README.md
1 To report a security issue please send an e-mail to security (a] tcpdump.org. 2 3 To report bugs and other problems, contribute patches, request a 4 feature, provide generic feedback etc please see the file 5 [CONTRIBUTING](CONTRIBUTING.md) in the libpcap source tree root. 6 7 The directory doc/ has README files about specific operating systems and 8 options. 9 10 LIBPCAP 1.x.y 11 Now maintained by "The Tcpdump Group" 12 https://www.tcpdump.org 13 14 Anonymous Git is available via: 15 https://github.com/the-tcpdump-group/libpcap.git 16 17 formerly from Lawrence Berkeley National Laboratory 18 Network Research Group <libpcap (a] ee.lbl.gov> 19 ftp://ftp.ee.lbl.gov/old/libpcap-0.4a7.tar.Z 20 21 This directory contains source code for libpcap, a system-independent 22 interface for user-level packet capture. libpcap provides a portable 23 framework for low-level network monitoring. Applications include 24 network statistics collection, security monitoring, network debugging, 25 etc. Since almost every system vendor provides a different interface 26 for packet capture, and since we've developed several tools that 27 require this functionality, we've created this system-independent API 28 to ease in porting and to alleviate the need for several 29 system-dependent packet capture modules in each application. 30 31 For some platforms there are README.{system} files that discuss issues 32 with the OS's interface for packet capture on those platforms, such as 33 how to enable support for that interface in the OS, if it's not built in 34 by default. 35 36 The libpcap interface supports a filtering mechanism based on the 37 architecture in the BSD packet filter. BPF is described in the 1993 38 Winter Usenix paper ``The BSD Packet Filter: A New Architecture for 39 User-level Packet Capture''. A compressed PostScript version can be 40 found at 41 42 ftp://ftp.ee.lbl.gov/papers/bpf-usenix93.ps.Z 43 44 or 45 46 https://www.tcpdump.org/papers/bpf-usenix93.ps.Z 47 48 and a gzipped version can be found at 49 50 https://www.tcpdump.org/papers/bpf-usenix93.ps.gz 51 52 A PDF version can be found at 53 54 https://www.tcpdump.org/papers/bpf-usenix93.pdf 55 56 Although most packet capture interfaces support in-kernel filtering, 57 libpcap utilizes in-kernel filtering only for the BPF interface. 58 On systems that don't have BPF, all packets are read into user-space 59 and the BPF filters are evaluated in the libpcap library, incurring 60 added overhead (especially, for selective filters). Ideally, libpcap 61 would translate BPF filters into a filter program that is compatible 62 with the underlying kernel subsystem, but this is not yet implemented. 63 64 BPF is standard in 4.4BSD, BSD/OS, NetBSD, FreeBSD, OpenBSD, DragonFly 65 BSD, and macOS; an older, modified and undocumented version is standard 66 in AIX. {DEC OSF/1, Digital UNIX, Tru64 UNIX} uses the packetfilter 67 interface but has been extended to accept BPF filters (which libpcap 68 utilizes). Also, you can add BPF filter support to Ultrix using the 69 kernel source and/or object patches available in: 70 71 https://www.tcpdump.org/other/bpfext42.tar.Z 72 73 Linux has a number of BPF based systems, and libpcap does not support 74 any of the eBPF mechanisms as yet, although it supports many of the 75 memory mapped receive mechanisms. 76 See the [README.linux](doc/README.linux.md) file for more information. 77 78 Note to Linux distributions and *BSD systems that include libpcap: 79 80 There's now a rule to make a shared library, which should work on Linux 81 and *BSD, among other platforms. 82 83 It sets the soname of the library to "libpcap.so.1"; this is what it 84 should be, *NOT* libpcap.so.1.x or libpcap.so.1.x.y or something such as 85 that. 86 87 We've been maintaining binary compatibility between libpcap releases for 88 quite a while; there's no reason to tie a binary linked with libpcap to 89 a particular release of libpcap. 90 91 Current versions can be found at https://www.tcpdump.org. 92 93 - The TCPdump group 94
