To build libpcap, run “./configure” (a shell script). The configure script will determine your system attributes and generate an appropriate Makefile from Next run “make”. If everything goes well you can su to root and run “make install”. However, you need not install libpcap if you just want to build tcpdump; just make sure the tcpdump and libpcap directory trees have the same parent directory.

If configure says:

configure: warning: cannot determine packet capture interface
configure: warning: (see INSTALL for more info)

then your system either does not support packet capture or your system does support packet capture but libpcap does not support that particular type. (If you have HP-UX, see below.) If your system uses a packet capture not supported by libpcap, please send us patches; don't forget to include an autoconf fragment suitable for use in

It is possible to override the default packet capture type, although the circumstance where this works are limited. For example if you have installed bpf under SunOS 4 and wish to build a snit libpcap:

./configure --with-pcap=snit

Another example is to force a supported packet capture type in the case where the configure scripts fails to detect it.

You will need an ANSI C compiler to build libpcap. The configure script will abort if your compiler is not ANSI compliant. If this happens, use the generally available GNU C compiler (GCC).

You will need either Flex 2.5.31 or later, or a version of Lex compatible with it (if any exist), to build libpcap. The configure script will abort if there isn‘t any such program. If you have an older version of Flex, or don’t have a compatible version of Lex, the current version of flex is available at

You will need either Bison, Berkeley YACC, or a version of YACC compatible with them (if any exist), to build libpcap. The configure script will abort if there isn‘t any such program. If you don’t have any such program, the current version of Bison can be found at and the current version of Berkeley YACC can be found at

Sometimes the stock C compiler does not interact well with Flex and Bison. The list of problems includes undefined references for alloca. You can get around this by installing GCC.

If you use Solaris, there is a bug with bufmod(7) that is fixed in Solaris 2.3.2 (aka SunOS 5.3.2). Setting a snapshot length with the broken bufmod(7) results in data be truncated from the FRONT of the packet instead of the end. The work around is to not set a snapshot length but this results in performance problems since the entire packet is copied to user space. If you must run an older version of Solaris, there is a patch available from Sun; ask for bugid 1149065. After installing the patch, use “setenv BUFMOD_FIXED” to enable use of bufmod(7). However, we recommend you run a more current release of Solaris.

If you use the SPARCompiler, you must be careful to not use the /usr/ucb/cc interface. If you do, you will get bogus warnings and perhaps errors. Either make sure your path has /opt/SUNWspro/bin before /usr/ucb or else:

setenv CC /opt/SUNWspro/bin/cc

before running configure. (You might have to do a “make distclean” if you already ran configure once).

If you are trying to do packet capture with a FORE ATM card, you may or may not be able to. They usually only release their driver in object code so unless their driver supports packet capture, there's not much libpcap can do.

If you get an error like:

tcpdump: recv_ack: bind error 0x???

when using DLPI, look for the DL_ERROR_ACK error return values, usually in /usr/include/sys/dlpi.h, and find the corresponding value.

Under {DEC OSF/1, Digital UNIX, Tru64 UNIX}, packet capture must be enabled before it can be used. For instructions on how to enable packet filter support, see:

Look for the “How do I configure the Berkeley Packet Filter and capture tcpdump traces?” item.

Once you enable packet filter support, your OSF system will support bpf natively.

Under Ultrix, packet capture must be enabled before it can be used. For instructions on how to enable packet filter support, see:

If you use HP-UX, you must have at least version 9 and either the version of cc that supports ANSI C (cc -Aa) or else use the GNU C compiler. You must also buy the optional streams package. If you don't have:


then you don't have the streams package. In addition, we believe you need to install the “9.X LAN and DLPI drivers cumulative” patch (PHNE_6855) to make the version 9 DLPI work with libpcap.

The DLPI streams package is standard starting with HP-UX 10.

The HP implementation of DLPI is a little bit eccentric. Unlike Solaris, you must attach /dev/dlpi instead of the specific /dev/* network pseudo device entry in order to capture packets. The PPA is based on the ifnet “index” number. Under HP-UX 9, it is necessary to read /dev/kmem and the kernel symbol file (/hp-ux). Under HP-UX 10, DLPI can provide information for determining the PPA. It does not seem to be possible to trace the loopback interface. Unlike other DLPI implementations, PHYS implies MULTI and SAP and you get an error if you try to enable more than one promiscuous mode at a time.

It is impossible to capture outbound packets on HP-UX 9. To do so on HP-UX 10, you will, apparently, need a late “LAN products cumulative patch” (at one point, it was claimed that this would be PHNE_18173 for s700/10.20; at another point, it was claimed that the required patches were PHNE_20892, PHNE_20725 and PHCO_10947, or newer patches), and to do so on HP-UX 11 you will, apparently, need the latest lancommon/DLPI patches and the latest driver patch for the interface(s) in use on HP-UX 11 (at one point, it was claimed that patches PHNE_19766, PHNE_19826, PHNE_20008, and PHNE_20735 did the trick).

Furthermore, on HP-UX 10, you will need to turn on a kernel switch by doing

echo 'lanc_outbound_promisc_flag/W 1' | adb -w /stand/vmunix /dev/mem

You would have to arrange that this happen on reboots; the right way to do that would probably be to put it into an executable script file “/sbin/init.d/outbound_promisc” and making “/sbin/rc2.d/S350outbound_promisc” a symbolic link to that script.

Finally, testing shows that there can't be more than one simultaneous DLPI user per network interface.

If you use Linux, this version of libpcap is known to compile and run under Red Hat 4.0 with the 2.0.25 kernel. It may work with earlier 2.X versions but is guaranteed not to work with 1.X kernels. Running more than one libpcap program at a time, on a system with a 2.0.X kernel, can cause problems since promiscuous mode is implemented by twiddling the interface flags from the libpcap application; the packet capture mechanism in the 2.2 and later kernels doesn‘t have this problem. Also, packet timestamps aren’t very good. This appears to be due to haphazard handling of the timestamp in the kernel.

Note well: there is rumoured to be a version of tcpdump floating around called 3.0.3 that includes libpcap and is supposed to support Linux. You should be advised that neither the Network Research Group at LBNL nor the Tcpdump Group ever generated a release with this version number. The LBNL Network Research Group notes with interest that a standard cracker trick to get people to install trojans is to distribute bogus packages that have a version number higher than the current release. They also noted with annoyance that 90% of the Linux related bug reports they got are due to changes made to unofficial versions of their page. If you are having trouble but aren't using a version that came from, please try that before submitting a bug report!

On Linux, libpcap will not work if the kernel does not have the packet socket option enabled; see the README.linux file for information about this.

If you use AIX, you may not be able to build libpcap from this release. We do not have an AIX system in house so it's impossible for us to test AIX patches submitted to us. We are told that you must link against /lib/pse.exp, that you must use AIX cc or a GNU C compiler newer than 2.7.2, and that you may need to run strload before running a libpcap application.

Read the README.aix file for information on installing libpcap and configuring your system to be able to support libpcap.

If you use NeXTSTEP, you will not be able to build libpcap from this release.

If you use SINIX, you should be able to build libpcap from this release. It is known to compile and run on SINIX-Y/N 5.42 with the C-DS V1.0 or V1.1 compiler. But note that in some releases of SINIX, yacc emits incorrect code; if grammar.y fails to compile, change every occurence of:

#ifdef YYDEBUG

to: #if YYDEBUG

Another workaround is to use flex and bison.

If you use SCO, you might have trouble building libpcap from this release. We do not have a machine running SCO and have not had reports of anyone successfully building on it; the current release of libpcap does not compile on SCO OpenServer 5. Although SCO apparently supports DLPI to some extent, the DLPI in OpenServer 5 is very non-standard, and it appears that completely new code would need to be written to capture network traffic. SCO do not appear to provide tcpdump binaries for OpenServer 5 or OpenServer 6 as part of SCO Skunkware:

If you use UnixWare, you might be able to build libpcap from this release, or you might not. We do not have a machine running UnixWare, so we have not tested it; however, SCO provide packages for libpcap 0.6.2 and tcpdump 3.7.1 in the UnixWare 7/Open UNIX 8 part of SCO Skunkware, and the source package for libpcap 0.6.2 is not changed from the libpcap 0.6.2 source release, so this release of libpcap might also build without changes on UnixWare 7.

If linking tcpdump fails with “Undefined: _alloca” when using bison on a Sun4, your version of Bison is broken. In any case version 1.16 or higher is recommended (1.14 is known to cause problems 1.16 is known to work). Either pick up a current version from:

or hack around it by inserting the lines:

#ifdef __GNUC__
#define alloca __builtin_alloca
#ifdef sparc
#include <alloca.h>
char *alloca ();

right after the (100 line!) GNU license comment in bison.simple, remove grammar.[co] and fire up make again.

If you use SunOS 4, your kernel must support streams NIT. If you run a libpcap program and it dies with:

/dev/nit: No such device

You must add streams NIT support to your kernel configuration, run config and boot the new kernel.


CHANGES - description of differences between releases ChmodBPF/* - macOS startup item to set ownership and permissions on /dev/bpf* CMakeLists.txt - CMake file CONTRIBUTING - guidelines for contributing CREDITS - people that have helped libpcap along - this file LICENSE - the license under which tcpdump is distributed - compilation rules (input to the configure script) - description of distribution doc/README.aix - notes on using libpcap on AIX doc/README.dag - notes on using libpcap to capture on Endace DAG devices doc/README.hpux - notes on using libpcap on HP-UX doc/ - notes on using libpcap on Linux doc/README.macos - notes on using libpcap on macOS doc/README.septel - notes on using libpcap to capture on Intel/Septel devices doc/README.sita - notes on using libpcap to capture on SITA devices doc/README.tru64 - notes on using libpcap on Digital/Tru64 UNIX doc/README.Win32 - notes on using libpcap on Win32 systems (with WinPcap) VERSION - version of this release acconfig.h - support for post-2.13 autoconf aclocal.m4 - autoconf macros arcnet.h - ARCNET definitions atmuni31.h - ATM Q.2931 definitions bpf/net - copy of bpf_filter.c bpf_dump.c - BPF program printing routines bpf_filter.c - symlink to bpf/net/bpf_filter.c bpf_image.c - BPF disassembly routine config.guess - autoconf support - autoconf input config.sub - autoconf support configure - configure script (run this first) - configure script source dlpisubs.c - DLPI-related functions for pcap-dlpi.c and pcap-libdlpi.c dlpisubs.h - DLPI-related function declarations etherent.c - /etc/ethers support routines ethertype.h - Ethernet protocol types and names definitions fad-getad.c - pcap_findalldevs() for systems with getifaddrs() fad-gifc.c - pcap_findalldevs() for systems with only SIOCGIFLIST fad-glifc.c - pcap_findalldevs() for systems with SIOCGLIFCONF filtertest.c - test program for BPF compiler findalldevstest.c - test program for pcap_findalldevs() gencode.c - BPF code generation routines gencode.h - BPF code generation definitions grammar.y - filter string grammar ieee80211.h - 802.11 definitions install-sh - BSD style install script lbl/os-.h - OS-dependent defines and prototypes llc.h - 802.2 LLC SAP definitions missing/ - replacements for missing library functions mkdep - construct Makefile dependency list msdos/* - drivers for MS-DOS capture support nametoaddr.c - hostname to address routines nlpid.h - OSI network layer protocol identifier definitions net - symlink to bpf/net optimize.c - BPF optimization routines pcap/bluetooth.h - public definition of DLT_BLUETOOTH_HCI_H4_WITH_PHDR header pcap/bpf.h - BPF definitions pcap/namedb.h - public libpcap name database definitions pcap/pcap.h - public libpcap definitions pcap/sll.h - public definition of DLT_LINUX_SLL header pcap/usb.h - public definition of DLT_USB header pcap-bpf.c - BSD Packet Filter support pcap-bpf.h - header for backwards compatibility pcap-bt-linux.c - Bluetooth capture support for Linux pcap-bt-linux.h - Bluetooth capture support for Linux pcap-dag.c - Endace DAG device capture support pcap-dag.h - Endace DAG device capture support pcap-dlpi.c - Data Link Provider Interface support pcap-dos.c - MS-DOS capture support pcap-dos.h - headers for MS-DOS capture support pcap-enet.c - enet support pcap-int.h - internal libpcap definitions pcap-libdlpi.c - Data Link Provider Interface support for systems with libdlpi pcap-linux.c - Linux packet socket support pcap-namedb.h - header for backwards compatibility pcap-nit.c - SunOS Network Interface Tap support pcap-nit.h - SunOS Network Interface Tap definitions pcap-npf.c - WinPcap capture support pcap-null.c - dummy monitor support (allows offline use of libpcap) pcap-pf.c - Ultrix and Digital/Tru64 UNIX Packet Filter support pcap-pf.h - Ultrix and Digital/Tru64 UNIX Packet Filter definitions pcap-septel.c - Intel/Septel device capture support pcap-septel.h - Intel/Septel device capture support pcap-sita.c - SITA device capture support pcap-sita.h - SITA device capture support pcap-sita.html - SITA device capture documentation pcap-stdinc.h - includes and #defines for compiling on Win32 systems pcap-snit.c - SunOS 4.x STREAMS-based Network Interface Tap support pcap-snoop.c - IRIX Snoop network monitoring support pcap-usb-linux.c - USB capture support for Linux pcap-usb-linux.h - USB capture support for Linux pcap.3pcap - manual entry for the library pcap.c - pcap utility routines pcap.h - header for backwards compatibility pcap_*.3pcap - manual entries for library functions pcap-filter.4 - manual entry for filter syntax pcap-linktype.4 - manual entry for link-layer header types ppp.h - Point to Point Protocol definitions savefile.c - offline support scanner.l - filter string scanner sunatmpos.h - definitions for SunATM capturing Win32 - headers and routines for building on Win32 systems