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PCAP-LINKTYPE(7)       Miscellaneous Information Manual       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
       libpcap 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
       corresponding 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
                 captured; 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
                 historical.

            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
                                (UNCOMPRESSED_TCP), with that byte being the
                                first byte of the raw IP header on the wire,
                                containing 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 address of the sender (if there are more than
                      8 bytes, only the first 8 are present, and if there are
                      fewer than 8 bytes, there are padding bytes after the
                      address to pad the field to 8 bytes);

                      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)