1412 lines
71 KiB
Text
1412 lines
71 KiB
Text
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The Wireshark FAQ
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Note: This is just an ASCII snapshot of the faq and may not be up to
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date. Please go to http://www.wireshark.org/faq.html for the up
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to date version. The version of this snapshot can be found at
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the end of this document.
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INDEX
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1. General Questions:
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1.1 What is Wireshark?
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1.2 What's up with the name change? Is Wireshark a fork?
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1.3 Where can I get help?
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1.4 What kind of shark is Wireshark?
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1.5 How is Wireshark pronounced, spelled and capitalized?
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1.6 How much does Wireshark cost?
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1.7 Can I use Wireshark commercially?
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1.8 Can I use Wireshark as part of my commercial product?
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1.9 What protocols are currently supported?
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1.10 Are there any plans to support {your favorite protocol}?
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1.11 Can Wireshark read capture files from {your favorite network
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analyzer}?
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1.12 What devices can Wireshark use to capture packets?
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1.13 Does Wireshark work on Windows Vista?
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2. Downloading Wireshark:
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2.1 Why do I get an error when I try to run the Win32 installer?
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3. Installing Wireshark:
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3.1 I installed the Wireshark RPM (or other package); why did it
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install TShark but not Wireshark?
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4. Building Wireshark:
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4.1 I have libpcap installed; why did the configure script not find
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pcap.h or bpf.h?
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4.2 Why do I get the error
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dftest_DEPENDENCIES was already defined in condition TRUE, which
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implies condition HAVE_PLUGINS_TRUE
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when I try to build Wireshark from SVN or a SVN snapshot?
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4.3 Why does the linker fail with a number of "Output line too long."
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messages followed by linker errors when I try to buil Wireshark?
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4.4 When I try to build Wireshark on Solaris, why does the link fail
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complaining that plugin_list is undefined?
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4.5 When I try to build Wireshark on Windows, why does the build fail
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because of conflicts between winsock.h and winsock2.h?
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5. Starting Wireshark:
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5.1 Why does Wireshark crash with a Bus Error when I try to run it on
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Solaris 8?
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5.2 When I run Wireshark on Windows NT, why does it die with a Dr.
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Watson error, reporting an "Integer division by zero" exception, when I
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start it?
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5.3 When I try to run Wireshark, why does it complain about
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sprint_realloc_objid being undefined?
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5.4 I've installed Wireshark from Fink on Mac OS X; why is it very slow
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to start up?
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6. Crashes and other fatal errors:
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6.1 I have an XXX network card on my machine; if I try to capture on
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it, why does my machine crash or reset itself?
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6.2 Why does my machine crash or reset itself when I select "Start"
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from the "Capture" menu or select "Preferences" from the "Edit" menu?
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7. Capturing packets:
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7.1 When I use Wireshark to capture packets, why do I see only packets
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to and from my machine, or not see all the traffic I'm expecting to see
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from or to the machine I'm trying to monitor?
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7.2 When I capture with Wireshark, why can't I see any TCP packets
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other than packets to and from my machine, even though another analyzer
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on the network sees those packets?
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7.3 Why am I only seeing ARP packets when I try to capture traffic?
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7.4 Why am I not seeing any traffic when I try to capture traffic?
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7.5 Can Wireshark capture on (my T1/E1 line, SS7 links, etc.)?
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7.6 How do I put an interface into promiscuous mode?
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7.7 I can set a display filter just fine; why don't capture filters
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work?
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7.8 I'm entering valid capture filters; why do I still get "parse
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error" errors?
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7.9 How can I capture packets with CRC errors?
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7.10 How can I capture entire frames, including the FCS?
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7.11 I'm capturing packets on a machine on a VLAN; why don't the
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packets I'm capturing have VLAN tags?
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7.12 Why does Wireshark hang after I stop a capture?
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8. Capturing packets on Windows:
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8.1 I'm running Wireshark on Windows; why does some network interface
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on my machine not show up in the list of interfaces in the "Interface:"
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field in the dialog box popped up by "Capture->Start", and/or why does
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Wireshark give me an error if I try to capture on that interface?
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8.2 I'm running Wireshark on Windows; why do no network interfaces show
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up in the list of interfaces in the "Interface:" field in the dialog
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box popped up by "Capture->Start"?
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8.3 I'm running Wireshark on Windows; why doesn't my serial port/ADSL
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modem/ISDN modem show up in the list of interfaces in the "Interface:"
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field in the dialog box popped up by "Capture->Start"?
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8.4 I'm running Wireshark on Windows NT 4.0/Windows 2000/Windows
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XP/Windows Server 2003; my machine has a PPP (dial-up POTS, ISDN, etc.)
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interface, and it shows up in the "Interface" item in the "Capture
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Options" dialog box. Why can no packets be sent on or received from
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that network while I'm trying to capture traffic on that interface?
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8.5 I'm running Wireshark on Windows; why am I not seeing any traffic
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being sent by the machine running Wireshark?
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8.6 When I capture on Windows in promiscuous mode, I can see packets
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other than those sent to or from my machine; however, those packets
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show up with a "Short Frame" indication, unlike packets to or from my
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machine. What should I do to arrange that I see those packets in their
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entirety?
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8.7 I'm trying to capture 802.11 traffic on Windows; why am I not
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seeing any packets?
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8.8 I'm trying to capture 802.11 traffic on Windows; why am I seeing
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packets received by the machine on which I'm capturing traffic, but not
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packets sent by that machine?
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8.9 I'm trying to capture Ethernet VLAN traffic on Windows, and I'm
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capturing on a "raw" Ethernet device rather than a "VLAN interface", so
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that I can see the VLAN headers; why am I seeing packets received by
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the machine on which I'm capturing traffic, but not packets sent by
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that machine?
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9. Capturing packets on UN*Xes:
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9.1 I'm running Wireshark on a UNIX-flavored OS; why does some network
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interface on my machine not show up in the list of interfaces in the
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"Interface:" field in the dialog box popped up by "Capture->Start",
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and/or why does Wireshark give me an error if I try to capture on that
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interface?
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9.2 I'm running Wireshark on a UNIX-flavored OS; why do no network
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interfaces show up in the list of interfaces in the "Interface:" field
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in the dialog box popped up by "Capture->Start"?
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9.3 I'm capturing packets on Linux; why do the time stamps have only
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100ms resolution, rather than 1us resolution?
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10. Capturing packets on wireless LANs:
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10.1 How can I capture raw 802.11 frames, including non-data
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(management, beacon) frames?
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10.2 How do I capture on an 802.11 device in monitor mode?
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11. Viewing traffic:
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11.1 Why am I seeing lots of packets with incorrect TCP checksums?
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11.2 I've just installed Wireshark, and the traffic on my local LAN is
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boring. Where can I find more interesting captures?
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11.3 Why doesn't Wireshark correctly identify RTP packets? It shows
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them only as UDP.
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11.4 Why doesn't Wireshark show Yahoo Messenger packets in captures
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that contain Yahoo Messenger traffic?
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12. Filtering traffic:
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12.1 I saved a filter and tried to use its name to filter the display;
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why do I get an "Unexpected end of filter string" error?
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12.2 How can I search for, or filter, packets that have a particular
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string anywhere in them?
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12.3 How do I filter a capture to see traffic for virus XXX?
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1. General Questions
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Q 1.1: What is Wireshark?
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A: Wireshark® is the world's most popular network protocol analyzer. It
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has a rich and powerful feature set and runs on most computing
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platforms including Windows, OS X, Linux, and UNIX. Network
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professionals, security experts, developers, and educators around the
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world use it regularly. It is freely available as open source, and is
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released under the GNU General Public License.
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It is developed and maintained by a global team of protocol experts,
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and it is an example of a disruptive technology.
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Wireshark used to be known as Ethereal®. See the next question for
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details about the name change. If you're still using Ethereal, it is
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strongly recommended that you upgrade to Wireshark.
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For more information, please see the About Wireshark page.
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Q 1.2: What's up with the name change? Is Wireshark a fork?
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A: In May of 2006, Gerald Combs (the original author of Ethereal) went
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to work for CACE Technologies (best known for WinPcap). Unfortunately,
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he had to leave the Ethereal trademarks behind.
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This left the project in an awkward position. The only reasonable way
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to ensure the continued success of the project was to change the name.
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This is how Wireshark was born.
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Wireshark is almost (but not quite) a fork. Normally a "fork" of an
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open source project results in two names, web sites, development teams,
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support infrastructures, etc. This is the case with Wireshark except
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for one notable exception -- every member of the core development team
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is now working on Wireshark. There has been no active development on
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Ethereal since the name change. Several parts of the Ethereal web site
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(such as the mailing lists, source code repository, and build farm)
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have gone offline.
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More information on the name change can be found here:
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*
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*
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* Many other articles in
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Q 1.3: Where can I get help?
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A: Community support is available on the wireshark-users mailing list.
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Subscription information and archives for all of Wireshark's mailing
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lists can be found at http://www.wireshark.org/mailman/listinfo. An IRC
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channel dedicated to Wireshark can be found at
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irc://irc.freenode.net/wireshark.
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Self-paced and instructor-led training is available at Wireshark
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University. A certification program will be announced in Q3 2007.
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Commercial support and development services are available from CACE
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Technologies.
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Q 1.4: What kind of shark is Wireshark?
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A: carcharodon photoshopia.
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Q 1.5: How is Wireshark pronounced, spelled and capitalized?
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A: Wireshark is pronounced as the word wire followed immediately by the
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word shark. Exact pronunciation and emphasis may vary depending on your
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locale (e.g. Arkansas).
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It's spelled with a capital W, followed by a lower-case ireshark. It is
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not a CamelCase word, i.e., WireShark is incorrect.
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Q 1.6: How much does Wireshark cost?
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A: Wireshark is "free software"; you can download it without paying any
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license fee. The version of Wireshark you download isn't a "demo"
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version, with limitations not present in a "full" version; it is the
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full version.
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The license under which Wireshark is issued is the GNU General Public
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License. See the GNU GPL FAQ for some more information.
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Q 1.7: Can I use Wireshark commercially?
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A: Yes, if, for example, you mean "I work for a commercial
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organization; can I use Wireshark to capture and analyze network
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traffic in our company's networks or in our customer's networks?"
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If you mean "Can I use Wireshark as part of my commercial product?",
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see the next entry in the FAQ.
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Q 1.8: Can I use Wireshark as part of my commercial product?
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A: As noted, Wireshark is licensed under the GNU General Public
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License. The GPL imposes conditions on your use of GPL'ed code in your
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own products; you cannot, for example, make a "derived work" from
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Wireshark, by making modifications to it, and then sell the resulting
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derived work and not allow recipients to give away the resulting work.
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You must also make the changes you've made to the Wireshark source
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available to all recipients of your modified version; those changes
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must also be licensed under the terms of the GPL. See the GPL FAQ for
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more details; in particular, note the answer to the question about
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modifying a GPLed program and selling it commercially, and the question
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about linking GPLed code with other code to make a proprietary program.
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You can combine a GPLed program such as Wireshark and a commercial
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program as long as they communicate "at arm's length", as per this item
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in the GPL FAQ.
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Q 1.9: What protocols are currently supported?
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A: There are currently hundreds of supported protocols and media.
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Details can be found in the wireshark(1) man page.
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Q 1.10: Are there any plans to support {your favorite protocol}?
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A: Support for particular protocols is added to Wireshark as a result
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of people contributing that support; no formal plans for adding support
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for particular protocols in particular future releases exist.
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Q 1.11: Can Wireshark read capture files from {your favorite network
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analyzer}?
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A: Support for particular protocols is added to Wireshark as a result
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of people contributing that support; no formal plans for adding support
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for particular protocols in particular future releases exist.
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If a network analyzer writes out files in a format already supported by
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Wireshark (e.g., in libpcap format), Wireshark may already be able to
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read them, unless the analyzer has added its own proprietary extensions
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to that format.
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If a network analyzer writes out files in its own format, or has added
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proprietary extensions to another format, in order to make Wireshark
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read captures from that network analyzer, we would either have to have
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a specification for the file format, or the extensions, sufficient to
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give us enough information to read the parts of the file relevant to
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Wireshark, or would need at least one capture file in that format AND a
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detailed textual analysis of the packets in that capture file (showing
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packet time stamps, packet lengths, and the top-level packet header) in
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order to reverse-engineer the file format.
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Note that there is no guarantee that we will be able to
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reverse-engineer a capture file format.
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Q 1.12: What devices can Wireshark use to capture packets?
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A: Wireshark can read live data from Ethernet, Token-Ring, FDDI, serial
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(PPP and SLIP) (if the OS on which it's running allows Wireshark to do
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so), 802.11 wireless LAN (if the OS on which it's running allows
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Wireshark to do so), ATM connections (if the OS on which it's running
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allows Wireshark to do so), and the "any" device supported on Linux by
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recent versions of libpcap.
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See the list of supported capture media on various OSes for details
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(several items in there say "Unknown", which doesn't mean "Wireshark
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can't capture on them", it means "we don't know whether it can capture
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on them"; we expect that it will be able to capture on many of them,
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but we haven't tried it ourselves - if you try one of those types and
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it works, please update the wiki page accordingly.
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It can also read a variety of capture file formats, including:
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* AG Group/WildPackets EtherPeek/TokenPeek/AiroPeek/EtherHelp/Packet
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Grabber captures
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* AIX's iptrace captures
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* Accellent's 5Views LAN agent output
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* Cinco Networks NetXRay captures
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* Cisco Secure Intrusion Detection System IPLog output
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* CoSine L2 debug output
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* DBS Etherwatch VMS text output
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* Endace Measurement Systems' ERF format captures
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* EyeSDN USB S0 traces
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* HP-UX nettl captures
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* ISDN4BSD project i4btrace captures
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* Linux Bluez Bluetooth stack hcidump -w traces
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* Lucent/Ascend router debug output
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* Microsoft Network Monitor captures
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* Network Associates Windows-based Sniffer captures
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* Network General/Network Associates DOS-based Sniffer (compressed or
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uncompressed) captures
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* Network Instruments Observer version 9 captures
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* Novell LANalyzer captures
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* RADCOM's WAN/LAN analyzer captures
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* Shomiti/Finisar Surveyor captures
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* Toshiba's ISDN routers dump output
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* VMS TCPIPtrace/TCPtrace/UCX$TRACE output
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* Visual Networks' Visual UpTime traffic capture
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* libpcap, tcpdump and various other tools using tcpdump's capture
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format
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* snoop and atmsnoop output
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so that it can read traces from various network types, as captured by
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other applications or equipment, even if it cannot itself capture on
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those network types.
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Q 1.13: Does Wireshark work on Windows Vista?
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A: Yes, but if you want to capture packets, you must make sure npf.sys
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is loaded. You can do this by selecting Start WinPcap service "NPF" at
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startup in the installer or by running sc config npf start= auto as
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Administrator from the command line. You can also run Wireshark as
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Administrator, but this is discouraged. See the CaputrePrivileges page
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on the wiki for more details.
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2. Downloading Wireshark
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Q 2.1: Why do I get an error when I try to run the Win32 installer?
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A: The program you used to download it may have downloaded it
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incorrectly. Web browsers and download accelerators sometimes may do
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this.
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Try downloading it with, for example:
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* Wget, for which Windows binaries are available from Christopher
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Lewis or wGetGUI, which offers a GUI interface that uses wget;
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* WS_FTP from Ipswitch,
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* the ftp command that comes with Windows.
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If you use the ftp command, make sure you do the transfer in binary
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mode rather than ASCII mode, by using the binary command before
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transferring the file.
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3. Installing Wireshark
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Q 3.1: I installed the Wireshark RPM (or other package); why did it
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install TShark but not Wireshark?
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A: Many distributions have separate Wireshark packages, one for non-GUI
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components such as TShark, editcap, dumpcap, etc. and one for the GUI.
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If this is the case on your system, there's probably a separate package
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named wireshark-gnome or wireshark-gtk+. Find it and install it.
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4. Building Wireshark
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Q 4.1: I have libpcap installed; why did the configure script not find
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pcap.h or bpf.h?
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A: Are you sure pcap.h and bpf.h are installed? The official
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distribution of libpcap only installs the libpcap.a library file when
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"make install" is run. To install pcap.h and bpf.h, you must run "make
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install-incl". If you're running Debian or Redhat, make sure you have
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the "libpcap-dev" or "libpcap-devel" packages installed.
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It's also possible that pcap.h and bpf.h have been installed in a
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strange location. If this is the case, you may have to tweak
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aclocal.m4.
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Q 4.2: Why do I get the error
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dftest_DEPENDENCIES was already defined in condition TRUE, which
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implies condition HAVE_PLUGINS_TRUE
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when I try to build Wireshark from SVN or a SVN snapshot?
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A: You probably have automake 1.5 installed on your machine (the
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command automake --version will report the version of automake on your
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machine). There is a bug in that version of automake that causes this
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problem; upgrade to a later version of automake (1.6 or later).
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Q 4.3: Why does the linker fail with a number of "Output line too
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long." messages followed by linker errors when I try to buil Wireshark?
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A: The version of the sed command on your system is incapable of
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handling very long lines. On Solaris, for example, /usr/bin/sed has a
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line length limit too low to allow libtool to work; /usr/xpg4/bin/sed
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can handle it, as can GNU sed if you have it installed.
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On Solaris, changing your command search path to search /usr/xpg4/bin
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before /usr/bin should make the problem go away; on any platform on
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which you have this problem, installing GNU sed and changing your
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command path to search the directory in which it is installed before
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searching the directory with the version of sed that came with the OS
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should make the problem go away.
|
|
|
|
Q 4.4: When I try to build Wireshark on Solaris, why does the link fail
|
|
complaining that plugin_list is undefined?
|
|
|
|
A: This appears to be due to a problem with some versions of the GTK+
|
|
and GLib packages from www.sunfreeware.org; un-install those packages,
|
|
and try getting the 1.2.10 versions from that site, or the versions
|
|
from The Written Word, or the versions from Sun's GNOME distribution,
|
|
or the versions from the supplemental software CD that comes with the
|
|
Solaris media kit, or build them from source from the GTK Web site.
|
|
Then re-run the configuration script, and try rebuilding Wireshark. (If
|
|
you get the 1.2.10 versions from www.sunfreeware.org, and the problem
|
|
persists, un-install them and try installing one of the other versions
|
|
mentioned.)
|
|
|
|
Q 4.5: When I try to build Wireshark on Windows, why does the build
|
|
fail because of conflicts between winsock.h and winsock2.h?
|
|
|
|
A: As of Wireshark 0.9.5, you must install WinPcap 2.3 or later, and
|
|
the corresponding version of the developer's pack, in order to be able
|
|
to compile Wireshark; it will not compile with older versions of the
|
|
developer's pack. The symptoms of this failure are conflicts between
|
|
definitions in winsock.h and in winsock2.h; Wireshark uses winsock2.h,
|
|
but pre-2.3 versions of the WinPcap developer's packet use winsock.h.
|
|
(2.3 uses winsock2.h, so if Wireshark were to use winsock.h, it would
|
|
not be able to build with current versions of the WinPcap developer's
|
|
pack.)
|
|
Note that the installed version of the developer's pack should be the
|
|
same version as the version of WinPcap you have installed.
|
|
|
|
5. Starting Wireshark
|
|
|
|
Q 5.1: Why does Wireshark crash with a Bus Error when I try to run it
|
|
on Solaris 8?
|
|
|
|
A: Some versions of the GTK+ library from www.sunfreeware.org appear to
|
|
be buggy, causing Wireshark to drop core with a Bus Error. Un-install
|
|
those packages, and try getting the 1.2.10 version from that site, or
|
|
the version from The Written Word, or the version from Sun's GNOME
|
|
distribution, or the version from the supplemental software CD that
|
|
comes with the Solaris media kit, or build it from source from the GTK
|
|
Web site. Update the GLib library to the 1.2.10 version, from the same
|
|
source, as well. (If you get the 1.2.10 versions from
|
|
www.sunfreeware.org, and the problem persists, un-install them and try
|
|
installing one of the other versions mentioned.)
|
|
Similar problems may exist with older versions of GTK+ for earlier
|
|
versions of Solaris.
|
|
|
|
Q 5.2: When I run Wireshark on Windows NT, why does it die with a Dr.
|
|
Watson error, reporting an "Integer division by zero" exception, when I
|
|
start it?
|
|
|
|
A: In at least some case, this appears to be due to using the default
|
|
VGA driver; if that's not the correct driver for your video card, try
|
|
running the correct driver for your video card.
|
|
|
|
Q 5.3: When I try to run Wireshark, why does it complain about
|
|
sprint_realloc_objid being undefined?
|
|
|
|
A: Wireshark can only be linked with version 4.2.2 or later of UCD
|
|
SNMP. Your version of Wireshark was dynamically linked with such a
|
|
version of UCD SNMP; however, you have an older version of UCD SNMP
|
|
installed, which means that when Wireshark is run, it tries to link to
|
|
the older version, and fails. You will have to replace that version of
|
|
UCD SNMP with version 4.2.2 or a later version.
|
|
|
|
Q 5.4: I've installed Wireshark from Fink on Mac OS X; why is it very
|
|
slow to start up?
|
|
|
|
A: When an application is installed on OS X, prior to 10.4, it is
|
|
usually "prebound" to speed up launching the application. (That's what
|
|
the "Optimizing" phase of installation is.)
|
|
Fink normally performs prebinding automatically when you install a
|
|
package. However, in some rare cases, for whatever reason the
|
|
prebinding caches get corrupt, and then not only does prebinding fail,
|
|
but startup actually becomes much slower, because the system tries in
|
|
vain to perform prebinding "on the fly" as you launch the application.
|
|
This fails, causing sometimes huge delays.
|
|
To fix the prebinding caches, run the command
|
|
sudo /sw/var/lib/fink/prebound/update-package-prebinding.pl -f
|
|
|
|
6. Crashes and other fatal errors
|
|
|
|
Q 6.1: I have an XXX network card on my machine; if I try to capture on
|
|
it, why does my machine crash or reset itself?
|
|
|
|
A: This is almost certainly a problem with one or more of:
|
|
* the operating system you're using;
|
|
* the device driver for the interface you're using;
|
|
* the libpcap/WinPcap library and, if this is Windows, the WinPcap
|
|
device driver;
|
|
|
|
so:
|
|
* if you are using Windows, see the WinPcap support page - check the
|
|
"Submitting bugs" section;
|
|
* if you are using some Linux distribution, some version of BSD, or
|
|
some other UNIX-flavored OS, you should report the problem to the
|
|
company or organization that produces the OS (in the case of a
|
|
Linux distribution, report the problem to whoever produces the
|
|
distribution).
|
|
|
|
Q 6.2: Why does my machine crash or reset itself when I select "Start"
|
|
from the "Capture" menu or select "Preferences" from the "Edit" menu?
|
|
|
|
A: Both of those operations cause Wireshark to try to build a list of
|
|
the interfaces that it can open; it does so by getting a list of
|
|
interfaces and trying to open them. There is probably an OS, driver,
|
|
or, for Windows, WinPcap bug that causes the system to crash when this
|
|
happens; see the previous question.
|
|
|
|
7. Capturing packets
|
|
|
|
Q 7.1: When I use Wireshark to capture packets, why do I see only
|
|
packets to and from my machine, or not see all the traffic I'm
|
|
expecting to see from or to the machine I'm trying to monitor?
|
|
|
|
A: This might be because the interface on which you're capturing is
|
|
plugged into an Ethernet or Token Ring switch; on a switched network,
|
|
unicast traffic between two ports will not necessarily appear on other
|
|
ports - only broadcast and multicast traffic will be sent to all ports.
|
|
Note that even if your machine is plugged into a hub, the "hub" may be
|
|
a switched hub, in which case you're still on a switched network.
|
|
Note also that on the Linksys Web site, they say that their
|
|
auto-sensing hubs "broadcast the 10Mb packets to the port that operate
|
|
at 10Mb only and broadcast the 100Mb packets to the ports that operate
|
|
at 100Mb only", which would indicate that if you sniff on a 10Mb port,
|
|
you will not see traffic coming sent to a 100Mb port, and vice versa.
|
|
This problem has also been reported for Netgear dual-speed hubs, and
|
|
may exist for other "auto-sensing" or "dual-speed" hubs.
|
|
Some switches have the ability to replicate all traffic on all ports to
|
|
a single port so that you can plug your analyzer into that single port
|
|
to sniff all traffic. You would have to check the documentation for the
|
|
switch to see if this is possible and, if so, to see how to do this.
|
|
See the switch reference page on the Wireshark Wiki for information on
|
|
some switches. (Note that it's a Wiki, so you can update or fix that
|
|
information, or add additional information on those switches or
|
|
information on new switches, yourself.)
|
|
Note also that many firewall/NAT boxes have a switch built into them;
|
|
this includes many of the "cable/DSL router" boxes. If you have a box
|
|
of that sort, that has a switch with some number of Ethernet ports into
|
|
which you plug machines on your network, and another Ethernet port used
|
|
to connect to a cable or DSL modem, you can, at least, sniff traffic
|
|
between the machines on your network and the Internet by plugging the
|
|
Ethernet port on the router going to the modem, the Ethernet port on
|
|
the modem, and the machine on which you're running Wireshark into a hub
|
|
(make sure it's not a switching hub, and that, if it's a dual-speed
|
|
hub, all three of those ports are running at the same speed.
|
|
If your machine is not plugged into a switched network or a dual-speed
|
|
hub, or it is plugged into a switched network but the port is set up to
|
|
have all traffic replicated to it, the problem might be that the
|
|
network interface on which you're capturing doesn't support
|
|
"promiscuous" mode, or because your OS can't put the interface into
|
|
promiscuous mode. Normally, network interfaces supply to the host only:
|
|
* packets sent to one of that host's link-layer addresses;
|
|
* broadcast packets;
|
|
* multicast packets sent to a multicast address that the host has
|
|
configured the interface to accept.
|
|
|
|
Most network interfaces can also be put in "promiscuous" mode, in which
|
|
they supply to the host all network packets they see. Wireshark will
|
|
try to put the interface on which it's capturing into promiscuous mode
|
|
unless the "Capture packets in promiscuous mode" option is turned off
|
|
in the "Capture Options" dialog box, and TShark will try to put the
|
|
interface on which it's capturing into promiscuous mode unless the -p
|
|
option was specified. However, some network interfaces don't support
|
|
promiscuous mode, and some OSes might not allow interfaces to be put
|
|
into promiscuous mode.
|
|
If the interface is not running in promiscuous mode, it won't see any
|
|
traffic that isn't intended to be seen by your machine. It will see
|
|
broadcast packets, and multicast packets sent to a multicast MAC
|
|
address the interface is set up to receive.
|
|
You should ask the vendor of your network interface whether it supports
|
|
promiscuous mode. If it does, you should ask whoever supplied the
|
|
driver for the interface (the vendor, or the supplier of the OS you're
|
|
running on your machine) whether it supports promiscuous mode with that
|
|
network interface.
|
|
In the case of token ring interfaces, the drivers for some of them, on
|
|
Windows, may require you to enable promiscuous mode in order to capture
|
|
in promiscuous mode. See the Wireshark Wiki item on Token Ring
|
|
capturing for details.
|
|
In the case of wireless LAN interfaces, it appears that, when those
|
|
interfaces are promiscuously sniffing, they're running in a
|
|
significantly different mode from the mode that they run in when
|
|
they're just acting as network interfaces (to the extent that it would
|
|
be a significant effor for those drivers to support for promiscuously
|
|
sniffing and acting as regular network interfaces at the same time), so
|
|
it may be that Windows drivers for those interfaces don't support
|
|
promiscuous mode.
|
|
|
|
Q 7.2: When I capture with Wireshark, why can't I see any TCP packets
|
|
other than packets to and from my machine, even though another analyzer
|
|
on the network sees those packets?
|
|
|
|
A: You're probably not seeing any packets other than unicast packets to
|
|
or from your machine, and broadcast and multicast packets; a switch
|
|
will normally send to a port only unicast traffic sent to the MAC
|
|
address for the interface on that port, and broadcast and multicast
|
|
traffic - it won't send to that port unicast traffic sent to a MAC
|
|
address for some other interface - and a network interface not in
|
|
promiscuous mode will receive only unicast traffic sent to the MAC
|
|
address for that interface, broadcast traffic, and multicast traffic
|
|
sent to a multicast MAC address the interface is set up to receive.
|
|
TCP doesn't use broadcast or multicast, so you will only see your own
|
|
TCP traffic, but UDP services may use broadcast or multicast so you'll
|
|
see some UDP traffic - however, this is not a problem with TCP traffic,
|
|
it's a problem with unicast traffic, as you also won't see all UDP
|
|
traffic between other machines.
|
|
I.e., this is probably the same question as this earlier one; see the
|
|
response to that question.
|
|
|
|
Q 7.3: Why am I only seeing ARP packets when I try to capture traffic?
|
|
|
|
A: You're probably on a switched network, and running Wireshark on a
|
|
machine that's not sending traffic to the switch and not being sent any
|
|
traffic from other machines on the switch. ARP packets are often
|
|
broadcast packets, which are sent to all switch ports.
|
|
I.e., this is probably the same question as this earlier one; see the
|
|
response to that question.
|
|
|
|
Q 7.4: Why am I not seeing any traffic when I try to capture traffic?
|
|
|
|
A: Is the machine running Wireshark sending out any traffic on the
|
|
network interface on which you're capturing, or receiving any traffic
|
|
on that network, or is there any broadcast traffic on the network or
|
|
multicast traffic to a multicast group to which the machine running
|
|
Wireshark belongs?
|
|
If not, this may just be a problem with promiscuous sniffing, either
|
|
due to running on a switched network or a dual-speed hub, or due to
|
|
problems with the interface not supporting promiscuous mode; see the
|
|
response to this earlier question.
|
|
Otherwise, on Windows, see the response to this question and, on a
|
|
UNIX-flavored OS, see the response to this question.
|
|
|
|
Q 7.5: Can Wireshark capture on (my T1/E1 line, SS7 links, etc.)?
|
|
|
|
A: Wireshark can only capture on devices supported by libpcap/WinPcap.
|
|
On most OSes, only devices that can act as network interfaces of the
|
|
type that support IP are supported as capture devices for
|
|
libpcap/WinPcap, although the device doesn't necessarily have to be
|
|
running as an IP interface in order to support traffic capture.
|
|
On Linux and FreeBSD, libpcap 0.8 and later support the API for Endace
|
|
Measurement Systems' DAG cards, so that a system with one of those
|
|
cards, and its driver and libraries, installed can capture traffic with
|
|
those cards with libpcap-based applications. You would either have to
|
|
have a version of Wireshark built with that version of libpcap, or a
|
|
dynamically-linked version of Wireshark and a shared libpcap library
|
|
with DAG support, in order to do so with Wireshark. You should ask
|
|
Endace whether that could be used to capture traffic on, for example,
|
|
your T1/E1 link.
|
|
See the SS7 capture setup page on the Wireshark Wiki for current
|
|
information on capturing SS7 traffic on TDM links.
|
|
|
|
Q 7.6: How do I put an interface into promiscuous mode?
|
|
|
|
A: By not disabling promiscuous mode when running Wireshark or TShark.
|
|
Note, however, that:
|
|
* the form of promiscuous mode that libpcap (the library that
|
|
programs such as tcpdump, Wireshark, etc. use to do packet capture)
|
|
turns on will not necessarily be shown if you run ifconfig on the
|
|
interface on a UNIX system;
|
|
* some network interfaces might not support promiscuous mode, and
|
|
some drivers might not allow promiscuous mode to be turned on - see
|
|
this earlier question for more information on that;
|
|
* the fact that you're not seeing any traffic, or are only seeing
|
|
broadcast traffic, or aren't seeing any non-broadcast traffic other
|
|
than traffic to or from the machine running Wireshark, does not
|
|
mean that promiscuous mode isn't on - see this earlier question for
|
|
more information on that.
|
|
|
|
I.e., this is probably the same question as this earlier one; see the
|
|
response to that question.
|
|
|
|
Q 7.7: I can set a display filter just fine; why don't capture filters
|
|
work?
|
|
|
|
A: Capture filters currently use a different syntax than display
|
|
filters. Here's the corresponding section from the wireshark(1) man
|
|
page:
|
|
"Display filters in Wireshark are very powerful; more fields are
|
|
filterable in Wireshark than in other protocol analyzers, and the
|
|
syntax you can use to create your filters is richer. As Wireshark
|
|
progresses, expect more and more protocol fields to be allowed in
|
|
display filters.
|
|
Packet capturing is performed with the pcap library. The capture filter
|
|
syntax follows the rules of the pcap library. This syntax is different
|
|
from the display filter syntax."
|
|
The capture filter syntax used by libpcap can be found in the
|
|
tcpdump(8) man page.
|
|
|
|
Q 7.8: I'm entering valid capture filters; why do I still get "parse
|
|
error" errors?
|
|
|
|
A: There is a bug in some versions of libpcap/WinPcap that cause it to
|
|
report parse errors even for valid expressions if a previous filter
|
|
expression was invalid and got a parse error.
|
|
Try exiting and restarting Wireshark; if you are using a version of
|
|
libpcap/WinPcap with this bug, this will "erase" its memory of the
|
|
previous parse error. If the capture filter that got the "parse error"
|
|
now works, the earlier error with that filter was probably due to this
|
|
bug.
|
|
The bug was fixed in libpcap 0.6; 0.4[.x] and 0.5[.x] versions of
|
|
libpcap have this bug, but 0.6[.x] and later versions don't.
|
|
Versions of WinPcap prior to 2.3 are based on pre-0.6 versions of
|
|
libpcap, and have this bug; WinPcap 2.3 is based on libpcap 0.6.2, and
|
|
doesn't have this bug.
|
|
If you are running Wireshark on a UNIX-flavored platform, run
|
|
"wireshark -v", or select "About Wireshark..." from the "Help" menu in
|
|
Wireshark, to see what version of libpcap it's using. If it's not 0.6
|
|
or later, you will need either to upgrade your OS to get a later
|
|
version of libpcap, or will need to build and install a later version
|
|
of libpcap from the tcpdump.org Web site and then recompile Wireshark
|
|
from source with that later version of libpcap.
|
|
If you are running Wireshark on Windows with a pre-2.3 version of
|
|
WinPcap, you will need to un-install WinPcap and then download and
|
|
install WinPcap 2.3.
|
|
|
|
Q 7.9: How can I capture packets with CRC errors?
|
|
|
|
A: Wireshark can capture only the packets that the packet capture
|
|
library - libpcap on UNIX-flavored OSes, and the WinPcap port to
|
|
Windows of libpcap on Windows - can capture, and libpcap/WinPcap can
|
|
capture only the packets that the OS's raw packet capture mechanism (or
|
|
the WinPcap driver, and the underlying OS networking code and network
|
|
interface drivers, on Windows) will allow it to capture.
|
|
Unless the OS always supplies packets with errors such as invalid CRCs
|
|
to the raw packet capture mechanism, or can be configured to do so,
|
|
invalid CRCs to the raw packet capture mechanism, Wireshark - and other
|
|
programs that capture raw packets, such as tcpdump - cannot capture
|
|
those packets. You will have to determine whether your OS needs to be
|
|
so configured and, if so, can be so configured, configure it if
|
|
necessary and possible, and make whatever changes to libpcap and the
|
|
packet capture program you're using are necessary, if any, to support
|
|
capturing those packets.
|
|
Most OSes probably do not support capturing packets with invalid CRCs
|
|
on Ethernet, and probably do not support it on most other link-layer
|
|
types. Some drivers on some OSes do support it, such as some Ethernet
|
|
drivers on FreeBSD; in those OSes, you might always get those packets,
|
|
or you might only get them if you capture in promiscuous mode (you'd
|
|
have to determine which is the case).
|
|
Note that libpcap does not currently supply to programs that use it an
|
|
indication of whether the packet's CRC was invalid (because the drivers
|
|
themselves do not supply that information to the raw packet capture
|
|
mechanism); therefore, Wireshark will not indicate which packets had
|
|
CRC errors unless the FCS was captured (see the next question) and
|
|
you're using Wireshark 0.9.15 and later, in which case Wireshark will
|
|
check the CRC and indicate whether it's correct or not.
|
|
|
|
Q 7.10: How can I capture entire frames, including the FCS?
|
|
|
|
A: Wireshark can only capture data that the packet capture library -
|
|
libpcap on UNIX-flavored OSes, and the WinPcap port to Windows of
|
|
libpcap on Windows - can capture, and libpcap/WinPcap can capture only
|
|
the data that the OS's raw packet capture mechanism (or the WinPcap
|
|
driver, and the underlying OS networking code and network interface
|
|
drivers, on Windows) will allow it to capture.
|
|
For any particular link-layer network type, unless the OS supplies the
|
|
FCS of a frame as part of the frame, or can be configured to do so,
|
|
Wireshark - and other programs that capture raw packets, such as
|
|
tcpdump - cannot capture the FCS of a frame. You will have to determine
|
|
whether your OS needs to be so configured and, if so, can be so
|
|
configured, configure it if necessary and possible, and make whatever
|
|
changes to libpcap and the packet capture program you're using are
|
|
necessary, if any, to support capturing the FCS of a frame.
|
|
Most OSes do not support capturing the FCS of a frame on Ethernet, and
|
|
probably do not support it on most other link-layer types. Some drivres
|
|
on some OSes do support it, such as some (all?) Ethernet drivers on
|
|
NetBSD and possibly the driver for Apple's gigabit Ethernet interface
|
|
in Mac OS X; in those OSes, you might always get the FCS, or you might
|
|
only get the FCS if you capture in promiscuous mode (you'd have to
|
|
determine which is the case).
|
|
Versions of Wireshark prior to 0.9.15 will not treat an Ethernet FCS in
|
|
a captured packet as an FCS. 0.9.15 and later will attempt to determine
|
|
whether there's an FCS at the end of the frame and, if it thinks there
|
|
is, will display it as such, and will check whether it's the correct
|
|
CRC-32 value or not.
|
|
|
|
Q 7.11: I'm capturing packets on a machine on a VLAN; why don't the
|
|
packets I'm capturing have VLAN tags?
|
|
|
|
A: You might be capturing on what might be called a "VLAN interface" -
|
|
the way a particular OS makes VLANs plug into the networking stack
|
|
might, for example, be to have a network device object for the physical
|
|
interface, which takes VLAN packets, strips off the VLAN header and
|
|
constructs an Ethernet header, and passes that packet to an internal
|
|
network device object for the VLAN, which then passes the packets onto
|
|
various higher-level protocol implementations.
|
|
In order to see the raw Ethernet packets, rather than "de-VLANized"
|
|
packets, you would have to capture not on the virtual interface for the
|
|
VLAN, but on the interface corresponding to the physical network
|
|
device, if possible. See the Wireshark Wiki item on VLAN capturing for
|
|
details.
|
|
|
|
Q 7.12: Why does Wireshark hang after I stop a capture?
|
|
|
|
A: The most likely reason for this is that Wireshark is trying to look
|
|
up an IP address in the capture to convert it to a name (so that, for
|
|
example, it can display the name in the source address or destination
|
|
address columns), and that lookup process is taking a very long time.
|
|
Wireshark calls a routine in the OS of the machine on which it's
|
|
running to convert of IP addresses to the corresponding names. That
|
|
routine probably does one or more of:
|
|
* a search of a system file listing IP addresses and names;
|
|
* a lookup using DNS;
|
|
* on UNIX systems, a lookup using NIS;
|
|
* on Windows systems, a NetBIOS-over-TCP query.
|
|
|
|
If a DNS server that's used in an address lookup is not responding, the
|
|
lookup will fail, but will only fail after a timeout while the system
|
|
routine waits for a reply.
|
|
In addition, on Windows systems, if the DNS lookup of the address
|
|
fails, either because the server isn't responding or because there are
|
|
no records in the DNS that could be used to map the address to a name,
|
|
a NetBIOS-over-TCP query will be made. That query involves sending a
|
|
message to the NetBIOS-over-TCP name service on that machine, asking
|
|
for the name and other information about the machine. If the machine
|
|
isn't running software that responds to those queries - for example,
|
|
many non-Windows machines wouldn't be running that software - the
|
|
lookup will only fail after a timeout. Those timeouts can cause the
|
|
lookup to take a long time.
|
|
If you disable network address-to-name translation - for example, by
|
|
turning off the "Enable network name resolution" option in the "Capture
|
|
Options" dialog box for starting a network capture - the lookups of the
|
|
address won't be done, which may speed up the process of reading the
|
|
capture file after the capture is stopped. You can make that setting
|
|
the default by selecting "Preferences" from the "Edit" menu, turning
|
|
off the "Enable network name resolution" option in the "Name
|
|
resolution" options in the preferences disalog box, and using the
|
|
"Save" button in that dialog box; note that this will save all your
|
|
current preference settings.
|
|
If Wireshark hangs when reading a capture even with network name
|
|
resolution turned off, there might, for example, be a bug in one of
|
|
Wireshark's dissectors for a protocol causing it to loop infinitely. If
|
|
you're not running the most recent release of Wireshark, you should
|
|
first upgrade to that release, as, if there's a bug of that sort, it
|
|
might've been fixed in a release after the one you're running. If the
|
|
hang occurs in the most recent release of Wireshark, the bug should be
|
|
reported to the Wireshark developers' mailing list at
|
|
wireshark-dev@wireshark.org.
|
|
On UNIX-flavored OSes, please try to force Wireshark to dump core, by
|
|
sending it a SIGABRT signal (usually signal 6) with the kill command,
|
|
and then get a stack trace if you have a debugger installed. A stack
|
|
trace can be obtained by using your debugger (gdb in this example), the
|
|
Wireshark binary, and the resulting core file. Here's an example of how
|
|
to use the gdb command backtrace to do so.
|
|
$ gdb wireshark core
|
|
(gdb) backtrace
|
|
..... prints the stack trace
|
|
(gdb) quit
|
|
$
|
|
|
|
The core dump file may be named "wireshark.core" rather than "core" on
|
|
some platforms (e.g., BSD systems).
|
|
Also, if at all possible, please send a copy of the capture file that
|
|
caused the problem; when capturing packets, Wireshark normally writes
|
|
captured packets to a temporary file, which will probably be in /tmp or
|
|
/var/tmp on UNIX-flavored OSes, \TEMP on the main system disk (normally
|
|
C:) on Windows 9x/Me/NT 4.0, and \Documents and Settings\your login
|
|
name\Local Settings\Temp on the main system disk on Windows
|
|
2000/Windows XP/Windows Server 2003, so the capture file will probably
|
|
be there. It will have a name beginning with ether, with some mixture
|
|
of letters and numbers after that. Please don't send a trace file
|
|
greater than 1 MB when compressed; instead, make it available via FTP
|
|
or HTTP, or say it's available but leave it up to a developer to ask
|
|
for it. If the trace file contains sensitive information (e.g.,
|
|
passwords), then please do not send it.
|
|
|
|
8. Capturing packets on Windows
|
|
|
|
Q 8.1: I'm running Wireshark on Windows; why does some network
|
|
interface on my machine not show up in the list of interfaces in the
|
|
"Interface:" field in the dialog box popped up by "Capture->Start",
|
|
and/or why does Wireshark give me an error if I try to capture on that
|
|
interface?
|
|
|
|
A: If you are running Wireshark on Windows NT 4.0, Windows 2000,
|
|
Windows XP, or Windows Server 2003, and this is the first time you have
|
|
run a WinPcap-based program (such as Wireshark, or TShark, or WinDump,
|
|
or Analyzer, or...) since the machine was rebooted, you need to run
|
|
that program from an account with administrator privileges; once you
|
|
have run such a program, you will not need administrator privileges to
|
|
run any such programs until you reboot.
|
|
If you are running on Windows Windows 2000/Windows XP/Windows Server
|
|
2003 and have administrator privileges or a WinPcap-based program has
|
|
been run with those privileges since the machine rebooted, this problem
|
|
might clear up if you completely un-install WinPcap and then re-install
|
|
it.
|
|
If that doesn't work, then note that Wireshark relies on the WinPcap
|
|
library, on the WinPcap device driver, and on the facilities that come
|
|
with the OS on which it's running in order to do captures.
|
|
Therefore, if the OS, the WinPcap library, or the WinPcap driver don't
|
|
support capturing on a particular network interface device, Wireshark
|
|
won't be able to capture on that device.
|
|
Note that:
|
|
1. 2.02 and earlier versions of the WinPcap driver and library that
|
|
Wireshark uses for packet capture didn't support Token Ring
|
|
interfaces; versions 2.1 and later support Token Ring, and the
|
|
current version of Wireshark works with (and, in fact, requires)
|
|
WinPcap 2.1 or later.
|
|
If you are having problems capturing on Token Ring interfaces, and
|
|
you have WinPcap 2.02 or an earlier version of WinPcap installed,
|
|
you should uninstall WinPcap, download and install the current
|
|
version of WinPcap, and then install the latest version of
|
|
Wireshark.
|
|
2. 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.
|
|
3. 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 libcap 0.7.2 and later.
|
|
If an interface doesn't show up in the list of interfaces in the
|
|
"Interface:" field, and you know the name of the interface, try
|
|
entering that name in the "Interface:" field and capturing on that
|
|
device.
|
|
If the attempt to capture on it succeeds, the interface is somehow not
|
|
being reported by the mechanism Wireshark uses to get a list of
|
|
interfaces; please report this to wireshark-dev@wireshark.org giving
|
|
full details of the problem, including
|
|
* the operating system you're using, and the version of that
|
|
operating system (for Linux, give both the version number of the
|
|
kernel and the name and version number of the distribution you're
|
|
using);
|
|
* the type of network device you're using.
|
|
|
|
If you are having trouble capturing on a particular network interface,
|
|
and you've made sure that (on platforms that require it) you've
|
|
arranged that packet capture support is present, as per the above,
|
|
first try capturing on that device with tcpdump.
|
|
If you can capture on the interface with tcpdump, send mail to
|
|
wireshark-users@wireshark.org giving full details of the problem,
|
|
including
|
|
* the operating system you're using, and the version of that
|
|
operating system (for Linux, give both the version number of the
|
|
kernel and the name and version number of the distribution you're
|
|
using);
|
|
* the type of network device you're using;
|
|
* the error message you get from Wireshark.
|
|
|
|
If you cannot capture on the interface with tcpdump, this is almost
|
|
certainly a problem with one or more of:
|
|
* the operating system you're using;
|
|
* the device driver for the interface you're using;
|
|
* the libpcap library;
|
|
|
|
so you should report the problem to the company or organization that
|
|
produces the OS (in the case of a Linux distribution, report the
|
|
problem to whoever produces the distribution).
|
|
You may also want to ask the wireshark-users@wireshark.org and the
|
|
tcpdump-workers@tcpdump.org mailing lists to see if anybody happens to
|
|
know about the problem and know a workaround or fix for the problem. In
|
|
your mail, please give full details of the problem, as described above,
|
|
and also indicate that the problem occurs with tcpdump not just with
|
|
Wireshark.
|
|
|
|
Q 9.2: I'm running Wireshark on a UNIX-flavored OS; why do no network
|
|
interfaces show up in the list of interfaces in the "Interface:" field
|
|
in the dialog box popped up by "Capture->Start"?
|
|
|
|
A: This is really the same question as the previous one; see the
|
|
response to that question.
|
|
|
|
Q 9.3: I'm capturing packets on Linux; why do the time stamps have only
|
|
100ms resolution, rather than 1us resolution?
|
|
|
|
A: Wireshark gets time stamps from libpcap/WinPcap, and libpcap/WinPcap
|
|
get them from the OS kernel, so Wireshark - and any other program using
|
|
libpcap, such as tcpdump - is at the mercy of the time stamping code in
|
|
the OS for time stamps.
|
|
At least on x86-based machines, Linux can get high-resolution time
|
|
stamps on newer processors with the Time Stamp Counter (TSC) register;
|
|
for example, Intel x86 processors, starting with the Pentium Pro, and
|
|
including all x86 processors since then, have had a TSC, and other
|
|
vendors probably added the TSC at some point to their families of x86
|
|
processors. The Linux kernel must be configured with the CONFIG_X86_TSC
|
|
option enabled in order to use the TSC. Make sure this option is
|
|
enabled in your kernel.
|
|
In addition, some Linux distributions may have bugs in their versions
|
|
of the kernel that cause packets not to be given high-resolution time
|
|
stamps even if the TSC is enabled. See, for example, bug 61111 for Red
|
|
Hat Linux 7.2. If your distribution has a bug such as this, you may
|
|
have to run a standard kernel from kernel.org in order to get
|
|
high-resolution time stamps.
|
|
|
|
10. Capturing packets on wireless LANs
|
|
|
|
Q 10.1: How can I capture raw 802.11 frames, including non-data
|
|
(management, beacon) frames?
|
|
|
|
A: That depends on the operating system on which you're running, and on
|
|
the 802.11 interface on which you're capturing.
|
|
This would probably require that you capture in promiscuous mode or in
|
|
the mode called "monitor mode" or "RFMON mode". On some platforms, or
|
|
with some cards, this might require that you capture in monitor mode -
|
|
promiscuous mode might not be sufficient. If you want to capture
|
|
traffic on networks other than the one with which you're associated,
|
|
you will have to capture in monitor mode.
|
|
Not all operating systems support capturing non-data packets and, even
|
|
on operating systems that do support it, not all drivers, and thus not
|
|
all interfaces, support it. Even on those that do, monitor mode might
|
|
not be supported by the operating system or by the drivers for all
|
|
interfaces.
|
|
NOTE: an interface running in monitor mode will, on most if not all
|
|
platforms, not be able to act as a regular network interface; putting
|
|
it into monitor mode will, in effect, take your machine off of whatever
|
|
network it's on as long as the interface is in monitor mode, allowing
|
|
it only to passively capture packets.
|
|
This means that you should disable name resolution when capturing in
|
|
monitor mode; otherwise, when Wireshark (or TShark, or tcpdump) tries
|
|
to display IP addresses as host names, it will probably block for a
|
|
long time trying to resolve the name because it will not be able to
|
|
communicate with any DNS or NIS servers.
|
|
See the Wireshark Wiki item on 802.11 capturing for details.
|
|
|
|
Q 10.2: How do I capture on an 802.11 device in monitor mode?
|
|
|
|
A: Whether you will be able to capture in monitor mode depends on the
|
|
operating system, adapter, and driver you're using. See the previous
|
|
question for information on monitor mode, including a link to the
|
|
Wireshark Wiki page that gives details on 802.11 capturing.
|
|
|
|
11. Viewing traffic
|
|
|
|
Q 11.1: Why am I seeing lots of packets with incorrect TCP checksums?
|
|
|
|
A: If the packets that have incorrect TCP checksums are all being sent
|
|
by the machine on which Wireshark is running, this is probably because
|
|
the network interface on which you're capturing does TCP checksum
|
|
offloading. That means that the TCP checksum is added to the packet by
|
|
the network interface, not by the OS's TCP/IP stack; when capturing on
|
|
an interface, packets being sent by the host on which you're capturing
|
|
are directly handed to the capture interface by the OS, which means
|
|
that they are handed to the capture interface without a TCP checksum
|
|
being added to them.
|
|
The only way to prevent this from happening would be to disable TCP
|
|
checksum offloading, but
|
|
1. that might not even be possible on some OSes;
|
|
2. that could reduce networking performance significantly.
|
|
|
|
However, you can disable the check that Wireshark does of the TCP
|
|
checksum, so that it won't report any packets as having TCP checksum
|
|
errors, and so that it won't refuse to do TCP reassembly due to a
|
|
packet having an incorrect TCP checksum. That can be set as an
|
|
Wireshark preference by selecting "Preferences" from the "Edit" menu,
|
|
opening up the "Protocols" list in the left-hand pane of the
|
|
"Preferences" dialog box, selecting "TCP", from that list, turning off
|
|
the "Check the validity of the TCP checksum when possible" option,
|
|
clicking "Save" if you want to save that setting in your preference
|
|
file, and clicking "OK".
|
|
It can also be set on the Wireshark or TShark command line with a -o
|
|
tcp.check_checksum:false command-line flag, or manually set in your
|
|
preferences file by adding a tcp.check_checksum:false line.
|
|
|
|
Q 11.2: I've just installed Wireshark, and the traffic on my local LAN
|
|
is boring. Where can I find more interesting captures?
|
|
|
|
A: We have a collection of strange and exotic sample capture files at
|
|
http://wiki.wireshark.org/SampleCaptures
|
|
|
|
Q 11.3: Why doesn't Wireshark correctly identify RTP packets? It shows
|
|
them only as UDP.
|
|
|
|
A: Wireshark can identify a UDP datagram as containing a packet of a
|
|
particular protocol running atop UDP only if
|
|
1. The protocol in question has a particular standard port number, and
|
|
the UDP source or destination port number is that port
|
|
2. Packets of that protocol can be identified by looking for a
|
|
"signature" of some type in the packet - i.e., some data that, if
|
|
Wireshark finds it in some particular part of a packet, means that
|
|
the packet is almost certainly a packet of that type.
|
|
3. Some other traffic earlier in the capture indicated that, for
|
|
example, UDP traffic between two particular addresses and ports
|
|
will be RTP traffic.
|
|
|
|
RTP doesn't have a standard port number, so 1) doesn't work; it
|
|
doesn't, as far as I know, have any "signature", so 2) doesn't work.
|
|
That leaves 3). If there's RTSP traffic that sets up an RTP session,
|
|
then, at least in some cases, the RTSP dissector will set things up so
|
|
that subsequent RTP traffic will be identified. Currently, that's the
|
|
only place we do that; there may be other places.
|
|
However, there will always be places where Wireshark is simply
|
|
incapable of deducing that a given UDP flow is RTP; a mechanism would
|
|
be needed to allow the user to specify that a given conversation should
|
|
be treated as RTP. As of Wireshark 0.8.16, such a mechanism exists; if
|
|
you select a UDP or TCP packet, the right mouse button menu will have a
|
|
"Decode As..." menu item, which will pop up a dialog box letting you
|
|
specify that the source port, the destination port, or both the source
|
|
and destination ports of the packet should be dissected as some
|
|
particular protocol.
|
|
|
|
Q 11.4: Why doesn't Wireshark show Yahoo Messenger packets in captures
|
|
that contain Yahoo Messenger traffic?
|
|
|
|
A: Wireshark only recognizes as Yahoo Messenger traffic packets to or
|
|
from TCP port 3050 that begin with "YPNS", "YHOO", or "YMSG". TCP
|
|
segments that start with the middle of a Yahoo Messenger packet that
|
|
takes more than one TCP segment will not be recognized as Yahoo
|
|
Messenger packets (even if the TCP segment also contains the beginning
|
|
of another Yahoo Messenger packet).
|
|
|
|
12. Filtering traffic
|
|
|
|
Q 12.1: I saved a filter and tried to use its name to filter the
|
|
display; why do I get an "Unexpected end of filter string" error?
|
|
|
|
A: You cannot use the name of a saved display filter as a filter. To
|
|
filter the display, you can enter a display filter expression - not the
|
|
name of a saved display filter - in the "Filter:" box at the bottom of
|
|
the display, and type the key or press the "Apply" button (that does
|
|
not require you to have a saved filter), or, if you want to use a saved
|
|
filter, you can press the "Filter:" button, select the filter in the
|
|
dialog box that pops up, and press the "OK" button.
|
|
|
|
Q 12.2: How can I search for, or filter, packets that have a particular
|
|
string anywhere in them?
|
|
|
|
A: If you want to do this when capturing, you can't. That's a feature
|
|
that would be hard to implement in capture filters without changes to
|
|
the capture filter code, which, on many platforms, is in the OS kernel
|
|
and, on other platforms, is in the libpcap library.
|
|
In releases prior to 0.9.14, you also can't search for, or filter,
|
|
packets containing a particular string even after you've captured them.
|
|
In 0.9.14, you can search for, but not filter, packets that have a
|
|
particular string; this has been added to the "Find Frame" dialog
|
|
("Find Frame" under the "Edit" menu, or control-F).
|
|
In 0.9.15 and later, you can search for those packets using either the
|
|
mechanism introduced in 0.9.14 or using the new "contains" operator in
|
|
filter expressions, which lets you search the entire packet or text
|
|
string or byte string fields in the packet; the "contains" operator can
|
|
also be used in expressions used to filter the display.
|
|
|
|
Q 12.3: How do I filter a capture to see traffic for virus XXX?
|
|
|
|
A: For some viruses/worms there might be a capture filter to recognize
|
|
the virus traffic. Check the CaptureFilters page on the Wireshark Wiki
|
|
to see if anybody's added such a filter.
|
|
Note that Wireshark was not designed to be an intrusion detection
|
|
system; you might be able to use it as an IDS, but in most cases
|
|
software designed to be an IDS, such as Snort or Prelude, will probably
|
|
work better.
|
|
The Bleeding Edge of Snort has a collection of signatures for Snort to
|
|
detect various viruses, worms, and the like.
|