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PCAP-LINKTYPE(7)					      PCAP-LINKTYPE(7)

NAME
       pcap-linktype - link-layer header types supported by libpcap

DESCRIPTION
       For  a  live  capture  or ``savefile'', libpcap supplies, as the return
       value of the pcap_datalink(3) routine, a value that indicates the  type
       of link-layer header at the beginning of the packets it provides.  This
       is not necessarily the type of link-layer header that the packets being
       captured	 have  on  the	network from which they're being captured; for
       example, packets from an IEEE 802.11 network might be provided by libp‐
       cap  with  Ethernet  headers  that  the	network adapter or the network
       adapter driver generates from the 802.11 headers.  The names for	 those
       values begin with DLT_, so they are sometimes called "DLT_ values".

       The  values  stored in the link-layer header type field in the savefile
       header are, in most but not all cases, the same as the values  returned
       by pcap_datalink().  The names for those values begin with LINKTYPE_.

       The  link-layer header types supported by libpcap are listed here.  The
       value corresponding to LINKTYPE_ names are given; the value correspond‐
       ing  to DLT_ values are, in some cases, platform dependent, and are not
       given; applications should check for particular DLT_ values by name.

	    DLT_NULL; LINKTYPE_NULL=0
		 BSD loopback encapsulation; the link layer header is a 4-byte
		 field,	 in  host  byte	 order,	 containing  a	PF_ value from
		 socket.h for the network-layer protocol of the packet.

		 Note that ``host byte	order''	 is  the  byte	order  of  the
		 machine on which the packets are captured, and the PF_ values
		 are for the OS of the machine on which the packets  are  cap‐
		 tured;	 if  a live capture is being done, ``host byte order''
		 is the byte order of the machine capturing the	 packets,  and
		 the  PF_  values are those of the OS of the machine capturing
		 the packets, but if a ``savefile'' is being  read,  the  byte
		 order and PF_ values are not necessarily those of the machine
		 reading the capture file.

	    DLT_EN10MB; LINKTYPE_ETHERNET=1
		 Ethernet (10Mb, 100Mb, 1000Mb, and up); the 10MB in the  DLT_
		 name is historical.

	    DLT_IEEE802; LINKTYPE_TOKEN_RING=6
		 IEEE  802.5  Token Ring; the IEEE802 in the DLT_ name is his‐
		 torical.

	    DLT_ARCNET; LINKTYPE_ARCNET=7
		 ARCNET

	    DLT_SLIP; LINKTYPE_SLIP=8
		 SLIP; the link layer header contains, in order:

		      a 1-byte flag, which is 0 for packets  received  by  the
		      machine and 1 for packets sent by the machine;

		      a	 1-byte	 field, the upper 4 bits of which indicate the
		      type of packet, as per RFC 1144:

			   0x40 an unmodified IP datagram (TYPE_IP);

			   0x70 an  uncompressed-TCP   IP   datagram   (UNCOM‐
				PRESSED_TCP),  with  that byte being the first
				byte of the raw IP header on  the  wire,  con‐
				taining	 the connection number in the protocol
				field;

			   0x80 a compressed-TCP IP datagram (COMPRESSED_TCP),
				with  that  byte  being	 the first byte of the
				compressed TCP/IP datagram header;

		      for  UNCOMPRESSED_TCP,  the  rest	 of  the  modified  IP
		      header,  and  for	 COMPRESSED_TCP, the compressed TCP/IP
		      datagram header;

		 for a total of 16 bytes; the uncompressed IP datagram follows
		 the header.

	    DLT_PPP; LINKTYPE_PPP=9
		 PPP;  if  the	first  2  bytes are 0xff and 0x03, it's PPP in
		 HDLC-like framing, with the PPP header	 following  those  two
		 bytes,	 otherwise  it's  PPP  without framing, and the packet
		 begins with the PPP header.

	    DLT_FDDI; LINKTYPE_FDDI=10
		 FDDI

	    DLT_ATM_RFC1483; LINKTYPE_ATM_RFC1483=100
		 RFC 1483 LLC/SNAP-encapsulated ATM; the packet begins with an
		 IEEE 802.2 LLC header.

	    DLT_RAW; LINKTYPE_RAW=101
		 raw IP; the packet begins with an IP header.

	    DLT_PPP_SERIAL; LINKTYPE_PPP_HDLC=50
		 PPP  in HDLC-like framing, as per RFC 1662, or Cisco PPP with
		 HDLC framing, as per section 4.3.1 of	RFC  1547;  the	 first
		 byte  will  be 0xFF for PPP in HDLC-like framing, and will be
		 0x0F or 0x8F for Cisco PPP with HDLC framing.

	    DLT_PPP_ETHER; LINKTYPE_PPP_ETHER=51
		 PPPoE; the packet begins with a  PPPoE	 header,  as  per  RFC
		 2516.

	    DLT_C_HDLC; LINKTYPE_C_HDLC=104
		 Cisco	PPP  with  HDLC	 framing,  as per section 4.3.1 of RFC
		 1547.

	    DLT_IEEE802_11; LINKTYPE_IEEE802_11=105
		 IEEE 802.11 wireless LAN

	    DLT_FRELAY; LINKTYPE_FRELAY=107
		 Frame Relay

	    DLT_LOOP; LINKTYPE_LOOP=108
		 OpenBSD loopback encapsulation; the link layer	 header	 is  a
		 4-byte	 field,	 in network byte order, containing a PF_ value
		 from OpenBSD's socket.h for the network-layer protocol of the
		 packet.

		 Note  that, if a ``savefile'' is being read, those PF_ values
		 are not necessarily those of the machine reading the  capture
		 file.

	    DLT_LINUX_SLL; LINKTYPE_LINUX_SLL=113
		 Linux	"cooked"  capture encapsulation; the link layer header
		 contains, in order:

		      a 2-byte "packet type", in network byte order, which  is
		      one of:

			   0	packet was sent to us by somebody else

			   1	packet was broadcast by somebody else

			   2	packet	was  multicast,	 but not broadcast, by
				somebody else

			   3	packet was sent by somebody else  to  somebody
				else

			   4	packet was sent by us

		      a	 2-byte	 field,	 in  network  byte order, containing a
		      Linux ARPHRD_ value for the link layer device type;

		      a 2-byte field, in network byte  order,  containing  the
		      length  of  the  link layer address of the sender of the
		      packet (which could be 0);

		      an 8-byte field containing that number of bytes  of  the
		      link  layer header (if there are more than 8 bytes, only
		      the first 8 are present);

		      a 2-byte field containing an Ethernet protocol type,  in
		      network  byte  order,  or	 containing 1 for Novell 802.3
		      frames without an 802.2  LLC  header  or	4  for	frames
		      beginning with an 802.2 LLC header.

	    DLT_LTALK; LINKTYPE_LTALK=104
		 Apple	LocalTalk;  the	 packet	 begins with an AppleTalk LLAP
		 header.

	    DLT_PFLOG; LINKTYPE_PFLOG=117
		 OpenBSD pflog;	 the  link  layer  header  contains  a	struct
		 pfloghdr  structure, as defined by the host on which the file
		 was saved.  (This differs from operating system to  operating
		 system	 and  release to release; there is nothing in the file
		 to indicate what the layout of that structure is.)

	    DLT_PRISM_HEADER; LINKTYPE_PRISM_HEADER=119
		 Prism monitor mode information followed by an 802.11 header.

	    DLT_IP_OVER_FC; LINKTYPE_IP_OVER_FC=122
		 RFC 2625 IP-over-Fibre Channel, with  the  link-layer	header
		 being the Network_Header as described in that RFC.

	    DLT_SUNATM; LINKTYPE_SUNATM=123
		 SunATM devices; the link layer header contains, in order:

		      a	 1-byte flag field, containing a direction flag in the
		      uppermost bit, which is set for packets  transmitted  by
		      the  machine  and	 clear	for  packets  received	by the
		      machine, and a 4-byte traffic type in  the  low-order  4
		      bits, which is one of:

			   0	raw traffic

			   1	LANE traffic

			   2	LLC-encapsulated traffic

			   3	MARS traffic

			   4	IFMP traffic

			   5	ILMI traffic

			   6	Q.2931 traffic

		      a 1-byte VPI value;

		      a 2-byte VCI field, in network byte order.

	    DLT_IEEE802_11_RADIO; LINKTYPE_IEEE802_11_RADIO=127
		 link-layer  information  followed  by	an 802.11 header - see
		 http://www.shaftnet.org/~pizza/software/capturefrm.txt for  a
		 description of the link-layer information.

	    DLT_ARCNET_LINUX; LINKTYPE_ARCNET_LINUX=129
		 ARCNET,  with no exception frames, reassembled packets rather
		 than raw frames, and an extra 16-bit offset field between the
		 destination host and type bytes.

	    DLT_LINUX_IRDA; LINKTYPE_LINUX_IRDA=144
		 Linux-IrDA  packets,  with a DLT_LINUX_SLL header followed by
		 the IrLAP header.

	    DLT_LINUX_LAPD; LINKTYPE_LINUX_LAPD=177
		 LAPD (Q.921) frames, with a DLT_LINUX_SLL header captured via
		 vISDN.

SEE ALSO
       pcap_datalink(3)

				23 October 2008		      PCAP-LINKTYPE(7)
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