/help/faq.py

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#!/usr/bin/env python
#
# faq.py
#
# Routines to assemble a FAQ list for the Wireshark web site.
# Questions and answer content can be found below. Section and
# question numbers will be automatically generated.
#
# $Id: faq.py 36221 2011-03-20 23:09:36Z gerald $

import sys
import string

class faq_section:
	def __init__(self, name, secnum):
		self.name = name
		self.secnum = secnum
		self.qa = []
		self.subsecs = []

	def add_qa(self, question, answer, tag):
		q_num = len(self.qa) + 1
		q_id = "%s.%d" % (self.get_num_string(), q_num)
		self.qa.append( (q_id, question, answer, tag) )

	def get_all_qa(self):
		return self.qa

	def add_subsec(self, subsec):
		self.subsecs.append(subsec)

	def get_all_subsecs(self):
		return self.subsecs

	def get_num_string(self):
		return "%d" % (self.secnum)

	def get_name(self):
		return self.name

	def get_num_name(self):
		return "%s. %s" % (self.get_num_string(), self.name)

	def get_header_level(self):
		return 3

	def print_index(self):
		print("<a href=#sec%s><h%d>%s:</h%d></a>\n" % (self.get_num_string(), self.get_header_level(), self.get_num_name(), self.get_header_level()))
		for qa in self.qa:
			id = qa[0]
			question = qa[1]
			print('<p class="faq_q">')
			print('<a class="faq_qnum" href=#q%s>%s %s</a>\n' % (id, id, question))
			print('</p>')
		for subsec in self.subsecs:
			subsec.print_index()

	def print_contents(self):
		# Table header
		print("""
  <a name="sec%s">
    <h%d>%s</h%d>
  </a>
""" % (self.get_num_string(), self.get_header_level(), self.get_num_name(), self.get_header_level()))

		# Questions and Answers
		for qa in self.qa:
			id = qa[0]
			question = qa[1]
			answer = qa[2]
			tag = qa[3]

			print('<p class="faq_q">')
			print('<a class="faq_qnum" name=q%s>Q %s:</a>' % (id, id))
			if tag is not None:
				print('<a name=%s>' % tag)
			print('<span>%s</span>' % (question))
			if tag is not None:
				print('</a>')
			print('</p>')

			print('<p class="faq_a">')
			print('<span class="faq_anum">A:</span>\n')
			print(answer)
			print('</p>')

		# Subsections
		for subsec in self.subsecs:
			subsec.print_contents()

		# Table footer
		print("")

class faq_subsection(faq_section):
	def __init__(self, name, secnum, subsecnum):
		self.name = name
		self.secnum = secnum
		self.subsecnum = subsecnum
		self.qa = []
		self.subsecs = []

	def get_num_string(self):
		return "%d.%d" % (self.secnum, self.subsecnum)

	def get_header_level(self):
		return 2

class faq_subsubsection(faq_section):
	def __init__(self, name, secnum, subsecnum, subsubsecnum):
		self.name = name
		self.secnum = secnum
		self.subsecnum = subsecnum
		self.subsubsecnum = subsubsecnum
		self.qa = []
		self.subsecs = []

	def get_num_string(self):
		return "%d.%d.%d" % (self.secnum, self.subsecnum, self.subsubsecnum)

	def get_header_level(self):
		return 2

sec_num = 0
subsec_num = 0
subsubsec_num = 0
sections = []
current_section = None
parent_section = None
grandparent_section = None
current_question = None
current_tag = None

# Make a URL of itself
def selflink(text):
	return "<a href=\"%s\">%s</a>" % (text, text)

# Add a section
def section(name):
	global sec_num
	global subsec_num
	global subsubsec_num
	global current_section
	global grandparent_section
	assert not current_question
	sec_num = sec_num + 1
	subsec_num = 0
	subsubsec_num = 0
	sec = faq_section(name, sec_num)
	sections.append(sec)
	current_section = sec
	grandparent_section = sec

# Add a subsection
def subsection(name):
	global subsec_num
	global subsubsec_num
	global current_section
	global parent_section
	global grandparent_section
	assert not current_question
	subsec_num = subsec_num + 1
	subsubsec_num = 0
	sec = faq_subsection(name, sec_num, subsec_num)
	grandparent_section.add_subsec(sec)
	current_section = sec
	parent_section = sec

# Add a subsubsection
def subsubsection(name):
	global subsubsec_num
	global current_section
	global parent_section
	assert not current_question
	subsubsec_num = subsubsec_num + 1
	sec = faq_subsubsection(name, sec_num, subsec_num, subsubsec_num)
	parent_section.add_subsec(sec)
	current_section = sec

# Add a question
def question(text, tag=None):
	global current_question
	global current_tag
	assert current_section
	assert not current_question
	assert not current_tag
	current_question = text
	current_tag = tag

# Add an answer
def answer(text):
	global current_question
	global current_tag
	assert current_section
	assert current_question
	current_section.add_qa(current_question, text, current_tag)
	current_question = None
	current_tag = None


# Create the index
def create_index():
	print("""
  <a name="index">
    <h1>Index</h1>
  </a>
""")
	for sec in sections:
		sec.print_index()

	print("""
""")


# Print result
def create_output(header='', footer=''):

	print(header)
	create_index()

	for sec in sections:
		sec.print_contents()

	print(footer)

def main():
	header = '''\
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE html
  PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
  "DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
<head>
  <title>Wireshark FAQ</title>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
</head>
<body>
'''
	footer = '''\
</body>
</html>
'''

	if len(sys.argv) > 1 and sys.argv[1] == '-b': # Only print the document body
		header = ''
		footer = ''

	create_output(header, footer)

#################################################################
section("General Questions")
#################################################################

question("What is Wireshark?")
answer("""
Wireshark&#174; 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.

<br />

It is developed and maintained by a global team of protocol experts, and
it is an example of a
<a href="http://en.wikipedia.org/wiki/Disruptive_technology">disruptive
technology</a>.

<br />

Wireshark used to be known as Ethereal&#174;.  See the next question
for details about the name change.  If you're still using Ethereal, it
is <a href="http://www.ethereal.com/appnotes/enpa-sa-00024.html">strongly
recommended that you upgrade to Wireshark</a>.

<br />

For more information, please see the
<a href="/about.html">About Wireshark</a>
page.
""")


question("What's up with the name change?  Is Wireshark a fork?")
answer("""
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.

<br />

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.

<br />

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.

<br />

More information on the name change can be found here:

<ul class="item_list">

  <li><href url="http://www.prweb.com/releases/2006/6/prweb396098.htm" name="Original press release">
  <li><href url="http://trends.newsforge.com/article.pl?sid=06/06/09/1349255&from=rss" name="NewsForge article">
  <li>Many other articles in <href url="bibliography.html" name="our bibliography">
</ul>
""")


question("Where can I get help?")
answer("""
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 %s.  An IRC channel dedicated to Wireshark can
be found at %s.

<br />

Self-paced and instructor-led training is available at
<a href="http://www.wiresharku.com">Wireshark University</a>.  A
certification program will be announced in Q3 2007.

<br />

Commercial support and development services are available
from <a href="http://www.cacetech.com/">CACE Technologies</a>.
""" % (selflink("https://www.wireshark.org/mailman/listinfo"),
       selflink("irc://irc.freenode.net/wireshark")
       ))


question("What kind of shark is Wireshark?")
answer("""
<i>carcharodon photoshopia</i>.
""")


question("How is Wireshark pronounced, spelled and capitalized?")
answer("""
Wireshark is pronounced as the word <i>wire</i> followed immediately by
the word <i>shark</i>.  Exact pronunciation and emphasis may vary
depending on your locale (e.g. Arkansas).

<br />

It's spelled with a capital <i>W</i>, followed by a lower-case
<i>ireshark</i>.  It is not a CamelCase word, i.e., <i>WireShark</i>
is incorrect.
""")


question("How much does Wireshark cost?", "but_thats_not_all")
answer("""
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
<em>is</em> the full version.

<br />

The license under which Wireshark is issued is <a
href="http://www.gnu.org/licenses/gpl.html">the GNU General Public
License version 2</a>.  See <a href="http://www.gnu.org/licenses/gpl-faq.html">the
GNU GPL FAQ</a> for some more information.
""")

question("But I just paid someone on eBay for a copy of Wireshark! Did I get ripped off?")
answer("""
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.

<br />

Wireshark is <a href="/download.html">available for anyone to download,
absolutely free, at any time</a>. Paying for a copy implies that you should
get something for your money.
""")

question("Can I use Wireshark commercially?")
answer("""
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?"

<br />

If you mean "Can I use Wireshark as part of my commercial product?", see
<a href="#derived_work_gpl">the next entry in the FAQ</a>.
""")


question("Can I use Wireshark as part of my commercial product?",
"derived_work_gpl")

answer("""
As noted, Wireshark is licensed under <a
href="http://www.gnu.org/licenses/gpl.html">the GNU General Public
License</a>.  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 <a
href="http://www.gnu.org/licenses/gpl-faq.html">GPL FAQ</a> for more
details; in particular, note the answer to <a
href="http://www.gnu.org/licenses/gpl-faq.html#GPLCommercially">the
question about modifying a GPLed program and selling it
commercially</a>, and <a
href="http://www.gnu.org/licenses/gpl-faq.html#LinkingWithGPL">the
question about linking GPLed code with other code to make a proprietary
program</a>.

<br />

You can combine a GPLed program such as Wireshark and a commercial
program as long as they communicate "at arm's length", as per <a
href="http://www.gnu.org/licenses/gpl-faq.html#GPLInProprietarySystem">this
item in the GPL FAQ</a>.

<br />

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.
""")

question("What protocols are currently supported?")
answer("""
There are currently hundreds of supported
protocols and media.  Details can be found in the
<a href="/docs/man-pages/wireshark.html">wireshark(1)</a> man page.
""")


question("Are there any plans to support {your favorite protocol}?")
answer("""
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.
""")


question("""Can Wireshark read capture files from {your favorite network
analyzer}?""")

answer("""
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.

<br />

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.

<br />

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
<strong>AND</strong> 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.

<br />

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


question("What devices can Wireshark use to capture packets?")
answer("""
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.

<br />

See <a href="http://wiki.wireshark.org/CaptureSetup/NetworkMedia">the list of
supported capture media on various OSes</a> 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.

<br />

It can also read a variety of capture file formats, including:

<ul>

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

</ul>

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.
""")

question("""
Does Wireshark work on Windows Vista or Windows Server 2008?
""")

answer("""
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
<a
href="http://wiki.wireshark.org/CaptureSetup/CapturePrivileges#windows">CapturePrivileges</a>
page on the wiki for more details.
""")

#################################################################
section("Downloading Wireshark")
#################################################################


question("""Why do I get an error when I try to run the Win32 installer?""")

answer("""
The program you used to download it may have downloaded it incorrectly.
Web browsers and download accelerators sometimes may do this.

<br />

Try downloading it with, for example:
<ul>
<li>Wget, for which Windows binaries are available from <a
href="http://www.christopherlewis.com/WGet/WGetFiles.htm">Christopher Lewis</a>
or
<a href="http://www.jensroesner.de/wgetgui/">wGetGUI</a>, which offers a GUI
interface that uses wget;

<li>WS_FTP from <a href="http://www.ipswitch.com/">Ipswitch</a>,

<li>the <tt>ftp</tt> command that comes with Windows.

</ul>

If you use the <tt>ftp</tt> command, make sure you do the transfer in
binary mode rather than ASCII mode, by using the <tt>binary</tt> command
before transferring the file.
""")



#################################################################
section("Installing Wireshark")
#################################################################


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

answer("""
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 <tt>wireshark-gnome</tt> or <tt>wireshark-gtk+</tt>.  Find it and
install it.
""")


#################################################################
section("Building Wireshark")
#################################################################


question("""I have libpcap installed; why did the configure script not
find pcap.h or bpf.h?""")

answer("""
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.

<br />

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.
""")


question("""
Why do I get the error

<blockquote><samp>dftest_DEPENDENCIES was already defined in condition TRUE,
which implies condition HAVE_PLUGINS_TRUE</samp></blockquote>

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

answer("""
You probably have automake 1.5 installed on your machine (the command
<kbd>automake --version</kbd> 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).
""")

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

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

<br />

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

question("""
When I try to build Wireshark on Solaris, why does the link fail
complaining that <tt>plugin_list</tt> is undefined?
""")

answer("""
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 <a
href="http://www.thewrittenword.com">The Written Word</a>, 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 <a href="http://www.gtk.org/">the GTK Web
site</a>.  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.)
""")

question("""
When I try to build Wireshark on Windows, why does the build fail because
of conflicts between <tt>winsock.h</tt> and <tt>winsock2.h</tt>?
""")

answer("""
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 <tt>winsock.h</tt> and in <tt>winsock2.h</tt>; Wireshark
uses <tt>winsock2.h</tt>, but pre-2.3 versions of the WinPcap
developer's packet use <tt>winsock.h</tt>.  (2.3 uses
<tt>winsock2.h</tt>, so if Wireshark were to use <tt>winsock.h</tt>, it
would not be able to build with current versions of the WinPcap
developer's pack.)

<br />

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

#################################################################
section("Starting Wireshark")
#################################################################


question("""Why does Wireshark crash with a Bus Error when I try to run
it on Solaris 8?""")

answer("""
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 <a href="http://www.thewrittenword.com">The Written
Word</a>, 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 <a href="http://www.gtk.org/">the GTK Web
site</a>.  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.)

<br />

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

question("""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?""")

answer("""
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.
""")

question("""When I try to run Wireshark, why does it complain about
<tt>sprint_realloc_objid</tt> being undefined?""")

answer("""
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.
""")

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

answer("""
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.)

<br />

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.

<br />

To fix the prebinding caches, run the command

<pre>
	sudo /sw/var/lib/fink/prebound/update-package-prebinding.pl -f
</pre>
""")

#################################################################
section("Crashes and other fatal errors")
#################################################################


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

answer("""
This is almost certainly a problem with one or more of:

<ul>
<li>the operating system you're using;
<li>the device driver for the interface you're using;
<li>the libpcap/WinPcap library and, if this is Windows, the WinPcap
device driver;
</ul>

so:

<ul>
<li>if you are using Windows, see <a
href="http://www.winpcap.org/contact.htm">the WinPcap support
page</a> - check the "Submitting bugs" section;
<li>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).
</ul>
""")

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

answer("""
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.
""")

#################################################################
section("Capturing packets")
#################################################################


question("""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?""", "promiscsniff")

answer("""
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.

<br />

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.

<br />

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 <i>vice
versa</i>.  This problem has also been reported for Netgear dual-speed
hubs, and may exist for other "auto-sensing" or "dual-speed" hubs.

<br />

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 <a href="http://wiki.wireshark.org/SwitchReference">the switch
reference page</a> on <a href="http://wiki.wireshark.org/">the Wireshark
Wiki</a> 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.)

<br />

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.

<br />

If your machine is <em>not</em> 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:

<ul>
<li>packets sent to one of that host's link-layer addresses;
<li>broadcast packets;
<li>multicast packets sent to a multicast address that the host has
		         configured the interface to accept.
</ul>

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
<tt>-p</tt> 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.

<br />

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
<strong>will</strong> see broadcast packets, and multicast packets sent
to a multicast MAC address the interface is set up to receive.

<br />

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.

<br />

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 <a
href="http://wiki.wireshark.org/CaptureSetup/TokenRing">the Wireshark
Wiki item on Token Ring capturing</a> for details.

<br />

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 <em>and</em> acting as regular network interfaces at the same
time), so it may be that Windows drivers for those interfaces don't
support promiscuous mode.
""")

question("""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?""")

answer("""
You're probably not seeing <em>any</em> 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.

<br />

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.

<br />

I.e., this is probably <a href="#promiscsniff">the same question
as this earlier one</a>; see the response to that question.
""")

question("""Why am I only seeing ARP packets when I try to capture
traffic?""")

answer("""
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.

<br />

I.e., this is probably <a href="#promiscsniff">the same question
as this earlier one</a>; see the response to that question.
""")

question("""
Why am I not seeing any traffic when I try to capture traffic?""")

answer("""
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?

<br />

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
<a href="#promiscsniff">this earlier question</a>.

<br />

Otherwise, on Windows, see the response to <a href="#capprobwin">this
question</a> and, on a UNIX-flavored OS, see the response to <a
href="#capprobunix">this question</a>.
""")

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

answer("""
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.

<br />

On Linux and FreeBSD, libpcap 0.8 and later support the API for <a
href="http://www.endace.com/products.htm">Endace Measurement Systems'
DAG cards</a>, 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.

<br />

See <a href="http://wiki.wireshark.org/CaptureSetup/SS7">the SS7 capture
setup page</a> on <a href="http://wiki.wireshark.org/">the Wireshark
Wiki</a> for current information on capturing SS7 traffic on TDM
links.
""")

question("""How do I put an interface into promiscuous mode?""")

answer("""
By not disabling promiscuous mode when running Wireshark or TShark.

<br />

Note, however, that:
<ul>
<li>the form of promiscuous mode that libpcap (the library that
programs such as tcpdump, Wireshark, etc.  use to do packet capture)
turns on will <strong>not</strong> necessarily be shown if you run
<tt>ifconfig</tt> on the interface on a UNIX system;
<li>some network interfaces might not support promiscuous mode, and some
drivers might not allow promiscuous mode to be turned on - see <a
href="#promiscsniff">this earlier question</a> for more information on
that;
<li>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 <a href="#promiscsniff">this earlier
question</a> for more information on that.
</ul>

I.e., this is probably <a href="#promiscsniff">the same question
as this earlier one</a>; see the response to that question.
""")

question("""
I can set a display filter just fine; why don't capture filters work?
""")

answer("""
Capture filters currently use a different syntax than display filters.  Here's
the corresponding section from the
<a href="/docs/man-pages/wireshark.html">wireshark(1)</a>
 man page:

<br />

"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.

<br />

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."

<br />

The capture filter syntax used by libpcap can be found in the
<a href="http://www.tcpdump.org/tcpdump_man.html">tcpdump(8)</a>
man page.
""")


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

answer("""
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.

<br />

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.

<br />

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.

<br />

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.

<br />

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 <a
href="http://www.tcpdump.org/">the tcpdump.org Web site</a> and then
recompile Wireshark from source with that later version of libpcap.

<br />

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.
""")

question("""
How can I capture packets with CRC errors?
""")

answer("""
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.

<br />

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.

<br />

Most OSes probably do <strong>not</strong> 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).

<br />

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.
""")

question("""
How can I capture entire frames, including the FCS?
""")

answer("""
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.

<br />

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.

<br />

Most OSes do <strong>not</strong> 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).

<br />

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.
""")

question("""
I'm capturing packets on a machine on a VLAN; why don't the packets I'm
capturing have VLAN tags?
""")

answer("""
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.

<br />

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 <a
href="http://wiki.wireshark.org/CaptureSetup/VLAN">the Wireshark Wiki
item on VLAN capturing</a> for details.
""")

question("""
Why does Wireshark hang after I stop a capture?
""")

answer("""
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.

<br />

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:
<ul><li>a search of a system file listing IP addresses and names;
<li>a lookup using DNS;
<li>on UNIX systems, a lookup using NIS;
<li>on Windows systems, a NetBIOS-over-TCP query.
</ul>

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.

<br />

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.

<br />

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 <em>all</em> your current
preference settings.

<br />

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 <a href="mailto:wireshark-dev@wireshark.org">the Wireshark
developers' mailing list</a> at <tt>wireshark-dev@wireshark.org</tt>.

<br />

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

<pre>
        $ gdb wireshark core
        (gdb) backtrace
        ..... prints the stack trace
        (gdb) quit
        $
</pre>

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

<br />

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
<tt>/tmp</tt> or <tt>/var/tmp</tt> on UNIX-flavored OSes, <tt>\TEMP</tt>
on the main system disk (normally <tt>C:</tt>) on Windows 9x/Me/NT 4.0,
and <tt>\Documents and Settings\</tt><var>your login
name</var><tt>\Local Settings\Temp</tt> 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 of the form,
<tt>wireshark_iface_YYYYmmddHHMMSS_XXXXXX</tt>.  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.
""")


#################################################################
section("Capturing packets on Windows")
#################################################################

question("""
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?
""", "capprobwin")

answer("""
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.

<br />

If you are running on Windows 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
<em>might</em> clear up if you completely un-install WinPcap and then
re-install it.

<br />

If that doesn't work, then note that Wireshark relies on the WinPcap
library…