283 lines
9.1 KiB
Plaintext
283 lines
9.1 KiB
Plaintext
.\" @(#) $Header: /tcpdump/master/libpcap/pcap-linktype.manmisc.in,v 1.1.2.4 2008-10-27 22:52:05 guy Exp $
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.\"
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.\" Copyright (c) 1987, 1988, 1989, 1990, 1991, 1992, 1994, 1995, 1996, 1997
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.\" The Regents of the University of California. All rights reserved.
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that: (1) source code distributions
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.\" retain the above copyright notice and this paragraph in its entirety, (2)
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.\" distributions including binary code include the above copyright notice and
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.\" this paragraph in its entirety in the documentation or other materials
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.\" provided with the distribution, and (3) all advertising materials mentioning
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.\" features or use of this software display the following acknowledgement:
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.\" ``This product includes software developed by the University of California,
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.\" Lawrence Berkeley Laboratory and its contributors.'' Neither the name of
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.\" the University nor the names of its contributors may be used to endorse
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.\" or promote products derived from this software without specific prior
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.\" written permission.
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.\" THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED
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.\" WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
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.\" MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
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.\"
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.TH PCAP-LINKTYPE 7 "23 October 2008"
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.SH NAME
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pcap-linktype \- link-layer header types supported by libpcap
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.SH DESCRIPTION
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For a live capture or ``savefile'', libpcap supplies, as the return
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value of the
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.BR pcap_datalink (3PCAP)
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routine, a value that indicates the type of link-layer header at the
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beginning of the packets it provides. This is not necessarily the type
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of link-layer header that the packets being captured have on the network
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from which they're being captured; for example, packets from an IEEE
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802.11 network might be provided by libpcap with Ethernet headers that
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the network adapter or the network adapter driver generates from the
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802.11 headers. The names for those values begin with
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.BR DLT_ ,
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so they are sometimes called "DLT_ values".
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.PP
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The values stored in the link-layer header type field in the savefile
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header are, in most but not all cases, the same as the values returned
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by
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.BR pcap_datalink() .
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The names for those values begin with
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.BR LINKTYPE_ .
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.PP
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The link-layer header types supported by libpcap are listed here. The
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value corresponding to
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.B LINKTYPE_
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names are given; the value corresponding to
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.B DLT_
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values are, in some cases, platform dependent, and are not given;
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applications should check for particular
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.B DLT_
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values by name.
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.RS 5
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.TP 5
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.BR DLT_NULL "; " LINKTYPE_NULL = 0
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BSD loopback encapsulation; the link layer header is a 4-byte field, in
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.I host
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byte order, containing a PF_ value from
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.B socket.h
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for the network-layer protocol of the packet.
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.IP
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Note that ``host byte order'' is the byte order of the machine on which
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the packets are captured, and the PF_ values are for the OS of the
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machine on which the packets are captured; if a live capture is being
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done, ``host byte order'' is the byte order of the machine capturing the
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packets, and the PF_ values are those of the OS of the machine capturing
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the packets, but if a ``savefile'' is being read, the byte order and PF_
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values are
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.I not
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necessarily those of the machine reading the capture file.
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.TP 5
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.BR DLT_EN10MB "; " LINKTYPE_ETHERNET = 1
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Ethernet (10Mb, 100Mb, 1000Mb, and up); the
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.B 10MB
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in the
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.B DLT_
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name is historical.
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.TP 5
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.BR DLT_IEEE802 "; " LINKTYPE_TOKEN_RING = 6
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IEEE 802.5 Token Ring; the
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.B IEEE802
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in the
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.B DLT_
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name is historical.
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.TP 5
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.BR DLT_ARCNET "; " LINKTYPE_ARCNET = 7
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ARCNET
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.TP 5
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.BR DLT_SLIP "; " LINKTYPE_SLIP = 8
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SLIP; the link layer header contains, in order:
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.RS 10
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.LP
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a 1-byte flag, which is 0 for packets received by the machine and 1 for
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packets sent by the machine;
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.LP
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a 1-byte field, the upper 4 bits of which indicate the type of packet,
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as per RFC 1144:
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.RS 5
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.TP 5
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0x40
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an unmodified IP datagram (TYPE_IP);
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.TP 5
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0x70
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an uncompressed-TCP IP datagram (UNCOMPRESSED_TCP), with that byte being
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the first byte of the raw IP header on the wire, containing the
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connection number in the protocol field;
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.TP 5
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0x80
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a compressed-TCP IP datagram (COMPRESSED_TCP), with that byte being the
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first byte of the compressed TCP/IP datagram header;
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.RE
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.LP
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for UNCOMPRESSED_TCP, the rest of the modified IP header, and for
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COMPRESSED_TCP, the compressed TCP/IP datagram header;
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.RE
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.RS 5
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.LP
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for a total of 16 bytes; the uncompressed IP datagram follows the header.
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.RE
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.TP 5
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.BR DLT_PPP "; " LINKTYPE_PPP = 9
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PPP; if the first 2 bytes are 0xff and 0x03, it's PPP in HDLC-like
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framing, with the PPP header following those two bytes, otherwise it's
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PPP without framing, and the packet begins with the PPP header.
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.TP 5
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.BR DLT_FDDI "; " LINKTYPE_FDDI = 10
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FDDI
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.TP 5
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.BR DLT_ATM_RFC1483 "; " LINKTYPE_ATM_RFC1483 = 100
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RFC 1483 LLC/SNAP-encapsulated ATM; the packet begins with an IEEE 802.2
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LLC header.
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.TP 5
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.BR DLT_RAW "; " LINKTYPE_RAW = 101
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raw IP; the packet begins with an IP header.
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.TP 5
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.BR DLT_PPP_SERIAL "; " LINKTYPE_PPP_HDLC = 50
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PPP in HDLC-like framing, as per RFC 1662, or Cisco PPP with HDLC
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framing, as per section 4.3.1 of RFC 1547; the first byte will be 0xFF
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for PPP in HDLC-like framing, and will be 0x0F or 0x8F for Cisco PPP
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with HDLC framing.
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.TP 5
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.BR DLT_PPP_ETHER "; " LINKTYPE_PPP_ETHER = 51
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PPPoE; the packet begins with a PPPoE header, as per RFC 2516.
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.TP 5
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.BR DLT_C_HDLC "; " LINKTYPE_C_HDLC = 104
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Cisco PPP with HDLC framing, as per section 4.3.1 of RFC 1547.
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.TP 5
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.BR DLT_IEEE802_11 "; " LINKTYPE_IEEE802_11 = 105
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IEEE 802.11 wireless LAN
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.TP 5
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.BR DLT_FRELAY "; " LINKTYPE_FRELAY = 107
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Frame Relay
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.TP 5
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.BR DLT_LOOP "; " LINKTYPE_LOOP = 108
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OpenBSD loopback encapsulation; the link layer header is a 4-byte field, in
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.I network
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byte order, containing a PF_ value from OpenBSD's
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.B socket.h
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for the network-layer protocol of the packet.
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.IP
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Note that, if a ``savefile'' is being read, those PF_ values are
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.I not
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necessarily those of the machine reading the capture file.
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.TP 5
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.BR DLT_LINUX_SLL "; " LINKTYPE_LINUX_SLL = 113
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Linux "cooked" capture encapsulation; the link layer header contains, in
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order:
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.RS 10
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.LP
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a 2-byte "packet type", in network byte order, which is one of:
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.RS 5
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.TP 5
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0
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packet was sent to us by somebody else
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.TP 5
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1
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packet was broadcast by somebody else
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.TP 5
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2
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packet was multicast, but not broadcast, by somebody else
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.TP 5
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3
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packet was sent by somebody else to somebody else
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.TP 5
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4
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packet was sent by us
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.RE
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.LP
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a 2-byte field, in network byte order, containing a Linux ARPHRD_ value
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for the link layer device type;
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.LP
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a 2-byte field, in network byte order, containing the length of the
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link layer address of the sender of the packet (which could be 0);
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.LP
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an 8-byte field containing that number of bytes of the link layer header
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(if there are more than 8 bytes, only the first 8 are present);
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.LP
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a 2-byte field containing an Ethernet protocol type, in network byte
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order, or containing 1 for Novell 802.3 frames without an 802.2 LLC
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header or 4 for frames beginning with an 802.2 LLC header.
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.RE
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.TP 5
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.BR DLT_LTALK "; " LINKTYPE_LTALK = 104
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Apple LocalTalk; the packet begins with an AppleTalk LLAP header.
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.TP 5
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.BR DLT_PFLOG "; " LINKTYPE_PFLOG = 117
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OpenBSD pflog; the link layer header contains a
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.B "struct pfloghdr"
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structure, as defined by the host on which the file was saved. (This
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differs from operating system to operating system and release to
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release; there is nothing in the file to indicate what the layout of
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that structure is.)
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.TP 5
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.BR DLT_PRISM_HEADER "; " LINKTYPE_PRISM_HEADER = 119
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Prism monitor mode information followed by an 802.11 header.
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.TP 5
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.BR DLT_IP_OVER_FC "; " LINKTYPE_IP_OVER_FC = 122
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RFC 2625 IP-over-Fibre Channel, with the link-layer header being the
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Network_Header as described in that RFC.
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.TP 5
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.BR DLT_SUNATM "; " LINKTYPE_SUNATM = 123
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SunATM devices; the link layer header contains, in order:
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.RS 10
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.LP
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a 1-byte flag field, containing a direction flag in the uppermost bit,
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which is set for packets transmitted by the machine and clear for
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packets received by the machine, and a 4-byte traffic type in the
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low-order 4 bits, which is one of:
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.RS 5
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.TP 5
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0
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raw traffic
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.TP 5
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1
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LANE traffic
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.TP 5
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2
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LLC-encapsulated traffic
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.TP 5
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3
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MARS traffic
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.TP 5
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4
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IFMP traffic
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.TP 5
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5
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ILMI traffic
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.TP 5
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6
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Q.2931 traffic
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.RE
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.LP
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a 1-byte VPI value;
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.LP
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a 2-byte VCI field, in network byte order.
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.RE
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.TP 5
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.BR DLT_IEEE802_11_RADIO "; " LINKTYPE_IEEE802_11_RADIO = 127
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link-layer information followed by an 802.11 header - see
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http://www.shaftnet.org/~pizza/software/capturefrm.txt for a description
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of the link-layer information.
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.TP 5
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.BR DLT_ARCNET_LINUX "; " LINKTYPE_ARCNET_LINUX = 129
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ARCNET, with no exception frames, reassembled packets rather than raw
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frames, and an extra 16-bit offset field between the destination host
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and type bytes.
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.TP 5
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.BR DLT_LINUX_IRDA "; " LINKTYPE_LINUX_IRDA = 144
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Linux-IrDA packets, with a
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.B DLT_LINUX_SLL
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header followed by the IrLAP header.
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.TP 5
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.BR DLT_LINUX_LAPD "; " LINKTYPE_LINUX_LAPD = 177
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LAPD (Q.921) frames, with a
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.B DLT_LINUX_SLL
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header captured via vISDN.
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.RE
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.SH SEE ALSO
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pcap_datalink(3PCAP)
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