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    Command:

    packet

    
    
    

    SYNOPSIS

           #include <sys/socket.h>
           #include <netpacket/packet.h>
           #include <net/ethernet.h> /* the L2 protocols */
    
           packet_socket = socket(AF_PACKET, int socket_type, int protocol);
    
    
    

    DESCRIPTION

           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 byte 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 AF_INET/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  get  packets  only  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.
    
           When the MSG_TRUNC flag is passed to recvmsg(2),  recv(2),  recvfrom(2)
           the real length of the packet on the wire is always returned, even when
           it is longer than the buffer.
    
           order  as  defined in the <linux/if_ether.h> include file.  It defaults
           to the socket's protocol.  sll_ifindex is the interface  index  of  the
           interface  (see  netdevice(7)); 0 matches any interface (only permitted
           for  binding).   sll_hatype  is  an  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_MULTI-
           CAST  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  sense  only  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.
    
           When you send packets it is enough  to  specify  sll_family,  sll_addr,
           sll_halen,  sll_ifindex.  The other fields should be 0.  sll_hatype and
           sll_pkttype are set on received packets for your information.  For bind
           only sll_protocol and sll_ifindex are used.
    
       Socket options
           Packet  socket  options  are  configured  by calling setsockopt(2) with
           level SOL_PACKET.
    
           PACKET_ADD_MEMBERSHIP
           PACKET_DROP_MEMBERSHIP
                  Packet sockets can be used to configure physical layer multicas-
                  ting and promiscuous mode.  PACKET_ADD_MEMBERSHIP adds a binding
                  and  PACKET_DROP_MEMBERSHIP  drops  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 mul-
                  ticast  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.
    
           PACKET_AUXDATA (since Linux 2.6.21)
                  If  this  binary  option  is enabled, the packet socket passes a
    
           PACKET_FANOUT (since Linux 3.1)
                  To scale processing across threads, packet sockets  can  form  a
                  fanout  group.   In  this mode, each matching packet is enqueued
                  onto only one socket in the group.   A  socket  joins  a  fanout
                  group  by calling setsockopt(2) with level SOL_PACKET and option
                  PACKET_FANOUT.  Each network namespace  can  have  up  to  65536
                  independent groups.  A socket selects a group by encoding the ID
                  in the first 16 bits of the integer  option  value.   The  first
                  packet  socket  to  join a group implicitly creates it.  To suc-
                  cessfully join an existing group, subsequent packet sockets must
                  have  the  same protocol, device settings, fanout mode and flags
                  (see below).  Packet sockets can leave a fanout  group  only  by
                  closing  the  socket.  The group is deleted when the last socket
                  is closed.
    
                  Fanout supports multiple algorithms to  spread  traffic  between
                  sockets.   The  default  mode, PACKET_FANOUT_HASH, sends packets
                  from the same flow to  the  same  socket  to  maintain  per-flow
                  ordering.   For  each  packet, it chooses a socket by taking the
                  packet flow hash modulo the number  of  sockets  in  the  group,
                  where  a  flow  hash  is  a  hash over network-layer address and
                  optional transport-layer port  fields.   The  load-balance  mode
                  PACKET_FANOUT_LB    implements    a    round-robin    algorithm.
                  PACKET_FANOUT_CPU selects the socket based on the CPU  that  the
                  packet arrived on.  PACKET_FANOUT_ROLLOVER processes all data on
                  a single socket, moves to the next when one becomes  backlogged.
                  PACKET_FANOUT_RND  selects the socket using a pseudo-random num-
                  ber generator.  PACKET_FANOUT_QM (available  since  Linux  3.14)
                  selects  the  socket  using  the  recorded  queue_mapping of the
                  received skb.
    
                  Fanout modes can  take  additional  options.   IP  fragmentation
                  causes packets from the same flow to have different flow hashes.
                  The flag PACKET_FANOUT_FLAG_DEFRAG, if set, causes packet to  be
                  defragmented before fanout is applied, to preserve order even in
                  this case.  Fanout mode and options are communicated in the sec-
                  ond   16   bits   of   the   integer  option  value.   The  flag
                  PACKET_FANOUT_FLAG_ROLLOVER enables the roll over mechanism as a
                  backup  strategy:  if  the  original  fanout algorithm selects a
                  backlogged socket, the packet rolls over to the  next  available
                  one.
    
           PACKET_LOSS (with PACKET_TX_RING)
                  If set, do not silently drop a packet on transmission error, but
                  return it with status set to TP_STATUS_WRONG_FORMAT.
    
           PACKET_RESERVE (with PACKET_RX_RING)
                  By default, a packet receive  ring  writes  packets  immediately
                  following  the  metadata  structure and alignment padding.  This
                  integer option reserves additional headroom.
    
           PACKET_RX_RING
                  the application.  During normal operation,  the  new  status  is
                  TP_STATUS_USER,  to  signal that a correctly received packet has
                  been stored.  When the application  has  finished  processing  a
                  packet, it transfers ownership of the slot back to the socket by
                  setting the status to TP_STATUS_KERNEL.  Packet  sockets  imple-
                  ment  multiple  variants of the packet ring.  The implementation
                  details     are     described     in      Documentation/network-
                  ing/packet_mmap.txt in the Linux kernel source tree.
    
           PACKET_STATISTICS
                  Retrieve packet socket statistics in the form of a structure
    
                      struct tpacket_stats {
                          unsigned int tp_packets;  /* Total packet count */
                          unsigned int tp_drops;    /* Dropped packet count */
                      };
    
                  Receiving  statistics resets the internal counters.  The statis-
                  tics structure differs when using a ring of variant  TPACKET_V3.
    
           PACKET_TIMESTAMP (with PACKET_RX_RING; since Linux 2.6.36)
                  The  packet  receive ring always stores a timestamp in the meta-
                  data header.  By default, this is a software generated timestamp
                  generated when the packet is copied into the ring.  This integer
                  option selects the type of timestamp.  Besides the  default,  it
                  support the two hardware formats described in Documentation/net-
                  working/timestamping.txt in the Linux kernel source tree.
    
           PACKET_TX_RING (since Linux 2.6.31)
                  Create a memory-mapped  ring  buffer  for  packet  transmission.
                  This  option  is  similar  to  PACKET_RX_RING and takes the same
                  arguments.  The application writes packets into slots with  sta-
                  tus  TP_STATUS_AVAILABLE  and schedules them for transmission by
                  changing the status to TP_STATUS_SEND_REQUEST.  When packets are
                  ready  to  be  transmitted,  the  application calls send(2) or a
                  variant thereof.  The buf  and  len  fields  of  this  call  are
                  ignored.  If an address is passed using sendto(2) or sendmsg(2),
                  then that overrides the socket default.  On successful transmis-
                  sion,  the  socket  resets  the slot to TP_STATUS_AVAILABLE.  It
                  discards packets silently on error unless PACKET_LOSS is set.
    
           PACKET_VERSION (with PACKET_RX_RING; since Linux 2.6.27)
                  By default, PACKET_RX_RING creates  a  packet  receive  ring  of
                  variant  TPACKET_V1.   To  create another variant, configure the
                  desired variant by setting this integer option  before  creating
                  the ring.
    
           PACKET_QDISC_BYPASS (since Linux 3.14)
                  By default, packets sent through packet sockets pass through the
                  kernel's qdisc (traffic control) layer, which is  fine  for  the
                  vast  majority  of  use cases.  For traffic generator appliances
                  using packet sockets that intend to brute-force flood  the  net-
    
       Error handling
           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.
    
    
    

    ERRORS

           EADDRNOTAVAIL
                  Unknown multicast group address passed.
    
           EFAULT User passed invalid memory address.
    
           EINVAL Invalid argument.
    
           EMSGSIZE
                  Packet is bigger than interface MTU.
    
           ENETDOWN
                  Interface is not up.
    
           ENOBUFS
                  Not enough memory to allocate the packet.
    
           ENODEV Unknown device name or interface index  specified  in  interface
                  address.
    
           ENOENT No packet received.
    
           ENOTCONN
                  No interface address passed.
    
           ENXIO  Interface address contained an invalid interface index.
    
           EPERM  User has insufficient privileges to carry out this operation.
    
                  In  addition,  other  errors  may  be generated by the low-level
                  driver.
    
    
    

    VERSIONS

           AF_PACKET is a new feature in Linux 2.2.  Earlier Linux  versions  sup-
           ported only SOCK_PACKET.
    
           The  include  file  <netpacket/packet.h>  is  present  since glibc 2.1.
           Older systems need:
    
               #include <asm/types.h>
               #include <linux/if_packet.h>
               #include <linux/if_ether.h>  /* The L2 protocols */
    
    
    

    NOTES

           For portable programs it is suggested to  use  AF_PACKET  via  pcap(3);
           although this covers only a subset of the AF_PACKET features.
    
           In  Linux  2.0,  the  only  way  to  get a packet socket was by calling
           socket(AF_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  inter-
           face, 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, for example, eth0.
    
           This structure is obsolete and should not be used in new code.
    
    
    

    BUGS

           glibc  2.1  does  not  have  a  define  for  SOL_PACKET.  The suggested
           workaround is to use:
    
               #ifndef SOL_PACKET
               #define SOL_PACKET 263
               #endif
    
           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.
    
           The  MSG_TRUNC  recvmsg(2)  extension  is  an  ugly  hack and should be
           replaced by a control message.  There is currently no way  to  get  the
           original destination address of packets via SOCK_DGRAM.
    
    
    

    SEE ALSO

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

    Linux 2014-02-26 PACKET(7)

    
    
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