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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 What kind of shark is Wireshark?
1.5 How is Wireshark pronounced, spelled and capitalized?
1.6 How much does Wireshark cost?
1.7 But I just paid someone on eBay for a copy of Wireshark! Did I
get ripped off?
1.8 Can I use Wireshark commercially?
1.9 Can I use Wireshark as part of my commercial product?
1.10 What protocols are currently supported?
1.11 Are there any plans to support {your favorite protocol}?
1.12 Can Wireshark read capture files from {your favorite network
analyzer}?
1.13 What devices can Wireshark use to capture packets?
1.14 Does Wireshark work on Windows Vista or Windows Server 2008?
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 build
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 try to run Wireshark, why does it complain about
sprint_realloc_objid being undefined?
5.3 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; why am I not seeing any
traffic being sent by the machine running Wireshark?
8.6 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?
8.7 I'm trying to capture 802.11 traffic on Windows; why am I not
seeing any packets?
8.8 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?
8.9 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: Wireshark® is a network protocol analyzer. It lets you capture
and interactively browse the traffic running on a computer
network. It has a rich and powerful feature set and is world's
most popular tool of its kind. It runs on most computing platforms
including Windows, OS X, Linux, and UNIX. Network professionals,
security experts, developers, and educators around the world use
it regularly. It is freely available as open source, and is
released under the GNU General Public License version 2.
It is developed and maintained by a global team of protocol
experts, and it is an example of a disruptive technology.
Wireshark used to be known as Ethereal®. See the next question for
details about the name change. If you're still using Ethereal, it
is strongly recommended that you upgrade to Wireshark.
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, Gerald Combs (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. There has
been no active development on Ethereal since the name change.
Several parts of the Ethereal web site (such as the mailing lists,
source code repository, and build farm) have gone offline.
More information on the name change can be found here:
* Original press release
* NewsForge article
* Many other articles in our bibliography
Q 1.3: Where can I get help?
A: Community support is available on the Q&A site and on the
wireshark-users mailing list. Subscription information and
archives for all of Wireshark's mailing lists can be found at
https://www.wireshark.org/mailman/listinfo. An IRC channel
dedicated to Wireshark can be found at
irc://irc.freenode.net/wireshark.
Self-paced and instructor-led training is available at Wireshark
University. Wireshark University also offers certification via the
Wireshark Certified Network Analyst program.
Q 1.4: What kind of shark is Wireshark?
A: carcharodon photoshopia.
Q 1.5: How is Wireshark pronounced, spelled and capitalized?
A: Wireshark is pronounced as the word wire followed immediately
by the word shark. Exact pronunciation and emphasis may vary
depending on your locale (e.g. Arkansas).
It's spelled with a capital W, followed by a lower-case ireshark.
It is not a CamelCase word, i.e., WireShark is incorrect.
Q 1.6: 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 version 2. See the GNU GPL FAQ for some more
information.
Q 1.7: But I just paid someone on eBay for a copy of Wireshark!
Did I get ripped off?
A: That depends. Did they provide any sort of value-added product
or service, such as installation support, installation media,
training, trace file analysis, or funky-colored shark-themed
socks? Probably not.
Wireshark is available for anyone to download, absolutely free, at
any time. Paying for a copy implies that you should get something
for your money.
Q 1.8: 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 1.9: 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.
We recommend keeping Wireshark and your product completely
separate, communicating over sockets or pipes. If you're loading
any part of Wireshark as a DLL, you're probably doing it wrong.
Q 1.10: 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 1.11: 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 1.12: Can Wireshark read capture files from {your favorite
network analyzer}?
A: Support for particular capture file formats is added to
Wireshark as a result of people contributing that support; no
formal plans for adding support for particular capture file
formats 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 1.13: 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.
See the list of supported capture media on various OSes for
details (several items in there say "Unknown", which doesn't mean
"Wireshark can't capture on them", it means "we don't know whether
it can capture on them"; we expect that it will be able to capture
on many of them, but we haven't tried it ourselves - if you try
one of those types and it works, please update the wiki page
accordingly.
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 1.14: Does Wireshark work on Windows Vista or Windows Server
2008?
A: Yes, but if you want to capture packets as a normal user, you
must make sure npf.sys is loaded. Wireshark's installer enables
this by default. This is not a concern if you run Wireshark as
Administrator, but this is discouraged. See the CapturePrivileges
page on the wiki for more details.
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 and download accelerators sometimes may
do this.
Try downloading it with, for example:
* Wget, for which Windows binaries are available from
Christopher Lewis or wGetGUI, which 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 build
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 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 5.3: 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 effort 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 \Documents and Settings\your login
name \Local Settings\Temp on the main system disk on Windows
Windows XP and Server 2003, and \Users\your login
name\AppData\Local\Temp on the main system disk on Windows Vista
and later, so the capture file will probably be there. If you are
capturing on a single interface, it will have a name of the form,
wireshark_<fmt>_<iface>_YYYYmmddHHMMSS_XXXXXX, where <fmt> is the
capture file format (pcap or pcapng), and <iface> is the actual
name of the interface you are capturing on; otherwise, if you are
capturing on multiple interfaces, it will have a name of the form,
wireshark_<N>_interfaces_YYYYmmddHHMMSS_XXXXXX, where <N> is the
number of simultaneous interfaces you are capturing on. 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 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 Windows XP or 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.
* 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.
* 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 a 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; 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 8.6: 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 8.7: 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 8.8: 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 8.9: 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
libpcap 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@lists.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.
After capture, you can search for text by selecting Edit→Find
Packet... and making sure String is selected. Alternately, you can
use the "contains" display filter operator or "matches" operator
if it's supported on your system.
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.