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2ac58aef3f
this is because the enc link type header which is supposed to have an address family field is populated by the kernel in the hosts native endian when it should be in a consistent order no matter what type of cpu it is run on. this re-uses the DLT_RAW handling to look at the ip version field.
$OpenBSD: README,v 1.7 2014/04/11 04:08:58 lteo Exp $ $NetBSD: README,v 1.2 1995/03/06 11:38:07 mycroft Exp $ LIBPCAP 0.5 Now maintained by "The Tcpdump Group" Send patches to patches@tcpdump.org See www.tcpdump.org formerly from Lawrence Berkeley National Laboratory Network Research Group <libpcap@ee.lbl.gov> ftp://ftp.ee.lbl.gov/libpcap.tar.Z (0.4) This directory contains source code for libpcap, a system-independent interface for user-level packet capture. libpcap provides a portable framework for low-level network monitoring. Applications include network statistics collection, security monitoring, network debugging, etc. Since almost every system vendor provides a different interface for packet capture, and since we've developed several tools that require this functionality, we've created this system-independent API to ease in porting and to alleviate the need for several system-dependent packet capture modules in each application. Note well: this interface is new and is likely to change. The libpcap interface supports a filtering mechanism based on the architecture in the BSD packet filter. BPF is described in the 1993 Winter Usenix paper ``The BSD Packet Filter: A New Architecture for User-level Packet Capture''. A compressed postscript version is in: ftp://ftp.ee.lbl.gov/papers/bpf-usenix93.ps.Z. Although most packet capture interfaces support in-kernel filtering, libpcap utilizes in-kernel filtering only for the BPF interface. On systems that don't have BPF, all packets are read into user-space and the BPF filters are evaluated in the libpcap library, incurring added overhead (especially, for selective filters). Ideally, libpcap would translate BPF filters into a filter program that is compatible with the underlying kernel subsystem, but this is not yet implemented. BPF is standard in 4.4BSD, BSD/386, NetBSD, and FreeBSD. DEC OSF/1 uses the packetfilter interface but has been extended to accept BPF filters (which libpcap utilizes). Also, you can add BPF filter support to Ultrix using the kernel source and/or object patches available in: ftp://gatekeeper.dec.com/pub/DEC/net/bpfext42.tar.Z. Problems, bugs, questions, desirable enhancements, source code contributions, etc., should be sent to the email address "patches@tcpdump.org".