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raw



SYNOPSIS

       #include <sys/socket.h>
       #include <netinet/in.h>
       raw_socket = socket(PF_INET, SOCK_RAW, int protocol);


DESCRIPTION

       Raw  sockets allow new IPv4 protocols to be implemented in
       user space.  A raw socket receives or sends the raw  data­
       gram not including link level headers.

       The  IPv4  layer  generates  an  IP  header when sending a
       packet unless the IP_HDRINCL socket option is  enabled  on
       the  socket.   When it is enabled, the packet must contain
       an IP header.  For  receiving  the  IP  header  is  always
       included in the packet.

       Only  processes  with  an  effective  user  id of 0 or the
       CAP_NET_RAW capability are allowed to open raw sockets.

       All packets or errors matching the protocol number  speci­
       fied  for the raw socket are passed to this socket.  For a
       list of the allowed protocols see RFC1700 assigned numbers
       and getprotobyname(3).

       A  protocol  of IPPROTO_RAW implies enabled IP_HDRINCL and
       is able to send any IP protocol that is specified  in  the
       passed   header.    Receiving  of  all  IP  protocols  via
       IPPROTO_RAW is not possible using raw sockets.

       +---------------------------------------------------+
       |IP Header fields modified on sending by IP_HDRINCL |
       +----------------------+----------------------------+
       |IP Checksum           |Always filled in.           |
       +----------------------+----------------------------+
       |Source Address        |Filled in when zero.        |
       +----------------------+----------------------------+
       |Packet Id             |Filled in when zero.        |
       +----------------------+----------------------------+
       |Total Length          |Always filled in.           |
       +----------------------+----------------------------+

       If IP_HDRINCL is specified and the IP header  has  a  non-
       zero  destination  address then the destination address of
       the socket is used to route the packet. When MSG_DONTROUTE
       is  specified  the  destination  address should refer to a
       local interface, otherwise a routing table lookup is  done
       anyways but gatewayed routes are ignored.

       If  IP_HDRINCL isn't set then IP header options can be set
       on raw sockets with  setsockopt(2);  see  ip(7)  for  more
       information.
       specify  the  IP  protocol  number,  but it is ignored for
       sending in Linux 2.2 and should be always set  to  0  (see
       BUGS) For incoming packets sin_port is set to the protocol
       of the packet.  See the <netinet/in.h>  include  file  for
       valid IP protocols.


SOCKET OPTIONS

       Raw  socket options can be set with setsockopt(2) and read
       with getsockopt(2) by passing the SOL_RAW family flag.

       ICMP_FILTER
              Enable a special filter for raw  sockets  bound  to
              the IPPROTO_ICMP protocol.  The value has a bit set
              for each ICMP message type which should be filtered
              out. The default is to filter no ICMP messages.

       In  addition  all  ip(7)  SOL_IP  socket options valid for
       datagram sockets are supported.


NOTES

       Raw sockets  fragment  a  packet  when  its  total  length
       exceeds  the interface MTU (but see BUGS).  A more network
       friendly and faster alternative is to implement  path  MTU
       discovery  as described in the IP_PMTU_DISCOVER section of
       ip(7).

       A raw socket can be bound  to  a  specific  local  address
       using the bind(2) call. If it isn't bound all packets with
       the specified IP protocol are received.  In addition a RAW
       socket  can  be  bound  to a specific network device using
       SO_BINDTODEVICE; see socket(7).

       An IPPROTO_RAW socket is send only.  If you really want to
       receive  all  IP  packets  use a packet(7) socket with the
       ETH_P_IP protocol. Note that packet sockets don't reassem­
       ble IP fragments, unlike raw sockets.

       If  you  want  to  receive all ICMP packets for a datagram
       socket it is often better to use IP_RECVERR on  that  par­
       ticular socket; see ip(7).

       Raw sockets may tap all IP protocols in Linux, even proto­
       cols like ICMP or TCP which have a protocol module in  the
       kernel.  In  this  case the packets are passed to both the
       kernel module and the raw socket(s). This  should  not  be
       relied  upon  in  portable programs, many other BSD socket
       implementation have limitations here.

       Errors originating from the network are only passed to the
       user  when  the socket is connected or the IP_RECVERR flag
       is enabled. For connected sockets only EMSGSIZE and EPROTO
       are  passed for compatibility. With IP_RECVERR all network
       errors are saved in the error queue.


ERRORS

       EMSGSIZE
              Packet  too  big.  Either  Path  MTU  Discovery  is
              enabled  (the  IP_PMTU_DISCOVER socket flag) or the
              packet size exceeds the maximum allowed IPv4 packet
              size of 64KB.

       EACCES User  tried  to send to a broadcast address without
              having the broadcast flag set on the socket.

       EPROTO An ICMP error has  arrived  reporting  a  parameter
              problem.

       EFAULT An invalid memory address was supplied.

       EOPNOTSUPP
              Invalid flag has been passed to a socket call (like
              MSG_OOB).

       EINVAL Invalid argument.

       EPERM  The user doesn't have permission to open raw  sock­
              ets.  Only  processes with a effective user id of 0
              or the CAP_NET_RAW attribute may do that.


VERSIONS

       IP_RECVERR and ICMP_FILTER are new in Linux 2.2. They  are
       Linux  extensions  and should not be used in portable pro­
       grams.

       Linux 2.0 enabled some bug-to-bug compatibility  with  BSD
       in  the raw socket code when the SO_BSDCOMPAT flag was set
       - that has been removed in 2.2.


BUGS

       Transparent proxy extensions are not described.

       When the IP_HDRINCL option is set datagrams  will  not  be
       fragmented  and are limited to the interface MTU.  This is
       a limitation in Linux 2.2.

       Setting the IP protocol for sending in sin_port  got  lost
       in  Linux  2.2.  The  protocol that socket was bound to or
       that was specified in the initial socket(2) call is always

Linux Man Page              1998-10-02                     RAW(7)
  
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