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RAW(7)                     Linux Programmer's Manual                    RAW(7)



NAME
       raw(3x,7,8,3x cbreak), SOCK_RAW - Linux IPv4 raw(3x,7,8,3x cbreak) sockets

SYNOPSIS
       #include <sys/socket.h>
       #include <netinet/in.h>
       raw_socket = socket(2,7,n)(PF_INET, SOCK_RAW, int protocol);


DESCRIPTION
       Raw  sockets  allow new IPv4 protocols to be implemented in(1,8) user space.
       A raw(3x,7,8,3x cbreak) socket(2,7,n) receives or sends the  raw(3x,7,8,3x cbreak)  datagram  not  including  link(1,2)
       level headers.

       The  IPv4 layer generates an IP header when sending a packet unless the
       IP_HDRINCL socket(2,7,n) 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(1,8) the packet.

       Only processes with an effective user id of 0 or the CAP_NET_RAW  capa-
       bility are allowed to open(2,3,n) raw(3x,7,8,3x cbreak) sockets.

       All  packets  or  errors matching the protocol number specified for the
       raw(3x,7,8,3x cbreak) socket(2,7,n) are passed to this socket.  For a list of the allowed proto-
       cols see RFC1700 assigned numbers and getprotobyname(3).

       A  protocol  of  IPPROTO_RAW  implies enabled IP_HDRINCL and is able to
       send(2,n) any IP protocol that is specified in(1,8) the passed header.  Receiving
       of  all IP protocols via IPPROTO_RAW is not possible using raw(3x,7,8,3x cbreak) sockets.


       +---------------------------------------------------+
       |IP Header fields modified on sending by IP_HDRINCL |
       +----------------------+----------------------------+
       |IP Checksum           |Always filled in.           |
       +----------------------+----------------------------+
       |Source Address        |Filled in(1,8) when zero.        |
       +----------------------+----------------------------+
       |Packet Id             |Filled in(1,8) 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(2,7,n) 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(7,n,1 builtins) then IP header options can be set(7,n,1 builtins) on raw(3x,7,8,3x cbreak)  sock-
       ets with setsockopt(2); see ip(7,8)(7) for more information.

       In  Linux  2.2  all  IP  header  fields and options can be set(7,n,1 builtins) using IP
       socket(2,7,n) options. This means raw(3x,7,8,3x cbreak) sockets are usually only needed for  new
       protocols or protocols with no user interface (like ICMP).

       When  a  packet is received, it is passed to any raw(3x,7,8,3x cbreak) sockets which have
       been bound to its protocol before it is passed to other  protocol  han-
       dlers (e.g. kernel protocol modules).


ADDRESS FORMAT
       Raw  sockets  use the standard sockaddr_in address structure defined in(1,8)
       ip(7,8)(7).  The The sin_port field could be used to specify the IP protocol
       number, but it is ignored for sending in(1,8) Linux 2.2 and should be always
       set(7,n,1 builtins) to 0 (see BUGS) For incoming packets sin_port is set(7,n,1 builtins) to the  proto-
       col  of  the  packet.  See the <netinet/in.h> include file(1,n) for valid IP
       protocols.


SOCKET OPTIONS
       Raw socket(2,7,n) options can be set(7,n,1 builtins) with setsockopt(2) and read(2,n,1 builtins) with getsock-
       opt(2) by passing the SOL_RAW family flag.


       ICMP_FILTER
              Enable   a   special   filter(1,3x,3x curs_util)  for  raw(3x,7,8,3x cbreak)  sockets  bound  to  the
              IPPROTO_ICMP protocol.  The value has a bit set(7,n,1 builtins)  for  each  ICMP
              message  type  which  should  be filtered out. The default is to
              filter(1,3x,3x curs_util) no ICMP messages.


       In addition all ip(7,8)(7) SOL_IP socket(2,7,n) options valid for datagram  sockets
       are supported.


NOTES
       Raw  sockets fragment a packet when its total length exceeds the inter-
       face MTU (but see BUGS).  A more network friendly and  faster  alterna-
       tive is to implement path MTU discovery as described in(1,8) the IP_MTU_DIS-
       COVER section of ip(7,8)(7).

       A raw(3x,7,8,3x cbreak) socket(2,7,n) can be bound to a specific local address using the bind(2,n,1 builtins)(2)
       call.  If it isn't bound all packets with the specified IP protocol are
       received.  In addition a RAW socket(2,7,n) can be bound to a specific  network
       device using SO_BINDTODEVICE; see socket(2,7,n)(7).

       An  IPPROTO_RAW socket(2,7,n) is send(2,n) only.  If you really want to receive all
       IP packets use a packet(7) socket(2,7,n) with the ETH_P_IP protocol. Note that
       packet sockets don't reassemble IP fragments, unlike raw(3x,7,8,3x cbreak) sockets.

       If  you  want  to  receive all ICMP packets for a datagram socket(2,7,n) it is
       often better to use IP_RECVERR on that particular socket(2,7,n); see ip(7,8)(7).

       Raw sockets may tap all IP protocols in(1,8) Linux, even protocols like ICMP
       or  TCP  which  have  a protocol module in(1,8) the kernel. In this case the
       packets are passed to both the kernel module  and  the  raw(3x,7,8,3x cbreak)  socket(2,7,n)(s).
       This  should  not  be  relied upon in(1,8) portable programs, many other BSD
       socket(2,7,n) implementation have limitations here.

       Linux never changes headers passed from the user (except for filling in(1,8)
       some  zeroed  fields  as  described for IP_HDRINCL).  This differs from
       many other implementations of raw(3x,7,8,3x cbreak) sockets.

       RAW sockets are generally rather unportable and should  be  avoided  in(1,8)
       programs intended to be portable.

       Sending  on raw(3x,7,8,3x cbreak) sockets should take the IP protocol from sin_port; this
       ability was lost in(1,8) Linux 2.2. Work around is to use IP_HDRINCL.


ERROR HANDLING
       Errors originating from the network are only passed to  the  user  when
       the  socket(2,7,n)  is  connected  or the IP_RECVERR flag is enabled. For con-
       nected sockets only EMSGSIZE and EPROTO are passed  for  compatibility.
       With IP_RECVERR all network errors are saved in(1,8) the error(8,n) queue.

ERRORS
       EMSGSIZE
              Packet  too  big.  Either  Path  MTU  Discovery  is enabled (the
              IP_MTU_DISCOVER socket(2,7,n) flag) or the packet size exceeds the max-
              imum allowed IPv4 packet size of 64KB.

       EACCES User  tried  to  send(2,n)  to a broadcast address without having the
              broadcast flag set(7,n,1 builtins) on the socket.

       EPROTO An ICMP error(8,n) has arrived reporting a parameter problem.

       EFAULT An invalid memory address was supplied.

       EOPNOTSUPP
              Invalid flag has been passed to a socket(2,7,n) call (like MSG_OOB).

       EINVAL Invalid argument.

       EPERM  The user doesn't have permission to open(2,3,n) raw(3x,7,8,3x cbreak) sockets. Only  pro-
              cesses  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(1,8) Linux 2.2. They are Linux  exten-
       sions and should not be used in(1,8) portable programs.

       Linux  2.0  enabled  some  bug-to-bug compatibility with BSD in(1,8) the raw(3x,7,8,3x cbreak)
       socket(2,7,n) code when the SO_BSDCOMPAT flag was set(7,n,1 builtins) - that has been  removed
       in(1,8) 2.2.


BUGS
       Transparent proxy extensions are not described.

       When  the IP_HDRINCL option is set(7,n,1 builtins) datagrams will not be fragmented and
       are limited to the interface MTU.  This is a limitation in(1,8) Linux 2.2.

       Setting the IP protocol for sending in(1,8) sin_port got lost in(1,8) Linux  2.2.
       The protocol that socket(2,7,n) was bound to or that was specified in(1,8) the ini-
       tial socket(2,7,n)(2) call is always used.


AUTHORS
       This man(1,5,7) page was written by Andi Kleen.


SEE ALSO
       recvmsg(2), sendmsg(2), capabilities(7), ip(7,8)(7), socket(2,7,n)(7)

       RFC1191 for path MTU discovery.

       RFC791 and the <linux/ip.h> include file(1,n) for the IP protocol.



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

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