it
   doesn't, as far as I know, have any "signature", so 2) doesn't work.

   That leaves 3). If there's RTSP traffic that sets up an RTP session,
   then, at least in some cases, the RTSP dissector will set things up so
   that subsequent RTP traffic will be identified. Currently, that's the
   only place we do that; there may be other places.

   However, there will always be places where Wireshark is simply
   incapable of deducing that a given UDP flow is RTP; a mechanism would
   be needed to allow the user to specify that a given conversation should
   be treated as RTP. As of Wireshark 0.8.16, such a mechanism exists; if
   you select a UDP or TCP packet, the right mouse button menu will have a
   "Decode As..." menu item, which will pop up a dialog box letting you
   specify that the source port, the destination port, or both the source
   and destination ports of the packet should be dissected as some
   particular protocol.

   Q 11.4: Why doesn't Wireshark show Yahoo Messenger packets in captures
   that contain Yahoo Messenger traffic?

   A: Wireshark only recognizes as Yahoo Messenger traffic packets to or
   from TCP port 3050 that begin with "YPNS", "YHOO", or "YMSG". TCP
   segments that start with the middle of a Yahoo Messenger packet that
   takes more than one TCP segment will not be recognized as Yahoo
   Messenger packets (even if the TCP segment also contains the beginning
   of another Yahoo Messenger packet).

12. Filtering traffic

   Q 12.1: I saved a filter and tried to use its name to filter the
   display; why do I get an "Unexpected end of filter string" error?

   A: You cannot use the name of a saved display filter as a filter. To
   filter the display, you can enter a display filter expression - not the
   name of a saved display filter - in the "Filter:" box at the bottom of
   the display, and type the key or press the "Apply" button (that does
   not require you to have a saved filter), or, if you want to use a saved
   filter, you can press the "Filter:" button, select the filter in the
   dialog box that pops up, and press the "OK" button.

   Q 12.2: How can I search for, or filter, packets that have a particular
   string anywhere in them?

   A: If you want to do this when capturing, you can't. That's a feature
   that would be hard to implement in capture filters without changes to
   the capture filter code, which, on many platforms, is in the OS kernel
   and, on other platforms, is in the libpcap library.

   In releases prior to 0.9.14, you also can't search for, or filter,
   packets containing a particular string even after you've captured them.

   In 0.9.14, you can search for, but not filter, packets that have a
   particular string; this has been added to the "Find Frame" dialog
   ("Find Frame" under the "Edit" menu, or control-F).

   In 0.9.15 and later, you can search for those packets using either the
   mechanism introduced in 0.9.14 or using the new "contains" operator in
   filter expressions, which lets you search the entire packet or text
   string or byte string fields in the packet; the "contains" operator can
   also be used in expressions used to filter the display.

   Q 12.3: How do I filter a capture to see traffic for virus XXX?

   A: For some viruses/worms there might be a capture filter to recognize
   the virus traffic. Check the CaptureFilters page on the Wireshark Wiki
   to see if anybody's added such a filter.

   Note that Wireshark was not designed to be an intrusion detection
   system; you might be able to use it as an IDS, but in most cases
   software designed to be an IDS, such as Snort or Prelude, will probably
   work better.

   The Bleeding Edge of Snort has a collection of signatures for Snort to
   detect various viruses, worms, and the like.