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       packet, PF_PACKET - packet interface on device level.


       #include <sys/socket.h>
       #include <features.h>    /* for the glibc version number */
       #if __GLIBC__ >= 2 && __GLIBC_MINOR >= 1
       #include <netpacket/packet.h>
       #include <net/ethernet.h>     /* the L2 protocols */
       #include <asm/types.h>
       #include <linux/if_packet.h>
       #include <linux/if_ether.h>   /* The L2 protocols */

       packet_socket = socket(PF_PACKET, int socket_type, int protocol);


       Packet  sockets are used to receive or send raw packets at the device driver (OSI Layer 2)
       level. They allow the user to implement protocol modules in  user  space  on  top  of  the
       physical layer.

       The  socket_type  is  either  SOCK_RAW  for raw packets including the link level header or
       SOCK_DGRAM for cooked packets with the link level header removed. The  link  level  header
       information  is available in a common format in a sockaddr_ll.  protocol is the IEEE 802.3
       protocol number in network order. See the <linux/if_ether.h> include file for  a  list  of
       allowed  protocols.  When  protocol  is  set  to  htons(ETH_P_ALL)  then all protocols are
       received.  All incoming packets of that protocol type will be passed to the packet  socket
       before they are passed to the protocols implemented in the kernel.

       Only processes with effective uid 0 or the CAP_NET_RAW capability may open packet sockets.

       SOCK_RAW  packets  are  passed  to  and  from the device driver without any changes in the
       packet data.  When receiving a packet, the  address  is  still  parsed  and  passed  in  a
       standard  sockaddr_ll  address  structure.   When transmitting a packet, the user supplied
       buffer should contain the physical layer header.  That packet is then queued unmodified to
       the  network  driver  of  the  interface  defined  by the destination address. Some device
       drivers always add other headers.  SOCK_RAW is similar to  but  not  compatible  with  the
       obsolete SOCK_PACKET of Linux 2.0.

       SOCK_DGRAM  operates on a slightly higher level. The physical header is removed before the
       packet is passed to the user.  Packets sent through  a  SOCK_DGRAM  packet  socket  get  a
       suitable  physical  layer  header  based on the information in the sockaddr_ll destination
       address before they are queued.

       By default all packets of the specified protocol type are passed to a  packet  socket.  To
       only  get  packets from a specific interface use bind(2) specifying an address in a struct
       sockaddr_ll to bind the packet socket to an  interface.  Only  the  sll_protocol  and  the
       sll_ifindex address fields are used for purposes of binding.

       The connect(2) operation is not supported on packet sockets.


       The sockaddr_ll is a device independent physical layer address.

              struct sockaddr_ll
                  unsigned short  sll_family;    /* Always AF_PACKET */
                  unsigned short  sll_protocol;  /* Physical layer protocol */
                  int             sll_ifindex;   /* Interface number */
                  unsigned short  sll_hatype;    /* Header type */
                  unsigned char   sll_pkttype;   /* Packet type */
                  unsigned char   sll_halen;     /* Length of address */
                  unsigned char   sll_addr[8];   /* Physical layer address */

       sll_protocol  is  the  standard  ethernet protocol type in network order as defined in the
       linux/if_ether.h include file.  sll_ifindex is the interface index of the  interface  (see
       netdevice(2)  );  0  matches  any interface (only legal for binding).  sll_hatype is a ARP
       type as defined in the linux/if_arp.h include file.  sll_pkttype contains the packet type.
       Valid types are PACKET_HOST for a packet addressed to the local host, PACKET_BROADCAST for
       a physical layer broadcast packet, PACKET_MULTICAST for a packet sent to a physical  layer
       multicast  address,  PACKET_OTHERHOST for a packet to some other host that has been caught
       by a device driver in promiscuous mode, and PACKET_OUTGOING for a packet  originated  from
       the  local  host  that  is looped back to a packet socket. These types make only sense for
       receiving.  sll_addr and sll_halen contain the physical layer (e.g.  IEEE  802.3)  address
       and its length. The exact interpretation depends on the device.


       Packet  sockets can be used to configure physical layer multicasting and promiscuous mode.
       It works by calling setsockopt(2) on a packet socket for SOL_PACKET and one of the options
       PACKET_ADD_MEMBERSHIP  to  add  a binding or PACKET_DROP_MEMBERSHIP to drop it.  They both
       expect a packet_mreq structure as argument:

              struct packet_mreq
                  int             mr_ifindex;    /* interface index */
                  unsigned short  mr_type;       /* action */
                  unsigned short  mr_alen;       /* address length */
                  unsigned char   mr_address[8]; /* physical layer address */

       mr_ifindex contains the interface index for the interface whose status should be  changed.
       The  mr_type  parameter  specifies  which  action  to  perform.  PACKET_MR_PROMISC enables
       receiving all  packets  on  a  shared  medium  -  often  known  as  ``promiscuous  mode'',
       PACKET_MR_MULTICAST  binds  the  socket to the physical layer multicast group specified in
       mr_address and mr_alen, and PACKET_MR_ALLMULTI sets the socket up to receive all multicast
       packets arriving at the interface.

       In  addition  the  traditional ioctls SIOCSIFFLAGS, SIOCADDMULTI, SIOCDELMULTI can be used
       for the same purpose.


       SIOCGSTAMP can be used to receive the time stamp of the last received packet. Argument  is
       a struct timeval.

       In  addition all standard ioctls defined in netdevice(7) and socket(7) are valid on packet


       Packet sockets do no error handling other than errors occurred while passing the packet to
       the device driver. They don't have the concept of a pending error.


       In  Linux  2.0,  the  only  way  to  get  a  packet  socket was by calling socket(PF_INET,
       SOCK_PACKET, protocol).  This is  still  supported  but  strongly  deprecated.   The  main
       difference between the two methods is that SOCK_PACKET uses the old struct sockaddr_pkt to
       specify an interface, which doesn't provide physical layer independence.

              struct sockaddr_pkt
                  unsigned short  spkt_family;
                  unsigned char   spkt_device[14];
                  unsigned short  spkt_protocol;

       spkt_family contains the device type, spkt_protocol is the IEEE  802.3  protocol  type  as
       defined  in  <sys/if_ether.h>  and  spkt_device  is  the  device name as a null terminated
       string, e.g. eth0.

       This structure is obsolete and should not be used in new code.


       For portable programs it is suggested to use PF_PACKET via  pcap(3);  although  this  only
       covers a subset of the PF_PACKET features.

       The SOCK_DGRAM packet sockets make no attempt to create or parse the IEEE 802.2 LLC header
       for a IEEE 802.3 frame.  When ETH_P_802_3 is specified as protocol for sending the  kernel
       creates  the  802.3  frame  and fills out the length field; the user has to supply the LLC
       header to get a fully conforming packet. Incoming 802.3 packets are not multiplexed on the
       DSAP/SSAP  protocol  fields; instead they are supplied to the user as protocol ETH_P_802_2
       with the LLC header prepended. It is thus not possible to bind  to  ETH_P_802_3;  bind  to
       ETH_P_802_2  instead  and  do the protocol multiplex yourself.  The default for sending is
       the standard Ethernet DIX encapsulation with the protocol filled in.

       Packet sockets are not subject to the input or output firewall chains.


              Interface is not up.

              No interface address passed.

       ENODEV Unknown device name or interface index specified in interface address.

              Packet is bigger than interface MTU.

              Not enough memory to allocate the packet.

       EFAULT User passed invalid memory address.

       EINVAL Invalid argument.

       ENXIO  Interface address contained illegal interface index.

       EPERM  User has insufficient privileges to carry out this operation.

              Unknown multicast group address passed.

       ENOENT No packet received.

              In addition other errors may be generated by the low-level driver.


       PF_PACKET  is  a  new  feature  in  Linux  2.2.  Earlier  Linux  versions  supported  only


       glibc 2.1 does not have a define for SOL_PACKET.  The suggested workaround is to use
              #ifndef SOL_PACKET
              #define SOL_PACKET 263
       This is fixed in later glibc versions and also does not occur on libc5 systems.

       The IEEE 802.2/803.3 LLC handling could be considered as a bug.

       Socket filters are not documented.


       This  man page was writen by Andi Kleen with help from Matthew Wilcox.  PF_PACKET in Linux
       2.2 was implemented by Alexey Kuznetsov, based on code by Alan Cox and others.


       ip(7), socket(7), socket(2), raw(7), pcap(3).

       RFC 894 for the standard IP Ethernet encapsulation.

       RFC 1700 for the IEEE 802.3 IP encapsulation.

       The linux/if_ether.h include file for physical layer protocols.